What impact will climate change have on malaria?
More than 600,000 people die from malaria every year. Will climate change make this worse?.
Malaria is a life-threatening disease caused by parasites transmitted to humans through the bites of infected female Anopheles mosquitoes. Today, malaria kills over 600,000 people annually, with nearly half a million of these deaths being children under five years old. The disease is most prevalent in tropical and subtropical regions, particularly in sub-Saharan Africa, which accounts for more than 95% of global malaria deaths. Within Africa, West Africa bears the highest burden, with countries like Nigeria and Sierra Leone experiencing the highest infection and death rates. For example, infection rates in sub-Saharan Africa are about 100 times higher than in South America and 50 times higher than in South Asia. Children are disproportionately affected, representing around 70% of all malaria deaths globally.
The spread of malaria depends heavily on temperature, as Anopheles mosquitoes thrive in specific conditions. Research shows that malaria transmission peaks at around 25°C (77°F) and drops to near zero below 16°C (61°F) or above 34°C (93°F). This creates a bell-shaped curve where temperatures outside this range reduce mosquito survival and parasite development. Other factors like rainfall and humidity also play a role: moderate rainfall creates ideal breeding grounds for mosquitoes, while high humidity extends their lifespan. These conditions explain why malaria is concentrated in warmer regions and why climate change could alter its spread by shifting temperatures outside or within this optimal range.
Since the early 1900s, global temperatures have risen by about 1.4°C due to climate change. A study by Colin Carlson and colleagues estimated that this warming has had a small but uneven impact on malaria in sub-Saharan Africa. While malaria prevalence increased slightly in some regions, it declined in others, resulting in a net effect that was relatively minor. Specifically, the study found that climate change may have increased malaria cases by about 1 per 1,000 children aged 2 to 10 in sub-Saharan Africa, where around 24% of children already carried the malaria parasite. The most significant changes occurred in West Africa, where temperatures rose above the optimal 25°C, reducing malaria transmission. Meanwhile, East and Southern Africa, which started with cooler temperatures, saw increases as warming pushed them closer to the ideal range.
Climate change has already caused malaria to decline in West Africa but increase in Eastern and Southern Africa. This shift is due to temperature changes pushing regions toward or away from the 25°C optimum for malaria transmission. For instance, West Africa's average temperature in 1901 was around 26°C, slightly above the ideal, and further warming has moved it further away from the peak transmission range. In contrast, Central and East Africa started at around 22°C, and Southern Africa at 17°C, so warming has brought them closer to the optimal temperature. These regional differences highlight how climate change can both reduce and exacerbate malaria risks depending on local conditions.
Future climate change scenarios suggest that malaria trends in sub-Saharan Africa will continue to diverge by region. Under low-emission scenarios (RCP2.6), malaria prevalence is projected to decline in West and Central Africa but remain relatively stable in East Africa. In Southern Africa, malaria is expected to increase initially, though it may later decline in the hottest scenarios. Higher emissions scenarios (RCP4.5 and RCP8.5) would accelerate these trends, with West Africa seeing the sharpest declines and Southern Africa experiencing the largest increases. Notably, warming could make malaria viable in higher-altitude areas of Southern Africa, which currently lack experience in managing the disease. These projections depend on global efforts to reduce greenhouse gas emissions.
While climate change has had a measurable impact on malaria distribution, its effect has been small compared to human interventions. Over the past few decades, malaria cases and deaths in sub-Saharan Africa have fallen dramatically, with infection rates in young children dropping by nearly 40% and death rates almost halving. These reductions are largely due to malaria control programs, such as insecticide-treated bed nets, antimalarial drugs, and improved healthcare access. The study by Carlson and colleagues notes that the influence of climate change is largely overshadowed by these efforts, which have reduced malaria prevalence by more than 200 times the impact of climate change alone. This underscores the importance of continued investment in malaria prevention and treatment alongside climate adaptation strategies.
