News and Outreach: Colette L. Heald

Katherine Boehrer
Huffington Post

Ozone pollution, which worsens breathing problems and causes air quality warnings, may compound global warming's damage to the world's food crops, according to a new study.

Ground-level ozone, formed mainly from pollutants emitted by burning fossil fuels for cars, industry and power plants, increases as temperatures rise. That's why air quality warnings are more frequent in hot weather and why global warming has the potential to boost ozone pollution. Once formed, ozone can travel long distances, affecting even remote areas.

The new study, published Sunday in the journal Nature Climate Change, used models and historical trends to analyze the impact of climate change and ozone on four of the world's major food crops: wheat, rice, maize and soybeans. Ozone can harm plants by slowing photosynthesis and killing cells. According to the U.S. Department of Agriculture, “Ground-level ozone causes more damage to plants than all other air pollutants combined.”

The study showed that climate change is likely to reduce crop yields at least 10 percent by 2050 from 2000 levels. When the researchers compared two pollution scenarios from the Intergovernmental Panel on Climate Change's Fifth Assessment Report, they found that ozone would have more complex effects. In a higher ozone pollution scenario the researchers called "pessimistic," crop yields would decrease 15 percent by 2050. But in an "intermediate" ozone scenario, crop yields would fall 9 percent.

"The climate projections are quite consistent" in the two scenarios, one of the study's authors, Colette Heald of the Massachusetts Institute of Technology, told The Huffington Post. But "the future of ozone pollution is very different ... leading to either offsetting or reinforcing effects [of climate change] on crops."

The authors also looked at what this drop in food production may mean for world nutrition. Undernourishment, or the number of people not getting enough food, would increase by 49 percent by 2050 in the pessimistic ozone pollution scenario, and it would increase by 27 percent in the intermediate scenario.

The researchers point out that the effects of ozone pollution and climate change vary by region and the type of crop. For example, wheat does poorly when exposed to ozone, while corn is more sensitive to heat.

According to the U.S. Environmental Protection Agency, an increase in CO₂ could mean some crops grow better, increasing yields. The study authors acknowledge this may offset effects of rising temperatures and pollution in some places.

However, the impact of climate change on agriculture also includes extreme weather events such as flooding, drought and exceptional temperatures, which may also damage crops. Weeds and pests may thrive in warmer temperatures, and ranges of certain pests and diseases could change, causing new challenges for farmers.

In a press release accompanying the new study, Heald said that the findings highlight the need for pollution reduction alongside climate action. “An air-quality cleanup would improve crop yields," she said. "Ozone is something that we understand the causes of, and the steps that need to be taken to improve air quality.”

Heald told HuffPost that the Clean Air Act has helped reduce surface ozone in the U.S. "Despite an increase in vehicle miles driven and energy consumption, surface ozone has declined by 25 percent on average across the U.S. from 1980 to 2012," she said. "However, the future of ozone air quality in the U.S. and around the world will depend on local emissions, the use of pollution control technology, regulations, and air quality policy."

By David L. Chandler

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.

The research was carried out by Colette Heald, an associate professor of civil and environmental engineering (CEE) at MIT, former CEE postdoc Amos Tai, and Maria van Martin at Colorado State University. Their work is described this week in the journal Nature Climate Change.

Heald explains 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 says. “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 says, 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, the authors say, due to 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.

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 following climate change. 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 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, they found.

Agricultural production is “very sensitive to ozone pollution,” Heald says, adding 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.”

Denise L. Mauzerall, a professor of environmental engineering and international affairs at Princeton University who was not involved in this research, says, “An important finding … is that controls on air-pollution levels can improve agricultural yields and partially offset adverse impacts of climate change on yields. Thus, the increased use of clean energy sources that do not emit either greenhouse gases or conventional air pollutants, such as wind and solar energy, would be doubly beneficial to global food security, as they do not contribute to either climate change or increased surface-ozone concentrations.”

The research was supported by the National Science Foundation, the National Park Service, and the Croucher Foundation.