Science In Action

Periodic Table of Videos

noreply@blogger.com (David) — Fri, 11 Nov 2011 20:48:00 +0000

The Periodic Table of the Elements compresses an amazing amount of information into 118 boxes, one for each chemical element. The most stunning revelation of the table is the regularity of patterns formed by the similar properties of elements in each group (column), which has come to be explained by the quantum structure of the electron clouds around atoms of each element. More about the table here (Wikipedia).

Unfortunately the periodic table can be a bit dry and boring. So much information! But by combining the delights of chemistry with the enthusiasm of videojournalist Brady Haran we get The Periodic Table of Videos--one of the coolest science teaching projects I have heard of since Khan Academy.

Here is a sort of history of the Periodic Table of Videos on the main page of its YouTube channel. The project's official site is here. Click on any of the elements in the table and view a video about the element and its properties, often with hands-on demonstrations, the more explosive the better.

Concerned about the radioactive strontium-90 released from the damaged Fukushima Daiichi reactors, or showered on many of us during the era of above-ground nuclear testing? Here is strontium's YouTube video.

Did you enjoy Uncle Tungsten, Oliver Sacks's biographical celebration of his early interest in chemistry (and one of the most delightful introductions to the periodic table)? Click "W" on the table and watch this video.

What about the most important element, number 47? (The number 47 rules the universe.) See silver on the screen.

And then there's gallium, used in semiconductors and fancy solar cells. Or why don't we end with a bang with caesium (aka cesium)?

Have fun exploring these videos on your own.

[Hat tip to Grrl Scientist for mentioning Periodic Table of Videos in her Guardian blog Punctuated Equilibrium.]

[Image from Periodic Table of Videos homepage.]

Show And Tell--Sharing Science By Video

noreply@blogger.com (David) — Thu, 29 Sep 2011 20:35:00 +0000

The Journal of Visualized Experiments (JoVE) makes hands-on science available by video. Real scientists demonstrate their experiments on line to accompany their publications. A picture being worth a thousand words, and a video being worth at least a thousand pictures, this novel channel gives fellow researchers (and budding scientists!) around the world clearer access to experimental procedures. Now JoVE is offering free access to developing-country researchers.

Those of us who have tried to figure out just how research was done by reading the often-cryptic "Materials and Methods" sections of scientific publications can appreciate the value of this approach.

JoVE has teamed up with the Health InterNetwork Access to Research Initiative (HINARI) of the World Health Organization to provide this free access. Here is a press release about the initiative.

Many schools and libraries in developing countries cannot afford to subscribe to scientific journals, which are among the most expensive of periodicals (and highly profitable to their publishers). See this blog post by George Monbiot about the high cost of access to the scientific literature. I agree with his complaint that these very high pay walls prevent the wide dissemination of information that is essential to progress in science, and to its understanding by the public. "Secret" science is a sin, especially in our digitally connected world.

At least through programs like HINARI some researchers and students in some developing countries can avoid being completely cut off from current information. It is important that students of science and medicine, wherever they are, have the best possible access to current research if they are to understand the latest methods and developments. And if they can see that research being done, so much the better.

The contributions of researchers in developing countries are essential to the solution of many of today's most challenging technical problems in agricultural, public health, and environmental fields. On-line resources like HINARI, JoVE and the Public Library of Science will help.

How Much Radiation Is Bad For You?

noreply@blogger.com (David) — Wed, 23 Mar 2011 23:36:00 +0000

Putting Fukushima In Perspective

This excellent chart puts in perspective the various amounts of radiation we might be exposed to. I know you can't read the reduced version shown here, so click on the image or go to the xkcd site to see the full-sized image. That site also has links to supporting information.

Yes, too much ionizing radiation can be very dangerous. But "too much" is a lot. We all tolerate minor amounts every day of our lives.

Smoking Sieverts

The chart doesn't include the very significant additional radiation exposure that tobacco smokers expose themselves to. (Info at this EPA site. The U.S. Army Corps of Engineers has a pdf here with some exposure examples.) This University of Iowa site says someone who smokes a pack and a half of cigarets a day exposes himself or herself to a dose of 1300 mrem/year, equivalent to a chest x-ray for each cigaret. That's one of the green boxes in the chart above per smoke. Second-hand smoke is similarly radioactive.

Nobody who smokes should complain about radiation. They expose themselves to more than anyone living around Fukushima is likely to receive. No tsunami required.

The Sievert Measures a Radiation Dose's Effect on Us

The sievert is the SI unit used to compare the effect of doses of ionizing radiation on the body. Different kinds of radiation have different effects, and different parts of the body are affected differently. The sievert takes this into account so we can compare, for example, the effect of the extra radiation received during an airplane flight with the extra radiation received by visiting Chernobyl. [Wikipedia article here.] Sieverts (Sv) and microsieverts (μSv), millisieverts (mSv) and so on are used in the chart above.

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

[Cross-posted from Doc's Green Blog.]

Climate Change--What We Know and What's Uncertain

noreply@blogger.com (David) — Fri, 01 Oct 2010 00:00:00 +0000

The Royal Society has published Climate change: A summary of the science. It has the aim "to summarise the current scientific evidence on climate change and its drivers." It is focused on how Earth's climate is changing and what is making it change. "The impacts of climate change, as distinct from the causes," are not considered.

Although the summary tries to be as non-technical as possible, it is after all a summary of the science, so it incorporates some scientific terminology necessary to convey the facts. It also includes some numbers, such as "240" and "3.6".

The report attempts to clarify which aspects of climate change science are widely agreed, which others have achieved consensus but where further research is expected to give more clarity, and which are not yet well understood.

It begins with a dozen paragraphs of "some background science", explaining very broadly what the greenhouse effect is, what is meant by "climate forcing" and "climate change", and why what may seem like small forcings of a few Watts per square meter can create the profound climate changes seen over past millennia.

At the risk of offering a précis of a summary, here are some of the key points of the report.

Aspects of climate change on which there is wide agreement

"Averaged over the globe, the surface has warmed by about 0.8°C (with an uncertainty of about ±0.2°C) since 1850."
"Each decade since the 1970s has been clearly warmer (given known uncertainties) than the one immediately preceding it. The decade 2000-2009 was, globally, around 0.15°C warmer than the decade 1990-1999."
Other changes include "increases in the average temperature of both the upper 700m of the ocean and the troposphere (the atmosphere up to 10-18km), widespread (though not universal) decreases in the length of mountain glaciers and increases in average sea level."
"Global-average CO₂ concentrations have been observed to increase from levels of around 280 parts per million (ppm) in the mid-19th century to around 388 ppm by the end of 2009."
"Present-day concentrations are higher than any that have been observed in the past 800,000 years, when CO₂ varied between about 180 and 300 ppm."
"Various lines of evidence point strongly to human activity being the main reason for the recent increase, mainly due to the burning of fossil fuels (coal, oil, gas) with smaller contributions from land-use changes and cement manufacture."
"About half of the CO₂ emitted by human activity since the industrial revolution has remained in the atmosphere."
"The concentration of methane has more than doubled in the past 150 years; this recent and rapid increase is unprecedented in the 800,000 year record and evidence strongly suggests that it arises mainly as a result of human activity."
"These additional gases have caused a climate forcing during the industrial era of around 2.9 Wm^-2 [Watt per square meter], with an uncertainty of about ±0.2 Wm^-2."
"The net effect of all human activity has caused a positive climate forcing of around 1.6 Wm^-2 with an estimated uncertainty of about ±0.8 Wm^-2."
"Changes in CO₂ can lead to climate change and climate change can also alter the concentrations of CO₂."

Aspects of climate change where there is a wide consensus but continuing debate and discussion

"Current understanding indicates that even if there was a complete cessation of emissions of CO₂ today from human activity, it would take several millennia for CO₂ concentrations to return to preindustrial concentrations."
"Natural forcing due to sustained variations in the energy emitted by the Sun over the past 150 years is estimated to be small (about 0.12 Wm^-2)" but this remains an active area of research.
"Particles have caused a negative climate forcing of around 0.5 Wm^-2 with an uncertainty of ±0.2 Wm^-2."
"Climate models indicate that the overall climate sensitivity (for a hypothetical doubling of CO₂ in the atmosphere) is likely to lie in the range 2°C to 4.5°C," with this wide range due to "uncertainties in how much water vapour amounts will change, and how these changes will be distributed in the atmosphere, in response to a warming."
"Unless [internal climate variability] has been grossly underestimated,
the observed climate change must result from natural and/or human-induced climate forcing."
"When only natural climate forcings are put into climate models, the models are incapable of reproducing the size of the observed increase in global-average surface temperatures over the past 50 years. However, when the models include estimates of forcings resulting from human activity, they can reproduce the increase."
"The observed vertical and latitudinal variations of temperature change are also broadly consistent with those expected from a dominant role for human activity. There is an ongoing controversy concerning whether or not the increased warming with height in the tropical regions given by climate models is supported by satellite measurements."
"The IPCC’s best estimate was that globally averaged surface temperatures would be between 2.5 - 4.7°C higher by 2100 compared to pre-industrial levels. The full range of projected temperature increases by 2100 was found to be 1.8 - 7.1°C based on the various scenarios and uncertainties in climate sensitivity."
"Climate models tend to predict that precipitation will generally increase in areas with already high amounts of precipitation and generally decrease in areas with low amounts of precipitation."
"Because of the thermal expansion of the ocean, it is very likely that for many centuries the rate of global sea-level rise will be at least as large as the rate of 20 cm per century that has been observed over the past century."

Aspects that are not well understood

"Projections of climate change are sensitive to the details of the representation of clouds in models. Particles originating from both human activities and natural sources have the potential to strongly influence the properties of clouds, with consequences for estimates of climate forcing. Current scientific understanding of this effect is poor." [Or, as Joni Mitchell wrote in 1967, "I've looked at clouds from both sides now, From up and down and still somehow, It's cloud's illusions I recall; I really don't know clouds at all."]
"The future strength of the uptake of CO₂ by the land and oceans (which together are currently responsible for taking up about half of the emissions from human activity…) is very poorly understood, particularly because of gaps in our understanding of the response of biological processes to changes in both CO₂ concentrations and climate."
"There is currently insufficient understanding of the enhanced melting and retreat of the ice sheets on Greenland and West Antarctica to predict exactly how much the rate of sea level rise will increase above that observed in the past century ... for a given temperature increase."
"There is little confidence in specific projections of future regional climate change, except at continental scales."

