Rain « JoNova

Do forests drive wind and bring rain? Is there a major man-made climate driver the models miss?

Clouds over Amazon forest (Rio Negro). Image NASA Earth Observatory.

What if winds were mainly driven by changes in water vapor, and those changes occurred commonly in air over forests? Forests would be the pumps that draw in moist air from over the oceans. Rather than assuming that forests grow where the rain falls, it would be more a case of rain falling where forests grow. When water vapor condenses it reduces the air pressure, which pulls in more dense air from over the ocean.

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 The paper is so controversial that many reviewers and editors said it should not be published.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 […]

Climate Models: 100% right except for rain, drought, storms, humidity and everything else

Yet more observations from the planet show that modelers misunderstand the water based part of the climate – on our water based planet.

Modelers thought that dry ground would decrease afternoon storms and rainfall over those frazzled parched lands (though I don’t remember many headlines predicting “More Drought means Fewer Storms” ). But observations show that storms are more likely to rain over dry soil. Why? Probably the dry soil heats up faster than moist areas thanks to the cooling effect of evaporation, and that in turn creates stronger thermals over dry land. Modelers assumed that wetter soils means more evaporation and thus more rain, but the moisture laden air is evidently coming from further away.

It’s another example of a point where climate modelers assume a positive feedback, yet the evidence suggests the feedback is negative. Once again water appears to be the dominant force with feedbacks (it does cover 70% of the surface). In a natural stable system the net feedbacks are likely to be negative. Positive feedbacks make the system less stable (and more scary and harder to predict.)

Climate change models misjudge drought: “A four-nation team led by Chris Taylor from Britain’s Centre for Ecology and […]

Clouds dominate everything

Al Gore describes how carbon dioxide beats up Mr Sunbeam and stops him leaving the atmosphere. But he “forgot” to mention that clouds reflect around a quarter of all the sunlight that hits the earth. Those beams of light travel all the way from the sun to get bounced off into space when they are just a few kilometers from the ground.

Any change in cloud cover makes a major difference. The IPCC assumes clouds respond to warming, but clouds could easily drive the warming.

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