This is important because scientists are concerned that unchecked global warming could cause already dry areas to get drier. (Global warming may also cause wet areas to get wetter.) Cao and Caldeira’s findings indicate that reducing atmospheric carbon dioxide could prevent droughts caused by climate change.
Via press release in Eurekalert, from Stanford, and the Carnegie Institution:
Cutting carbon dioxide helps prevent drying
Washington, D.C.—Recent climate modeling has shown that reducing the concentration of carbon dioxide in the atmosphere would give the Earth a wetter climate in the short term. New research from Carnegie Global Ecology scientists Long Cao and Ken Caldeira offers a novel explanation for why climates are wetter when atmospheric carbon dioxide (CO2) concentrations are decreasing. Their findings, published online today by Geophysical Research Letters, show that cutting carbon dioxide concentrations could help prevent droughts caused by global warming.
Cao and Caldeira’s new work shows that this precipitation increase is due to the heat-trapping property of the greenhouse gas carbon dioxide in the atmosphere. Carbon dioxide traps heat in the middle of the atmosphere. This warm air higher in the atmosphere tends to prevent the rising air motions that create thunderstorms and rainfall.
As a result, an increase in the atmospheric concentration of carbon dioxide tends to suppress precipitation. Similarly, a decrease in the atmospheric concentration of carbon dioxide tends to increase precipitation.
The results of this study show that cutting the concentration of precipitation-suppressing carbon dioxide in the atmosphere would increase global precipitation. This is important because scientists are concerned that unchecked global warming could cause already dry areas to get drier. (Global warming may also cause wet areas to get wetter.) Cao and Caldeira’s findings indicate that reducing atmospheric carbon dioxide could prevent droughts caused by climate change.
“This study shows that the climate is going to be drier on the way up and wetter on the way down,” Caldeira said, adding:”Proposals to cool the earth using geo-engineering tools to reflect sunlight back to space would not cause a similar pulse of wetness.”
The team’s work shows that carbon dioxide rapidly affects the structure of the atmosphere, causing quick changes precipitation, as well as many other aspects of Earth’s climate, well before the greenhouse gas noticeably affects temperature. These results have important implications for understanding the effects of climate change caused by carbon dioxide, as well as the potential effects of reducing atmospheric carbon dioxide concentrations.
“The direct effects of carbon dioxide on precipitation take place quickly,” said Cao. “If we could cut carbon dioxide concentrations now, we would see precipitation increase within the year, but it would take many decades for climate to cool.”
Recently, it was found that a reduction in atmospheric CO2 concentration leads to a temporary increase in global precipitation. We use the Hadley Center coupled atmosphere-ocean model, HadCM3L, to demonstrate that this precipitation increase is a consequence of precipitation sensitivity to changes in atmospheric CO2 concentrations through fast tropospheric adjustment processes. Slow ocean cooling explains the longer-term decrease in precipitation. Increased CO2 tends to suppress evaporation/precipitation whereas increased temperatures tend to increase evaporation/precipitation. When the enhanced CO2 forcing is removed, global precipitation increases temporarily, but this increase is not observed when a similar negative radiative forcing is applied as a reduction of solar intensity. Therefore, transient precipitation increase following a reduction in CO2-radiative forcing is a consequence of the specific character of CO2 forcing and is not a general feature associated with decreases in radiative forcing.
If someone will send me a copy of the paper (willis [at) surfacetemps.org) I’ll be happy to take a look.
The beauty of the paper seems to be that it describes a situation (a quick reduction in atmospheric CO2 concentration) that, as far as I know, hasn’t been observed in nature …
So usually I’d ask “Where’s the comparison of the model with the observations?” But it appears they’ve sidestepped that very neatly.
But heck, I could be wrong, it’s just a press release and an abstract. The paper may say something different.
w.
“”””” Cindy in San Diego says:
March 26, 2011 at 1:03 pm
I have asked this question on several sites and it is never even acknowledged: what is the optimal ‘global’ temp and why. “””””
Well Cindy, you should never ask a rational question while standing between an otherwise unemployed, and maybe unemployable “researcher”. and his bottomless source of research grant funds; aka the taxpaying profit making segment of society.