The authors conclude

"There is strong evidence that changes in greenhouse gas concentrations due to human activity are the dominant cause of the global warming that has taken place over the last half century. This warming trend is expected to continue as are changes in precipitation over the long term in many regions. Further and more rapid increases in sea level are likely which will have profound implications for coastal communities and ecosystems."
"Like many important decisions, policy choices about climate change have to be made in the absence of perfect knowledge. Even if the remaining uncertainties were substantially resolved, the wide variety of interests, cultures and beliefs in society would make consensus about such choices difficult to achieve. However, the potential impacts of climate change are sufficiently serious that important decisions will need to be made. Climate science – including the substantial body of knowledge that is already well established, and the results of future research – is the essential basis for future climate projections and planning, and must be a vital component of public reasoning in this complex and challenging area."

A nice effort by the Royal Society. What we know is sobering. What we don't know is scary. The fact that we don't know everything is unsurprising. That we know so much is among the great achievements of science over the past few decades. That we are unable to deal with the problem, or that some even deny that it is a problem, is just human nature.

The report is available in PDF here.

The Royal Society of London for the Improvement of Natural Knowledge, better known as just the "Royal Society", is one of the world's premiere national scientific organizations. It acts as the United Kingdom's "academy of sciences".

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

What Is The "Greenhouse" Effect?

noreply@blogger.com (David) — Thu, 16 Sep 2010 20:40:00 +0000

This post will help you understand

Why the "greenhouse effect" has to do with gases in the atmosphere,
How these "greenhouse gases" in the atmosphere warm the Earth (and what that has to do with things that are "red hot"),
What this implies for future warming as we put more of these gases into the atmosphere.

The use of a toaster is not required, but it helps if you know how one works.

What Is The Greenhouse Effect?

The "greenhouse effect" refers to how gases in the atmosphere which absorb infrared radiation make the Earth warmer than it would be without them. (It has nothing to do with the way greenhouses work to protect plants by trapping warm air in an enclosure. That's just its name.)

There are two ways to understand this phenomenon:

Some gases in the atmosphere absorb infrared radiation emitted from the surface of the earth. This warms them up and they radiate energy, some of which heats the surface in turn.
Gases in the atmosphere that absorb infrared radiation from the surface make the atmosphere more opaque to that radiation, preventing transmission from the surface into space. (Radiation into space still happens, but from high in the atmosphere where it is colder and thus radiates less.)

Both of these ideas involve reduction in the flow of energy from the surface and lower atmosphere into space as radiation. The loss of radiation to space is less than it would have been if there were less of these "greenhouse gases". Since the flow of energy is reduced, the Earth is kept warmer.

Over time the Earth reaches a temperature that radiates away as much energy as it receives from the Sun. But when the amount of greenhouse gases in the atmosphere change for some reason it takes time for the planet to warm or cool enough to restore that energy balance. That is why the "greenhouse effect" is in the news so much today--the concentrations of these greenhouse gases in the atmosphere are changing at unprecedented rates.

The Physics of the Greenhouse Effect

It is easy to understand the greenhouse effect if you comprehend these simple facts:

The Earth is a big warm rock
Warm things emit radiation
Other things absorb some of that radiation

In particular the "greenhouse gases" in the atmosphere strongly absorb the infrared radiation the Earth emits

When something absorbs radiation it heats up
Warm things emit radiation (2. again)
Other things absorb some of that radiation (3. again)

Some of the radiation from the atmosphere (see 5.) is absorbed by the Earth, which warms it (see 4.)
Some of the radiation from the atmosphere escapes into space, but less than if the atmosphere hadn't absorbed it on its way from the surface and sent some of it back down.

Let's look at that process in more detail:

1. The Earth is a big warm rock. The average surface temperature is about 14.5 degrees C (287.5 degrees K). This is the near-surface atmospheric temperature (as would be measured by a thermometer at a weather station) averaged the seasons, over day and night, and over the geography of the earth. (See Wikipedia article Instrumental temperature record.) The Earth is warmed by radiation from the Sun that it absorbs, and by its own internal heat, some left over from its formation and some from radioactive decay of elements it is made from.

2. Warm things emit radiation. Any object radiates heat, in the form of electromagnetic radiation. Everybody is familiar with the idea of an object being "red hot". An object that hot emits enough light that we can see it, mostly in the infrared part of the spectrum but some at long visible wavelengths. When an object is "white hot" it emits even more radiation, including a lot of visible light and a substantial amount of ultraviolet radiation.

2a. The warmer a thing is the more radiation it emits. This is known as the Stefan–Boltzmann law. (See Wikipedia article Thermal radiation.)

You can easily demonstrate this. If you hold your hand near a toaster (not in a toaster!), where the radiation from the toaster's coils can hit it, the radiation from the toasters coils will be absorbed by your hand. Your skin will be warmed by this radiation, and the more radiation there is the more it will be warmed.

When the toaster is off and the coils are at room temperature you won't feel the warming of your skin. The nerves in your skin don't do much when they are just at room temperature.

(Everything that is not at a temperature of absolute zero emits radiation. But hotter things emit a lot more radiation than colder things. Notice that the Stefan-Boltzmann law says that the amount of energy radiated is proportional to the fourth power of the temperature: j*=εσT⁴. So coils glowing red hot--about 1,000 K--are hotter than coils at room temperature of about 293 K, about 700 degrees Kelvin hotter. They are three times as hot, but they emit more than 100 times as much radiation.)

But when the toaster is on, and the coils are glowing red hot, they will emit a lot of infrared radiation (and a little visible radiation). Your hand would be warmed noticeably as it absorbed this greater quantity of radiation.

At 287.5 degrees Kelvin (14.5 degrees Celsius) most of the radiation the Earth emits is infrared radiation. None of it is in the visible range. (Even at 45 degrees Celsius, a really hot day, none none of the Earth's radiation is in the visible range. This is why the Earth does not appear to glow on a really hot night.)

3. The atmosphere absorbs radiation. Molecules of the gases that make up our atmosphere absorb radiation. Obviously the atmosphere doesn't absorb all wavelengths of radiation equally. It doesn't absorb much in the range of visible light (it is transparent to visible light). This is why we can see the Sun, Moon and stars. The oxygen and ozone in the atmosphere absorb a lot of ultraviolet radiation coming from the Sun. That is why organisms can live on the surface of the Earth (UV kills microorganisms and causes skin cancer in people, for example).

The atmosphere is mostly oxygen and nitrogen, but it is about 0.035% carbon dioxide. Carbon dioxide absorbs infrared radiation very strongly. Since the warm Earth emits mostly infrared radiation (with a peak at wavelengths of about 10^-5 meters) and CO₂ absorbs infrared radiation (especially that with a wavelength longer than about 1.3x10^-5 meters) you can see that a lot of the infrared radiation from the surface of the Earth is absorbed by CO₂ in the atmosphere. (The situation is similar for other "greenhouse gases" such as CFCs, nitrous oxide, methane and water vapor.) (See Greenhouse Gas Absorption Spectrum.)

4. When something absorbs radiation it heats up. The photons of radiation can interact with matter. How they interact depends on the properties of the photon (wavelength) and the properties of the atom or molecule of matter. (At the wavelengths we are talking about these properties mainly have to do with the energy states of its electrons.) When substances absorb radiative energy they increase their thermal energy. They get warmer.

2. again: Warm things emit radiation (see above). The warmer they are the more radiation they emit. The warmed greenhouse gases emit more infrared radiation than they did when it was cooler (see 2a. above). Some of that radiation escapes into space. Some is absorbed by other parts of the atmosphere. And some if it is absorbed by the Earth below, making it a little warmer (see 4. above).

So that's how the "greenhouse effect" works:

Radiation from the Sun warms the Earth and the atmosphere
The Earth emits infrared radiation (the warmer it is the more it emits)
The "greenhouse gases" in the atmosphere, especially CO₂, absorb some of that radiation from the earth, and this warms them up (the more of these gases there are the more they absorb)
The warm gases in the atmosphere emit infrared radiation (and the warmer they are, and the more of them there are, the more they emit)
Some of the infrared radiation from the "greenhouse gases" in the atmosphere is absorbed by the Earth, warming it a little more
Loop back and repeat

So it doesn't work at all like a greenhouse. (Not that most people have much idea how greenhouses, also called glasshouses, work, or even what they are.) It isn't a result of the atmosphere "insulating" the Earth, like a blanket. It has to do with the gases in the atmosphere absorbing radiation, heating up, and warming the Earth below by their own radiation. But the names "greenhouse effect" and "greenhouse gases" are well established, so we might as well go ahead and use them.

The Net Result

The diagram below shows how all this works in terms of the Earth's energy balance.

As you can see, the net imbalance (energy in minus energy out) is only 0.9 Watts per square meter. (Other estimates give net forcing of approximately 1 to 3 Watts per square meter.) Whatever the actual figure, it is enough to warm the Earth significantly over time.

Consequences

Also note that the net absorbed is only 0.26% of the total incoming energy flux. It only takes a small change in the transparency of the atmosphere in the infrared to change the outgoing long-wave (infrared) radiation enough to affect the surface temperature. And of course the more greenhouse gases in the atmosphere, the greater the climate forcing.

How much will the Earth's temperature rise because of this 1 or 2 Watt per square meter forcing? That is the subject of urgent research. Current thinking is that the level of greenhouse gas in the atmosphere today, if we didn't put any more up there, might lead to a further increase in global temperature of one or two degrees Celsius or so.

But there are many difficulties with this estimate:

Feedback effects. As the Earth warms up there will be changes in the global energy balance that might make it warm faster or slower, such as

Melting of ice. Ice is highly reflective, so if it melts to expose bare ground or open sea less incoming solar radiation will be reflected back to space ("Reflected by Surface" in the diagram above).
Vaporization of methane in permafrost and undersea deposits. Methane is one of the most significant greenhouse gases, and there are vast amounts of it tied up in frozen permafrost or in deposits of methane hydrates on the sea floor. If warming of the sea causes melting and release of some methane hydrates this could vastly decrease the transparency of the atmosphere to long-wave radiation, keeping more heat on the Earth. It is thought that when this happened in the geologic past it led to an earth many degrees hotter than today's.
Warming seas. Cold water can absorb more carbon dioxide than warmer water. So as that 1 Watt per square meter radiative forcing warms the oceans, more carbon dioxide will be left in the atmosphere to act as a greenhouse gas.
Clouds. As the climate warms the weather will change. There might be more clouds, or less, or their distribution might change. Clouds are an important part of the "Reflected by Clouds and Atmosphere" component of the energy budget in the diagram.
Water vapor. Warmer air can hold more water vapor, and water vapor is a significant greenhouse gas.

Continued emissions.

We have already perturbed the planet's energy balance by putting around a trillion tonnes of greenhouse gases into the atmosphere over the past couple of centuries by burning fossil fuels and by land-use changes (burning forests). That is why the energy budget is out of balance by one or two Watts per square meter. But we continue to put about 35 billion additional tonnes of greenhouse gases into the air every year. And that annual emission figure continues to increase. So the concentration in the atmosphere will increase, the transparency of the atmosphere to infrared radiation will decrease, and the greenhouse climate forcing will increase. We are on course to put at least another trillion tonnes of greenhouse gases into the atmosphere by 2050, probably closer to two trillion.

