The Carbon Brief

Scientists: How Matt Ridley misinterpreted new climate sensitivity paper

2013-05-22T16:30:00

A new paper suggesting temperatures might not rise as much as some models predict in the near future has been interpreted in some corners - notably by Matt Ridley in the Times - as a sign that climate change no longer poses a problem. But the authors have spoken out against Ridley's arguments, highlighting why pinpointing earth's sensitivity to greenhouse gases relies on more than one estimate.

The story stems from a letter in Nature Geoscience on Sunday with a new estimate of what scientists call equilibrium climate sensitivity. That's the total warming we can expect from a doubling of carbon dioxide in the atmosphere, compared with pre-industrial levels.

Climate sensitivity is important because the higher it is, the more warming there will be. In its 2007 report, the Intergovernmental Panel on Climate Change (IPCC) estimated a likely range of between two and 4.5 degrees Celsius, with a best estimate of three degrees.

More than one way to estimate climate sensitivity

There are different ways to go about calculating climate sensitivity - which is part of the reason the IPCC's range is so large. The new study used what's called an energy budget model, which used land, atmosphere, ice and ocean temperatures between 1970 to 2009 to see how warming in all parts of the climate system has changed in that time. We wrote more about the new paper here.

Scientists can also use natural recorders of temperature - called climate proxies - to look at how earth's temperature has changed in response to greenhouse gases throughout its distant past. The third way is using complex climate models to simulate how processes affecting temperature rise are likely to evolve in the future.

Uncertainties about some of these processes - particularly how clouds affect the rate of warming - means climate model estimates can vary quite widely.

New estimate

Most of the media coverage surrounding the new paper focusses on earth's Transient Climate Response (TCR). This is a simplified measure of climate sensitivity that estimates the amount of surface warming we can expect at the point of a doubling of carbon dioxide.

Importantly, TCR doesn't take into account heat that's going into the deep oceans rather than staying in the atmosphere. Scientists think natural cycles are driving the deep oceans to take up more heat at the moment, causing surface temperatures to rise slower recently than in previous decades.

The new paper suggests a best estimate of TCR based on data from the last decade of 1.3 degrees, but because of uncertainty around the measurements it could be as low as 0.9 degrees or as high as two degrees.

The authors suggest that unlike their estimate of equilibrium climate sensitivity - which is largely consistent with model projections - their range of TCR is lower than some models predict. This is the point some parts of the media have picked up on.

Media misinterpretation

In a piece for the Times, Conservative peer and member of skeptic thinktank the Global Warming Policy Foundation, Matt Ridley, compared the new paper's estimate of TCR with that of the Met Office's HadGem2 model, which suggests a value of 2.5 degrees.

In a blog for yesterday's Guardian, co author on the new paper Myles Allen disagrees with the point Ridley's trying to make with his comparison. Allen says:

"[Ridley] is worried that government policies are misguided because they place their faith in climate models, like one of the Met Office models that puts the warming instead at 2.5 degrees Celsius, almost twice our estimate."

But, as Allen explains, scientists don't place all their confidence in just one model. He says:

"Climate scientists are all well aware the Met's model (HadGEM2) is at the top end of the current range. The Met Office's advice to government is based on the range of results from current climate models, not just their own."

Allen is making the point that scientists use a number of climate models to make robust temperature projections - and if a comparison is to be made, it should be with the average of all the models, not just HadGem2. He says:

"The relevant comparison is not with the 2.5 degrees Celsius response of one model, but with the average of climate models used by the UN's climate science panel [the IPCC] in its upcoming major report, which is 1.8 degrees Celsius. Now, 1.3 degrees is 30 per cent less than 1.8 degrees Celsius, but this is hardly a game changer."

Allen's explains that at 1.8 degrees, the average value of climate sensitivity from all the models is within the 0.9 to two degree range of uncertainty that accompanies the new paper's estimate. In other words, the two estimates aren't inconsistent with each other.

As part of a longer discussion on the paper's conclusions, lead author on the paper Alexander Otto makes a similar point in an article for the Met Office.

The fact that the uncertainty ranges of different methods of estimating climate sensitivity are still quite large is another reason the IPCC's range is unlikely to be refined just yet.

