Researchers at Lawrence Livermore National Laboratory, led by atmospheric scientist Govindasamy Bala, find that climate engineering to cancel the warming effects of CO2 would reduce net global rainfall.
In the new climate modeling study, which appears in the May 27-30 early online edition of the Proceedings of the National Academy of Sciences, Bala and his colleagues Karl Taylor and Philip Duffy demonstrate that the sunshade geoengineering scheme could slow down the global water cycle.
The sunshade schemes include placing reflectors in space, injecting sulfate or other reflective particles into the stratosphere, or enhancing the reflectivity of clouds by injecting cloud condensation nuclei in the troposphere. When CO2 is doubled as predicted in the future, a 2 percent reduction in sunlight is sufficient to counter the surface warming.
This new research investigated the sensitivity of the global mean precipitation to greenhouse and solar forcings separately to help understand the global water cycle in a geoengineered world.
While the surface temperature response is the same for CO2 and solar forcings, the rainfall response can be very different.
“We found that while climate sensitivity can be the same for different forcing mechanisms, the hydrological sensitivity is very different,” Bala said.
The global mean rainfall increased approximately 4 percent for a doubling of CO2 and decreases by 6 percent for a reduction in sunlight in his modeling study.
“Because the global water cycle is more sensitive to changes in solar radiation than to increases in CO2, geoengineering could lead to a decline in the intensity of the global water cycle” Bala said.
Sunlight is probably more important than global atmospheric since the sunlight hits the surface of the oceans and cause more localized heating right on the surface of the oceans where the heat does the most to cause water to evaporate.
I can imagine at least one method to counteract the reduction in water evaporation: Use large floating windmills on the ocean to pump up and spray water into the atmosphere. But I have no idea what scale of windmills would be needed to do this. I suspect it would not be cost effective.
Here's another idea: Use satellites to block sunlight from hitting Earth. But only block the sunlight over land. That way the oceans would still get the full force of solar radiation. Still, satellites are a far more expensive way to reduce solar radiation as compared to spraying aerosols into the atmosphere. So this approach has problems as well.
Anyone have a good idea on how to climate engineer to lower temperatures without lowering water evaporation from the oceans?
|Share |||Randall Parker, 2008 May 28 10:45 PM Climate Engineering|