I hope you can see why putting more CO2 into the atmosphere, more than the land and the seas can reabsorb, could make the atmosphere, and thus the Earth, warmer, perhaps much warmer.

The toaster image is from Explain that Stuff published under a Creative Commons License.

The energy balance diagram is from this UK government site, and is protected by Crown copyright. Used by permission.

Here is another explanation of the greenhouse effect.

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

484TFZMUEH2N

Latent Heat--Sweat, Storms and Cooling Towers

noreply@blogger.com (David) — Tue, 14 Sep 2010 19:54:00 +0000

If you don't understand "latent heat" you can't understand how much of the biosphere or a lot of engineering works. The latent heat of water is the energy absorbed when water is evaporated, or released when it condenses. Weather, thermoregulation, global warming and industrial cooling all depend on the high latent heat of water and its ability to transform heat to work and vice versa, and to move energy from one place to another.

Water is Magic

Water is marvelous stuff and has many interesting properties. This is a good thing (for us) since these properties are necessary for life (as we know it) to exist.

(This is an example of the anthropic principle--we are only able to observe water's interesting properties because we exist, and we are only able to exist because of water's interesting properties. So it is unavoidable that in our world--in any world where we could have evolved-- water must have such interesting properties.)

Among water's most important properties is its high latent heat. This property creates much of Earth's most violent weather and drives the thermodynamics of climate.

What is "Latent Heat"?

To understand latent heat you first have to understand the idea of states of matter and phase changes.

Chemical substances can exist in several "states". The common ones that we encounter in everyday life are the solid state, the liquid state, and the gaseous state. When matter changes from one state to another we call it a "phase change". So liquid water can undergo a phase change to become the gas water vapor, and it can reverse that transition and condense from a gas into a liquid. It can undergo a different phase change from a liquid to become solid ice, and the reverse to melt from ice into liquid. See the diagram below.

The names of the various common states of matter
and of the phase transitions between them

The reason this is important (to us and our planet) is that it takes a lot of energy to change water from a liquid to a gas. This is because water molecules in a liquid are attracted to each other because of their polarity.

illustrative separation of
charges on water molecule:
negative red, positive blue

Water molecules are highly polar molecules. This means they have uneven distribution of their electrons, with more electrons bunching around the oxygen atom and thus creating lower electron density around the hydrogen atoms. So the molecule is more negative on one side (where the electrons are concentrated) and more positive on the other side. It is like a little magnet, a dipole. As you are no doubt aware, "opposites attract". So the negative side, or middle, of a water molecule will tend to attract the positive sides, or ends, of other water molecules. This is an example of "hydrogen bonding". Hydrogen bonding is extremely important in the machinery of life. This attraction tends to hold the water molecules in liquid water together. To evaporate water--to make some of those molecules break away from the liquid mass and fly off as a gas--takes a lot of energy.

To evaporate one kilogram of water by boiling it, changing it from liquid to gas at 100 degrees C, takes 2,260 kilojoules. That is about two and a half times as much energy as is needed to vaporize a kilogram of ethyl alcohol.

Latent Heat in the Kitchen

Pot of boiling water

You are undoubtedly familiar with the large amount of heat needed to bring about this phase transition of water from liquid to gas. Imagine a pot of boiling water. To keep it on the boil lots of heat has to be supplied. As soon as the heat is reduced it stops boiling and steam stops coming off. Consider the flame or other heat source that is needed to keep it boiling. You wouldn't want to contact such a concentrated heat source directly. (Warning: please do not put your hand on the stove to confirm this!)

The truly amazing thing about the latent heat of evaporation of water is that when the phase change is reversed, when water vapor condenses into liquid water, the same amount of heat is released. This isn't as obvious to us as the amount of heat consumed in boiling, but you may have experienced it if you have gotten your hand in the stream of steam escaping from a teakettle.

This is the reasons that burns caused by steam can be so severe. Besides the heat of the steam, some of the steam will condense on the skin, releasing its latent heat of condensation. This is equal to the latent heat of vaporization of the same amount of water. You wouldn't want to put your hand in the flame needed to vaporize even a small amount of water. But when that small amount of water condenses out of steam on your skin it releases just that amount of heat. This is why a burn from steam can be more severe than a burn by boiling water itself, if the quantity of steam is significant.

How Latent Heat Drives Storms

So when water evaporates it takes up heat (cooling the local environment). As water vapor it carries that heat around as latent heat. Then when that vapor condenses it releases that latent heat, heating up the local environment, usually the air.

This is what drives some types of storms, including thunderstorms, tornadoes, hurricanes and typhoons. Such storms are driven by "heat engines" based on water vapor. The key to such systems is rising warm air containing water vapor. As it rises it expands (because the atmospheric pressure is lower the higher you go) and as it expands it cools (the same amount of heat is spread through a larger volume--adiabatic cooling).

At some point the parcel of moist air has cooled enough that it cannot hold all the water vapor it contains. (The amount of water vapor air can hold is strongly dependent on its temperature.) So some of the water vapor condenses out as water droplets--clouds, rain or snow. As that water vapor condenses to liquid it releases heat (the latent heat of condensation or latent heat of fusion), warming the parcel of air. Because of this warming, the moist parcel of air will be warmer and more buoyant than neighboring air, so it will continue to rise.

As it rises and expands more condensation will occur, continuing the process. (This gives rise to towering "thunderhead" cloud formations.) Essentially this creates a strong updraft as water condenses out of the rising air. This updraft causes locally lower air pressure below it and sucks in surrounding air to fill the gap, creating surface wind--the storm as we experience it. (There may also be downdrafts associated with falling precipitation.)

Without the heat released by the condensation of water vapor these systems couldn't grow to their towering size.

Tropical cyclone driven by energy
released by condensation of moisture

In a tropical cyclone (hurricane or typhoon) more warm moist air is drawn into the cyclone as it moves over warm ocean waters, feeding and perpetuating the system. This is why hurricanes can grow so large, persist so long, and have such high winds. "A tropical cyclone's primary energy source is the release of the heat of condensation from water vapor condensing, with solar heating being the initial source for evaporation. Therefore, a tropical cyclone can be visualized as a giant vertical heat engine supported by mechanics driven by physical forces such as the rotation and gravity of the Earth. [source Wikipedia]"

Latent Heat of Evaporation and Climate Change

There are several processes where the latent heat of water becomes important in trying to understand climate change associated with global warming.

Tropical Cyclones
Increases in sea surface temperatures could affect the formation and behavior of hurricanes. As noted above, warm ocean waters put a lot of moisture into the air (the air can hold more moisture at higher temperature), and it is water vapor in the air that makes the hurricane heat engine work once one gets started. Wider areas of warm ocean waters could mean tropical cyclones will form in places they didn't form before.

There is a lot of scientific discussion about this because warming causes other simultaneous changes. For instance, hurricanes can't form if the local winds are too high--only where there are just light breezes. Will warming change the distribution of winds over warm areas of the seas?

There is some evidence that Atlantic hurricane numbers have been rising (previous post) but this is still in dispute.

If seas are warmer they might also contribute to the strength of tropical cyclones that do form. This previous post discusses research that suggests increased destructiveness of hurricanes associated with warmer seas. This question is still not settled though.

Cooling By Irrigation
Because of the latent heat of water, more evaporation means more cooling in some places, and more rain means more warming in other places. A recent article in the Journal of Geophysical Research (pdf here, New York Times Green blog post about it here) says irrigation may be causing cooling in some regions, locally masking the effects of global warming.

The model runs reported in this paper suggest that parts of norther India may have experienced several degrees of cooling due to all the heat absorbed by irrigation water applied to crops in the later part of the 20th century. Weather patterns may even have been affected enough to reduce the amount of rain in the Bay of Bengal branch of the Southwest Monsoon. (Other researchers got somewhat different or even contradictory results with different models.)

This is a bit scary because if groundwater depletion leads to reduction in irrigation in the future, the reduction of cooling effect could have both local an regional climate effects, including sharply higher temperatures and changes in rainfall amounts and distribution.

Evaporative Thermoregulation

Evaporation is used to cool the bodies of many animals. Sweat evaporating from the skin makes it possible for us to deal with hot weather. On a hot day in dry weather a person can lose more than a liter of water by evaporation of sweat (even several liters if it is really hot or you are exercising). Think of the amount of heat it would take to boil away a liter of water.

Other Uses of Latent Heat

There are many other uses of the latent heat of water for cooling, for example:

Evaporative coolers, a kind of air conditioning.
Some cooling towers at power plants

Cooling towers at Didcot Power Station,

and other industrial facilities use evaporative cooling. Steam turbines require a condenser to cool the steam after it leaves the turbine so that it condenses into water and can be pumped back through the cycle. Such condensers often use evaporative cooling by spraying or dripping water over coils carrying hot water from the system. At big power plants these may be enclosed in characteristic hyperboloid chimney-like structures to provide draft to move the moisture-laden air out of the cooling unit. Other systems use fans. [Here is a video of the inside of a cooling tower showing water being sprayed over cooling circuits.]

Understand latent heat and many phenomena will be less mysterious to you.

The diagram of phase changes is a public domain image from Wikimedia Commons. Rights information here.

The illustration of charges on a water molecule has been placed in the public domain by its author, from Wikimedia Commons. Rights information here.

The picture of the pot of boiling water is from Wikimedia Commons, with the permission of the copyright holder under the terms of the GNU Free Documentation License.

Diagram of tropical cyclone by Jannev, placed in the public domain at Wikimedia Commons.

Picture of Didcot Power Station by Dave Price from Wikimedia Commons, used under a Creative Commons Attribution Share-alike license 2.0

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

Plants Unhappy About Global Warming

noreply@blogger.com (David) — Fri, 03 Sep 2010 18:20:00 +0000

Rice field in Bangladesh

New science raises serious concerns about the negative impact of global warming on crop yields and plant productivity in general.

This could be one of the most severe social and economic effects of climate change.

Rice Yields Hurt By Warming

Researchers from the University of California, Duke, National Bureau of Economic Research, IRRI and FAO published a very revealing paper in PNAS. They studied 227 intensively managed irrigated rice farms in six important rice-producing countries over several years. Their findings "imply a net negative impact on yield from moderate warming in coming decades. Beyond that, the impact would likely become more negative, because prior research indicates that the impact of maximum temperature becomes negative at higher levels." Rising temperatures, especially nighttime temperatures, will hurt rice yields.

The paper is behind a pay wall, but there is a good BBC News article on their results. It says they "found that over the last 25 years, the growth in yields has fallen by 10-20% in some locations, as night-time temperatures have risen. ... Although yields have risen as farming methods improved, the rate of growth has slowed as nights have grown warmer." And "if temperatures continue to rise as computer models of climate project, Mr Welch says hotter days will eventually begin to bring yields down."

