The relationship between malaria and climate is a complex one. While the exact climate-related health risks and impacts have yet to be fully understood, evidence does should that climate change impacts malaria transmission. Over the long term, rising temperatures and increases in rainfall could spread the disease to previously malaria-free zones. The suitable temperature range for the malaria parasite or the mosquito that transmits the parasite between humans is relatively well established by field and laboratory studies and forms the basis for current projections of the impact of climate change on malaria. Recent studies even found that malaria parasites need less time to develop at lower temperatures than previously thought, meaning that even slighter warming may be enough to heighten malaria risk. Surface water is equally crucial, as it provides habitat for the mosquitoes to lay their eggs. Nevertheless, different scenarios in which climate change remains under control, economic growth continues, and urbanization progresses offer some hope that the impact of malaria worldwide could still decrease in the decades to come.
Climate change causes increasing global temperatures, extreme weather events and change in rainy seasons. As seen on the map below taken from the Global Fund’s Strategy Development Landscape Analysis for Malaria, the malaria burden is predicted to increase in contexts that previously did not have malaria, with low population immunity, and may decrease or disappear in tropical, previously endemic, regions. The map outlines the worst-case scenario with the ‘business-as-usual’ scenario where society does not make concerted efforts to cut greenhouse gas emissions, and in which the quantity of greenhouse gas emissions are therefore the highest.
In many places, malaria transmission is seasonal, with the peak during and just after the rainy season. Variation in climatic conditions, such as temperature, rainfall patterns, and humidity, have a profound effect on the longevity of the mosquito and on the development of malaria parasites within the mosquito and, subsequently, on malaria transmission. Malaria epidemics can occur when climate and other conditions suddenly favor transmission in areas where people have little or no immunity to malaria. They can also occur when people with low immunity move into areas with intense malaria transmission, for instance to find work, or as refugees.
WHO estimates that climate change will lead to 60,000 additional deaths per year due to malaria between 2030 and 2050, an increase of nearly 15% in overall annual deaths from this preventable disease, even when accounting for economic growth and health progress. It also projects that about 5% of the global malaria cases, or 21 million cases, would be attributable to climate change in 2030.
By 2050, climate change alone might expose some areas in South America, sub-Saharan Africa and China to a 50% higher probability of malaria transmission.
A recent study in Africa found that estimated geographic shifts in endemic and seasonal suitability for malaria transmission were observed across all future scenarios of climate change on the continent. The worst-case regional scenario of climate change predicted an additional 75.9 million people at risk from endemic exposure to malaria transmission in Eastern and Southern Africa by the year 2080, with the greatest population at risk in Eastern Africa. In general, the changes in malaria presence occur at the borders of current transmission zones. Once again, the largest changes are predicted in Africa.
However, malaria transmission is also strongly associated with GDP: in cases where temperatures and greenhouse gas emissions continue rising, urbanizations and economic development could offer some hope for either only modest malaria expansion, no further expansion, or even reduction or malaria disappearance in certain parts of South America and Asia. As urbanization is associated with economic growth, having increasing number of people living in urban areas would be beneficial in the fight against malaria, because they have fewer breeding sites suitable for the most effective malaria vectors, treatment is easier to reach and prevention measures such as insecticide-treated bed nets are more widely available.
The populations that are most vulnerable to climate change are also the ones that are most vulnerable to malaria. The link between climate change and health is getting increasingly noticed—in 2015, the Lancet launched a Health and Climate Change Commission, and health systems around the world have started to take some steps to be better prepared for extreme weather hazards, and businesses have become more engaged in the discussions around the climate-health nexus. Nevertheless, malaria has remained by the side of the road of these emerging conversations. There clearly is a need for a greater dialogue on how to grapple with the interlinked challenges of climate change and malaria elimination to identify strategies and opportunities for mitigating the impact of the disease—and ensure that it does not spread to new areas where populations are the most vulnerable physiologically, economically and socially.