Damage done

Ridley goes on to suggest that given the new lower estimate of sensitivity, the negative effects of climate change we're likely to experience before the end of the century are negligible. He says:

"There is little doubt that the damage being done by climate-change policies currently exceeds the damage being done by climate change, and will for several decades yet … At this rate, it will be the last decades of this century before global warming does net harm."

Part of Ridley's argument is that rolling out renewables "dwarf[s] any possible [economic] effects of worse weather, for which there is still no actual evidence anyway: recent droughts, floods and storms are within historic variability."

Although it's certainly difficult to attribute particular events to climate change, scientists suggest rising temperatures are stacking the decks towards more extreme weather. As Allen puts it:

"Try explaining to a casino bouncer that it doesn't matter you are using loaded dice because a triple-six is within historic variability."

Warming in the pipeline

While TCR gives a useful indication of the surface warming we can expect in the next few decades, scientists turn to equilibrium climate sensitivity for the full picture of the total warming - at earth's surface and in the oceans - we can expect in the long term. We wrote a bit more about the difference between the two measures of sensitivity here.

The new paper's estimated range of equilibrium climate sensitivity is consistent with that of current climate models. Contrary to Ridley's suggestion that scientists are "backing away from rapid warming", this means projections of how much warming we can expect in the future remain unchanged - at least for now.

While the precise value of climate sensitivity poses an interesting scientific question, many argue tackling the policy response is by far the bigger problem. As Allen puts it:

"If this means we can move on from a sterile debate about the global response to much more interesting questions about regional impacts, the rights of different generations, and, most interesting of all, what to do about it, that's great. Ridley, welcome to the real climate debate."

Tornadoes and climate change - what does the science say?

2013-05-22T16:15:00

Monday's tornado in Oklahoma highlights the threat extreme weather poses to human life, and has prompted some to ask if human-caused climate change is partly to blame. Unfortunately, that's a question scientists still can't answer.

The overwhelming response in the media and online in the wake of the tornado has done a pretty good job of accurately reflecting the science, which is so far unclear over whether theres a link between climate change and tornadoes.

This statement from scientist Michael Wehner sums up the situation pretty well:

"With tornadoes, what we don't know is as much as what we do know."

Tornadoes 101

Before we dig into the science in more detail, here's a quick introduction to what tornadoes are and how they form.

Tornadoes are narrow, spinning columns of air reaching from a the base of a thunderstorm down to the ground. They actually only account for a fraction of the energy released in a thunderstorm, but that energy is concentrated on a small area.

As the video below shows, tornadoes need two critical conditions to form: warm moist air and high 'wind shear'. Wind shear is the spinning motion caused when winds at different heights blow at different speeds. It's the moisture and high winds which cause most of the destruction when a tornado hits.

What does the science say?

Trying to establish whether tornadoes activity will change as the climate warms is tricky for a number of reasons, as a recent report from the Intergovernmental Panel on Climate Change (IPCC) highlights.

First, scientists don't have a complete, good quality data set on tornadoes that have already occurred. Without a long reliable record, scientists can't easily look to see how tornadoes have changed since temperatures started rising.

Second, computer models used to simulate the climate can't tell scientists much about tornadoes either. That's because these models work on large scales, simulating changes in the ocean and the atmosphere on a global scale. In comparison, tornadoes are small weather events. As Dr Suzanne Gray, a meteorologist from Reading University explains:

"Tornadoes are too small-scale for current climate models to simulate, so it is not possible to say very much about how strength and occurrence might alter under climate change."

Then, there's one final problem. Climate change is likely to affect the two critical conditions for tornado formation - atmospheric moisture and wind shear - in opposite ways. The atmosphere is expected to hold more moisture as temperatures rise, making tornadoes more likely. But wind shear will probably decrease, having the opposite effect. Scientists can't say whether one force will override the other.

Climate change and the Oklahoma tornado

Given how hard it is to find any link between climate change and tornadoes, it's no surprise scientists say individual events, like the tornado which struck Oklahoma, cannot be pinned to climate change. As IPCC chair Rajendra Pachauri reiterated yesterday:

"One really cannot relate an event of this nature to human-induced climate change. It's just not possible. Scientifically, that's not valid."

