Monday, April 30, 2007

Science and Global Warming: Part 1

In my previous blog post, I indicated that I had an interest in learning more about the science behind the debate. Here, for your perusal, is the first topic I tackled.

Debate #1 - Global Warming will or will not lead to a greater instance of insect-borne diseases

*World Health Organization (quoted from a BBC article):

"The World Health Organisation (WHO) says global warming could lead to a major increase in insect-borne diseases in Britain and Europe. It has called for urgent government action to prepare for the spread of diseases like malaria and encephalitis. The average temperature in Europe has increased by 0.8C during the past century and the average global temperature could rise by another 3.5C by the year 2100.... This would be accompanied by changes in rainfall patterns, greater precipitation and humidity in the atmosphere, and many new areas of floodwater. This in turn could lead to an increase in disease-carrying pests such as ticks, mosquitoes and rats, which live in warmer climates and whose breeding-grounds are often in damp areas."

*Professor Paul Reiter, Dept of Medical Entymology, Pasteur Institute, Paris
(transcribed by me from "The Great Global Warming Swindle", at appx 55 min into the program... please excuse any typos or inaccuracies)
"Mosquitoes are not specifically tropical. Most people will realize that in temperate regions there are mosquitoes. In fact, mosquitoes are extremely abundant in the Arctic. The most devastating epidemic of malaria was in the Soviet Union in the 1920's. There was something like 13 million cases a year, and something like 600,000 deaths - a tremendous catastrophe that reached up to the Arctic Circle. Archangel had 30,000 cases and about 10,000 deaths. So it's not a tropical disease. Yet these people in the global warming fraternity invent the idea that malaria will move northward."
The following questions are raised from this debate:
1) Are malaria and encephalitis warm-climate diseases?
2) Do rats, mosquitoes and ticks currently live in cold climates in sufficient numbers to create outbreaks of disease?

First, malaria and encephalitis:
These days, malaria does tend to be a tropical/subtropical disease. However, before the use of insecticides, malaria was found in virtually every country in the world. King Louis XIV and Charles II both were struck with malaria. There was indeed an epidemic of malaria in Russia as far north as Archangel, which is a port on the Arctic Sea. Mosquitoes are found everywhere -- although they hibernate for part of the year in colder climates. This may be one part of the argument which is founded. In temperatures under ~50F, the female mosquitoes go into hibernation. If the climate change was sufficient enough to raise winter temperatures that high, there would be mosquitoes all year round. This might explain the difficulty in eradicating the disease in tropical locations. I would say that there is a possibility of regions where there are already incidences of malaria to have increased (perhaps even epidemic) numbers of cases, depending on the actual rise in temperature. Countries where the disease has already been eradicated are already using insecticides to prevent the re-introduction of the disease -- their problem, I would imagine, would be finding new ways to kill resistant mosquitoes, not dealing with epidemics.

Prior to today, I knew next to nothing about encephalitis. The disease is often a complication to another disease, such as rabies, syphilis, toxoplasma, or bacterial meningitis. Rabies is transmitted by the bite of a mammal (rodents, such as rats, are rarely infected). Bacterial meningitis is not transmitted through insects or rodents. Syphilis is an STD. Toxoplasma is often contracted through contact with house cat feces, and is not very easy to catch. Only sensitive individuals, such as pregnant women, the very young or elderly, and those already sick would be likely to contract encephalitis through this method. There is one form of encephalitis that is transmitted through ticks, known as Tick Borne Encephalitis (TBE). This form is most common in Europe and Asia, with the death rate somewhere around 1% of all cases. Encephalitis epidemics are pretty rare. There was an outbreak of a rare form of encephalitis (known as 'sleeping sickness', not to be confused with the disease with the same name transmitted via tse-tse fly) which was perhaps caused by diplococcus bacterium, or perhaps infected individuals who were weak from the Spanish Flu outbreak which occurred in the same general time frame. I found no link between this outbreak and the TBE variant of the disease. I do not see how an increase in temperature would hasten the spread of encephalitis.

Conclusion: Encephalitis is NOT a warm-weather disease. Malaria might possibly have an easier time spreading in a climate that rarely dips below 50F, but has historically appeared in extremely cold climates.

Rats, mosquitoes, and ticks:
I already learned that mosquitoes do live in the arctic, so they are not exclusively warm-weather insects. However, in a warmer climate they would have much more time available to reproduce. So how do they live up North? Answer: swarms. No wonder the outbreak in Archangel was so bad! Rats live almost everywhere on earth. Good luck getting rid of them, even if the world were to go into another Ice Age. I'm having a hard time finding information on where ticks live, but from the best I can tell, their habitat is generally in the eastern coast of Africa, North America, the Eurasian Steppe, India, and the Mediterranean. Typical tropical areas such as Central and South America, Central Africa, and Southeast Asia are conspicuously absent from the maps I was able to find. This does not mean that they do not live in tropical areas, just that they were not on those maps. It does, however, mean that ticks live in non-tropical regions all over the world.

Conclusion: rats, mosquitoes, and ticks do not exclusively live in tropical areas. They are all present in sufficient numbers in non-tropical areas to be causing troubles already.

Based on the evidence I found, I would tend to agree with Dr Reiter rather than the WHO. I think he might have oversimplified a few things, but then again I am not the Professor of Medical Entymology.

And for your further enjoyment, here is more from the documentary (continuing on after the original quote at the top of the page):
According to the Intergovernmental Panel on Climate Change (IPCC), "mosquito species that transmit malaria do not usually survive where the mean winter temperature dips below 16-18C." Professor Reiter responds, "I was horrified to read the second and the third assessment reports, because there was so much misinformation without any kind of recourse, or virtually without mention of the scientific literature -- the truly scientific literature, literature by specialists in those fields." He further states, "When I resigned from the IPCC, I thought that was the end of it. But when I saw the final draft, my name was still there, so I asked for it to be removed. Well, they told me that I had contributed, so it would remain there. So I said, 'No, I haven't contributed, because they haven't listened to anything I've said.' So in the end it was quite a battle, but finally I threatened legal action against them and they removed my name. And I think this happens a great deal. Those people who are specialists but don't agree with the polemic and resign -- there have been a number that I know of -- they are simply put on the author list and become part of this '2500 of the world's top scientists'."

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