Overcoming the Climate: The Case of Malaria

By Chip Knappenberger -- February 23, 2012

“Malaria already kills a million people a year and now, researchers fear, climate change could make the problem even worse.” –ABC News, April 1, 2011

“Based on the new numbers, malaria deaths have fallen by 32 percent since 2004, dropping from 1.8 million deaths worldwide to 1.2 million in 2010.” –ABC News, February 3, 2012

Malaria has been long postulated to benefit from rising global temperatures and is included near the top of most alarming lists of the bad things that will happen if greenhouse gas emissions limitations are not immediately put into place. And while this seems good in theory, real world data show little, if any, connection between climate change and malaria outbreaks. In fact, while the climate has been warming, malaria has been in decline—being beaten back by direct measures aimed at reducing the spread of the disease.

And malaria is not alone. There are many examples of positive trends in measures that climate change is supposed to worsen. The broader lesson is that directed actions trump climate change. In fact, in some cases, climate change may even hasten positive change. Yet, the recognition of such is largely absent from assessments of the impacts associated with human-caused climate changes. Consequently, the assessments present overly pessimistic and unreliable visions of our future based on overly simplistic modeling exercises.

The Case of Malaria

One of the key elements of global warming alarmism is proposing a link from rising global temperatures to the increasing occurrence of really bad things. Think of any bad thing, and almost assuredly, a Google search of “global warming” and “[insert really bad thing here]” will turn up loads of hits. Try it! It is kind of fun to see just how absurd a link you can find. “Global warming” and “shark bites”? You betcha. “Global warming” and “UFO attacks”? Ding ding! “Global warming” and “malaria”? Of course.

In fact, global warming’s proposed link to “spreading tropical disease” such as malaria goes way back to near the beginning. Here is what the very first Intergovernmental Panel on Climate Change (IPCC) report, published in 1990 had to say:

Since global warming changes rainfall and temperature, distribution and abundance of many vector species should change. Some infectious diseases including parasitic and viral diseases such as malaria, schistosomiasis and dengue have the potential to increase in many countries, especially tropical and subtropical areas.

And in the IPCC’s 2007 Fourth Assessment Report (AR4), they were still holding onto the idea that climate change could ultimately make malaria worse (from AR4 WGII, p. 47):

Mixed projections for malaria are foreseen: globally an estimated additional population at risk between 220 million (A1FI) and 400 million (A2) has been estimated. In Africa, estimates differ from a reduction in transmission in south-east Africa in 2020 and decreases around the Sahel and south-central Africa in 2080, with localised increases in the highlands, to a 16-28% increase in person-months of exposure in 2100 across all scenarios. For the UK, Australia, India and Portugal, some increased risk has been estimated.

However, at least, now the IPCC was recognizing differences between projections of populations “at risk” and the actual spread of the disease—a distinction that is patently obvious from our experience with malaria here in the U.S., and now noted by the IPCC. From page 407 of the AR4 Working Group II Report:

Projections of climate-change-related health impacts use different approaches to classify the risk of climate-sensitive health determinants and outcomes. For malaria and dengue, results from projections are commonly presented as maps of potential shifts in distribution. Health-impact models are typically based on climatic constraints on the development of the vector and/or parasite, and include limited population projections and non-climate assumptions. However, there are important differences between disease risk (on the basis of climatic and entomological considerations) and experienced morbidity and mortality. Although large portions of Europe and the USA may be at potential risk for malaria based on the distribution of competent disease vectors, locally acquired cases have been virtually eliminated, in part due to vector- and disease-control activities.

That the direct application of “vector- and disease-control activities” is vastly more effective at reducing malaria transmission than any impacts from climate change has long been the message being delivered by Dr. Paul Reiter to virtually anybody who cared to listen (and many who cared not to listen—Reiter resigned from the IPCC over his view that the IPCC wasn’t listening to him). Reiter is one of the world’s leading experts in mosquito-borne diseases, now Chief of the Insects and Infections Disease Unit at the Pasteur Institute in Paris after having spent 22 years at the U.S Centers for Disease Control in Atlanta. And since at least the mid-1990s, he has been the leading voice in trying to educate folks (including the U.K. Parliment and U.S. Congress) that when it comes to the spread of malaria, “the principal factors involved are deforestation, new agricultural practices, population increase, urbanization, poverty, civil conflict, war, AIDS, resistance to anti-malarials, and resistance to insecticides, not climate.” Reiter’s article “From Shakespeare to Defoe: Malaria in England in the Little Ice Age” is a classic lesson in the history of malaria in temperate climates and how humans have triumphed over it (spoiler alert: climate had nothing to do with it).

Reiter strongly believes that it is a huge mistake to try to divine the future course of malaria transmission (or that of any of the major mosquito-borne diseases) by using climate models. His views are summarized nicely in the Abstract from his 2001 paper in Environmental Health Perspectives titled appropriately, “Climate change and mosquito-borne disease”:

Global atmospheric temperatures are presently in a warming phase that began 250–300 years ago. Speculations on the potential impact of continued warming on human health often focus on mosquito-borne diseases. Elementary models suggest that higher global temperatures will enhance their transmission rates and extend their geographic ranges. However, the histories of three such diseases–malaria, yellow fever, and dengue–reveal that climate has rarely been the principal determinant of their prevalence or range; human activities and their impact on local ecology have generally been much more significant. It is therefore inappropriate to use climate-based models to predict future prevalence.