The question is whether rice improvement efforts (plant breeding) can get ahead of the negative effects of rising temperatures.

This EurekAlert release summarizes the results.

Net Plant Primary Production Down

Researchers at the University of Montana studied terrestrial net primary production. Net primary production (NPP) is the total net fixation of carbon by photosynthesis in an ecosystem. They found that "Large-scale droughts have reduced regional NPP, and a drying trend in the Southern Hemisphere has decreased NPP in that area, counteracting the increased NPP over the Northern Hemisphere."

These results were surprising since earlier studies had shown increasing plant carbon capture with rising temperatures in the 80s and 90s. However temperatures since 2000 have been the highest in modern records and accompanying droughts have apparently cut into global plant growth.

Again the Science article is not open access, but this EurekAlert release has some more information on the results and their implications.

While longer growing seasons and higher atmospheric carbon dioxide levels may favor more carbon fixation in some northerly regions, more of the globe is water-limited and more drought could hurt total carbon fixation more than warming trends would boost it. As the authors say in their abstract, "A continued decline in NPP would not only weaken the terrestrial carbon sink, but it would also intensify future competition between food demand and proposed biofuel production."

Plankton Declining With Warming Seas

Researchers from Dalhousie University studied the concentrations of phytoplankton in the oceans. Writing in Nature report "declines in eight out of ten ocean regions, and estimate a global rate of decline of ~1% of the global median per year". "We conclude that global phytoplankton concentration has declined over the past century" and "long-term declining trends are related to increasing sea surface temperatures." Since phytoplankton, minute plants, "account for approximately half the production of organic matter on Earth" this could be bad news.

Marine phytoplankton

According to a Reuters story, "The study estimates the decline in marine algae has been approximately 40 percent since 1950." Half of all photosynthetic carbon fixation, cut by 40%!? That's significant and scary.

The story quotes study co-author Boris Worm: "I think that if this study holds up, it will be one of the biggest biological changes in recent times simply because of its scale. The ocean is two-thirds of the earth’s surface area, and because of the depth dimension it is probably 80 to 90 percent of the biosphere. Even the deep sea depends on phytoplankton production that rains down. On land, by contrast, there is only a very thin layer of production."

Here is an excellent release in Science Daily summarizing the report.

Yield Reductions in China?

A review paper in Nature by Shilong Piao et al. assesses "the impacts of historical and future climate change on water resources and agriculture in China. They find that in spite of clear trends in climate (especially temperature), overall impacts are overshadowed by natural variability and uncertainties in crop responses and projected climate, especially precipitation. In a best-case scenario, crop production is constant, whereas the worst-case scenario suggests that production could fall by about 20% by 2050." (From Editor's Summary.)

A Reuters article quotes further from the paper, "Countrywide, a 4.5 percent reduction in wheat yields is attributed to rising temperatures over the period 1979-2000," and says "They forecast that rice yields would decrease by 4 to 14 percent, wheat by 2 to 20 percent and maize by zero to 23 percent by the middle of the 21st century."

(Grist carries an AFP story about this research.)

What Does It Mean?

These results from several unrelated fields of research suggest that we should be concerned that continued warming will negatively affect both wild plants (which act as a carbon dioxide sink) and agriculture (fundamental to social stability).

If forests, grasslands, phytoplankton in the sea and other ecosystems absorb less of the CO₂ we release by unrestrained burning of fossil fuels, then atmospheric CO₂ levels may rise faster than models currently predict.

If higher temperatures and drought reduce agricultural output more land will have to be brought under the plow. Such land-use changes usually release significant additional carbon dioxide.

We should significantly increase spending on agronomy and plant breeding, especially in Africa, India and East Asia, if we want to maintain the yields we have.

[Crossposted from sister blog A Very Different Earth.]

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

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Oil Spill Math: How Much Risk for How Much Oil?

noreply@blogger.com (David) — Thu, 24 Jun 2010 23:37:00 +0000

How much oil has spilled?

Big quantities are sometimes hard to grasp. They are outside our everyday experience. When you hear that millions of gallons of crude are spilling in the Gulf, how much is that really? Professor James Corbett of the University of Delaware has done the math in a creative way.

Assuming the gusher is was gushing 50,000 barrels of crude a day (you can adjust this assumption on the site), "As of day 66 (today), if that oil had been refined to fuel in a typical US refinery, it would have produced gasoline, diesel fuel, and fuel oil capable of powering these vehicles:

118,000 Cars for a year, and
9,800 Trucks for a year, and
163 Containership days"

All the cars in Topeka

Most of us don't have a good feel for how many a hundred thousand cars are. So the U. Delaware site also shows the cities in the U.S. with 100,000 or more cars. This includes such cities as Pasadena, California, Buffalo, New York, Brownsville, Texas, Hartford, Connecticut and Alexandria, Virginia. All the cars in one of those cities could do all their driving for a year on the gas that could be made from the oil spilled so far. And the same crude would also provide diesel fuel for 10,000 trucks for a year, and bunker for ships.

If that's too hard to grasp, consider that you could drive your car on that gas for 100,000 years. (But what fun would that be?)

If the first Homo sapiens had started driving with that gas he or she could still be driving today (assuming fewer miles driven during the first 199,900 years, when there weren't any decent roads). Our species is only about 200,000 years old.

How risky was it to drill there?

And was that a risk worth taking? The U. Delaware site also provides a good discussion of how we try to quantify such risks. In fact, we can look at the environmental impact statement approved by the Minerals Management Service and see the probabilities BP assigned to the type of accident that occurred. The EIS "estimated the probability of a blowout in deep water drilling to range between 2 and 7 in a thousand".

If you had such a 0.2% to 0.7% chance of a disaster costing $100 billion (and the bill might be that high--not counting the damage which can't be repaired at any cost), then you would have to expect a proportionately huge upside potential to make such a well worth drilling. In fact you would have to expect to make about $500 billion in profit on the well to take such a risky bet. Since BP only makes about $30 billion in profit a year, the well would have to generate as much profit as all of BP's other activities put together every year for more than a decade, which seems unlikely. So why did they drill there?

Oil companies get special math

The reason oil companies will drill in the face of such odds is this: They know they won't have to pay the whole bill. Also, they probably told themselves that it couldn't possibly be this bad. (In fact we can read their EIS and see that they told government regulators it couldn't be this bad--and the regulators believed them!)

The Oil Pollution Act "limits the liability of responsible parties for offshore facilities, such as the Deepwater Horizon facility, to all removal costs (i.e., direct cleanup cost) plus $75 million and other language places a limit of $3,200 per gross ton".

This gross ton number tells you why BP has been so cagey about accurately quantifying just how much oil is spilling, has spilled, or will spill. Expect lawyers to argue about this for the next few decades. There's more detailed discussion on the site.

So even if the Gulf blowout ends up gushing two million barrels, as seems likely, that is about 300,000 tons of crude, for a total liability of around a billion dollars. (See conversion factors here.)

So the math for oil companies is not so bad. Downside say a couple of billion max, with a probability of 0.5%, so you only have to plan on making $10 million profit on the project to make it an even bet. The U.S. taxpayer and those who would have benefited from an undegraded environment bear the rest of the liability.

The severity and cost of the current spill may change that calculus, but they haven't yet.

[This is cross-posted from the Doc's Green Blog.]

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

Is There Scientific Consensus on Climate Change?

noreply@blogger.com (David) — Wed, 23 Jun 2010 20:22:00 +0000

Research Shows Scientists Agree on Global Warming

Researchers at Stanford and the University of Toronto noted that some people dispute whether there is "scientific consensus" on the reality and causes of climate change. They decided to find out how much consensus there really is.

The Intergovernmental Panel on Climate Change concluded that anthropogenic greenhouse gases have been responsible for "most" of the "unequivocal" warming of the Earth's average global temperature over the second half of the 20th century. But how many scientists who study the subject really believe that? And which scientists disagree?

They tried to "examine a metric of climate-specific expertise and a metric of overall scientific prominence as two dimensions of expert credibility in two groups of researchers", that is, those who agree with the IPCC's conclusion and those who do not.

They "compiled a database of 1,372 climate researchers based on authorship of scientific assessment reports and membership on multisignatory statements about ACC [anthropomorphic climate change]. We tallied the number of climate-relevant publications authored or coauthored by each researcher (defined here as expertise) and counted the number of citations for each of the researcher’s four highest-cited papers (defined here as prominence) using Google Scholar. We then imposed an a priori criterion that a researcher must have authored a minimum of 20 climate publications to be considered a climate researcher, thus reducing the database to 908 researchers."

Of those climate researchers, only a few percent were unconvinced of the IPCC's conclusion. The other 97-98% agreed with the IPCC that climate change is real and is mostly caused by human activities. The study also found that those researchers who published more and were cited more often in the field were more likely to be convinced by the evidence, and that those unconvinced by the evidence were generally those with fewer publications and citations.

"Not all climate researchers are equal"

They concluded that "the expertise and prominence, two integral components of overall expert credibility, of climate researchers convinced by the evidence of ACC vastly overshadows that of the climate change skeptics and contrarians. This divide is even starker when considering the top researchers in each group. Despite media tendencies to present both sides in ACC debates, which can contribute to continued public misunderstanding regarding ACC, not all climate researchers are equal in scientific credibility and expertise in the climate system."

The abstract of the PNAS paper is here, with access to the full paper as PDF. (Bless scientists and their grant providers who pay so that their papers can be open access, not restricted just to the academic community and other professional researchers.)

Dueling Experts

Often debates about climate policy come down to "My experts can beat up your experts". This research shows that there are objective measurements that can reveal which experts are more expert, and therefore should be given more weight in guiding policy. (Not that policy is driven by experts--it's politics.)

Science, after all, is substantially about measuring and quantifying. Even scientific expertise can be measured and quantified. This particular method is not the last word in such analysis. It is true that the lonely dissenter, out of step with the general consensus, who can't get a grant and therefore publishes less, may have a useful contribution to make. In fact she may be right and all the experts may be wrong. But this is not likely. When the skew is 881 to 27, the consensus is clear.

Know Your Spills--Confusing Names and Oil Quantity Equivalents

noreply@blogger.com (David) — Mon, 14 Jun 2010 19:47:00 +0000

Confused about the many names for the Gulf of Mexico oil spill? Here is a useful list of equivalents.