But in fact,we have no idea, just what the global Temperature actually is; becasue for one thing, we don’t have anyway of doing so. Well we do know of a way; but we don’t have any where near enough Thermometers to measure it.
Mother Gaia, knows exactly what it is, because she does have enogh thermometers; but she has no way to tell us the answer.
So the most we know is global “anomalies”, which are differences between what things are, and what they are supposed to be.
We also don’t have enough thermometers to figure that out either. The reason why the wagon wheels go backwards in your favorite horse opera, is because the movie film compoany, didn’t have enough film to take enough pictures to show that they really go forwards. Same problem as not having enough thermometers.
But that is the $64,000 question; isn’t it. If you gave the thermostat remote control to the people who complain the most about the Temperature; where do you suppose they would set it; and why ?
Well many in Scandinavia, would want to set it higher; and in Minnesota too. And many in Iraq and Sudan, would like to set it lower. You’d have an even bigger argument than we now have between people who think we are in the midst of man made runaway heating, and people who don’t think that we are.
But keep on asking questions; becasue those who complain the most don’t have any practical answers on what to do either. Well they are not paid to do so; they are paid to complain about what the people who pay their research grants, are doing to help earn the money to pay those grants.
davidmhoffer, HadCM2 is a climate model that has been tested against real climate data in numerous publications. The authors did not have to test it again. I think you misunderstood this point.
Also, civil engineers can use computers these days to test construction designs against stresses like high wind or earthquakes, and don’t always rely on scaled down real models.
Jim D says:
March 27, 2011 at 3:02 pm
… Climate models are tested and improved by comparing with real data …
—————————-
You know Jim, I don’t think this actually happening.
The IPCC AR4 climate models were given the specific instruction to only submit models which had a sensitivity between 2.0C to 4.5C. Actually, the same numbers that Manabe (the low number) and Hansen (the high number) submitted as the sensitivity in 1979 (which when averaged produced 3.25C which is how the original estimate was derived).
In the 32 years since then, nobody has been given the freedom to operate a climate model which differs from this theoritical range.
Even though the sensitivity to date (the real data) obviously indicates a lower number than this.
I just ran through the numbers in detail on the 23 AR4 climate model simulations out to 2100. It is a standard 3.25C per doubling result. The lowest result is 2.0C per doubling and the highest is 4.5C per doubling. It is, in effect, a strictly mathematical calculation, not a climate simulation.
Jim D says:
March 28, 2011 at 6:14 pm
davidmhoffer, HadCM2 is a climate model that has been tested against real climate data in numerous publications. The authors did not have to test it again. I think you misunderstood this point.>>>
Hind casting it can’t reproduce natural variability, nor the LIA or MWP. When results from older runs are compared to current results, it has constantly over estimated increases. The point misunderstood however is by you. The model has NOT been tested against reductions in CO2 in the atmosphere since there are NONE to test against. To compound matters, they created an impossible physical scenario and then extrapolated the results to a scenario a fraction of the size. Tell me, if this idiotic model is so freaking accurate, why not simulate a slow and steady decline in the first place since that is what they claim they wanted to quantify?
“Also, civil engineers can use computers these days to test construction designs against stresses like high wind or earthquakes, and don’t always rely on scaled down real models.”>>>
For starters, they wouldn’t test with scaled down models in the first place. There’s a property of material strength called the “square-cube law” that makes any such testing invalid. What the engineers MIGHT do is use computers to design bridges using components with extensive real world testing in terms of the components themselves and real world testing of how combinations of those components react to various stresses. But the final design might look like it came out of computer, and it did, but ONLY because there was a tremendous amount of real world testing and results for the computer program to draw upon. And under no circumstances would data simulated out of thin air of circumstances impossible to happen be used to make recommendations for possible designs.
I’m being nice here Jim, I really am, because you said you bothered to read. You’ve demonstrated that you can read. Unfortunately you’ve also demonstrated that you’ve made up your mind and don’t really want to understand what you’ve read. You just keep regurgitating things you *think* engineers might do, things you *think* climate models do, testing you *think* might have been done, and when explained why that’s nonsense, you just come up with a new list of things you *think* might be true.
When are you going to actually think?