Jed wrote:- <<To put it another way, does anyone seriously assert that we should cut down all the trees in Canada to help prevent global warming?>>
No-one is asserting this as far as I know. That would be bonkers. The Wiki article was talking about afforestation (planting forest on land that has never been a forest) or reforestation in far Northerly or Southerly latitudes where there is significant long lasting snow and ice on the ground. New forest is much darker and less reflective than snow and ice so absorbs more solar radiation hence more global warming potential. Obviously the growing forest absorbs carbon but boreal forest is pretty slow growing and so absorbs less per tree per year than tropical forest. The Polar areas seem to be the bits that are heating up fastest so extra heat there, whether through retention by global warming gases or by extra absorption by decreased albedo, is to be discouraged. Boreal forests are not the large transpirers of water vapour (hence generators of reflective cloud) that tropical forests are. This general reasoning is recognised by reputable carbon offset companies such as http://www.carbonneutral.com/ who concentrate on tropical reforestation while allowing a few temperate ones to keep the customers happy.
Nick Palmer
