Possum or polar bear?

If you are like me, global warming usually conjures up thoughts of melting glaciers and stressed-out polar bears. But the polar and boreal regions, while spectacular in many ways, are relatively poor in biodiversity. Species in chilly climes are in serious trouble, but they are vastly outnumbered by a biota that may be even more vulnerable to global warming – the myriad denizens of lush rainforests.

We all know that tropical rainforests are the Earth’s richest ecosystems biologically; and, with an expanse of forest the size of 50 football fields going up in smoke every minute, that rainforests and their wildlife are unquestionably imperilled by habitat destruction. But how could global warming jeopardise animals and plants that are already adapted for warm, sultry conditions?

In a big way, evidently. Tropical species differ from their boreal and temperate-zone counterparts in one key respect: most are thermal specialists. Rather than enduring a huge contrast between freezing winters and warm summers each year, as their northern counterparts do, tropical species live in hot or balmy weather year-round.

University of Pennsylvania biologist Daniel Janzen grasped this years ago when...

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