From Roger Adams
Isn’t global warming caused by an increase in total heat energy on the planet? How then can “forests help to cool the atmosphere as water evaporating from leaves absorbs heat”? (12 October, p 18).
Surely the heat energy is still there, in the water vapour, although the trees will be cooler. Total energy on the planet is still the same. If plants do not cool the planet by their transpiration, but just cool themselves, then the modellers will have to re-examine their assumptions and start again.
Danny Penman writes: It is true that the only direct cooling effect of increased transpiration will be on the trees and their immediate environment. But transpiration also leads to increased cloud cover, so more sunlight is reflected into space, thus cooling the planet.
Exeter, Devon, UK
