A new paper is causing a major stir. The paper is so controversial that many reviewers and editors said it should not be published. After two years of deliberations, Atmospheric Chemistry and Physics decided it was too important not to discuss.
The physics is apparently quite convincing, the question is not whether it happens, but how strong the effect is. Climate models assume it is a small or non-existent factor. Graham Lloyd has done a good job describing both the paper and the reaction to it in The Australian.
Sheil says the key finding is that atmospheric pressure changes from moisture condensation are orders of magnitude greater than previously recognised. The paper concludes “condensation and evaporation merit attention as major, if previously overlooked, factors in driving atmospheric dynamics”.Judith Curry has been following this idea for some time.
“Climate scientists generally believe that they already understand the main principles determining how the world’s climate works,” says Sheil. “However, if our hypothesis is true then the way winds are driven and the way rain falls has been misunderstood. What our theory suggests is that forests are the heart of the earth, driving atmospheric pressure, pumping wind and moving rain.”
Judith Curry of the Georgia Institute of Technology, an author of the standard textbook Thermodynamics of Atmospheres and Oceans, is encouraging. “The process they describe is physically correct,” she said. “The main question is its relative magnitude compared with other processes.” She thinks it could explain why climate models do not get monsoons and hurricanes right.If this is a strong driver, it means Australia is not covered in arid land because rainfall is low. If the trees were planted the rain would fall:
“I would have said Australia is a desert because of the global climate cycles, but if you do the calculations, a forest across the surface of Australia would produce forces strong enough to water it and you wouldn’t need to irrigate.”Even New Scientist admits this paper could be a big one.
The implications are huge. “In standard theories, if we lose forests the rainfall in the continental interiors generally declines by 10 to 30 per cent. In our theory, it is likely to decline by 90 per cent or more,” says Sheil.
[New Scientist, Fred Pearce]