Global Warming Spreads Malaria

sppiyellowreprintlogo.jpgNovember 15, 2008
The scare
: The Times of India reported in the autumn of 2008 that James H. Diaz, program director for environmental and occupational health at Louisiana State University, had said that as international travel increased and climate patterns changed the US was becoming a more stable ecosystem for malaria mosquitoes. Diaz said that warm, dry summers followed by heavy rain caused mosquitoes to rush their breeding and to seek out more blood meals, which in turn bred more mosquitoes in less time.

    (Illustrations, full text, footnotes and references available in PDF version)

He added that warmer climate in major US cities with heavy international air traffic, such as New York and Los Angeles, seemed to have created an environment in which infected mosquitoes could survive.

Diaz said that the cycle began with a mosquito transported during an international flight from a malaria-endemic region. Once the infected female mosquito left the aircraft, it could survive long enough to seek blood meals and transmit the disease to other humans within the airport. This type of international transmission created an increased possibility for the reintroduction not only of malaria, but also of other vector-borne diseases such as dengue haemorrhagic fever and Chikungunya virus.

People infected with malaria could travel anywhere in the world in 24 hours or less. As long as the malaria-transmitting mosquitoes were present, countries might face larger local outbreaks of imported malaria, according to a release issued by the American Society of Tropical Medicine and Hygiene.

The truth: According to Professor Paul Reiter of the Institut Pasteur, the world’s foremost expert on vector-borne infectious diseases, the anopheles mosquito that carries the plasmodium parasite that causes malaria is almost entirely insensitive to ambient temperature. It needs a temperature of at least 59 degrees F (15 degrees C) during the breeding season, but is otherwise capable of surviving in the open at temperatures as low as -25 degrees C.

Since most regions of the planet reach 15 degrees C in the summer, malaria is not – repeat not – a tropical disease. There is almost no region where the anopheles mosquito is incapable of surviving. For instance, the largest outbreak of malaria in modern times occurred in the 1920s and 1930s in northern Siberia, a territory not noted for its tropical climate. During the epidemic, some 13 million people were infected and 600,000 died; 30,000 of them as far north as the port of Arkhangelsk on the Arctic Circle.

Similar considerations apply to dengue, Chikungunya, and other diseases, which flourish in the tropics not so much because the tropics are warm as because the governments in tropical countries do not maintain efficient public-health measures to control the transmission of infectious diseases. The colonial powers often had effective measures in place: in Barbados during British rule, for instance, malaria was eradicated by the simple expedient of outlawing and eradicating any standing water so that there was nowhere for the mosquitoes to breed. In the United States malaria was once endemic, but public health and sanitation measures had almost entirely eradicated it by the end of the Second World War.

It is self-evidently true that the increased traffic between nations will tend to facilitate the transmission of any infectious disease. The Times of India’s report is characteristic of alarmist reports generally, in that it conflates this problem with that of climate change, deliberately leaving readers with the impression that “global warming” will facilitate the spread of malaria. It will do no such thing.

The IPCC rejected Professor Reiter’s nomination to write the malaria segment of the health chapter of its 2007 Climate Assessment Report first by pretending he had not been nominated and then by pretending that it had not received the four copies of the nomination papers that he had sent to separate officials. The two lead authors of that segment, unlike Professor Reiter, were not experts on malaria, and had published only one paper on the subject between them. One was not a scientist but an environmental campaigner.

Professor Reiter’s public testimony to the UK House of Lords on this less-than-transparent conduct on the part of the IPCC eventually shamed it into appointing him as an expert reviewer of the 2007 report. He was, therefore, able to remove from the report most of the previously-included suggestions that “global warming” would lead to the spread of malaria. The malaria segment of the 2007 report was, therefore, considerably less inaccurate and alarmist than previous IPCC assessment reports.

Nevertheless, the public health authorities in many countries (including the United Kingdom, which as a former colonial power ought to know better) continue to issue inaccurate and misleading statements to the effect that “global warming” will facilitate the transmission of malaria. There is no scientific basis for any such statement. End of scare.

(See Full Report: Illustrations, full text, footnotes and references available in PDF version
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The Science and Public Policy Institute (SPPI) is a nonprofit institute of research and education dedicated to sound public policy based on sound science. Free from affiliation to any corporation or political party, we support the advancement of sensible public policies for energy and the environment rooted in rational science and economics. Only through science and factual information, separating reality from rhetoric, can legislators develop beneficial policies without unintended consequences that might threaten the life, liberty, and prosperity of the citizenry.

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