Global precipitation changes depend strongly on the climate change mechanism and how it perturbs the atmospheric and surface energy budgets (as opposed to TOA energy budgets for temperature, for example). Simple relationships such as global radiative forcing that work well for mean temperature change are not useful for the hydrologic response.

The precipitation response can also be decomposed into several components, depending on the nature of the forcing. For CO2 increase, precipitation actually goes down at fixed temperature. However, precipitation ultimately goes up due to temperature-dependent responses. These dependencies introduce variability in the response between shortwave perturbations felt predominately at the surface or longwave perturbations which modify the atmospheric absorption properties.

Precipitation needn’t increase for all warming agents however. Consider black carbon which absorbs shortwave radiation in the troposphere and has a positive TOA forcing, but reduces the shortwave radiation available at the surface. This atmospheric absorption can reduce the lapse rate and suppress precipitation even with a warming column, though it also depends on the vertical structure of the shortwave absorber. (see e.g., Ming et al., 2010, GRL)

For very warm climates, precipitation hits an upper bound that is determined by the incoming absorbed solar radiation (divided by the latent heat of vaporization). This is true even if temperature increases due to CO2 at fixed solar irradiance. There are some subtle effects that can modify that argument somewhat, but it’s pretty robust and the argument becomes rather simple in that limit where the atmosphere is optically thick in the longwave. One wouldn’t be able to sustain a planet for example with constant downpour (the star wars clones planet in Episode 2?) on purely energetic grounds.

Hope that helps!

Passengers were extremely eager to learn the results of these interesting scientific studies.

Mind if I frame that and put it on the wall?

I think you’re asking whether the world warms _the_same_way_ from an increase in CO2, or from the Sun getting brighter?

Those models would be assuming the Sun stays about the same, and greenhouse gases and sulfates and whatnot change.

I think they would not see “polar amplification” if it were the Sun for example, or cooling of the stratosphere. But I don’t know what difference it would make — early on — eliminating both of those, and having instead more heat along the tropics under with the sun high overhead for 12-hour days.

In the long run, if the Sun got a bit warmer, we’d be seeing the kind of feedbacks — including in increase in greenhouse gases.

Lather rinse repeat.

Dunno if any of the models can be run with the Sun changing. Some of the astronomers who study how stars like our Sun can vary and even flare brightly might have looked at what that would do to us.

‘oogle for
Variable-brightness star and climate change?

Do we have any data yet on the prediction of increased intensity of extreme rain and drought? …

For extreme precipitation events, I would suggest the fingerprint study:

Our results provide to our knowledge the first formal identification of a human contribution to the observed intensification of extreme precipitation. We used probability-based indices of precipitation extremes that facilitate the comparison of observations with models. Our results also show that the global climate models we used may have underestimated the observed trend, which implies that extreme precipitation events may strengthen more quickly in the future than projected and that they may have more severe impacts than estimated. There are, however, uncertainties related to observational limitations, missing or uncertain external forcings and model performance.

Seung-Ki Min, Xuebin Zhang, Francis W. Zwiers, Gabriele C. Hegerl(2011 Feb 17) Human contribution to more-intense precipitation extremes, Nature, 470(7334):378-81

As for drought, a good place to begin would be:

[from the abstract:]All the four forms of the PDSI show widespread drying over Africa, East and South Asia, and other areas from 1950 to 2008, and most of this drying is due to recent warming. The global percentage of dry areas has increased by about 1.74% (of global land area) per decade from 1950 to 2008.

Aiguo Dai (2011) Characteristics and trends in various forms of the Palmer Drought Severity Index during 1900-2008. Journal of Geophysical Research-Atmospheres, 116, D12115.

… which is available at:

http://www.cgd.ucar.edu/cas/adai/

Or is this a fingerprint of warming regardless of the cause of the warming?

http://news.bbcimg.co.uk/media/images/60347000/jpg/_60347194_60347193.jpg

—excerpt follows—
researchers on the new Arctic project, led by Katey Walter Anthony from the University of Alaska at Fairbanks (UAF), were able to identify long-stored gas by the ratio of different isotopes of carbon in the methane molecules.

Using aerial and ground-based surveys, the team identified about 150,000 methane seeps in Alaska and Greenland in lakes along the margins of ice cover.

Local sampling showed that some of these are releasing the ancient methane, perhaps from natural gas or coal deposits underneath the lakes, whereas others are emitting much younger gas, presumably formed through decay of plant material in the lakes.

“We observed most of these cryosphere-cap seeps in lakes along the boundaries of permafrost thaw and in moraines and fjords of retreating glaciers,” they write, emphasising the point that warming in the Arctic is releasing this long-stored carbon.

“If this relationship holds true for other regions where sedimentary basins are at present capped by permafrost, glaciers and ice sheets, such as northern West Siberia, rich in natural gas and partially underlain by thin permafrost predicted to degrade substantially by 2100, a very strong increase in methane carbon cycling will result, with potential implications for climate warming feedbacks.”

If there is not yet a measurable trend, do any of the models indicate how long we need to wait for a detectable trend?