Deepwater Horizon Oil Spill--This follows the convention that spills are named after the vessel involved. The semi-submersible floating oil drilling rig Deepwater Horizon was technically an oceangoing vessel, registered in the Marshal Islands. This term unfortunately suggests that the event is a "spill", an unintended release of oil from a container like a vessel, pipeline or tank. It is really a "blowout" or "gusher".
Macondo Blowout--The Macondo Prospect is an oil and gas prospect in the Gulf of Mexico, in which the Deepwater Horizon was drilling when the blowout occurred. This was the codename applied to the field during early exploration. "BP is the operator and principal developer of the oil field with 65% of interest, while 25% is owned by Anadarko Petroleum Corporation, and 10% by MOEX Offshore 2007, a unit of Mitsui." [Source: Wikipedia.]
BP Oil Spill--BP plc has been named the responsible party in the incident by the U.S. government. It has the majority interest in the field, was in charge of its development, had leased the Deepwater Horizon and had contracted with various firms to carry out the drilling.
Mississippi Canyon 252 (MC‐252) Incident--The Macondo Prospect was referred to by the U.S. Minerals Management Service as "Mississippi Canyon Block 252" in its lease sale. This is the terminology often used by NOAA and other U.S. government agencies in official communications.
Gulf of Mexico Spill--This imprecise name is sometimes used in the media. There have been many oil spills in the Gulf of Mexico, and there are probably several active ones there at the moment.

How Much Oil?

Press reports and official announcements about the quantities of oil, gas and other materials released from the blowout use various units. A million here, a million there, pretty soon you're talking about a real mess. Here are some handy equivalencies.

one tonne of crude oil

approximately 7.3 barrels of crude oil

about 307 U.S. gallons of crude oil

one barrel of crude oil

42 U.S. gallons of crude oil

159 liters of crude oil

10,000 barrels of crude oil

420,000 U.S. gallons of crude oil

1,590,000 liters of crude oil

about 1,400 tonnes of crude oil

60,000 barrels of crude oil

2.5 million U.S. gallons of crude oil

9.5 million liters of crude oil

about 8,200 tonnes of crude oil

The conversions between weight measures (tonnes) and volume measures (barrels, gallons, or liters) depend on the density of the oil, which varies considerably.

Further useful conversion factors are here.

Carl Sagen "Sings" of Science (with Dawkins, Hawking, et al.)

noreply@blogger.com (David) — Fri, 04 Jun 2010 18:48:00 +0000

Can the coolness of science be conveyed by a sort of synthetic music video? You decide:

[If you can't see the video, watch it at YouTube here.]

This is one of several videos created by John Boswell and his collaborators at Symphony of Science. "Boswell uses pitch corrected audio and video samples from television programs featuring popular scientists and educators. The audio and video clips are mixed into digital mashups and scored with Boswell's original compositions." Symphony of Science "aims to spread scientific knowledge and philosophy through musical remixes" and to "deliver scientific knowledge and philosophy in musical form". [Source: Wikipedia article.]

How science works: Auto-Tune, the software that "bends" spoken phrases into song in these videos, "was initially created by Andy Hildebrand, an engineer working for Exxon. Hildebrand developed methods for interpreting seismic data, and subsequently realized that the technology could be used to detect, analyze, and modify pitch." [At least according to Wikipedia.] Everything is connected?

Don't Sign If You Can't Do The Math

noreply@blogger.com (David) — Sun, 16 May 2010 17:38:00 +0000

A recent research paper found that there was a strong correlation between basic understanding of numbers and ability of subprime borrowers to keep their homes. People who understood percents, discounts, and compounding were much more likely to be able to avoid default, even compared to less numerate people in similar economic circumstances. Math skills pay.

Here is the first numeracy question they used:

1. In a sale, a shop is selling all items at half price. Before the sale, a sofa costs $300. How much will it cost in the sale?

The study was published by the Federal Reserve Bank of Atlanta (abstract and full study here). It found "a large and statistically significant negative correlation between numerical ability and various measures of delinquency and default." The authors even say "Our results raise the possibility that limitations in certain aspects of financial literacy played an important role in the subprime mortgage crisis."

People with limited math skills caused the global meltdown?? It might be fairer to say that by lending to people with unstable or inadequate income and bad math skills lenders were lending to people likely to default, and probably knew it. It should have been no surprise when those loans went bad. If the risk hadn't been multiplied by layers of collateralized debt obligations and credit default swaps we wouldn't have had a global financial meltdown. But that's another story.

The interesting thing is that similar subprime borrowers with somewhat more robust financial math skills were much less likely to default, even controlling for socioeconomic factors. "We find a large and statistically significant negative correlation between financial literacy and measures of mortgage delinquency and default, and the finding is robust to the inclusion of controls for income, education, risk aversion, and time preferences, thus ruling out a broad set of potential biases from omitted variables. Foreclosure starts are approximately two-thirds lower in the group with the highest measured level of numerical ability compared with the group with the lowest measured level." "20 percent of the borrowers in the bottom quartile of our financial literacy index have experienced foreclosure, compared to only 5 percent of those in the top quartile. Furthermore, borrowers in the bottom quartile of the index are behind on their mortgage payments 25 percent of the time, while those in the top quartile are behind approximately 10 percent of the time."

Same income, same mortgage provisions, same problems, but moderate math skills: much lower likelihood of default. Paying attention in math class, or maybe just having a half-way competent math teacher in 7th grade, really paid off for some borrowers. "We include as control variables measures of other aspects of financial literacy and a general measure of cognitive ability, but find that the correlation is highly specific to one aspect of financial literacy: numerical ability."

To see the degree of numerical literacy we are talking about, try this quiz put together by The Economist. It uses the same five questions posed by the researchers. Here is the Economist article on the research findings. The abstract of the study is here (with access to the whole paper in PDF).

A Hard Rain's A-Gonna Fall

noreply@blogger.com (David) — Tue, 06 Apr 2010 19:01:00 +0000

Researchers at the University of New Hampshire have analyzed 60 years' worth of National Weather Service rainfall records in nine Northeastern states and found that storms that produce an inch or more of rain in a day are coming more frequently. An increase in the frequency of extreme precipitation events
is one of the predicted impacts of a world warmed by heat-trapping
gases.

The researchers looked at several indicators of changing incidence of heavy rain events:

Frequency of 24-hour periods when one inch of rain fell at a particular weather station site (a "one-inch event")
Similarly, the occurrence of "two-inch events" and "four-inch events", when two or four inches fell at a site in 24 hours
The frequency of extreme precipitation events, defined as the top one percent of 24-hour precipitation measurements for each year. "Changes in the threshold of the 99th percentile of daily accumulations exemplify changes in precipitation intensity" (how much rain has to fall in 24 hours to put an event in the 99th percentile for the year?)
A third method was to define extreme precipitation events using recurrence intervals. They looked at the change in the amount of time between storms of a given magnitude.

According to each of the indicators studied extreme rainfall events have increased over the 50-year period. For 11 stations the records go back far enough to track such events from 1900 to 2007. For all of the indicators the increases at those stations since 1948 were faster than for the whole period 1900 to 2007.

The increase in more-intense rainfall was correlated with increases in temperature seen over the period. This suggests that further increases in temperature will correlate to further increases in the occurrence of heavy rainfall events.

They also found that over the whole 50-year study period rainfall in the Northeast has an overall increasing trend of about three-quarters of an inch per decade.

The study concludes that communities are likely to experience increased flooding due to intense storms (as they have this year, for instance) and that planning and expenditure to minimize the impacts of flooding will be increasing drains on the public purse.

The report, Trends in Extreme Precipitation Events for the Northeastern United States 1948-2007, is available in PDF here.

Weird Science Words

noreply@blogger.com (David) — Mon, 23 Mar 2009 12:04:00 +0000

Science Dictionary

Here are some weird science words. Be careful how you use them.

Auscultation—Listening. Especially listening to the sounds of the internal organs, as with a stethoscope.

Borborygmus, pl. borborygmi—Rumbling and gurgling noises from the intestines. Stomach "growling".

Bromhidrosis—Body odor, B.O. From the Greek bromos, a stench, and hidros, sweat.

Cacophony—Jarring, discordant sound. Cacophonous: having a harsh, discordant sound. From the Greek kakophnos, kakos, bad+ phōnē, sound. Kakos goes back to one of the oldest words we still use, the Indo-European root kakka-, to defecate.

Cacodyl—The arsenic group (CH₃)₂As, or a poisonous oil (As₂(CH₃)₄) with a strong garlicky odor. Same root as cacophony.

Emesis, pl. emeses—The act of vomiting

Eructation—Belching, burping

Flatus—The gas that comprises a belch or fart

Formication—A sensation that feels like insects crawling on the skin, a type of paresthesia. From formica, Latin for "ant".

Googol—The number 10 raised to the power 100 (10¹⁰⁰), written out as the numeral 1 followed by 100 zeros. Not to be confused with "Google", a trademark of Google Inc.

Mastication—chewing

Micturation—Urination; needing to pee

Osculant—Intermediate in characteristics between two similar or related taxonomic groups. Closely adhering or joined; embracing

Osculation—Kissing; a kiss

Oscitancy—the act of yawning

Pandiculation—The act of stretching and yawning at the same time.

Radicle—A small root, specifically the part of a plant embryo that develops into the root. Not to be confused with "radical", meaning the root (e.g. of a word), at the root, the mathematical root sign (√) or a highly reactive atom, molecule or person. Nor with "ridicule".

Sternutation—Sneezing

Stertor—The sound of snoring

Syzygy—Lots of meanings in different sciences (and in poetry, rhetoric etc.) generally having something to do with being paired, joined, aligned or something. From the Greek zugon, yoke

Vomiturition—Forceful attempts at vomiting without bringing up the contents of the stomach; retching

Vomitus—Vomited matter

Wamble—To turn or roll (said of the stomach), an upset stomach, nausea

Your assignment: Use all these words in a sentence.

This list is revised or updated from time to time.

Do Cow Farts Cause Global Warming?

noreply@blogger.com (David) — Wed, 02 Jan 2008 20:43:00 +0000

Bovine Flatulence--Threat or Menace?

Cows can digest things we can't, especially including the cellulose in grass and grain. They do this by maintaining cultures of microorganisms in their complicated series of "stomachs" that can break down cellulose. The cows then digest the microbes and the sugars and fatty acids they produce.

(Brief overview of ruminant digestion here. If you are interested in delving into the digestive physiology of ruminants in more detail, start here.)

Some of these microbes produce methane (CH₄). Some of the other microbes can use that methane as food, but a certain amount of it escapes as belches or farts (mostly belches). (Some people have microbes in their guts which produce methane, and thus their farts also contain methane--but nothing compared to the amount cows produce.)

The publication Emissions of Greenhouse Gases in the United States 2006 (pdf) summarizes the total greenhouse gas output of the US:

Of the 605 million metric tonnes CO₂ equivalent of methane shown in the graph, about 115 million tonnes CO₂e is from "livestock enteric fermentation"--mostly cow burps and farts. That is less than 20% of the methane load, and less than 2% of the 7 billion tonne CO₂e total.

Of course raising cattle causes other greenhouse gas emissions.

