Climate change, which means global warming, has been blamed (rightly or wrongly) for a lot of things: extreme weather, damaged crops, dying forests, dying and deformed frogs, mudslides, the economy--you name it. Among the scientists who study climate change, which according to one estimate has been a warming of between 0.3 and 0.6 degrees Celsius in the last 100 years, there is disagreement about the extent of change and the effects.
One reported effect of climate change that has generated controversy is the assertion that it is contributing to the spread of tropical diseases. According to one theory, diseases are spreading because warming of the earth not only makes it warmer or hotter where it is already warm and hot, but it also makes traditionally cooler areas a little warmer too. When cooler areas get warmer, they become more suitable habitats for vectors, particularly disease-transmitting mosquitoes, which opportunistically move into these new areas. Some media reports already have cited cases of "opportunistic movement" by mosquitoes expanding into higher (and now slightly warmer) elevations that previously had been mosquito-free.
According to Henry Gee, in a Nature Science Update article in March 1997, a 1996 World Health Organization report warned that the world stands "on the brink of a global crisis in infectious diseases," with no country safe. Gee cites the report as saying that about 17 million people died from infectious diseases in 1995 and that "up to half of the present global population of 5.72 billion is at risk from a wide range of endemic, entrenched infectious diseases."
The World Health Organization says that the main re-emerging diseases are
- tuberculosis, "the world's largest killer among infectious diseases,"
- cholera,
- dengue fever,
- diphtheria,
- bubonic plague,
- E. coli O157:H7, and
- cryptosporidosis.
Despite many assertions that diseases are linked to the environment through climate change, not everyone agrees with the purported connection.
The "Brief Analysis" (that's its name) from the National Center for Policy Analysis (NCPA) on Sept., 29, 1997, says that blaming global warming for the spread of tropical diseases is a "sick argument." The NCPA analysis paper argues that malaria, yellow fever and dengue fever were extensive as far north as Philadelphia, New York, Baltimore and Minnesota at various times up to 1945. More recently, dengue fever is "raging" in places in Mexico but only Texas reported U.S. cases (86) in 1995 , 78 of which were in immigrants who brought the disease with them. Most U.S. cases of malaria occur in immigrants, foreign travelers and U.S. citizens coming home from the tropics. Thus, the NCPA analysis says, climate change can't be blamed for the increase in malaria or it would have spread to the United States.
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