From World Climate Report: Malaria Declines Despite Local Warming
“Spreading tropical disease” is high on the list of bad things that are going to happen as the world warms—if you believe the doomsayers. And topping their list of spreading tropical diseases is malaria.
But, as we have on many past occasions pointed out, malaria is neither “tropical” nor is it “spreading.”
In fact, back in the late 19th century, malaria was thought to be endemic in most regions east of the Rocky Mountains—brought to the U.S. in the 16th and 17th century by European colonists and African slaves and spreading across the country with the migration of those populations (Zucker, 1996).
Figure 1. Region of the U.S. where malaria was thought to be endemic in 1882 (source: Zucher, 1996).
Malaria transmission was still a problem in some parts of the U.S. into the mid-20th century, and, in 1946, when the CDC was established (back then it was known as the Communicable Disease Center) its primary goal was to eradicate malaria from the U.S.—which it successful achieved within a few years (with the help of DDT).
All the while, the average temperature in the U.S. was on the rise, increasing by some 1 to 2 degrees between 1882 and the early 1950s.
Clearly, a warming climate did not leading to an expansion of malaria in the U.S.
Nor does it appear to be doing so elsewhere.
About 10 years ago, a paper by Simon Hay and colleagues was published in Nature magazine that made this abundantly clear. Hay et al. analyzed the occurrence of malaria in the east Africa highlands and found the number of cases to be expanding rapidly, however, and here is the kicker, try as they might, they could find no evidence of a driver in the form of climate change. They concluded:
The absence of long- and short-term change in the climate variables and the duration of [malaria transmission] suitability at these highland sites are not consistent with the simplistic notion that recent malaria resurgences in these areas are caused by rising temperatures.
That would seem to throw some cold water on the heated rhetoric of the global warming/tropical disease crowd.
But wait. Within a few months time, Nature published a comment by noted global warming/tropical disease advocate Jonathan Patz and colleagues who challenged Hay’s conclusions—not about the increase of malaria occurrence (of course), but that the climate in the African highlands had not changed to become more suitable for malaria transmission. Patz et al.’s basic contention was that:
• The Hay et al. weather data were interpolated over mountainous terrain.
• Because of mosquitoes’ response to climate thresholds, you don’t need a significant trend in climate—climate variability is important, too;
•Nevertheless, based on a different analysis, regional warming trends do exist that match the increase in malaria.
And of course, the press loved this take, for now everything was right again in the world of global warming doom-and-gloom. For example, Reuters reporter Patricia Reaney wrote:
Climate change could be causing more than higher temperatures—it may also be helping to fuel a rise in Malaria in East Africa…Earlier research had suggested the upsurge was due to drug resistance and population growth, and not global warming. But scientists in the United States and Britain say it may not be just a coincidence that the rise in malaria parallels East African warming trends.
So take that, you naysayers.
At the time, Hay et al. answered their critics, and continued to stand by their conclusions writing in response to Patz et al.:
“Evidence against the epidemiological significance of climate change in the recent malaria resurgences in Africa is mounting and remains unmatched by any contrary evidence.”
Now forward the clock to the present day.
Several members of the original team gathered by Simon Hay have gotten back together to see how malaria and climate have evolved in East Africa over the intervening 10 years since their Nature publication. Their results have just been published in the scientific (open access) journal PLoS ONE. The lead author of the new study is David Stern from the Crawford School of Economics and Government, Australian National University.
What Stern et al. found was quite interesting. With 10 more years of climate data, they have identified significant increases in the temperature throughout their study region. Stern explains that “We conclude that there is now clear evidence of increased temperatures in highland East Africa especially in the last 15 years.”
So perhaps their critics were correct all along, the climate has indeed been warming in East Africa concomitant with the spread of malaria?
Not so fast.
It turns out, that over the past decade or so, the occurrence of malaria in the region has plummeted!
That’s right, despite rising temperature, malaria cases have bottomed out to historically low levels.
Stern postulates that the rise in malaria cases in the region during the 1990s “was probably due to resistance to chloroquine, an older antimalarial drug, and not climate change.”
And the decline in malaria cases in the face of rising temperature is further proof that climate change is not a major player in the rates of malaria transmission in the region. No greenhouse-gases-fuelled apocalypse here. Time to turn your attention elsewhere.
But before leaving, Stern gets in a parting shot.
This screenshot below is taken from Stern’s weblog posting on September 17, 2011 in which he seems to give some advice to the IPCC.
Nice idea, but call us cynical as we seriously doubt that we’ll be seeing this “iconic” figure in the IPCC’s next Assessment Report (AR5)!