That article was written in 2001. Now, more than 10 years later, data continue to pour in in support of Reiter’s contention.

About a year and a half ago in the summer of 2010, a major paper was published in Nature magazine by Peter Gething and colleagues titled “Climate change and global malaria recession” (note that the final word is recession not expansion). Gething’s team compared the current spatial limits of malaria against maps of its historical range, while mindful of the climate changes that have taken place. Here is how they described what they found:

Our findings have two key and often ignored implications with respect to climate change and malaria. First, widespread claims that rising mean temperatures have already led to increases in worldwide malaria morbidity and mortality are largely at odds with observed decreasing global trends in both its endemicity and geographic extent. Second, the proposed future effects of rising temperatures on endemicity are at least one order of magnitude smaller than changes observed since about 1900 and up to two orders of magnitude smaller than those that can be achieved by the effective scale-up of key control measures. Predictions of an intensification of malaria in a warmer world, based on extrapolated empirical relationships or biological mechanisms, must be set against a context of a century of warming that has seen marked global declines in the disease and a substantial weakening of the global correlation between malaria endemicity and climate.

That’s a pretty strong condemnation of the idea that the spread of malaria can be effectively controlled by reining in global climate change through greenhouse gas emissions restrictions.

Then in September 2011, a research team led by David Stern presented the results of a follow-up study to research that originally was published in Nature back in 2002 and which looked at the relationship between climate change and malaria outbreaks in the highlands of East Africa. The original study (led by Simon Hay) concluded that climate change was not a strong factor in the upswing of malaria in the region. However, those results were roundly criticized by supporters of the global-warming-will-spread-malaria meme as being inadequate and incomplete. So Stern gathered up many members of the original Hay team and updated and expanded the climate and malaria data through the mid-to-late 2000s and redid the analysis. What they found confirmed their earlier results. While temperatures in the region have been climbing, malaria cases largely acted independent of temperature change—after a period of “resurgent epidemics” in the region from 1994-2002, malaria cases have since returned to a low level. Stern et al. ultimately concluded “regardless of its etiology, malaria in Kericho and many other areas of East Africa has decreased during periods of unambiguous warming.”

And just a few weeks ago came a paper in the British medical journal The Lancet, by Christopher Murray and colleagues (supported by the Bill & Melinda Gates Foundation), that sought, through systematic analysis, to produce a robust and comprehensive dataset on malaria mortality across the globe since 1980. What they found was that about twice as many people were actually dying annually from malaria as had been previously realized (by the World Health Organization). Murray et al found that about 1.2 million people died globally from malaria in 2010 compared with about 650,000 reported by the WHO. But what is more relevant to the climate change tie-in, they found that the global deaths from malaria peaked at about 1.8 million in 2004 and have fallen by some 30% by the year 2010. Murray et al note this decline and posit a reason: “There has been a rapid decrease in malaria mortality in Africa because of the scaling up of control activities supported by international donors.”

In less than a decade, direct measures have reduced global malaria mortality by nearly 1/3rd. All the while the global average temperature has changed little—or to hear climate alarmists tell it, the climate has gotten much worse during that time.

Which all leads back to the point that Paul Reiter has been making all along. There is no reason include “spreading tropical diseases” in the list of ills that will befall us if we fail to enact regulations aimed at controlling the climate.

Beyond Malaria

And this situation is by no means limited to climate change/malaria. In fact, there is a broader message here. The impacts of climate change on a wide array of human/environment interactions is dwarfed by direct action applied to the situation at hand. This has been proven time and time again. Here are just a few examples from the U.S.:

• Climate change is supposed to increase heat-related mortality, yet heat-related mortality is on the decline,

• Climate change is supposed to worsen ozone pollution, yet ozone air quality is improving,

• Climate change is supposed to harm crop yields, yet crop yields are improving,

• Climate change is supposed to “endanger public health and welfare,” yet human life expectancy, perhaps the best integrator of public health and welfare, is increasing.

This is not to say that climate change is responsible for the improvements, but neither is it driving trends the other direction. Instead, direct actions (e.g., respectively in the list above, access to air conditioning, pollution controls, fertilizer application, improvements in health care) have pushed the trends beyond any slight wiggle that climate change may induce. Humans by and large try to overcome the limitations put on us by the climate; if anything, climate change will induce us to try even harder and perhaps succeed even faster.

References

Hay, S.I., et al., 2002. Climate change and the resurgence of malaria in the East African highlands, Nature, 415, 905–909.

Gething, P.W., Smith, D.L., Patil, A.P., Tatem, A.J., Snow, R.W. and S.I. Hay, 2010. Climate Change and the Global Malaria Recession. Nature, 465, 342-346.

Murray, C.J.L, et al., 2012. Global malaria mortality between 1980 and 2010: a systematic analysis. The Lancet, 379, 413-431, doi:10.1016/S0140-6736(12)60034-8.

Reiter, P., 2001. Climate change and mosquito-borne disease, Environmental Health Perspectives, 109, 141–161.

Stern, D., et al., 2011. Temperature and malaria trends in Highlands East Africa. PLoS ONE, 6, e24524.