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Column: The IPCC, malaria and climate change: neither scaremongering or ignorant

May 8, 2014 - 18:51 -- Bart G.J. Knols
I freely admit that I have not read all 2155 pages of the draft report by the International Panel on Climate Change (IPCC) released last month. Furthermore, I am not an expert on global climate change. However, motivated by this report and a recent comment posted to MalariaWorld entitled ‘IPCC, malaria and climate: scaremonging or ignorance’ (1), I will try to relate the IPCC assessments of climate change to malaria and the future...

Contemporary malaria really is a tropical disease
I suspect it will come as a surprise to many MalariaWorld members how commonly the assertion that malaria is ‘not a tropical-disease’ is used in generic attempts to undermine the validity of the scientific evidence of human mediated climate change. This argument forms part of a recent comment (1) posted to MalariaWorld  (now cross-posted to other websites).
 
‘Malaria is not a tropical disease. It was common throughout Europe, not only in Spain, Sardinia, Greece but as far North as the Baltic and northern Russia. Siberia registered 600,000 deaths due to Plasmodium falciparum in 1920.’ (1)
 
However, as has been repeatedly pointed out, this assertion relies on the unlikely assumption that P. falciparum was the major cause. As the late Professor Chris Curtis put it in a reasoned and polite exchange on this topic,
 
‘surely the great majority of the malaria cases in Russia (as in other northern climates) were P.vivax’ (2)
 
Given that most P. vivax strains adapted to moderate climates are now extinct or have mostly been under control for the last 40 years (3), it is quite reasonable to describe contemporary malaria as predominantly a tropical disease. While climate obviously plays a role in the intensity of contemporary malaria transmission, it does not necessarily follow that current projections of climate change are of a magnitude that would significantly alter current disease patterns and trends. 
 
So what does the 5th IPCC assessment say about malaria and the future? 
The IPCC assessment (4) clearly states that under a range of scenarios the potential for increased malaria risk in the future does exist. Rather than attempt to summarise their reasoning I highlight just three of the many points made:
 
The assessment notes ‘Impacts on health will be reduced, but not eliminated, in populations that benefit from rapid social and economic development (high confidence), particularly among the poorest and least healthy groups (very high confidence). Climate change is an impediment to continued health improvements in many parts of the world.’ (page 3, (4))
 
Based on observations for the period 2008-2012 there was an association between change in climatic drivers and malaria prevalence at local levels (high confidence). Intriguingly, dengue showed an association at both global and local levels (high confidence). (Table 11-1, (4)).
 
Interestingly, of the eight health-related sectors examined, vectored diseases are proportionally among the least likely to exhibit large increased risks on a global scale (Figure 11-6, (4), reproduced below). Though the authors make it clear that none of the eight sectors are likely to remain truly independent, e.g. it is almost inconceivable that disease control will be effective where undernutrition becomes common.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure legend:  Conceptual presentation of the health impacts from climate change and the potential for impact reduction through adaptation. Impacts are identified in eight health-related sectors based on assessment of the literature and expert judgments by authors of Chapter 11.The width of the slices indicates in a qualitative way the relative importance in terms of burden of ill-health globally at present and should not be considered completely independent. Impact levels are presented for the near-term era of committed climate change (2030-2040), in which projected levels of global mean temperature increases do not diverge substantially across emissions scenarios. For some sectors, e.g., vector-borne diseases, heat/cold stress, and agricultural production and undernutrition, there may be benefits to health in some areas, but the net impact is expected to be negative. Estimated impacts are also presented for the longer-term era of climate options (2080-2100), for global mean temperature increase of 4°C above preindustrial levels, which could potentially be avoided by vigorous mitigation efforts taken soon. For each timeframe, impact levels are estimated for the current state of adaptation and for a hypothetical highly adapted state, indicated by different colors. Figure and legend reproduce with written permission from IPCC (Figure 11-6, 4).
The IPCC, malaria and climate change: reasoned and insightful assessment based on currently available evidence.
 
Clearly, given the magnitude of the suffering caused by vectored diseases even a small proportional increase in risk is of concern. Inevitably, there is also an acknowledged degree of uncertainty in attempting to predict future risks on a global scale. However, based on the three chapters I have read I find their arguments reasoned and the evidence they are based on clearly identified. In my personal opinion the latest IPCC assessment is not scaremongering, though many of the risks it projects warrant immediate action.
 
With respects to malaria control resources it is not immediately clear to me if there is much in the assessment to justify shifting the current focus away from applying proven techniques and addressing pressing problems like insecticide and drug resistance.
 
However, I am a little troubled my personal one sentence appraisal could be interpreted as an ill-considered call for inaction, so feel very free to disagree below.
 
References
(1) Comment #1511 ‘IPCC, malaria and climate: scaremonging or ignorance’ posted to MalariaWorld Feb 2013 before IPCC report publication.  http://www.malariaworld.org/comment/1511 - comment-1511
(2) UK broadcast regulator OFCOM correspondence 2007, see last page http://www.ofcomswindlecomplaint.net/emails/ReiterCurtisCorrespondence.pdf
(3) Petersen E, Severini C, Picot S: Plasmodium vivax malaria: A re-emerging threat for temperate climate zones? Travel Med Infect Dis 2013, 11:51–9.
(4)IPCC Final Draft Report, Fifth Assessment Report Climate Change 2014:Impacts, Adaptation, and Vulnerability: Chapter 11 Human health: impacts, adaptation, and co-benefits.  http://ipcc-wg2.gov/AR5/images/uploads/WGIIAR5-Chap11_FGDall.pdf Note that the IPCC report is a scientific assessment based on best available evidence (up to August 2013) according to the judgment of its authors, also that regionally risks can differ considerably from global assessments, see regional chapters.
 
The views expressed in this article are the authors alone and not intended to reflect those of their organizations.
 

 Rasha Azrag is a medical entomologist working in the department of Zoology/ University of Khartoum, Sudan and used to teach basic entomology courses to undergraduate students and molecular entomology to master students in the Medical Entomology and Vector Control program. She has experience from working in different vector control programmes, from basic classic control methods to the use of genetic methods. 
 
Guy Reeves is a research scientist at the Max Planck Institute for Evolutionary Biology in Plön, Germany. Part of his research involves the exploration of genetic methods to control vectored diseases.
 

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