Tropical diseases in a changing climate.

• Author: Wilken, Elena

Global warming poses dangers more subtle than melting ice caps and flooded cities. According to epidemiologists at the World Health Organization, climate change could increase the range of many diseases that are now predominantly tropical. Most pathogens are geographically constrained by the distribution of their host species, or by environmental restrictions on their life-cycles. For example, incubation periods (the time between infection and when the host is capable of spreading the disease) are often temperature-determined. And the length of time a pathogen can survive without a host is usually governed by temperature and the amount of moisture available.

WHO scientists have been looking at the effects of global warming on such diseases as malaria, dengue, and yellow fever--and on the insects and mammals that spread them. Their modeling indicates that with a warming of just a few degrees Celsius, and with regional precipitation increases of 7 to 15 percent, these diseases could spread to more temperate latitudes, or into areas that...