For years, scientists have forecast that global warming will
have a disproportionate impact on the world's poorest countries.
Flooding will worsen in Bangladesh; the deserts in East Africa
will expand; bigger, stronger cyclones will hit Indonesia. Now,
two economists have divined yet another negative outcome of a
hotter world for low-income countries: less trade. Benjamin
Jones of Northwestern and Benjamin Olken of MIT analyzed global
import-export data as well as temperature and precipitation
readings. They found that for poor countries, in a given year,
every 1-degree Celsius increase in average nationwide
temperature cut the growth rate of exports 2 to 5.7 percentage
points. For rich countries, hotter or cooler temperatures had no
measurable effect. Poor countries are especially at risk because
they depend so heavily on farming and light manufacturing --
think cornfields and T-shirt factories. Temperature rises wipe
out crops and hurt performance among factory workers. And
because such countries tend to ha