There are many legitimate reasons to be concerned about climate change (such as its likely effects on water supplies. The potential of a warmer world to spread insect-borne diseases is not one of them, however. Given current technology, climate is a relatively insignificant factor in the distribution of malaria and other such ailments around the world. As Paul Reiter and Roger Bate explain, those who wish to combat malaria and other insect-borne diseases have better things to worry about than climate change.
It may come as a surprise that malaria was once common in most of Europe and North America. In parts of England, mortality from "the ague" was comparable to that in sub-Saharan Africa today. William Shakespeare was born at the start of the especially cold period that climatologists call the "Little Ice Age," yet he was aware enough of the ravages of the disease to mention it in eight of his plays.
Malaria disappeared from much of Western Europe during the second half of the 19th century. Changes in agriculture, living conditions and a drop in the price of quinine, a cure still used today, all helped eradicate it. However, in some regions it persisted until the insecticide DDT wiped it out. Temperate Holland was not certified malaria-free by the WHO until 1970.
The concept of malaria as a "tropical" infection is nonsense. It is a disease of the poor. Alarmists in the richest countries peddle the notion that the increase in malaria in poor countries is due to global warming and that this will eventually cause malaria to spread to areas that were "previously malaria free." That's a misrepresentation of the facts and disingenuous when packaged with opposition to the cheapest and best insecticide to combat malaria -- DDT.
It is true that malaria has been increasing at an alarming rate in parts of Africa and elsewhere in the world. Scientists ascribe this increase to many factors, including population growth, deforestation, rice cultivation in previously uncultivated upland marshes, clustering of populations around these marshes, and large numbers of people who have fled their homes because of civil strife. The evolution of drug-resistant parasites and insecticide-resistant mosquitoes, and the cessation of mosquito-control operations are also factors.
Of course, temperature is a factor in the transmission of mosquito-borne diseases, and future incidence may be affected if the world's climate continues to warm. But throughout history the most critical factors in the spread or eradication of disease has been human behavior (shifting population centers, changing farming methods and the like) and living standards. Poverty has been and remains the world's greatest killer.
In other words, those concerned with disease control in the developing world should devote their energies to increasing wealth and distributing available medical technologies, rather than cooling the earth.