There are about 56 million tonnes CO₂e of methane and 55 million tonnes CO₂e of nitrogen oxides released from cattle wastes as they decompose. (Some of that methane can be captured and used to generate electricity or heat, while releasing carbon dioxide, a much less potent greenhouse gas.)
About 227 million tonnes CO₂e of nitrous oxide is released from nitrogen fertilization of soils (30% of it from nitrogen fixed by the crops themselves, not from industrially produced fertilizers).
Most of the nitrogen fertilizer used on crops (89%) is used on corn (maize). About half of the corn produced in the US is fed to livestock, a large fraction to cattle, especially dairy cows. So about 50 million tonnes CO₂e emissions associated with fertilizer use should be indirectly blamed on cows.
(Another large fraction of corn is used to make ethanol as a motor fuel, indirectly causing the release of significant amounts of greenhouse gases in the corn production. But that's another story.)

So cattle are responsible for about 3.5% of US greenhouse gas emissions, on a CO₂ equivalent basis. To keep this in perspective:

2% of greenhouse gas production is in the form of methane from garbage decomposing in landfills.
Roughly 2% is chlorofluorocarbons (CFCs) from air conditioners, refrigerators and industrial processes.
Other industrial processes (especially cement manufacture) produce about 2%.
Burning jet fuel accounts for more than 3%.
12% of greenhouse gas emissions are CO₂ emitted generating electricity which is used in residential applications like lighting, TVs, computers, and refrigerators.
17% came from burning gasoline in cars and trucks.

So cow farts and burps do contribute some to greenhouse gases, and thus to global climate change. But they are not a major cause. Nonetheless, improvements in fertilizer use and waste management in agriculture could reduce the cow-related burden on our atmosphere.

Reduced consumption of beef and dairy products would probably have little effect. (If half of US consumers cut their consumption of beef and dairy products in half -- and the resulting drop in prices didn't stimulate the other half to increase their consumption, or drive more exports -- it would reduce national greenhouse gas emissions by about 1%.) Maybe this will become more of an issue in the future.

Update 8 May 2012: If you think cow burps are bad, recent research suggests dinosaur flatulence was a lot worse.

Science on the Small Screen

noreply@blogger.com (David) — Mon, 03 Dec 2007 23:53:00 +0000

Check out these science video sites

Several sites have been set up to allow research scientists and educators to post videos of their experiments, lab projects, or results. It's a chance to see real science in action.

Scivee
The Journal of Visualized Experiments
LabAction
DNATube

There's everything from an animation about how the lac operon works to preparing T cell growth factor from rat splenocytes with a French accent to a lecture on centripetal force.

Explore to see some real scientists doing real science, as well as a lot of science stuff lifted from TV, etc.

Why Is The Sky Blue?

noreply@blogger.com (David) — Sun, 25 Nov 2007 18:41:00 +0000

Think of the colors you see in the sky. On a clear day, when the Sun is out, the sky may appear blue.

Take the "Why is the sky blue?" quiz (multiple choice)

Why is the sky blue?
a. It isn't colored blue--it only looks blue.
b. Because it isn't red.
c. The sky is colorless--that blue light is from the Sun.
d. all of the above.

The correct answer is "d. All of the above".

The light of the Sun is white (it glows "white hot", emitting lots of radiation over the whole range of wavelengths our eyes can respond to). But when you glance at the Sun it appears yellow. (Don't look too long at the Sun--the UV radiation will hurt your eyes. And never ever look at the Sun with a telescope or binoculars. That could damage your eyes instantly.)

So we really have two questions:

Why does the disc of the Sun appear yellow (rather than white, as it does from space)?
Why does the sky only appear blue when the Sun is out (rather than black as the Moon's sky appears if you are on the Moon, or the Earth's sky when the Sun is down)?

The answer to both questions is the same: The light from the Sun is broken up as it passes through the atmosphere. The blue you see is just part of the sunlight that took a roundabout route.

What breaks the Sun's light into yellow and blue light and sends these colors on different paths?

Most of the atmospheric gases are transparent to visible light. They don't filter the Sun's light and make it yellow, as a yellow filter would. Besides, if colored gases made the Sun appear yellow, where does the blue come from? The part of the atmosphere that changes the Sun's light is the molecules and tiny particles that are floating in it.

There are particles of water--tiny droplets too small to be seen as clouds. There are particles of organic material--smog or haze, condensed from volatile organic chemicals that have gotten into the air. There are particles of sulfuric acid from volcanoes and power plants. There are molecules of gases in the atmosphere.

These tiny particles, much smaller than the wavelengths of sunlight, scatter the sunlight as photons from the Sun interact with the particles. This is called Rayleigh scattering after the British physicist who described how it works. (Larger particles, like the water droplets in clouds, are closer to the wavelengths of sunlight, and they scatter it differently. This is why clouds are not blue.)

You can see the effects of Rayleigh scattering by tiny particles floating in a liquid by trying the following demonstration. Particles in a gas (like the atmosphere) work the same way.

Fill a tall jar or beaker with water. Shine a bright light through it. (An overhead projector works well. You want the bright light to take a long path through the water.) If you look at the light that goes straight through the water (and is projected on the screen if you use an overhead projector) it will appear about the same color that it would appear without the water in the way. If you look at the sides of the jar, at right angles to the beam of bright light, you won't see much of that light. The beam of light goes right through. (Water is transparent and colorless.)

Now add a small amount of milk (about 1/8 teaspoon or less per quart of water). The water will become cloudy as the milk disperses. The tiny particles of fat and protein in homogenized milk will disperse in the water in what is called a colloidal suspension. They float in the water like aerosol particles float in the air.

Now put the suspension in the light beam again. If you look at the light through the suspension (or look at the screen) the light will appear to have a reddish color, different from the color it had when viewed through clear water. If you look at the sides of the jar the cloudy contents may have a bluish tinge. The blue light from the light source is being scattered more than the red light. So some of the blue light emerges from the sides of the jar, leaving a reddish (blue taken away) color in the transmitted light that wasn't scattered.

Here is a description of a similar demonstration. Here is another.

This scattering by suspended particles much smaller than the wavelength of the radiation being scattered makes the sky blue, sunsets red, and the Sun yellow. But how?

When you look at the sky during the day you only see the Sun in one spot, and it appears yellow. But light from the Sun that is not heading directly toward you is being scattered to the sides of the direct path to those other locations, with more blue light being scattered. Any place in the sky where the Sun isn't, as seen from your location, you can see some of this side-scattered blue light. In the sunlight coming directly from the Sun to your eye there has been side-scattering of some of the blue wavelengths, so the Sun is left looking yellow.

If you look toward the Sun at sunset or sunrise, you are seeing the light that has not been scattered, the longer wavelengths. And since at sunset and sunrise the light takes a longer path through the atmosphere to your eye the Sun appears orange or red, not just yellow.

Why is blue light scattered more and red light less?

In 1859 John Tyndall discovered that when light passes through a clear fluid holding small particles in suspension, the shorter blue wavelengths are scattered more strongly than the red (as in the demonstration above). Later John William Strutt, 3rd Baron Rayleigh, developed equations which approximately describe the behavior of light scattered by small particles and molecules, objects with dimensions much smaller than the wavelength of the radiation in question. Rayleigh's equations predict scattering in terms of the object's size relative to the light's wavelength, and the object's refractive index.

The probability that light will be scattered is proportional to 1/λ⁴. The wavelength of the light ( λ ) has a very pronounced effect when raised to the fourth power like this. The probability that blue light (wavelength 460 nm, 460 nanometers) will be scattered is four times the probability that red light of wavelength 650 nm will be scattered. Stated alternatively, I_α=1/λ⁴ where I_α is the intensity of the scattered radiation.

The shorter the wavelength of the incident light, the more the light is scattered.

for larger particles one would use the equations of Mie theory, of which the Rayleigh equations are a special case. In Mie scattering the wavelength of the incident light has much less effect on the amount and direction of scattering.

Further reading:

http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html

http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html#c2

demonstration cribbed from Earth Under Siege by Richard P. Turco, 1997 edition, Oxford U. Press, pages 500-501.

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

tags: science, light, atmosphere, education, Science In Action

Is Sex Necessary? Part 1

noreply@blogger.com (David) — Mon, 27 Aug 2007 18:45:00 +0000

*Motile Plant Gametes*

"Mommy, Where Do Gametes Come From?"

"I'm glad you asked that, Honey. We usually don't see gametes, but just because they are small doesn't mean they're not important.

"You see, gametes are special haploid cells produced by a kind of cell division called 'meiosis'. Two gametes can unite to form a diploid cell again. That's called 'fertilization' or 'syngamy'. Diploid cells have a set of pairs of chromosomes, but haploid cells have just one copy of each chromosome. In people, most cells have 23 pairs of chromosomes. Chickens have 39 pairs of chromosomes in their diploid cells. Mosquitoes have 4, isn't that cute?

*Day-Old Chick*

"There are two reasons gametes are important, Snookums. First, although human gametes can't survive on their own, they can live long enough for a swimming gamete from a daddy to get to a big round nonmotile gamete in a mommy. When they join they bring genes from the daddy and genes from the mommy together. So a baby has its own set of genes, some from its daddy and some from its mommy. With our 23 pairs of chromosomes there are lots of ways the daddy's genes, half of which he got from his daddy and half from his mommy, can be shuffled and distributed in his gametes. In fact there are about 8 million possible results from shuffling 23 chromosomes, so you can see the possibility of two gametes from the same individual having the same assortment of grandpa and grandma's chromosomes is really, really tiny.

"And there's a second thing even more wonderful about meiosis, Dear. When the pairs of sister chromatids are in the pachytene stage of prophase I, non-sister chromatids can exchange some of their DNA by 'crossing over'. So the DNA from

*A Boy's Chromosomes*

the grandpa and grandma can be even more mixed up! Here, maybe this will be clearer after you watch this little movie.

"All this shuffling and exchanging of DNA means that the baby that grows from the zygote formed by the union of those two gametes probably has a unique set of genes never born on Earth before! Of course if the zygote splits into twins, they will each have the same genetic makeup, but you get the idea.

"This way of making babies is called 'sexual reproduction'. Lots of different life forms do it, but not always in the same way. Bacteria and archaea don't do it at all, since they can't do meiosis. Still, they seem to get along OK. In fact, they are the dominant life forms on our planet!

*A Girl's Chromosomes*

"If such successful and important organisms as bacteria and archaea can get along without it, why do so many other kinds of protists, fungi, plants and animals go to all the trouble to use sexual reproduction? I think the answer, Sweetie, is that by creating so many combinations of genes, and by mixing them up generation after generation, sexually reproducing organisms can try out new combinations of mutations faster. So there is more variation for natural selection to work on, you see. And if the environment is changing novel combinations of genes might be better able to handle the changing selective pressures, so a baby with an adaptive combination of genes might be more likely to grow up to make gametes of its own.

