watervole posts a link to this New Scientist map of the world in 100 years time following a 4C rise in temperature.
ALLIGATORS basking off the English coast; a vast Brazilian desert; the mythical lost cities of Saigon, New Orleans, Venice and Mumbai; and 90 per cent of humanity vanished.
Wasn't it considerably hotter than that in the Eocene, and the planet was heavily wooded and supported a massive number of mammals? However, I suppose it is the speed of change is what would cause the problem.
Worth reading the whole article.