MIT study: human-generated ozone could damage crops - temperate regions hit hard, tropics spared

A novel MIT study concludes that increasing levels of ozone due to the growing use of fossil fuels could damage global vegetation, resulting in serious costs to the world's economy. Ozone is a form of oxygen that is an atmospheric pollutant at ground level. In the upper troposphere it acts as a greenhouse gas, absorbing some of the infrared energy emitted by the earth. The analysis, reported in the November issue of Energy Policy, focused on how three environmental changes (increases in temperature, carbon dioxide and ozone) associated with human activity will affect crops, pastures and forests.

The research shows that increases in temperature and in carbon dioxide may actually benefit vegetation. However, those benefits may be more than offset by the detrimental effects of increases in ozone, notably on crops. 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 here. 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 net result: 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 [who have a very large agricultural potential left, ed.].

At Biopact we think the Machiavellian argument often heard that temperate regions (which happen to house the industrialised world) stand to benefit agriculturally from increased levels of atmospheric CO2 and therefor shouldn't put too much effort in fighting climate change, is hereby partly debunked.

The MIT scientists say 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. According to the analysis, if nothing is done, by 2100 the global value of crop production could fall by 10 to 12 percent.

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 tropospheric ozone. Moreover, they looked at the combined impact of all three environmental 'stressors' at once. Changes in ecosystems and human health and other impacts of potential concern were left outside the of study.

They performed their analysis using the MIT Integrated Global Systems Model, which combines linked state-of-the-art economic, climate and agricultural computer models to project emissions of greenhouse gases and ozone precursors based on human activity and natural systems.

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:
energy :: sustainability :: biomass :: bioenergy :: climate change :: global warming :: fossil fuels :: carbon dioxide :: ozone :: emissions :: agriculture :: forests ::

But the effects of ozone are decidedly different. Without emissions restrictions, growing fuel combustion worldwide will push global average ozone up 50 percent by 2100 (graph, click to enlarge). 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 M. Reilly

What is the net effect of the three environmental changes? Without emissions restrictions, yields from forests and pastures decline slightly or even increase because of the climate and carbon dioxide effects. But crop yields fall by nearly 40 percent worldwide.

However, those yield losses do not translate directly into economic losses. According to the economic model, the world adapts by allocating more land to crops. That adaptation, however, comes at a cost. The use of additional resources brings a global economic loss of 10-12 percent of the total value of crop production.

Global estimates do not tell the whole story, however, as regional impacts vary significantly. The net result of the projections show 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.

It is part of the MIT Energy Initiative (MITEI), an Institute-wide initiative designed to help transform the global energy system to meet the challenges of the future. MITEI includes research, education, campus energy management and outreach activities, an interdisciplinary approach that covers all areas of energy supply and demand, security and environmental impact.

Graphs: 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.

References:
J. Reilly, et al. "Global economic effects of changes in crops, pasture, and forests due to changing climate, carbon dioxide, and ozone", Energy Policy, Volume 35, Issue 11, November 2007, Pages 5370-5383, doi:10.1016/j.enpol.2006.01.040

MIT News: Human-generated ozone will damage crops, according to MIT study - October 26, 2007.