Scientists worldwide are continually researching tornadoes to find out how their frequency and intensity might change in the future. As time goes on, the record of past tornadoes will grow too - providing a bigger set of data to spot trends in. It seems logical that climate change will have some effect on tornadoes, but for now it's very hard to say what that effect will be.

ECC committee says government must outline what Green Deal success looks like

2013-05-22T10:20:00

Parliament's Energy and Climate Change (ECC) committee has told the government to get a move on with monitoring the success of its core energy efficiency policies in a new report, out today.

The ECC committee is concerned the government hasn't worked out what a successful energy efficiency rollout would look like, let alone how to assess whether it meets those criteria. Says the report:

"It is unacceptable that, three years into the life of this parliament, ministers are incapable of defining the actual goals of one of the coalition's flagship policies."

Despite the government's assertion that the Green Deal is intended as a long-term project, press attention has focused on the number of people to sign up - or not - over its first few months in operation.

According to the committee, the Department of Energy and Climate Change (DECC) said the Green Deal and ECO schemes' main objective is to reduce carbon. It has calculated potential carbon savings of 4.5 million tonnes of carbon dioxide per year by 2020.

DECC also hopes the schemes will benefit an extra 100,000 low-income households per year. In written evidence, DECC also estimated the schemes would support between 39,000 and 60,000 jobs in the energy efficiency sector by 2015.

Beyond carbon savings, the committee suggests the government could measure "boosting the low carbon economy, empowering consumers, empowering businesses, levering in new private investment, and ensuring consumer standards are met" to get a wider picture of the success of the Green Deal and ECO.

There's a lot riding on the success of the Green Deal and ECO: government advisor the Committee on Climate Change told the committee that for the UK to stay within its carbon budgets, six to seven million cavity walls, seven million lofts and over one million solid walls must be insulated by 2020.

But the committee advises against setting targets for efficiency schemes, warning they could lead to hard selling "or even mis-selling" to reach goals.

Assessing whether or not the Green Deal and its sister policy, the Energy Company Obligation (ECO) - aimed at supporting the fuel poor to insulate their houses - are a success requires long-term monitoring. While it's not possible to assess a project's success or failure in a few short months, it's not possible simply to trust that takeup will improve with time, either.

Daily climate and energy links - 22nd May 2013

2013-05-22T09:55:00

Households 'ripped off' over energy bills as Ofgem says investigating company profits too 'intrusive'
Families are at risk of being ripped off over their energy bills because the regulator is refusing to find out why companies are making "outrageous" profits, MPs said today.
Telegraph

News:

Businesses hail plans for energy efficiency payments
Businesses and green groups have welcomed government plans to pay companies to curb their energy use, despite concerns that its chosen method for driving reductions in power demand could fail deliver the £2.3bn of promised economic savings by 2030. The Times criticises the move, saying consumers will foot the bill.
BusinessGreen

Shale gas could supply a third of UK needs, says IoD
Britain's shale gas reserves could "be a new North Sea for Britain", meeting more than a third of annual gas needs, reducing dependence on imports and generating significant tax revenues, according to the Institute of Directors.
Financial Times

Insurers: Tornadoes have done record damage in last five years
Analysts at insurance companies say the weather is getting worse over the long term - and damages are more severe.
Washington Post

High energy prices for industry occupy officials at EU summit
Since 2005, electricity prices in the EU have become significantly higher than in other major economies - a fact that will exercise delegates at the EU summit today.
Financial Times

China reveals details of first carbon trading scheme
New details of China's pilot carbon trading scheme have been released.
Financial Times

Commentary:

Nuclear futures: Renewables blossom in Germany's post-nuclear vision
Germany's decision to end using nuclear power has paved the way for the rise of renewables in the country.
The Conversation UK

UKIP's rise may undo the climate change consensus
Cardiff University's Adam Corner warns UKIP's popularity could undermine cross-party resolve to tackle climate change.
The Conversation UK

Matt Ridley has joined the real climate debate
Climate scientist Myles Allen examines a skeptic's anlysis of his study on climate sensitivity.
Guardian

