Reproduced, with permission, from:
In the 1980s, the Environmental Protection Agency (EPA) commissioned many major studies of the potential effects of climate change on U.S. agriculture (87)[1]. The Agency emphasized the use of crop simulation models to predict the effects of various climate-warming scenarios on crop yields (75, 80), and gave little attention to technical changes in agricultural systems or the adaptive responses of farmers. The warming scenarios were generated by general circulation model (GCM) experiments under the assumption of doubled atmospheric carbon dioxide (CO2). The GCMs used predict eventual atmospheric temperature increases of 7 to 9 deg.F (4 to 5 deg.C) for many regions of the United States, and one of the models predicts severe drying for most of the agricultural land in the United States (see ch. 2). Representative projections of yield changes from two GCMs are presented in the figure at right.
EPA found that climate change would affect crop yields and livestock productivity and would result in a northward shift in the crop production zones. Although warming alone might lead to sharply reduced agricultural yields (over 50 percent decline in some regions), the direct effects of doubled CO2 could offset much of the potential decline in crop yields. Still, EPA predicted that yields would decline substantially under the more-severe climate scenarios, especially where droughts become more frequent. Yields across the Southern and Central States were considered particularly vulnerable, largely because of drying. A few northern locations, such as Minnesota, were expected to show yield improvements (in some cases, by more than 40 percent). Including CO2 effects and assuming no adaptive response, a reduction in the Nation's agricultural yields was projected as the most likely outcome of climate change.
Projected yield changes such as those described in the EPA studies suggest potential harmful effects of climate change but, ultimately, cost changes to consumers and agricultural producers are the concern. Exactly how consumer food prices and the profitability of farm production are affected will depend on farm-level reactions and market adjustments to climate change. Indeed, it is often not understood that farmers could benefit from the higher prices that would result from a reduction in all farm yields. Farming systems will change in response to crop productivity shifts and changes in commodity prices. Market-level adjustments in the location and intensity of food production worldwide will determine the prices faced by the individual farmers and consumers.
Although the EPA studies did not explicitly consider farm-level adaptations, they suggested that farmers could act to offset some of the projected yield declines (3,26, 80). A few basic agronomic adjustments were considered (80). For dryland corn (i.e., corn that is not irrigated) in the Southern Plains, altered planting dates showed little effect in offsetting the yield reduction caused by climate warming. More dramatic effects of short-term adaptations were found for dryland and irrigated wheat. A switch in cultivars led to improved wheat yields in most of the simulations.
Others studies took a more comprehensive look at on-farm adaptation. One examined the natural resource base of the Missouri-Nebraska-Kansas (MINK) region, investigating the effectiveness of several farm practices and innovations in offsetting effects of climate change (79). In the absence of adaptive response, they found that a permanent shift to warmer and drier climate conditions reduces net regional income by 1.3 percent. After accounting for direct CO2 effects and short-term adaptations by farmers, regional economic losses are reduced to 0.3 percent (11). More significantly, the study considers plausible innovations in crop genetics and farm management that could further reduce the risks to the region's future economy that are posed by climate change.
Effects of economic adjustments through shifts in the location and intensity of production were considered in one study (3). Shifting crops to better-suited locations would be an important adaptive mechanism that would offset much of the potential economic cost of climate change. The study used a regional-market model of U.S. agriculture to examine the economic effects of changes in crop productivity due to climate change. Economic damages were significantly less than would have resulted in the absence of shifts in the location and intensity of production. Economic effects range from damages of $10.3 billion to benefits of $10.9 billion, depending on which GCM scenario is considered (4). Depending on the climate scenario, overall crop production decreases by 20 percent or increases by 9 percent. Corresponding to these supply changes, commodity prices increase by 34 percent or decrease by 17 percent. In either case, farmers benefit while consumers bear the burden of higher prices under the harsher climate scenario.
One assessment of the world trade in agricultural products under climate change found that despite a potential for substantial effects of climate change on crops, interregional shifts in location and intensity of production and the opportunity for trade very much buffer the world from the threat of climate change(46). Price changes in international markets promote interregional adjustment in production and consumption. Essentially no aggregate economic effect on the United States results, and economic effects on the overall world economy are estimated to be similarly small. Another assessment of world agricultural trade under a climate change found beneficial effects from world trade, with interregional adjustments offsetting 70 to 80 percent of the potential yield declines (81). Despite this finding, that assessment reached an important and less-than-optimistic conclusion: although the United States itself may not face market losses, some parts of the developing world that must import food could suffer from higher food prices and an increased risk of hunger.
SOURCE: Office of Technology Assessment, 1993; W.E. Easterling, "Adapting United States Agriculture to Climate Change," contractor report for the Office of Technology Assessment, January 1993.