By ecoRI News staff
CAMBRIDGE — Many studies have shown the potential for global
climate change to cut food supplies. But these studies have, for the most part,
ignored the interactions between increasing temperature and air pollution —
specifically ozone pollution, which is known to damage crops.
A new study involving researchers at MIT shows
that these interactions can be quite significant, suggesting that policymakers
need to take both warming and air pollution into account in addressing food
security.
The study looked in detail at global production of four leading
food crops — rice, wheat, corn and soy — that account for more than half the
calories humans consume worldwide. It predicts that effects will vary
considerably from region to region, and that some of the crops are much more
strongly affected by one or the other of the factors. For example, wheat is
very sensitive to ozone exposure, while corn is much more adversely affected by
heat.
Heald said that while it’s known that both higher temperatures
and ozone pollution can damage plants and reduce crop yields, “nobody has
looked at these together.” And while rising temperatures are widely discussed,
the impact of air quality on crops is less recognized.
The effects are likely to vary widely by region, the study
predicts. In the United States, tougher air-quality regulations are expected to
lead to a sharp decline in ozone pollution, mitigating its impact on crops. But
in other regions, the outcome “will depend on domestic air-pollution policies,”
Heald said. “An air-quality cleanup would improve crop yields.”
Overall, with all other factors being equal, warming may reduce
crop yields globally by about 10 percent by 2050, the study found. But the
effects of ozone pollution are more complex — some crops are more strongly
affected by it than others — which suggests that pollution-control measures
could play a major role in determining outcomes.
Ozone pollution can also be tricky to identify, Heald said,
because its damage can resemble other plant illnesses, producing flecks on
leaves and discoloration.
Potential reductions in crop yields are worrisome. The world is
expected to need about 50 percent more food by 2050, according to the study’s
authors, because of population growth and changing dietary trends in the
developing world. So any yield reductions come against a backdrop of an overall
need to increase production significantly through improved crop selections and
farming methods, as well as expansion of farmland, according to the study.
While heat and ozone can each damage plants independently, the
factors also interact. For example, warmer temperatures significantly increase
production of ozone from the reactions, in sunlight, of volatile organic
compounds and nitrogen oxides. Because of these interactions, the team found
that 46 percent of damage to soybean crops that had previously been attributed
to heat is actually caused by increased ozone.
Under some scenarios, the researchers found that
pollution-control measures could make a major dent in the expected crop
reductions because of a changing climate. For example, while global food
production was projected to fall by 15 percent under one scenario, larger
emissions decreases projected in an alternate scenario reduce that drop to 9
percent.
Air pollution is even more decisive in shaping undernourishment
in the developing world, the researchers found. Under the more pessimistic
air-quality scenario, rates of malnourishment might increase from 18 percent to
27 percent by 2050 — about a 50 percent jump; under the more optimistic
scenario, the rate would still increase, but that increase would almost be cut
in half.
Agricultural production is “very sensitive to ozone pollution,”
Heald said, noting that these findings “show how important it is to think about
the agricultural implications of air-quality regulations. “Ozone is something
that we understand the causes of, and the steps that need to be taken to
improve air quality.”
