Climate Change, Health, and Costs Climate Change and Health I n May 2009, Costello et al. (2009) called climate change “the biggest global health threat of the 21st century.” It further noted that the “epidemiological outcome of climate change on disease patterns worldwide will be profound, especially in developing countries, where existing vulnerabilities to poor health remain.” It is projected that several negative health impacts will be exacerbated as a result of climate change in Asia and the Pacific. While the nature of the relationship remains uncertain, climate change is likely to affect health through a number of different pathways, as shown in Table 1. A first, and perhaps most immediate, pathway through which climate change may affect health is water. Adequate and clean water resources are vulnerable to climate change stress, and the lack of these heightens the risk of diarrhea and cholera in rural and urban areas. Greater rainfall, combined with warmer temperatures, is likely to make provision of clean water and adequate sanitation more complex and costly, and expand the vectors for waterborne communicable diseases, including malaria and dengue fever. For example, by 2080, approximately 6 billion people may be at risk of contracting dengue fever as a consequence of climate change, 2.5 billion more than if climate were to remain unchanged (Hales et al. 2002). In Indonesia (Figure 1) and the Philippines (Figures 2 and 3), there is a clear correlation between the incidence of dengue fever and La Niña’s years (Indonesia) and rainfall (the Philippines). Recent data from Kathmandu, Nepal also show the number of typhoid cases at their highest annual levels, with peaks in maximum and minimum temperatures (Figure 4), as well as in rainfall (Figure 5). A second pathway, independent of water-related issues, is temperature increases. The urban population in developing countries is rapidly increasing, and is often combined with poor housing and living conditions. These conditions increase the risk of heat strokes due to the heat island effect.3 A third pathway is agriculture, as the agricultural productivity of existing crops is expected to be challenged significantly. Agriculture is extremely vulnerable to climate change. Higher temperatures eventually reduce yields of desirable crops, while encouraging weed and pest proliferation. Changes in precipitation patterns increase the likelihood of short-run crop failures and long-run production declines. Although there will be gains in some crops in some regions of the world, the overall impacts of climate change on agriculture are expected to be negative. In turn, this may have adverse impacts on nutrition and food security. Climate change is expected to boost the number of malnourished children by 2050. More specifically, in East Asia, instead of 2.3 million malnourished children in 2050—which is projected in the case of no change in the climate—this number is projected to reach between 4.9 million to 5.3 million with climate change. In South Asia, instead of 52.3 million malnourished children in 2050 under prevailing climate conditions, predictions indicate that between 57.2 million and 58.2 million will be malnourished due to climate change (ADB 2009a). In a recent report, it was estimate that calorie availability in 2050 may not only be lower than in the no-climate-change scenario, but that it may actually decline relative to 2000 levels throughout the developing world (IFPRI 2009). Finally, a fourth pathway is extreme weather events and heat waves (e.g., droughts, storms, rainfalls), which are expected to become more severe and/or more frequent. Over the period 1960–2007, the number of people around the world affected by droughts, floods, storms, and extreme temperatures has increased 3 The heat island effect is a phenomenon that has accompanied, and increased with, urbanization. It refers to the fact that humanmade structures tend to attract and retain heat at a higher rate than is normal in nature. 3