Saturday, October 27, 2007

Climate Change: The Cup Half Full Perspective

Accepting the fact that there are two (or more) sides to most issues, the authors present the positive.

ECONOMIST, n. a scoundrel whose faulty vision sees things as they really are, not as they ought to be.—after Ambrose Bierce

The Benefits of Climate Change
By Daniel K. Benjamin

Many people believe that human-caused emissions of greenhouse gases will lead to higher temperatures and increased precipitation during the 21st century. Similarly, it is thought that these changes may have an impact on economic well-being. The question remains: If such changes occur, will their economic effects be positive or negative? A definitive answer to this question is likely to be a long time coming, but recent research has shed new light on one important aspect. Olivier DeschĂȘnes and Michael Greenstone (2007) show that the changes in temperatures and precipitation forecast by the standard models of climate change will actually benefit agriculture in America.

The authors take no position on whether existing models of global climate change are valid. Instead, they ask this question: Assuming that the models’ predicted increases in temperatures and precipitation occur, what are the consequences for American agriculture? They find that the lengthened growing seasons and added precipitation implied by the most widely cited global climate change models will modestly increase agricultural yields and thereby enhance the profitability of American agriculture.

Past research into the possible impact of climate change on agriculture has produced wildly varying results, with almost any set of consequences—positive or negative—seemingly possible. At one extreme, it has been estimated that climate change might reduce agricultural productivity so much as to cut the value of agricultural land by almost 20 percent. At the other extreme, the outcome might be increased productivity that pushes the value of agricultural land up by almost 30 percent.

DeschĂȘnes and Greenstone show that these widely differing numbers from past research are not the result of uncertainty about the climate and its effects on agriculture. Instead, they are the result of the statistical methods used by researchers. In particular, these methods turn out to be highly sensitive to small changes in the data samples, and to small changes in the way the data are used. To avoid this sensitivity, the authors employ a method in which the observed productivity impacts of past changes in temperatures and precipitation are used to infer the likely impacts of future changes in temperature and precipitation.

The most widely cited models of climate change predict that, over the remainder of the century, average temperatures will rise by about 50F and precipitation will eventually average about eight inches more per year. Using these predictions, combined with the effects of past swings in temperature and precipitation, the authors conclude that agricultural productivity in the United States is likely to rise slightly (about 4 percent) due to climate change, yielding modest positive economic benefits.