General Findings On Climate Change Impact

Across the large number of climate change-related studies several key findings have emerged regarding physiological effects on crops and, to a lesser extent, livestock. Following McCarl et al. (2003), the main findings are:

Table 29.1 Ranges of Estimated Effects on Country Crop Yields

Location

Indonesia Malaysia

Pakistan Sri Lanka Bangladesh Mongolia Kazakhstan

Czech Republic United Kingdom The Gambia

Zimbabwe Brazil

Argentina Uruguay United States

Impact (Crop: % Change in Yield)

Rice: -2.5% and +5.4%; soybeans: -2.3%; maize: -40% Rice: -22% to -12%; maize: no change; rubber:

-30% to -3% Wheat -60% to -10% Rice: -2.1% to +3% Rice: -6% to +8% Spring wheat: -74.3% to +32.0% Spring wheat: -56% to -44%; winter wheat: -35% to +15%

Winter wheat: -3% to +16% Crop productivity: +5% to +15%

Maize: -26% to -15%; early millet: -44% to -29%; late millet: -21% to -14%; groundnuts: +40% to +52% Maize: -13.6% to -11.5%

-6% to +38% Maize: -17% to +4%; wheat: -12% to +6% Barley: -40%; wheat: -31% to -11% Wheat: -14% to -2%; maize: -29% to -15%; rice: -23% to +1%

Source: From Rosenzweig, C., and Iglesias, A. 1994. Implications of Climate Change for International Agriculture: Crop Modeling Study. U.S. Environmental Protection Agency, Climate Change Division, Washington, DC; and Intergovernmental Panel on Climate Change. 1995. Climate Change: The IPCC Second Assessment Report, Volume 2: Scientific-Technical Analyses of Impacts, Adaptations, and Mitigation of Climate Change. Watson, R.T., M.C. Zinyowera, and R.H. Moss, Eds. Cambridge University Press, Cambridge, MA.

• Dryland and irrigated crop yields are altered as is irrigation water use. Table 29.1 presents crop yield implications for selected countries, while Table 29.2 shows yield impacts for irrigated and rainfed crops in the United States projected for 2030.

• Production effects vary by crop, location, temperature, and precipitation change (as reviewed in Adams et al., 1998a, and Lewandrowski and Schimmelfen-nig, 1999).

Table 29.2 Projected National Average Data on Irrigated and Dryland Crop Yield and Irrigation Water Use Sensitivity to Global Climate Change for 2030, United States

Without Adaptation With Adaptation

Table 29.2 Projected National Average Data on Irrigated and Dryland Crop Yield and Irrigation Water Use Sensitivity to Global Climate Change for 2030, United States

Without Adaptation With Adaptation

Dryland

Irrigated

Irrigated

Dryland

Irrigated

Irrigated

Crop

Yield

Yield

Water Use

Yield

Yield

Water Use

Cotton

+18% to +32%

+36% to +56%

-11% to +36%

NA

NA

NA

Corn

+11 to +19%

-1% to +21%

-30% to +57%

+11 to +20%

+1% to +21%

-32% to +57%

Soybeans

+7% to +34%

+16% to +17%

-12% to 0%

+7% to +49%

+23%

0% to +18%

Hard red spring wheat

+15% to +20%

-10% to +4%

-28% to -17%

+17% to +23%

-6% to +10%

-12%

Hard red winter wheat

-16% to +24%

-4% to +5%

-8% to +5%

-9% to +24%

-1% to +8%

-6% to +9%

Soft wheat

-5% to +58%

-6% to +3%

-12% to +5%

-3% to +58%

-5% to +5%

-26% to +3%

Durham wheat

+10% to +21%

-10% to +5%

-25% to +15%

+10% to +22%

+2% to +9%

-10% to -5%

Sorghum

+15% to +17%

-1% to +1%

-9% to -7%

+32% to +43%

+22% to +22%

+2% to +3%

Rice

NAa

-2% to +9%

-10% to -2%

NA

+7% to +9%

+2% to +5%

Potatoes

+6% to +7%

-6% to -3%

-5% to -1%

+7% to +8%

-4% to -1%

-3% to 0%

Tomatoes

NA

-9% to +1%

-9% to -5%

NA

+1% to +10%

-8% to +2%

Citrus

NA

+32% to +40%

-21% to -6%

NA

NA

NA

Hay

-10% to +43%

+3% to +37%

-29% to +44%

NA

NA

NA

Pasture

+3% to +22%

NA

NA

NA

NA

NA

Note: The data provide percentage changes in the item from a no climate change case.

