[mkl]

> Think of this: those forests that are there, when the climate was different before there were probably different sorts of plants, no? I'm not talking millions of years ago, I'm talking ten thousand years ago, way too short of a timeframe for evolution. So how did those plants get there?

Forests migrate during slow natural climate change. The current climate change is much faster. If we wait and let it happen naturally, it will take a very long time, but we need to be soaking up carbon now, and it needs to be held by trees that will survive as long as possible in the currently-changing climate.