[Editors] MIT: Human-generated ozone will damage crops

[Elizabeth Thomson]

MIT News Office
Massachusetts Institute of Technology
Room 11-400
77 Massachusetts Avenue
Cambridge, MA  02139-4307
Phone: 617-253-2700
http://web.mit.edu/newsoffice/www

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MIT: Human-generated ozone will damage crops

--Could reduce production by more than 10 percent by 2100

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For Immediate Release
MONDAY, OCT. 29, 2007
Contact: Elizabeth A. Thomson, MIT News Office -- Phone: 617-258-5402  
-- Email: thomson at mit.edu

PHOTO, GRAPHIC AVAILABLE


CAMBRIDGE, Mass.--An MIT study concludes that increasing levels of  
ozone due to the growing use of fossil fuels will damage global  
vegetation, resulting in serious costs to the world's economy.

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, especially in northern  
temperate regions. However, those benefits may be more than offset by  
the detrimental effects of increases in ozone, notably on crops.  
Ozone is a form of oxygen that is an atmospheric pollutant at ground  
level.

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 will 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,” said John M. Reilly, associate director of the MIT  
Joint Program on the Science and Policy of Global Change. “That  
result is both surprising and worrisome.”
	
The MIT study is novel. 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 are outside the scope  
of this 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.

EXPECTED AND UNEXPECTED FINDINGS
	
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 percent 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,” said Reilly. “It's a little like going out and  
exercising really hard on a high-ozone day.”	

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.

THE REGIONAL VIEW
	
Global estimates do not tell the whole story, however, as regional  
impacts vary significantly.
	
For example, 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 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.
	
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. For more information,  
please visit web.mit.edu/mitei/.

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Written by Nancy Stauffer, MIT Energy Initiative