a NA indicates that results were not developed for this case due to the small acreage involved or that the simulation was not done to

(in the adaptation cases as only selected crops were studied). ¡5

Source: From Reilly, J., et al. 2000b. Report of the Agricultural Sector Assessment Team. In U.S. Global Change Research Program, g

National Assessment Report on Changing Climate and Changing Agriculture. Available at: www.nacc.usgcrp.gov/sectorslagriculturel. ^

Note: The data provide percentage changes in the item from a no climate change case.

a NA indicates that results were not developed for this case due to the small acreage involved or that the simulation was not done to

(in the adaptation cases as only selected crops were studied). ¡5

Source: From Reilly, J., et al. 2000b. Report of the Agricultural Sector Assessment Team. In U.S. Global Change Research Program, g

National Assessment Report on Changing Climate and Changing Agriculture. Available at: www.nacc.usgcrp.gov/sectorslagriculturel. ^

• Different crops exhibit different degrees of sensitivity. Treatment of only selected crops can bias the results. For example, early U.S. studies only examined corn, soybeans, and wheat, in contrast to later studies that included many more heat-tolerant crops. Economic implications were moderated as a result. (For an example of such an effect, see the experiment on cotton in McCarl [1999], which showed that inclusion of the differential response by this more heat-tolerant crop caused a reversal in sign of the total welfare impact, thus showing a beneficial effect rather than a detrimental effect of climate change.)

• CO2 fertilization is an important factor. Inclusion of this effect in yield studies significantly raises the estimates of climate-affected yields. It is, however, somewhat controversial (see discussion in Reilly et al., 2000b, or Council for Agricultural Science and Technology, 1992, 2000).

• Yield effects vary latitudinally. These are generally positive in the higher latitudes, but are frequently negative in low-latitude and semi-arid areas. (See reviews in Adams et al., 1998a, and Lewandrowski and Schimmelfennig, 1999.) Mohamed et al. (2002a, 2002b) estimate that by 2025, climate change might lower Niger millet yields by 13%, groundnuts by 11% to 25%, and cowpeas by 30%.

• Human adaptations help mitigate climate change effects. Adaptations can be made in planting and harvest dates, crop choice, crop rotations, crop varieties, irrigation, fertilization, and tillage practices. Livestock producers can adapt by the provision of shading, sprinklers, improved airflow, lessened crowding, altered diets, and more care in handling animals. In the longer term, new crop varieties and livestock breeds may be developed that perform better under the anticipated future climate regime. (See reviews in Adams et al., 1998b, 1999; Rosenzweig and Hillel, 1998; Kaiser et al., 1993; Reilly et al., 2002; and Yates and Strzepek, 1998.)

• Livestock effects can be significant. Adams et al. (1999) and a recent U.S. national assessment (Reilly et al., 2000a, 2000b) estimated livestock productivity reductions ranging from 1.5% to 5%.

• Changes in agricultural supply result from the combined effect of changes in yields and changes in crop acreage, with livestock herd size and location, livestock diets, human consumption, international trade adjustments, and many other factors also adjusting to the new conditions (Adams et al., 1999; Reilly et al., 2000a, 2000b).

• Commodities that decline in supply will rise in price. Higher prices reduce consumption and consumer welfare. The negative consumer effects are offset by producer gains, but in general, total welfare tends to decline (Adams et al., 1999; Reilly et al., 2000a, 2000b). Yates and Strzepek (1998) found minor gains in economic welfare for Egypt attributable to lower projected international prices of food imports, and mildly harsh to mildly beneficial climate change projections for the country.

• Downing (1992) studied the implications of climate change for the water balance in Zimbabwe and found that over the entire surface of the country, water evaporation would be increased by 15% for a 1°C increase in temperature, while with a 2°C temperature increase, the country's core agricultural zone would be reduced by 67% due to high evaporation rates.

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