Rain rain go away, let’s chop a forest down today?
Mark Andrich and Jorg Imberger compare the rainfall patterns in different regions of southwest Western Australia. The areas where the most land was cleared show the greatest decline. They estimate that as much as 50 – 80% of the observed decline in rainfall is the result of land clearing, which doesn’t leave much to blame on CO2. The paper came out in 2012.
This fits with other researchers working on the Amazon who estimated chopping down the forests could reduce rain by as much as 90%. Once again: it’s not so much that trees grow where the rain falls, but that the rain falls where the trees grow, and the taller the trees, the better.
So the good news for Greenies is that we ought to plant more trees (and I’m all for that). But driving a Prius, building windmills, and using solar panels won’t do much for our rainfall. (It’s so strange anyone thought it would. The witchdoctors have them completely bamboozled.) The Abbott government’s plan to plant trees to sequester carbon may work, but by accident, not because of anything to do with CO2.
Oh the [...]
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 The paper is so controversial that many reviewers and editors said it should not be published.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 [...]
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 [...]