Q. What effects would global climate change likely have
on world agriculture?
 A.
Four recent analyses of projected increases
in global temperature of 2.8 to 5.2°C (5.0 to 9.4°F)
indicate that climate change would likely inhibit world
agricultural production by the end of the 21st century.
Declines are due to reductions in aggregate crop production
of between 0.5 and 1.3 percent, depending on the analysis.
Although wheat production may either rise or fall relative
to production under current climatic conditions, world
production of other grains (primarily rice and corn) and
nongrain crops would likely decrease.
Declines in crop production would likely be offset somewhat by
increases in livestock production. Livestock production increases
on average primarily because losses in areas where farmers depend
on crops for livestock feed are more than offset by the expansion
of grazing on lands no longer suitable for crop production. Grazing
land expands because cropland soils become drier in many locations
(Darwin et al., 1995). Total agricultural production declines by
0.3 to 0.8 percent. These production changes are associated with
changes in average per capita expenditures on consumer goods and
services that range from -0.11 to 0 percent (Darwin, 1999). These
generally lower levels of consumer purchases are due to declines
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.
Climate-induced impacts on agricultural productivity are not equally
distributed around the world. In many tropical areas, warming reduces
soil moisture, thereby lowering productivity on existing and potential
agricultural lands. In many cooler areas, however, warming increases
soil temperature, and, if not constrained by low soil moisture,
raises productivity on existing agricultural lands and expands the
potential agricultural land base. Aggregate crop production in Southeast
Asia (e.g., Indonesia, Malaysia, Philippines, Singapore, and Thailand),
for example, would likely decline (by 2.6 to 4.8 percent in recent
analyses), but would likely rise in Japan (by 6.2 to 10.4 percent).
Previous results from the Future Agricultural Resources Model as
well as from other models are available in Darwin et al. (1995)
and Schimmelpfennig et
al. (1996).
These results are subject to a number of limitations.
- First, links in the chain from climate to water resources and
on to agricultural production are inadequately simulated. Water
storage in alpine snowpack, for example, is not taken into account.
Water is also treated as though it could be transported cost-free
anywhere within a given region. And water is implicitly assumed
to always be beneficial.
- Second, potential impacts on weather variability—both year-to-year
and short-term extreme events such as floods, storms, and dry
spells—are overlooked.
- Third, climate changes are applied to 1990 economic conditions
rather than projections of future economic conditions.
- Fourth, the direct growth-promoting effects of greater atmospheric
concentrations of carbon dioxide on plants are not considered.
Research that overcomes shortcomings with regard to water resources,
weather variability, and future economic conditions is underway. Research
on the direct growth-promoting effects of
greater concentrations of atmospheric carbon dioxide has recently
been completed.
References
- Darwin, R.F. 1999. "A FARMer's View of the Ricardian Approach
to Measuring Effect of Climatic Change on Agriculture," Climatic
Change 41(3/4):371-411.
- Darwin, R.F., M. Tsigas, J. Lewandrowski, and A. Raneses. 1995.
World Agriculture and Climate Change: Economic Adaptations.
AER-703. U.S. Dept. Agr., Econ. Res. Serv., Washington, DC.
- Schimmelpfennig, D., J. Lewandrowski, J. Reilly, M. Tsigas,
and I. Parry. 1996. Agricultural
Adaptation to Climate Change: Issues of Longrun Sustainability.
AER-740. U.S. Dept. Agr., Econ. Res. Serv., Washington, DC.
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