limate change will have wide-ranging and mostly damaging impacts on human health. Longer and hotter heat waves may kill many people annually in large cities. More extreme weather such as storms and hurricanes may kill and injure more people, contaminate drinking water and inflict psychological trauma.

Meanwhile, warmer and sometimes wetter weather is already extending the range of infectious diseases such as malaria, dengue and yellow fever beyond regions where they are endemic and inhabitants have some immunity. According to the recent IPCC Second Assessment Report, by 2100, 60% of the world's population will be living in potential malarial zones, including inhabitants of some temperate zones. A likely 20% rise in incidence would mean an extra 50-80 million cases of malaria. Other diseases likely to increase and change in connection with the climate include Guinea worm, leishmaniasis, lymphatic filiasis, onchocerciasis and chagas disease, which today affect more than 147 million people.

We cannot afford to continue "business-as-usual." Changing course will not be easy, but is necessary. There are costs associated with acting now to slow global warming. But in terms of future health care, productivity, tourism, international trade, and insurance costs, the pay-offs, could be huge. Industrialized governments should commit to rapidly reducing their carbon dioxide emissions and to increase support for environmentally sustainable development in the developing world.