1. Crop yields

Effects of climate change alone may reduce average yields of corn, soybeans and wheat, both rainfed and irrigated.

Direct effects of CO₂ may modify yield declines.

Climate variability will likely lead to decreased yield stability.

2. Economic Impacts

Small to moderate aggregate reduction in the nation's agricultural output is estimated for a doubling of CO₂.

Reduced output would decrease exports.

Continued technological advances may be essential to offset losses.

Crop production may shift northward.

3. Irrigation demand

Demand for irrigation likely will increase in all regions.

Demand for irrigation likely will increase competition for existing water supplies.

4. Agricultural pests

Ranges and populations of agricultural pests may change.

5. Farm-level adjustments

Changed planting dates.

Changed crop species or varieties, double cropping.

Equipment changes, particularly at cropping boundaries.

Equipment changes, particularly at cropping boundaries.

6. Livestock effects

Higher temperature may increase diseases and heat stress.

Cold stress may either increase or decrease.

Reproductive capabilities may decrease.

7. Policy implications

Research on agricultural productivity should be maintained.

Agricultural research on vulnerabilities should be increased, including heat and drought tolerant crops, and germ plasm maintenance.

Farm policy should be evaluated for ability to adapt to global warming. Flexibility will be needed in shifting crop types and farm practices, and consideration is needed for issues such as soil erosion and water quality.

International balance of trade issues need to be evaluated.

A national drought policy needs to be established.