【NEWS】Don’t sweat it

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Don’t sweat it
# ~. Q4 C$ |  H/ z* GDevelopment and public-health initiatives will matter much more to malaria than the climate will8 X4 E7 [1 y# @. z
May 19th 2010 | From The Economist online! q0 s7 [6 N$ K9 k/ B* ]
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ONE of the obvious problems with predicting the future effects of climate change is that they haven’t happened. This makes climate studies highly dependent on models, which invariably and unavoidably make simplifying assumptions. This means that using their results to say anything of practical import needs care and caveats, both of which can often be in short supply, or stripped out to make a point.6 L) t; t  s* M4 l
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However, it is now ever more possible for studies of climate change to look at the past, not the future. The 20th century saw a fair amount of warming, and it is sometimes possible to compare what this warming did and didn’t do with what future warming might or might not do. This is what a paper published in Nature this week does in an attempt to re-examine, and perhaps close down, long-running debates about malaria and climate change.& j! g$ I" e, r7 t+ N
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Both the malaria parasite and the mosquitoes which spread it respond to temperature and moisture. Understanding those responses makes it possible to model what changes in climate might mean to the incidence of the disease. Such models have suggested that in a warmer world the area subject to endemic malaria would increase, perhaps quite a lot, though some places would see a reduction due to increased aridity. The caveats here include noting that the climate models can make no great claims to accuracy at the regional level and that such an approach does almost nothing to deal with changes in land use, wealth and public health programmes.
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$ B* d' s2 j& @7 P2 K4 ?One of the main thrusts of the new Nature paper, which is an offshoot of a project funded by the Wellcome Trust to produce an accurate worldwide atlas of where cases of malaria actually take place, is to see how much of what happened to the spread of malaria in the 20th century can be explained by what happened to the climate. The answer, according to Peter Gething of Oxford University and his colleagues there and in Florida, is not much. They conclude that claims that a warming climate has led to more widespread disease and death due to malaria are largely at odds with the evidence, which shows the areas effected shrinking, and the size of the effect shrinking too. Increases in the spread and severity of the disease burden foreseen over the next 40 years by the biological models are far smaller than the decreases in comparable measures seen over the past century.9 k3 z" U, V% f$ p! T3 q& x

$ x4 c. e" C; @# k" {The second tack of their argument is to compare the sort of effect seen in biology-based models of where malaria might spread with both models of and data on the effects direct intervention against the disease can have. Again the effects due to climate are small, even negligible, compared with the effects that interventions have achieved already and might achieve in decades to come. The marginal areas where climate might enlarge the area at risk are also, the article argues, the areas where the greatest declines in transmission have recently been seen thanks to increased intervention5 ]) u( {+ f/ P; S# r( i
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The conclusion is clear. People who are thinking about what to do about malaria should bear in mind that the biological basis of its distribution may change in a warmer world. Those thinking about the overall danger that climate change represents should not spend their time worrying about its impact on malaria.) H. T( z4 s$ D$ g& I. C- Y
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Caveats that count
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Is there a wider conclusion to draw about computer models such as those that underlay frightening statements about malaria in a climate-changed world? Perhaps; but like the models themselves, it comes with caveats.# `3 I: R( f+ `7 E% _
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Scientists tend to model what can be modelled, and natural scientists, in particular, tend to prefer models that incorporate at least some aspects of the underlying processes which they are interested in, rather than working purely on empirical correlations. This means that if you search the scientific literature for approaches to the future, you will tend to find answers based on natural processes. If other knowledge suggests that natural processes aren’t the most important aspect of the problem at hand, then it’s a good idea to look at the models with that provision in the forefront of your mind. ' S, D# h( m# R. l
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The other vital lesson is that the caveats matter. Pretty much every paper presenting a biology-based model of malaria’s dependence on climate contains a warning that changes in economy, technology and society matter too, and aren’t in the model. To transmit the model’s results without important caveats is reckless.
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The recklessness may, at times, be deliberate. In the reporting of climate change, as in the reporting of pretty much everything else, bad news gets a better airing than good. There is no doubt that some environmental advocates are willing to exploit that dynamic to the full. Paul Reiter, a researcher into medical entomology at the Institut Pasteur, has spent the past decade pushing back against exaggerated claims about the effects of climate on malaria. But he and others have not done so in vain.
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* `- g, ~! V* x, ^7 s( ELook at what the reports of the Intergovernmental Panel on Climate Change say about malaria. The 1995 report made much of the effects of climate on the basis of biological models, and exaggerated some of the risk through factual error. One does not need sophisticated insights into modelling or epistemology to realise that a climate-enabled spread of malarial mosquitoes to altitudes above 2,500 metres would have little impact, in itself, on Nairobi or Harare: pace the IPCC, both cities sit only about 1,500 metres above sea level.* [' L' p  {9 S3 Y: l; x7 c
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Even in that report, though, there were caveats. The subsequent 2001 report strengthened them and softened the conclusion. In its 2007 report the IPCC pulled back from what it had said in 2001. In its next report, currently slated to appear in 2014, it will doubtless take the new Oxford work on board. If one is going to be optimistic about the future of malaria, one might also, with caution, be optimistic about the future of assessments of climate change. Things can, over time, get better, especially when the record of what has happened to date gets taken seriously. They will do so quicker if people accept both the usefulness and limits of models of the future, as well as the appeal of models of the past.
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/ y9 s% f: L# M* T+ e8 g- K' ?% ^) JFROM:http://www.economist.com/world/i ... m?story_id=16160473