References:
Hay, S.I., et al., 2002. Climate change and the resurgence of malaria in the East African highlands, Nature, 415, 905–909.
Hay, S.I., et al., 2002. Hay et al. reply, Nature, 420, 628.
Patz, J.S., et al., 2002. Regional warming and malaria resurgence, Nature, 420, 627–628.
Stern, D., et al., 2011. Temperature and malaria trends in Highlands East Africa. PLoS ONE, 6, e24524.
Zucker, J.R., 1996. Changing patterns of autochthonous malaria transmission in the United States: A review of recent outbreaks. Emerging Infectious Diseases, 2, 37-43.
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Related, from Marin County Mosquito Control District
Alan the Brit has beaten me to it in reminding everyone abour Paul Reiter, who years ago trashed the link between more warming and more malaria. He caused quite a stir by demanding to have his name taken off one of the IPCC reports because it edited out or somehow diminished his (unarguably) expert view. Because the AGW-ers are playing a political game, they think the ‘little people’ will be too stupid to remember stuff from 15 years or so ago, so they blithely wheel out again the old scare story, more warming = more malaria, knowing full well its been discredited. Completely. And they are scientists?
DDT.was.never.banned.for.use.on.Malaria. Got it ? NEVER. 3,000 – 10,000 TONS are used NOW EVERY YEAR and have been for decades. The Bates know-nothings are quite annoying.
The work sited significant warming over the last 10 years. I tried to find the numbers but they elude me. Anyone know what significant is?
Steamboat Jack says: Read these and weep …
I weep because I have to read drivel like this again and again. DDT is not a magic bullet, it remains available, it is easily synthesized, and it is not irreplaceable. The real cause of failures in the fight against malaria, as well as tuberculosis, as well as HIV, is poverty. Got it? TB is, or was, practically extinct in developed nations. Among developed nations, the U.S. give rise to and spread more resistant TB strains than others, which simply due to their dysfunctional system of health insurance. Now there is something for the market-solves-all-problems crowd to think about.
I think Mike has brought up some very strong social economic points. Lots of good discussions from many others. We will continue to be bombarded with this pseudo science stupidity and much more too. All to many fool themselves substituting ideology and dogma for deductive reasoning and a broad base of factual knowledge.
If this is a science blog, and the commentators want to make valid points, then they should at least try to get their science on a firm basis before spouting off. Human malaria requires a human reservoir of the disease (it is not a zoonotic), an appropriate vector (only mosquitoes in the genus Anopheles, and then really only those species that like to hang around where people do and bite them), and a long enough period of time above a critical temperature for (a) an Anopheles mosquito who has bitten someone with malaria to mature the infective stages of the malarial protozoan and (b) to find and bite another person. The shorter the period of time above the critical temperature, the less likely it is that malaria will be transmitted, even if you have a people with malaria feeding the right mosquitoes. Therefore, an increase in global temperatures could support the increase of malaria transmission at higher latitudes and at higher elevations.
Since all of these conditions could be met in many parts of the world that once had malaria but are now malaria-free (e.g. most of Europe and North America, much of Asia and Australia), and since the purported increase in temperatures has not lead to a recolonization of these areas (in spite of the migration of many people carrying the disease into the malaria-free zone) indicates that other, more critical, factors are in play. The most important of these is undoubtedly a functional public health system and an absence of war.
It isn’t a diminished ability to use DDT which has lead to the deaths of so many Africans from malaria over the last fifty years, but the decay of their public health infrastructure due to social upheaval. If our public health system fell apart, then we would have malaria again in a decade or two – even if the global temperature fell a few degrees and we had warehouses full of DDT.
Dave October 4, 2011 at 4:19 pm said “requires a human reservoir of the disease (it is not a zoonotic)”
Correct for 4 out of 5 Plasmodium species which cause Malaria. A fifth species, Plasmodium knowlesi, is a zoonosis that causes malaria in macaques but can also infect humans.
“If our public health system fell apart, then we would have malaria again in a decade or two”
Quite likely in a lot less time, depending completely on the numbers of human carriers in any particular area. The Anopheles spp. vectors are already present and disease endemism would take less than several year provided infective Plasmodium spp. was present and accessible by vectors in sufficient numbers in the local population.
So malaria doesn’t cause Global Warming?
Anthony you said “….Nice idea, but call us cynical as we seriously doubt that we’ll be seeing this “iconic” figure in the IPCC’s next Assessment Report (AR5)!”
I think we will see that chart but they will chop it off at 1995 and only show the increase.
