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Contrary to oft-repeated claims, climate change is unlikely to cause a major rise in malaria, says medical entomologist Paul Reiter.
Climate change is incriminated in a wide range of environmental and public health disasters. A contender for the top calamity is the idea that climate change is encouraging malaria and other mosquito-borne diseases, and that this rise will become catastrophic in coming years.
To the layperson, the notion is persuasive because it is intuitive — malaria is rife where the world is hot, so if the world gets hotter there will be more of it.
Not so to the scientist. The epidemiology of the disease is highly complex, and the dominant factors are the ecology and behaviour of both humans and mosquitoes.
Alarmists have nurtured three common ‘myths’ that have no grounding in historical or scientific evidence.
The first, which began circulating in the early 1990s, is that ‘tropical’ infections, particularly malaria, are moving to higher latitudes as global temperatures rise.
Not so: historical records show that malaria has previously been widespread in temperate regions — as far north as Scandinavia — and survived even during the coldest years of the Little Ice Age.
Moreover, in much of Europe and North America the disease began a rapid decline in the mid-nineteenth century, just as global temperatures started to rise.
This decline was due to complex changes in rural ecology and living conditions linked to industrialisation, including depopulation of the countryside, new cropping and rearing practices, drainage, improved building structure, better health care and a substantial drop in the price of quinine.
Another myth is that the disease is moving to higher altitudes. Al Gore, former US vice president and a ruthless campaigner on climate change, has repeatedly stated that "because of global warming, [mosquitoes] are now travelling to places where they’ve never been before. For instance, in Africa, the city of Nairobi…used to be above the mosquito line (the highest point at which mosquitoes can live)…".
Not so: Nairobi is at 1680m above sea level, yet until the mid-1950s, epidemic malaria was a serious problem at altitudes up to 2450m. Indeed, in 1927 the colonial government assigned £40,000, equivalent to about US$1.2 million today, for malaria control in Nairobi and the surrounding highlands.
Highland malaria was conquered in the 1950s by the effective application of the insecticide DDT. Control campaigns have all but ceased and there is widespread resistance to anti-malarial drugs. For these and other reasons, the disease is returning, but this return has nothing to do with climate.
The third myth is that climate change is already causing an increase of malaria in Sub-Saharan Africa, and there are wild predictions that millions, tens of millions, even hundreds of millions more people will contract the disease as temperatures rise.
This is naïve. Across much of the region, the climate is already more than adequate for transmission, the disease is endemic and ubiquitous, and in most cases people are already exposed to numerous infective mosquito bites every year. You can’t add water to a glass that is already full.
Malaria is certainly a ruinous problem for Sub-Saharan Africa. But again, the driving forces are economic, ecological and societal. They include population growth, increasing mobility of people, deforestation (which creates ideal conditions for malarial mosquitoes), irrigation, deteriorating health infrastructures (accelerated by the ravages of HIV/AIDS), drug resistance, and war and civil strife. Above all, the driving force is poverty.
How have these myths arisen?
In large part they stem from an escalating trend for political activists to use the ‘big talk’ of science to manipulate public opinion with emotive and fiercely judgmental ‘scientific’ pronouncements.
These activists legitimise their cause by publishing opinion articles in professional journals and quoting each other liberally, while essentially ignoring the mainstream of science.
Less than a dozen authors dominate this practice in the field of public health. Nearly all are non-scientists, yet they have been the main authors of the relevant chapters in the Assessment Reports published by the Intergovernmental Panel on Climate Change.
Legitimate scientists who try to counter their statements are ignored, or even denounced as a tiny minority of ‘sceptics’, paid stooges of the oil industry
Genuine concern for humankind and the environment demands the inquiry, accuracy and scepticism of authentic science. Without these, the public is vulnerable to abuse.
Human activities may be affecting global climate, but a true perspective on the problem must be based on science, not politics.
Paul Reiter is professor of medical entomology at the Institut Pasteur in France.
Reiter, P. Global warming and malaria: Knowing the horse before hitching the cart Malaria Journal 7 (2008)
Reiter, P. The IPCC and technical information. Example: Impacts on human health Written evidence for the Select Committee on Economic Affairs (2005) of the House of Lords