(November 2009) There is near consensus among the scientific community that CO2 emissions are causing climate change, including increased temperature, precipitation, and variability in weather. However, the social and economic costs of climate change will not be spread evenly across the globe. Some countries and regions will be more negatively affected than others, complicating the policy response across developed and developing countries. In the case of the United States and India, the difference in the impact of rising temperatures on mortality is dramatic.

Michael Greenstone, 3M professor of environmental economics at the Massachusetts Institute of Technology, shared his recent research findings on the mortality impact of rising temperatures using data from the United States and India at a recent PRB policy seminar. Greenstone pointed out that it is common for media reports and research to focus on isolated, extreme events such as the 2003 heat wave in France and powerful hurricanes. His research, on the other hand, uses a much wider set of mortality, weather, consumption, and economic data to more accurately determine the relationship between climate change and health.

Greenstone's major finding is that rising temperatures do not appear to have a big impact on mortality in the United States, but have a major impact in India, especially in rural areas. For example, one extra day of 36 degree Celsius temperature in India is associated with a 1 percent annual mortality rate rise, according to Greenstone's model.

Why are the effects of temperature change so different in the United States and India? Greenstone highlights "adaptation opportunities"—actions that individuals can take to mitigate the effects of temperature change. In the United States, there is a huge spike in energy consumption on days hotter than 90 degrees as people use more air conditioning. Individuals in the United States are willing and able to engage in costly adaptation strategies to mitigate the effects of higher temperatures. Climate change will likely result in higher energy consumption in the United States (costing an additional $15 billion to $35 billion a year, according to Greenstone). In India, on the other hand, there are fewer opportunities for adaptation, especially in rural areas where the effects will be greatest. Hot days are associated with a sharp decline in rural agricultural wages and reduced access to credit.

Greenstone highlighted the central tension over the costs of and responsibility for climate change between developed and developing countries. He expects the costs of climate change will be higher in developing countries even though consumption is much higher in developed countries. In fact, debates between developing and developed countries over emission-cut guidelines in talks before the 2009 Copenhagen summit highlight this tension. "If the developed countries paid for all reductions in the globe, the costs in terms of consumption could be as high as 10 percent," said Greenstone. "The developed countries are not going to give up 10 percent of their consumption, particularly when the impacts for developed countries are likely to not be very large."

Eric Zuehlke is an editor at the Population Reference Bureau.