A novel 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."
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.
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Source:
Massachusetts Institute of Technology
Published on 30th
October 2007
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