"Lots and lots of eukaryotes have meiosis and fertilization as part their life cycle. Did you know that we are eukaryotes? We (or our ancestor eukaryotes) evolved meiosis and most of us have never given it up. It is strongly selected by natural selection. One result of the more flexible evolution that results from using sexual reproduction is the origin over the ages of so many new species with so many different ways of living -- like us, Pumpkin! That's why people have sex! Isn't that interesting?"

"Yes, I guess so. . . . Mommy, what are 'cells'?"

Two good articles:

Wikipedia on Evolution of Sex

Good review article

Hurricane Numbers Up With Sea Surface Temperatures

noreply@blogger.com (David) — Wed, 01 Aug 2007 21:18:00 +0000

Global Warming Means More Atlantic Tropical Storms and Hurricanes

A previous post discussed how global warming seems to be increasing the intensity of Atlantic hurricanes. At that time it wasn't certain that the number of tropical storms in the Atlantic was increasing along with global warming, too.

Now the evidence is in. Recent work shows that there has been a significant increase in the number of tropical storms and hurricanes in the Atlantic over the past century, and especially over the last 20 years. More detailed information is available in a slide presentation in this large pdf file.

The year 2006 was a respite after a series of recent major storms in 2004 and 2005, with only five hurricanes and four other named tropical storms. But it would have been an above average hurricane season in the early 1900s.

"These numbers are a strong indication that climate change is a major factor in the increasing number of Atlantic hurricanes," says study co-author Greg Holland of the National Center for Atmospheric Research. (See NCAR press release.) Although our ability to count tropical storms has improved a lot with the development of aircraft and satellites, "We are of the strong and considered opinion that data errors alone cannot explain the sharp, high-amplitude transitions between the climatic regimes, each with an increase of around 50 percent in cyclone and hurricane numbers, and their close relationship with SSTs," the authors state. (SSTs = sea surface temperatures, which have increased about 0.7 degrees C. in the Atlantic hurricane-forming region over the last century. The area of warm water has expanded also.)

Here is the abstract of the recent article by Holland and Webster

We find that long-period variations in tropical cyclone and hurricane frequency over the past century in the North Atlantic Ocean have occurred as three relatively stable regimes separated by sharp transitions. Each regime has seen 50% more cyclones and hurricanes than the previous regime and is associated with a distinct range of sea surface temperatures (SSTs) in the eastern Atlantic Ocean. Overall, there appears to have been a substantial 100-year trend leading to related increases of over 0.7°C in SST and over 100% in tropical cyclone and hurricane numbers. It is concluded that the overall trend in SSTs, and tropical cyclone and hurricane numbers is substantially influenced by greenhouse warming. Superimposed on the evolving tropical cyclone and hurricane climatology is a completely independent oscillation manifested in the proportions of tropical cyclones that become major and minor hurricanes. This characteristic has no distinguishable net trend and appears to be associated with concomitant variations in the proportion of equatorial and higher latitude hurricane developments, perhaps arising from internal oscillations of the climate system. The period of enhanced major hurricane activity during 1945–1964 is consistent with a peak period in major hurricane proportions.

Fire Alarm: Global Warming and Wildfires

noreply@blogger.com (David) — Sat, 07 Jul 2007 18:13:00 +0000

Fires Increase Due To Global Temperature Rise

While everybody talks about the threat posed by stronger hurricanes due to global warming (see this earlier post ), the greater danger in the American West is from increased number and severity of forest fires. (Fires are likely to increase in other regions as well: Australia, the Mediterranean basin, and so forth.)

The increase in temperature (0.9 degrees C over recent decades) is primarily responsible for the significant increase in wildfires in the West since the '80s.

Recent research shows that warmer temperatures appear to be increasing the duration and intensity of the wildfire season in the West. Since 1986, longer, warmer summers have resulted in a fourfold increase of major wildfires and a sixfold increase in the area of forest burned, compared to the period from 1970 to 1986. A similar increase in wildfire activity has been reported in Canada from 1920 to 1999.

Research by Westerling et al. (2006) shows that the increase in western U.S. forest wildfires is correlated with warmer spring and summer temperatures, reduced precipitation associated with warmer temperatures, reduced snowpack and earlier spring snowmelts, and longer, drier summer fire seasons. Climate models indicate that these trends are part of plausible climate change scenarios (Running 2006), implying a further increase in the risk of large, damaging forest wildfires in parts of the western U.S.

These simulations unanimously project June to August temperature increases of 2° to 5°C by 2040 to 2069 for western North America. The simulations also project precipitation decreases of up to 15% for that time period. Even assuming the most optimistic result of no change in precipitation, a June to August temperature increase of 3°C would be roughly three times the spring-summer temperature increase that Westerling et al. have linked to the current trends. Wildfire burn areas in Canada are expected to increase by 74 to 118% in the next century, and similar increases seem likely for the western United States. (Running, 2006)

An analysis by Westerling & Bryant predicts significant increases in wildfire damage in Northern California forests as global warming continues. They conclude that this may make "wildfire a particularly important source of potential climate change impacts for the state." So though you might escape hurricanes or sea-level rise by moving to the foothills, you can't run from global warming.

[See update link to 2012 Climate Central report below.]

The Really Bad News

According to Running (2006), wildfires add an estimated 3.5 × 10¹⁵ g to atmospheric carbon emissions each year, or roughly 40% as much as fossil fuel carbon emissions. If climate change is increasing wildfire increases in this source of carbon emissions will accelerate the buildup of greenhouse gases and could provide a feed-forward acceleration of global warming.

In other words, the warmer it gets, the more and larger wildfires in western forests, releasing more CO₂ to the atmosphere, resulting in more global warming, which might increase fire numbers, duration, and intensity even more.

In the long run the increase in wildfires in western montane forests will change the composition of plant communities, so that in time the Rockys of Colorado may look like the Sangre de Cristo Mountains of New Mexico look today.

Sources:

Westerling et al., 2006. Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity. http://www.sciencemag.org/cgi/content/full/313/5789/940

Running, 2006. Is Global Warming Causing More, Larger Wildfires?
http://www.sciencemag.org/cgi/content/full/313/5789/927

Westerling & Bryant, in prep. Climate Change and Wildfire in California. http://ulmo.ucmerced.edu/~westerling/pdffiles/07CC_WesterlingBryant.pdf

Update 2012-09-19:
Recent report confirms substantial increase in major fires, and predicts more in the future. Report here. Reuters article here.

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

tags: science, global warming, climate change, education, Science In Action

What Causes Global Warming?

noreply@blogger.com (David) — Tue, 13 Mar 2007 01:34:00 +0000

Did You Know?

For every pound of gasoline your car burns, about three pounds of CO₂ come out the tailpipe. So if your car gets 20 miles per gallon, you are emitting about a pound of CO₂ per mile.

(For every kilo of petrol your car burns, about three kilos of CO₂ come out the tailpipe. So if your car gets 8.5 km per liter, you are emitting about a quarter of a kilogram per kilometer.)

How can the amount of CO₂ that comes out be three times the amount of gas that goes in? It's because of the oxygen. Your car uses a lot of O₂ to burn that pound of gasoline, and some of that oxygen becomes part of the CO₂ emitted. You can review the math here.

So that trip to the store to buy a loaf of bread, bag of dog food, quart of milk or bottle of wine probably put a pound or more of CO₂ into the atmosphere. That is likely as much as all the CO₂ emitted by all the processes involved in growing, manufacturing and packaging that product, and transporting it to your local store.

That is what causes global warming.

Probability and Profiling

noreply@blogger.com (David) — Mon, 12 Mar 2007 18:40:00 +0000

The Set-Up:

I am going to test your understanding of "probability" and "randomness". For purposes of this demonstration, assume that the person in this picture has been randomly selected from all Americans. This is a picture of a randomly selected American.

The Question:

Is this person more likely to be a farmer, or a librarian?

The Answer:

Whatever you answered, your answer was almost certainly influenced by your previous knowledge, biases, and thinking about what the woman "probably" was.

You probably ignored the repeated information that this was supposed to be a randomly selected American.

In fact, any "randomly selected" American is much more likely to be a farmer than a librarian, since there are almost seven times as many farmers as librarians in the U.S.A. There are twice as many women farm operators as there are librarians and library technicians put together.

Because I showed you a picture of a woman, and you "know" than most librarians are women and most farmers are men (is that really true?), you probably guessed that the "randomly selected" American in the picture was a librarian. If so, you let your previous knowledge affect your answer. You probably lacked the relevant knowledge about the numbers of farmers and librarians in the U.S. population.

People have a very hard time forgetting their prejudices, biases, and prior information (some of which may be erroneous) when making judgments about things they are told are "random". They impose a structure of belief even on randomness, which by definition has no structure. (Previous post on "randomness".)

This is why "profiling" is so difficult. People go with their "gut feel", their biases, rather than using a true analysis of the situation.

Here are the sources and links to further information:

US Department of Labor, Bureau of Labor Statistics
all occupations
education, training and library occupations

149,680 librarians and 113,520 library technicians -- about 263,000

US Department of Agriculture, National Agricultural Statistics Service, Census of Agriculture 2002

tables
farm operators
pdf version

1,792,000 operators on farms where farming is the principal occupation of the principal operator. 455,500 woman operators same definition.

Here is a really interesting article about profiling. (It is about profiling, not pit bulls, so just keep reading.)

What Are Flowers For?

noreply@blogger.com (David) — Mon, 14 Aug 2006 01:31:00 +0000

Flowers, sex and seeds

Flowers are the specialized plant structures which produce pollen and where seeds develop within an enclosing fruit. Each seed (like the faba bean seeds at the right) contains a baby plant.

A baby plant (plant embryo), and its surrounding seed, cannot develop unless pollen is transferred from the pollen-producing parts of the flower to the parts which contain ovules, which can become seeds.

So flowers serve two basic purposes:

they package genetic material (into pollen and ovules) and help move it around so it can combine to produce the seeds for the next generation, and

they enclose those seeds in a fruit to help them successfully grow into a new plant.

If you look closely at this picture of some peanuts, you can see a baby plant where one of the peanut seeds has split in two. Each seed was enclosed in a "seed coat" (the red, papery covering) and several seeds were in each fruit (the peanut shell with the seeds inside -- not shown). (Better yet -- get some peanuts and look at them carefully. This is called "observation" -- a big part of science.)

Not all plants have flowers

Some plants don't make seeds at all (like ferns or mosses). And others (gymnosperms like pines, ginkgos and cycads) make seeds without flowers. (The seeds of gymnosperms aren't enclosed in a fruit that develops from part of a flower. They are just borne externally, although a cone or fleshy outgrowth may surround them as they mature.)