Universal and useless? The 2015 global climate agreement
Everyone will be happy to sign the next global climate agreement because it will require very little in terms of emissions reductions from signatories.
The Conversation

Climate disasters displace millions of people worldwide
The Guardian continues its special feature on climate-induced displacement with an infographic.
Guardian

Science:

Timing made Oklahoma tornado toll worse
This week's tornado in Oklahoma has devastated communities - due, some scientists think, to the fact it occurred in the middle of the working day.
New Scientist

Surface warming slowdown doesn’t affect climate sensitivity, study says

2013-05-21T12:00:00

A group of scientists has just published a new estimate of how sensitive earth is to rising greenhouse gases. Their value for 'climate sensitivity' is at the low end of what scientists have previously suggested - but there's still a lot of uncertainty.

Importantly, the study shows slower surface temperature rise over the past decade doesn't change scientists' projections of how much warming we can expect in the long term.

What scientists call 'equilibrium climate sensitivity' is the warming we can expect from a doubling of carbon dioxide in the atmosphere, compared with pre-industrial levels. It's a number scientists are still trying to pin down - and it's important, because the higher climate sensitivity is, the more warming there will be.

In its last report, published in 2007, the Intergovernmental Panel on Climate Change (IPCC) estimated a likely range of climate sensitivity of between two and 4.5 degrees Celsius, with a best estimate of three degrees. But it didn't rule out lower or higher values and since then, scientists have continued to try to narrow the range of uncertainty surrounding the number.

Energy inventory

The short new study, published as a letter in Nature Geoscience, is based on measurements of how much heat the land, ocean, ice and atmosphere have absorbed between 1970 and 2009.

The new calculations produced a best estimate for climate sensitivity of 1.9 degrees Celsius, which is similar to a couple of other studies taking a similar approach that have attracted media attention recently.

A value of 1.9 degrees Celsius sits just below the IPCC's likely range. But the new estimate also comes with a large uncertainty range - of 0.9 to five degrees. One of the co-authors on the new study, Professor Piers Forster, tells us:

"The message is that the uncertainties are really too large to offer tight constraints on climate sensitivity - a wide range is still possible."

Hence, the paper isn't a conclusive argument for a lower value of climate sensitivity. But lead author Alexander Otto tells us it might support lowering the bottom boundary of the IPCC's likely range a bit:

"[T]he energy budget allows lower values than two degrees, but it is also consistent with values up to four or five degrees."

Other scientists argue that these new results make the upper end of the IPCC range for climate sensitivity look unlikely. Professor James Annan says on his blog:

"I hope [the new estimate] reflects a change in thinking from the IPCC authors involved … [The result] implies a marked lowering of the IPCC 'likely' range."

Sensitivity and the surface warming slowdown

Despite surface temperatures rising relatively slowly in the last decade and a half, the new study finds temperature data from the last decade suggests a best estimate of climate sensitivity that's consistent with the previous three decades - around two degrees Celsius. The uncertainty range is a bit narrower though at 1.2 to 3.9 degrees.

The similarity between decades doesn't support some media suggestions that the recent surface warming slowdown might be explained by a lower value of climate sensitivity. As Otto explains:

"[T]he important message on equilibrium climate sensitivity is that there isn't [a message] … [T]here isn't any obvious inconsistency between the energy budget of the past decade and the conventional range."

In other words, looking at the whole climate system, the earth warmed by a similar amount during the last decade as it did in previous ones. That's because estimating climate sensitivity the way the authors did takes into account all elements of the climate system - not just the atmosphere. While surface temperatures may have risen relatively slowly recently, the study suggests the slower pace of warming is being compensated by faster temperature rise elsewhere.

The authors' top line conclusion is that although their best estimate of climate sensitivity for the last decade is relatively low, the range accompanying the data is consistent with the range projected by current climate models. The overlap for the whole period - 1970 to 2009 - with climate models is even stronger, say the authors, which means there's no reason to revise down scientists' estimates of the warming we can expect in the long term.

Transient response

Scientists say the most likely reason for the shift from more to less atmospheric warming in the last decade is that natural climate variability is causing more heat to enter the oceans.

