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-19th 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 1,680m above sea level, yet until the mid-1950s, epidemic malaria was a serious problem at altitudes up to 2,450m. 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.
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