Dateline: Kericho, Western Kenya — Malaria is on the rise in this tea plantation region of east Africa. Over the 13-year period from 1986 to 1998, the number of severe malaria cases has surged from 16 per 1,000 population per year to 120—an alarming 750 percent increase!

Dateline: Kabale, Uganda — This region has seen a rapid increase in malaria occurrence over the past decade. Over the five-year period from 1992 to 1996, 17 cases per 1,000 victims per month were reported on average. But during 1997–1998, the rate jumped to 24 cases per month.

Dateline: Burundi — Muhanga, in the tiny east African country of Burundi, has seen a significant increase in malaria incidences. During the decade of the 1980s, there were only 18 malaria deaths per 1,000. But in 1991 the death rate rose to 25 to 35 deaths per 1,000 population.

Dateline: Washington — Reports from the world's leading climate scientists, the IPCC, claim that global temperatures have risen by 0.6°C during the 20th century. Even the noisiest climate change contrarians now agree that this increase is caused by humans. The repercussions that will arise should this rate of temperature increase continue, or even accelerate, remain to be seen, but some changes are no doubt already occurring.

To non-scientific minds (i.e., most of the world's population), it's a simple matter to assume that global warming is producing a malaria epidemic in the highlands of eastern Africa. We keep hearing from climate and public health experts that models show mosquitoes will thrive as the planet warms, spreading untold disease and death throughout the Third World.

It has unfortunately become commonplace in climate change impact studies to begin with the assumption that a significant warming is occurring. If you already know the cause, it's easy to study the impact. But such thinking reminds us of the old standard statisticians use to warn about the difference between correlation and cause and effect: Studies have shown that most people suffering from lung cancer carry matches in their pockets. Clearly match-carrying should be avoided at all costs!

All the changes in malaria occurrence we reported are probably true, but the culprit is not climate change. So reports Oxford University's Simon Hay and seven coauthors in a recent article in Nature. Suspicious of the simple assumption that the climate change in East Africa is altering the range, population, and survivability of malaria-carrying mosquitoes, the researchers decided to examine the climate data in detail. And they found no warming signal.

Plasmodium falciparum malaria can be transmitted when average temperatures exceed 15°C and rainfall exceeds 152 mm for two consecutive months. Using those criteria, Hay plotted the number of months in which malaria could be transmitted at four East African sites where recent malaria increases have been observed (Figure 1). The only site with a statistically significant increase is Kabale (1b), and even there the biggest increase occurred in the 1960s, not recently.

Figure 1. Number of months per year in which P. falciparum malaria could be transmitted, from 1901 to 1995, at a) Kericho, Kenya; b) Kabale, Uganda; c) Gikonko, Rwanda; and d) Muhanga, Burundi.

The team also examined temperature and precipitation trends. For example, Figure 2a shows mean, maximum, and minimum temperatures at Kericho, Kenya, since 1970; Figure 2b shows the monthly rainfall. No amount of smoothing or data mangling could generate an increase in those data. Results were similar at three other highland stations. As the authors so succinctly state:

The absence of long- and short-term change in the climate variables and the duration of P. falciparum malaria transmission suitability at these highland sites are not consistent with the simplistic notion [emphasis ours] that recent malaria resurgences in these areas are caused by rising temperatures.

Figure 2. a) Maximum, mean, and minimum temperature time series for Kericho, Kenya. b) Total monthly rainfall time series for Kericho, Kenya. All data have a 13-month moving average superimposed to show the long-term change (or lack thereof).

So why is malaria increasing? There are myriad reasons. At Kericho and in the Usambara mountains of Tanzania, there has been an increase in antimalarial drug resistance. In southern Uganda, recent increases seem linked to weather changes, perhaps associated with the recent El Niño. In other locations, population migrations and the breakdown of the health service infrastructure have made people more susceptible.

We at WCR have been claiming since 1995 that the impact of climate change on public health is extremely small compared with other issues that people can actually do something about. According to Hay, "Economic, social, and political factors can therefore explain recent resurgences in malaria and other mosquito-borne diseases with no need to invoke climate change."

The research team ends the paper with a call for health researchers to be more responsible and question implicit assumptions about climate change:

The more certain climatologists become that humans are affecting global climates, the more critical epidemiologists should be of the evidence indicating that these changes affect malaria.

Some climatologists will take umbrage at being slammed by a group of epidemiologists. But if the climate community were more responsible about spreading climate change propaganda, then our once noble profession would not be under attack.

Reference:

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