“If our public health system fell apart, then we would have malaria again in a decade or two”
And exactly what public health measures is it that is keeping malaria at bay now? As is well known there is no vaccine. It is certainly not vector control – here in Sweden we have the misfortune to live in one of the worst parts of the World for mosquitos (a fair proportion of them Anopheles) and yet malaria went extinct almost a century ago.
If it was public health measures that exterminated malaria, contemporaries were apparently unaware of them, they noted that malaria was gradually disappearing, but they had no clear idea why. And to speak plainly the Swedish public health system wasn’t that hot in 1850, or 1900 for that matter.
It seems that the important thing is actually housing. When people live in reasonable houses, separated from their livestock and where lighting and general cleanliness makes it practical to get rid of insect pests indoor, malaria disappears. The livestock is important, for while human malaria does not infect other species, Anopheles mosquitos are highly dependent on livestock, at least the species occurring in northern Europe are.
Malaria should not be allowed to exist in either a warmer or a colder world-period! It is disgraceful that the disease and the suffering it causes gets caught up in the politics of both the right and the left. Unfortunately for malaria victims- malaria eradication may be the first victim to suffer casualties inflicted by two environmental ideology wars some forty years apart (DDT and AGW)
The CDC was formed for the initial purpose of combating malaria. Malaria was extinguished in the US by 1951 -semi tropical states and the colder northern states included. The threat of malaria is not climate -it is will, resources and public health infrastructure.
And to Mike- DDT has a “de-facto ban” with foreign aid tied to a country’s promise not to use DDT. The biggest advantage of DDT may not be as a pesticide but the aversion response mosquitos have to its presence. Spraying DDT on the walls of rural abodes has a tendency to keep mosquitos from entering and its persistence is also a plus in those remote locations where public health workers cannot easily access at frequent intervals. I’m not saying DDT is any longer a silver bullet but in places it can be an important tool. Those of us who don’t face the malaria threat shout just butt out.
tty – malaria is repeatedly introduced into Western countries and sometimes there have been localized outbreaks – in he US, Australia, etc. It is the public health systems – broadly defined to include mosquito abatement – that keeps it from establishing. I said nothing about exterminating malaria – you would have to exterminate the people who have malaria to do that.
But you are right in a sense – screening and public health services that convince people to use various forms of screening are important. In Finland, houses were actually a critical factor in maintaining malaria by allowing Anopheles sufficient day degrees to mature their plasmodia. I haven’t seen a similar study for Sweden, but I would bet (a small amount) that it was true there too.
BioBob – is Plasmodium knowlesi actually a significant cause of malaria in people? There are probably lots of other plasmodia out there that may someday cause problems, but right now we have the big two and the other two to worry about.
Dave,
P. knowlesi is found in SE Asia especially Borneo. In many of the affected areas it has been reported to comprise 70% of the reported malaria cases. Macaques of at least 2 species are the normal end-target of the P. knowlesi, but humans are commonly infected as well. Diagnosis often is confounded with Plasmodium malariae.
Pat Moffitt October 5, 2011 at 11:23 am says:
“DDT has a “de-facto ban” with foreign aid tied to a country’s promise not to use DDT.”
Widely posted, actually completely false, in fact. More simply this is propaganda bullcrap.
Any and all countries signatories to the Stockholm convention of 2001 / 2004 can apply for an will always receive permission to employ DDT for vector control and in fact any who have malaria problems have received permission for its use and have used megatons of DDT — some/much of which ends up used on crops via diversion due to corruption. DDT is so cheap that any country can afford to buy tons out of petty cash. Actually using it effectively is a different matter entirely
Malaria persists not because DDT is not used but in spite of its continual use Use your imagination about WHY that happens considering the realities of corruption, stupidity, failures/lack of public health infrastructure, etc. You try to eliminate a insect that can reproduce by the hundreds in a wet footprint or old soup can in 10 days, fly unimpeded into a shack/mud hut in a village hundreds of miles from the closest clinic offering effective treatment of Plasmodium.. And good luck !
I’m old enough (67) to remember when DDT was touted as the magic bullet for pest control. I recall the canal across the street being sprayed and the breeze blowing the noxious stuff towards the residences. Got rid of the mosquitoes… FOR TWO WHOLE WEEKS! Then they were BACK IN FULL FORCE.
I don’t understand why so many people can grasp that AGW is a fabrication of the global elitists, but don’t seem able to comprehend that corporate Agribusiness invented the so-called Green Revolution that gave us the pesticides and herbicides that have caused so many illnesses and allergies. Do you honestly think that Monsanto has the best interests of humanity in mind and that if it weren’t for those dad-blamed hippie envarnmentists we’d be living in a bug-free paradise!? (Never mind that bugs, even annoying and disease carrying ones, are vital to ecosystems everywhere…)