Flowers facilitate plant sex

They typically include structures which produce pollen and other structures where seeds can develop if pollen reaches them. Sexual reproduction means the parent organisms produce “gametes”, which carry a sample of the parent's genetic information (just half of it, but one of every chromosome). These gametes must unite to reconstitute the complete genetic complement that the next generation will need—two of each chromosome. In people the gametes are sperm and the egg. In seed plants they are pollen and ovules.

Usually a seed can develop from union of pollen and an ovule on the same plant. But many flowering plants promote broader mixing of genetic material. They have have forms which encourage the transfer of pollen from one flower to another, and thus often from one plant to another. This transfer of pollen can be done by wind, or by birds, insects or other animals which visit the flowers. Many flowers have evolved specific forms, colors, or other features to attract such “pollinators”.

After pollination (the transfer of pollen to the parts of the flower where the ovule is waiting) and fertilization (the joining of the genetic material from the two gametes), a seed can develop. In flowering plants, seeds are enclosed in a structure called a fruit. A fruit can contain just one seed (like an olive) or many (like a tomato). A fruit can be dry and hard, like a grain of rice, or fleshy like an apple.

Dandelion fruits

Many fruits have specialized structures to help carry the seeds away from their parent plants, like a dandelion (which floats on the wind), burdock (which has prickles to catch on fur of passing animals), Impatiens (“touch-me-not”, where the fruit explodes and scatters the seeds), coconuts (which can float), or the cherry (which has an edible portion surrounding a tough digestion-resistant seed).

So flowers make fruits, and a fruit has three parts:

the embryo (baby plant)

the seed that contains the embryo

the fruit that contains the seed (or seeds). The fruit develops from the structure that contained the ovules before fertilization.

More about plant sex

Flowers are all about sex. Sexual reproduction produces offspring which are not genetically identical to their parents. In fact, each offspring can contain a novel combination of genes never seen before. This helps plants deal with changing environments and other challenges (new competitors, new predators). The plant gets the most novel new combinations if pollen is transferred from one parent to another. Plant sexuality is very diverse, with many complicated sexual mechanisms even just within the flowering plants. These various mechanisms include differences in which flowers produce pollen and which produce ovules, whether the pollen-producing flowers and the ovule-producing flowers are even on the same plant, where within the flowers pollen is released and where it can be received, when the pollen is released and when the ovules are receptive, how the pollen is transferred, and chemical signals which determine which pollen will be allowed to fertilize an ovule. The incredible diversity of the flowering plants (90% of all plants living today, comprising hundreds of thousands of species) is all about trying new ways to have sex.

Although many plants don't use pollinators such as insects (wind pollination is common), the fossil record suggests that flowers and insects evolved together, and that the diversity of each stimulated diversity in the other.

Flowers work

Flowering plants provide the basis of nearly all human nutrition, except for the wild-caught fish we eat. (A few calories also come from algae, pine nuts, fern fiddleheads and the like.) Without flowering plants civilization would certainly be impossible with today's technology. (Could a civilization develop that depended entirely on fish for nutrition?) Flowers, seeds and fruits have, ultimately, made the internet, and every other aspect of civilization, possible.

To review:

Flowers have pollen. If pollen is transferred, flowers grow seeds, and turn into fruits.

Homework

So next time you are looking at a flower, try to see where the pollen is and where it might go to make a seed. How does pollination happen?

Next time you are looking at a fruit, consider how it formed and how it helps its seeds get around. Where are the seeds and how are they dispersed?

Next time you consider a seed, think about the baby plant inside, and how it might grow into a mature plant with flowers of its own.

Here are some links for further information:

Wikipedia: flowers, flowering plants, seeds
Parts of a flower (floral structure)
Good pdf document about floral structure
Good summary page with images of various flowers
Diversity of flowering plants
The Seed Biology Place

The photo of dandelion fruits is by Andreas Trepte licensed under the Creative Commons Attribution-Share Alike 2.5 Generic license. Rights information here.

Why Is Urine Yellow?

noreply@blogger.com (David) — Sat, 01 Jul 2006 18:04:00 +0000

What true scientist has not asked, at some time or other, "Why is pee yellow?"

Some European alchemists in the middle ages apparently thought one possible reason was that there was gold in urine. This led to fruitless, and possibly quite disgusting, efforts to extract that gold.

The yellow color in urine is due to chemicals called urobilins. These are the breakdown products of the bile pigment bilirubin. Bilirubin is itself a breakdown product of the heme part of hemoglobin from worn-out red blood cells. Most bilirubin is partly broken down in the liver, stored in the gall bladder, broken down some more in the intestines, and excreted in the feces (its metabolites are what make feces brown), but some remains in the bloodstream to be extracted by the kidneys where, converted to urobilins, it gives urine that familiar yellow tint. (Here is a great diagram of some of these reactions, from the Boehringer Mannheim Biochemical Pathways at ExPASy.)

These same yellow chemicals also cause the yellow color of jaundice and of bruises, both of which result when more hemoglobin than usual is being broken down and/or the processing of its breakdown products by the liver is not able to keep up.

Why do we pee at all?

Urine is mostly water, which just has to be replaced. We excrete water not just to get rid of it if we have drunk too much, but primarily to carry away toxins that would otherwise build up in our systems. The important part of urine is urea (also known as carbamide), (NH₂)₂CO. The real waste product our bodies have to get rid of is ammonia (NH₄⁺, when in solution), which is formed by the breakdown of amino acids -- the building blocks of proteins. But ammonia is so toxic that only tiny concentrations can be tolerated. So any ammonia in the bloodstream is rapidly converted to urea in the liver. That urea is then removed from the bloodstream in the kidneys, and left in concentrated form in the urine (about 2% of urine is urea.) (More on the "urea cycle")

Urea was "discovered" by Hilaire Rouelle in 1773 (that is, he was the first chemist to isolate it in pure form and begin to understand its composition). It was the first organic compound to be artificially synthesized from inorganic starting materials when, in 1828, Friedrich Woehler prepared it by the reaction of potassium cyanate with ammonium sulfate. Woehler was really trying to make ammonium cyanate, but by synthesizing urea he disproved the theory that the chemicals of living organisms are fundamentally different from inanimate matter, thus inventing the field of organic chemistry.

Fish and amphibians lack the urea cycle for removing ammonia from the blood, since they can usually excrete ammonia directly via the gills or through the skin. This is one reason that ammonia in the environment is so highly toxic to aquatic animals. So do fish need to pee? Yes: not to excrete nitrogenous compounds, but for osmoregulatory purposes. Freshwater fish are always absorbing water from their environment by osmosis, and have to pump it out. Saltwater fish don't absorb water from the sea (blood and seawater have about the same saltiness and osmotic potential), but they do have some wastes to get rid of. More here.

(More on industrial uses of urea here.)

Where does the ammonia in our systems come from?

Ammonia is generated during the deamination (breakdown) of amino acids in the liver. Other sources of ammonia include bacterial hydrolysis of urea and other nitrogenous compounds in the intestine, the purine-nucleotide cycle and amino acid transamination in skeletal muscle, and other metabolic processes in the kidneys and liver. The normal physiological concentration in blood is less than 35 micromol/l. A five- to ten-fold increase in this concentration causes toxic effects, especially on the central nervous system.

Other urine facts

Unusual-colored urine (black, dark orange, or brown, for example) can be a sign of serious medical problems.
Some other colors can result from pigments in the diet, such as betacyanin found in red beets.
Urea is apparently used as an additive in cigarettes, to enhance flavor.
Urea is widely used as fertilizer, since plants can use it as a source of nitrogen.
Although today urea is manufactured by the millions of tonnes through industrial processes, the urea in urine can be economically valuable if other sources of fixed nitrogen are scarce.
- It can be used as plant fertilizer (when diluted). (It's organic, you know.)
- The urea in urine can be broken down into ammonia again (generating the characteristic smell of stale urine) which be further oxidized by bacteria to nitrate, so useful in the production of gunpowder.

What Does "Survival of the Fittest" Mean?

noreply@blogger.com (David) — Tue, 06 Jun 2006 15:16:00 +0000

Does "survival of the fittest" mean anything?

The phrase "survival of the fittest" is sometimes used as a kind of metaphor to explain what is meant by "evolution by means of natural selection". The phrase was first applied not by a biologist but by an economist, Herbert Spencer. Darwin did incorporate this phrase into later editions of The Origin of Species, using it as a synonym for "natural selection."

The fittest individuals, however, do not survive. Even the fittest is mortal. The fittest die just as inevitably as the less fit. (Remember that "fit", at the time of Darwin and Spencer, usually meant “suited for” or “appropriate to”, not “robust in health”).

What do survive are the traits, genes, alleles, or heritable factors, and those of the more fit (better adapted to the environment or other selection pressures) survive in greater numbers than those of the less fit. That is what “fitness” means to a biologist.

The fittest, the individuals whose traits enable them to leave more progeny than those contemporaries less well suited for the current environment, have more grandchildren. Those grandchildren carry some of the heritable characteristics which made their fitter ancestors capable of begetting more offspring.

Being strong, happy, or living to a ripe old age might be interpreted by the layperson as representing higher fitness, compared to another individual who did not survive as long or who suffered more in life. But this has nothing to do with evolution or natural selection. Natural selection is only concerned with the effect of the environment on the flow of genes to following generations. The age or health of the surviving individuals means nothing if their genes are not represented in offspring.

Let me repeat this important point: Natural selection is not something that happens to individuals, but to populations. It causes changes in those populations (changes in the commonness, or frequency, of genes) across generations.

To the extent that it is a statement about evolution or natural selection, “The survival of the fittest” probably causes more confusion than clarification. If you interpret it to mean “the survival and propagation of the fittest genes”, then it is a restatement of evolution by natural selection, but it is still a tautology, true by its own definition. The “fittest” individuals contribute more of their genes to subsequent generations than do less “fit” contemporaries, but this is just a definition of “fitness”.

The worst influence of this phrase is the sneaky way “fitter” sometimes is taken to mean “better”. This is especially pernicious when the concept is (mis-)applied to social contexts, such as politics or economics. There it is sometimes taken to mean “success of those most worthy of success”. A whole doctrine of “social Darwinism” arose around this concept. Since social dominance, economic success, or political power do not involve the winnowing of heritable traits by natural selection, they have nothing to do with Darwin or biological evolution. Social Darwinism was an effort to borrow the scientific language of biology to justify various social and political programs.

Confusion between the ethical concept of social Darwinism and the scientific concept of evolution hampers communication between scientists and the public to this day. Thanks a lot, Mr. Spencer.

Additional Resources

Social Darwinism:
Wikipedia
social darwinism

Stephen Jay Gould, "Darwin's Untimely Burial," 1976; from Michael Ruse, ed., Philosophy of Biology, New York: Prometheus Books, 1998, pp. 93-98.

Wikipedia "survival of the fittest" article

Here are some other posts on evolutionary topics from this series:
Evolution in a Nutshell
What Species is Best?
Are Humans Still Evolving?