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.
However, a new study published in Nature Climate Change suggests that these interactions can be quite significant, suggesting that policymakers need to take both warming and air pollution into account in addressing food security.
"Climate change adaptation and ozone regulation have been identified as important strategies to safeguard food production, but little is known about how climate and ozone pollution interact to affect agriculture, nor the relative effectiveness of these two strategies for different crops and regions," wrote the research team.
Led by Colette Heald from the Massachusetts Institute of Technology (MIT), the research 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.
"We show that warming reduces global crop production by more than 10% by 2050 with a potential to substantially worsen global malnutrition in all scenarios considered. Ozone trends either exacerbate or offset a substantial fraction of climate impacts depending on the scenario, suggesting the importance of air quality management in agricultural planning," said Heald and her colleagues.
The team noted that the effects of ozone pollution are more complex than that of rising temperatures, with some crops more strongly affected by it than others. This suggests that pollution-control measures could play a major role in determining outcomes, said the team.
Heald and her colleagues suggested that the effects are likely to vary widely by region. In the United States, for example, tougher air-quality regulations are expected to lead to a sharp decline in ozone pollution, mitigating its impact on crops. However in other regions, the outcome "will depend on domestic air-pollution policies," she said.
"An air-quality cleanup would improve crop yields."
An additional issue is that ozone pollution can also be tricky to identify, Heald suggested - noting that its damage can resemble other plant illnesses, producing flecks on leaves and discoloration.
While heat and ozone can each damage plants independently, the factors also interact, said the team. 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% of damage to soybean crops that had previously been attributed to heat is actually caused by increased ozone.
Under some scenarios, they found that pollution-control measures could make a major dent in the expected crop reductions following climate change - noting that while global food production was projected to fall by 15% under one scenario, larger emissions decreases projected in an alternate scenario reduce that drop to 9%.
Ozone is key
Indeed, air pollution is even more decisive in shaping undernourishment in the developing world, the team found.
Under the more pessimistic air-quality scenario, rates of malnourishment might increase from 18% to 27% by 2050 said the team — about a 50% 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 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."
Source: Nature Climate Change
Published online ahead of print, doi: 10.1038/nclimate2317
"Threat to future global food security from climate change and ozone air pollution"
Authors: Amos P. K. Tai, Maria Val Martin, Colette L. Heald