Climate sensitivity calculated for surface temperatures alone is called the Transient Climate Response (TCR). TCR is easier to estimate than equilibrium climate sensitivity because it doesn't consider long term climate feedbacks, like the delay in atmospheric warming caused by heat entering the oceans. But for that same reason, it only gives part of the picture.

The study calculates TCR based on the last decade, giving an estimate of 1.3 degrees with an uncertainty range of 0.9 to 2.0 degrees. The new TCR range is slightly lower than some IPCC models project. Otto tells us:

"[H]ence we conclude that the more extreme versions of these models might be inconsistent with the data and less likely … [but] we need to be careful about interpreting just one decade, and the 1970 to 2009 period as a whole suggests 0.7 to 2.5 degrees."

It's this result that much of the media coverage of the paper has picked up on. It's arguable that TCR gives a useful indication of the amount of warming we'll directly experience in the short term. But for a complete impression of the warming we can expect in the long term, equilibrium climate sensitivity remains the relevant number.

Sensitivity is not the same as eventual warming

The overall scientific view of the likely range of equilibrium climate sensitivity won't be altered on the back of one study. It seems fair to say scientists' projections of long term temperature rise remain largely unchanged - for now at least.

Finally, it's worth stressing that equilibrium climate sensitivity is not equivalent to total warming, it's the eventual warming expected per doubling of carbon dioxide after all feedbacks have been accounted for.

The IPCC's high emissions scenario (A1F1 ) suggests we could see a doubling of carbon dioxide above pre-industrial levels by 2050. That means that even with a climate sensitivity sitting at or just below the lower end of the IPCC range, by mid century the world would be committed to two degrees of warming above pre-industrial levels.

Two degrees is the target set by the United Nations Framework Convention on Climate Change (UNFCCC), which is often suggested as a threshold to avoid dangerous climate change. And after 2050, unless emissions had fallen to zero, further warming would occur.

As Forster puts it:

"[The new study] has an effect but not a massive effect on projections. We still need to mitigate carbon dioxide emissions very significantly to keep below two degrees [of warming above pre-industrial levels]."

Meanwhile, if climate sensitivity is at the upper end of the IPCC's likely range, reports suggesting a four degree temperature rise above pre-industrial levels by the end of the century look optimistic given current emission trajectories.

Daily climate and energy links - 21st May 2013

2013-05-21T09:10:00

'Saloon bar politics' by Ukip could harm Britain's climate change credibility and drag Tories to right on environment, warns minister
Ed Davey suggests vested interests and parts of the media are to blame for a rise in climate change scepticism, which could be further fuelled by the growing popularity of UKIP.
The Independent

News:

Households to get doubled subsidies of £2,300 off green boilers to boost flagging renewable scheme
The government is doubling the value of grants available for homeowners looking to install certain green energy measures until March 2013.
The Telegraph

Renewable heat payments doubled for householders
Business Green has more detail on the newly announced rise in government funding for homes looking to switch to renewable heat.
BusinessGreen

Commentary:

Oil, the marketing wolf pack, and EU price-fixing
Following recent allegations that major oil companies are artificially keeping fuel costs high, the Conversation takes a closer look at price fixing behaviour.
The Conversation

'We Would All Like Climate Sensitivity To Be Lower But It Isn't' Says Lead Scientist Of New Study
Whatever the value of climate sensitivity, our current emissions path is "all but certain to be catastrophic", says Joe Romm.
Climate Progress

No matter how strong the evidence on climate change, deniers will keep denying
Research on climate consensus is critical, says Stephan Lewandowsky, because if people see that scientists agree on the issue their beliefs will follow suit. But it still won't change the mind of "dissenters", he says.
The Conversation UK

Science:

Warming Causing Rockies, Everest to Lose Ice and Snow
New research identifies temperature rise as a major factor driving the decline of snow in the Rockies, and possibly at Mt. Everest too.
Climate News Network

Amazon River exhales virtually all carbon taken up by rain forest
New research suggests carbon-rich material washed into the river isn't locked up in the deep sea, but is instead converted to earth-warming carbon dioxide and released into the atmosphere.
PhysOrg