Silman’s plots are arranged along a ridge. Plot 1, at the top of the ridge, has the highest
elevation and hence the lowest annual temperature.
In the popular imagination, global warming is mostly seen as a threat
to cold-loving species, and there are good reasons for this. As the world
warms, the poles will be transformed. In the Arctic, perennial sea ice
covers just half the area it did thirty years ago, and thirty years from now,
it may well be gone entirely. Obviously, any animal that depends on the
ice—ringed seals, say, or polar bears—is going to be hard-pressed as it
melts away.
But global warming is going to have just as great an impact—indeed,
according to Silman, an even greater impact—in the tropics. The reasons
for this are somewhat more complicated, but they start with the fact that
the tropics are where most species actually live.
CONSIDER for a moment the following (purely hypothetical) journey.
You are standing on the North Pole one fine spring day. (There is, for the
moment, still plenty of ice at the pole, so there’s no danger of falling
through.) You start to walk, or better yet ski. Because there is only one