Climate change and the global malaria recession

Abstract

A comparison of a recently published evidence-based map of the distribution of the Plasmodium falciparum malaria parasite with data from 1900, before the introduction of major malaria control measures, suggests that concerns that rising temperatures are a threat to malaria control efforts are misplaced. During a century when increases in global temperature have been unequivocal, the range and intensity of malaria has diminished dramatically. The postulated effect of warming is at least an order of magnitude smaller than the effects of control measures, suggesting that the success or failure of the antimalaria programme is likely to be determined by factors other than climate. Rising global temperatures resulting from climate change have been predicted to increase the future incidence of infectious diseases, including malaria. However, it is known that the range of malaria has contracted through a century of economic development and disease control. This contraction has now been quantified, and compared with the predicted effects of climate on malaria incidence. It is suggested that the impact of rising temperature is likely to be minor. The current and potential future impact of climate change on malaria is of major public health interest1,2. The proposed effects of rising global temperatures on the future spread and intensification of the disease3,4,5, and on existing malaria morbidity and mortality rates3, substantively influence global health policy6,7. The contemporary spatial limits of Plasmodium falciparum malaria and its endemicity within this range8, when compared with comparable historical maps, offer unique insights into the changing global epidemiology of malaria over the last century. It has long been known that the range of malaria has contracted through a century of economic development and disease control9. Here, for the first time, we quantify this contraction and the global decreases in malaria endemicity since approximately 1900. We compare the magnitude of these changes to the size of effects on malaria endemicity proposed under future climate scenarios and associated with widely used public health interventions. 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.