Unfortunately, I think human land use is impeding that feedback mechanism, as there are large portions of land area that are not allowed to freely green up anymore.
That'll change as human-caused global warming results in widespread crop failures and migration of people. We're at the top of the food pyramid; change an ecosystem and (most of) humanity is the first to go. It only takes about one human generation for an ecosystem to recover after humans leave: Chernobyl and the Korean DMZ are among the most pristine environments on earth now.
This is probably cold comfort for the billions of people that will die.
This is probably cold comfort for the billions of people that will die.