It’s not just warming that’s an issue, it’s potentially a continual change in the climate. The changes are extremely rapid compared to historical fluctuations, which might make it hard for any new environment to establish itself. We’re currently not headed to a warmer equilibrium, we’re heading to a constantly warming future.
"But forests take time to establish themselves, and climate may outrun the process, leaving vast areas in transition until soils and plants can adapt to a new climate regime. To make matters worse, any climatic state we envision for the future is itself a moving target, since the greenhouse gases we're adding to the air now will be warming the climate for a century or more. Will new forests be able to take root in these ever-shifting conditions?" — The Thinking Person’s Guide to Climate Change, pg. 222