This Nature paper reviews evidence that a changing climate poses significant health risks and that global warming over the past few years has already increased illness and death worldwide.

Infectious diseases are strongly affected by climatic variations because the vectors that carry the bacteria or viruses do not have thermoregulatory mechanisms, say the authors. One of the most important existing sources of climatic variability is El Niño. This weather system has been shown to influence malaria in South America, rift valley fever in east Africa, cholera in Bangladesh and dengue fever in Thailand. If, as some scientists have suggested, climate change alters El Niño, the consequences will be significant.

The authors say there are some promising early warning systems for infectious disease. In Botswana, for example, two-thirds of the inter-annual variability of malaria can be predicted from sea surface temperatures and monthly rainfall.