 The
upper figure shows MIT projections of global average percentage change in
crop yield under three scenarios. In the highest curve, emissions of carbon
dioxide (CO2) and other greenhouse gases (GHGs) are unregulated, and any impact
of ozone is excluded. In the lowest curve, GHGs are unregulated, and crop damage
from ozone is included. In the middle curve, GHGs are regulated, and ozone
damage is included. The message: rising temperatures and CO2 concentrations
cause crops to thrive (top curve), but that positive effect is more than offset
by the negative impacts of rising ozone concentrations (bottom curve). When
GHG emissions are regulated, fuel combustion declines, reducing ozone
concentrations and related crop damage (middle curve). The lower figure shows
changes in total crop production under the same three scenarios. While crop
yields may drop dramatically, crop production never declines by more than 8
percent because the world adapts by allocating more resources to growing food.
Courtesy John Reilly / MIT
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