Q. What eirect effects would rising concentrations of
atmospheric carbon dioxide likely have on world and U.S.
agriculture?
 A.
Recent analyses of a 225-ppmv (parts per million by volume)
increase in atmospheric carbon dioxide (CO2)—about
63 percent above 1990 levels and within the 35- to 170-percent
range projected by the Intergovernmental Panel on Climate
Change (1996) for the end of the 21st century—indicate
that its direct growth-promoting effects on crops would
likely boost world and U.S.
agricultural production.
World production of each agricultural commodity increases when
the 225-ppmv increase is applied to 1990 climatic and economic conditions.
Estimated increases in production of wheat, other grains, and nongrains
are 3.6, 2.4, and 2.4 percent; aggregate crop production rises by
2.5 percent. Livestock production rises by 0.8 percent. These production
changes generate a 0.67-percent increase in average per capita expenditures
on consumer goods and services (Darwin, 1999). This is due to an
increase in the availability to consumers not only of agricultural
commodities themselves, but also of consumer goods and services
that rely on agricultural commodities as inputs.
U.S. production increases for some commodities and declines for
others. Wheat and other grains decline by 1.3 and 5.6 percent, while
nongrain crops increase by 6.5 percent. Aggregate crop production
rises by 1.0 percent. Livestock production increases by 0.2 percent.
Differences from world impacts are attributable to the current position
of the United States as a net exporter of wheat, corn, and soybeans
in international trade. Increases in foreign production reduce the
net export demand for U.S. wheat. A similar reduction in the net
export demand for other grains is reinforced by a loss in U.S. comparative
advantage due to the relatively small (7 percent)
growth-promoting effects of atmospheric CO2 on
corn, the major component of U.S. other grains. Corn does, however,
become more available for domestic livestock production. The potential
reduction in the net export demand for nongrains, on the other hand,
is more than offset by an increase in U.S. comparative advantage
due to the relatively large (34 percent) growth-promoting
effects of atmospheric CO2 on soybeans, a major
component of U.S. nongrain crops.
Due to the greater availability of consumer goods and services
generated by the increases in both U.S. and world production of
agricultural commodities, U.S. expenditures on consumer goods and
services increase by 0.13 percent (Darwin, 1999). Income earned
in the U.S. agricultural sector, however, falls by 10.9 percent.
This is due to a fall in revenues and the reallocation of resources
(e.g., land, labor, and capital) from agriculture to other sectors
following a 5.1-percent decline in agricultural prices.
These results are subject to a number of limitations.
- First, the methods used to link CO
2-induced increases
in yield from experimental agronomic studies into increases in
economic supplies need to be improved (Darwin and Kennedy, 2000).
- Second, the growth-reducing effects of other gases released
by burning fossil fuels (particularly ozone, sulfur dioxide, and
nitrogen dioxide) are excluded.
- Third, changes in atmospheric concentrations of CO
2
are applied to 1990 rather than future economic and climatic conditions.
Research that jointly analyses climate change and the direct growth-promoting
effects of atmospheric CO2 on plants under future economic
conditions is underway. Research on the effects of climate change
on world and U.S.
agricultural production under 1990 economic conditions has been completed.
References
Darwin, R.F. and D. Kennedy. 2000. "Economic Effects of CO2
Fertilization of Crops: Transforming Changes in Yield into Changes
in Supply." Environmental Modeling and Assessment 5(3):157-168.
Intergovernmental Panel on Climate Change. 1996. Climate
Change 1995: Impacts, Adaptations and Mitigation of Climate Change:
Scientific-Technical Analysis. Cambridge University Press,
Cambridge.
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