An MIT study concludes that increasing levels of tropospheric ozone due to the increasing use of fossil fuels under a business-as-usual scenario could cut global crop yields by nearly 40% worldwide by 2100, forcing a greater global allocation of land to agriculture.
Published in the journal Energy Policy, the study focuses on the affect of three environmental changes (increases in temperature, carbon dioxide and ozone) associated with human activity. The research shows that while increases in temperature and in carbon dioxide may actually benefit vegetation on a global basis, especially in northern temperate regions, those benefits may be more than offset by the detrimental effects of increases in tropospheric ozone, notably on crops.
The economic cost of the damage will be moderated by changes in land use and by agricultural trade, with some regions more able to adapt than others. But the overall economic consequences will be considerable, with a global economic loss of 10-12% of the total value of crop production.
Even assuming that best-practice technology for controlling ozone is adopted worldwide, we see rapidly rising ozone concentrations in the coming decades. That result is both surprising and worrisome.—John M. Reilly, associate director of the MIT Joint Program on the Science and Policy of Global Change
While others have looked at how changes in climate and in carbon dioxide concentrations may affect vegetation, Reilly and colleagues added to that mix changes in ozone. Moreover, they looked at the combined impact of all three environmental stressors at once, using the MIT Integrated Global Systems Model.
Results for the impacts of climate change and rising carbon dioxide concentrations (assuming business as usual, with no emissions restrictions) brought few surprises. For example, the estimated carbon dioxide and temperature increases would benefit vegetation in much of the world. The effects of ozone are decidedly different.
Without emissions restrictions, growing fuel combustion worldwide will push global average ozone up 50% by 2100. That increase will have a disproportionately large impact on vegetation because ozone concentrations in many locations will rise above the critical level where adverse effects are observed in plants and ecosystems.
Crops are hardest hit. Model predictions show that ozone levels tend to be highest in regions where crops are grown. In addition, crops are particularly sensitive to ozone, in part because they are fertilized.
When crops are fertilized, their stomata open up, and they suck in more air. And the more air they suck in, the more ozone damage occurs. It’s a little like going out and exercising really hard on a high-ozone day.—John Reilly
Northern temperate regions generally benefit from climate change because higher temperatures extend their growing season. However, the crop losses associated with high ozone concentrations will be significant. In contrast, the tropics, already warm, do not benefit from further warming, but they are not as hard hit by ozone damage because ozone-precursor emissions are lower in the tropics.
The study thus concluded that regions such as the United States, China and Europe would need to import food, and supplying those imports would be a benefit to tropical countries.
Reilly warns that the study’s climate projections may be overly optimistic. The researchers are now incorporating a more realistic climate simulation into their analysis.
Reilly’s colleagues are from MIT and the Marine Biological Laboratory. The research was supported by the Department of Energy, the Environmental Protection Agency, the National Science Foundation, NASA, the National Oceanographic and Atmospheric Administration and the MIT Joint Program on the Science and Policy of Global Change.
J. Reilly, S. Paltsev, B. Felzer, X. Wang, D. Kicklighter, J. Melillo, R. Prinn, M. Sarofim, A. Sokolov and C. Wang (November 2007) “Global economic effects of changes in crops, pasture, and forests due to changing climate, carbon dioxide, and ozone” Energy Policy 35 (11) 5370-5383 doi:10.1016/j.enpol.2006.01.040