The malaria map is moving. In Pakistan’s highlands, regions that were too cool for mosquitoes a generation ago now face regular outbreaks. Scottish health officials track ticks that can now survive winter, potentially establishing year-round Lyme disease transmission. And across Africa’s eastern highlands—from Ethiopia to Tanzania—communities with little prior exposure to malaria are seeing the disease arrive as warming temperatures push Anopheles mosquitoes to higher elevations. For Dr. Madeleine Thomson, whose career has centered on climate-sensitive disease forecasting, these shifts represent both a vindication of decades of research and an urgent call for scaled-up intervention.
Thomson’s work on malaria early warning systems began in earnest during her time at Columbia University’s International Research Institute for Climate and Society, where she directed the WHO Collaborating Centre focused specifically on climate-informed disease surveillance. Originally trained as a field entomologist, she spent her early career conducting operational research supporting large-scale health interventions in Africa, including Gambia’s national impregnated bednet program. This combination of field experience and climate science expertise positioned her uniquely to understand how warming temperatures would fundamentally alter disease geography.
The numbers tell a sobering story. The WHO’s 2024 World Malaria Report estimates 263 million cases globally in 2023—11 million more than the previous year. While some increase reflects improved diagnosis and population growth, climate change is adding an estimated 550,000 additional malaria deaths between 2030 and 2049, according to analysis from the Malaria Atlas Project and Boston Consulting Group. Most of these deaths will result not from gradual warming but from extreme weather events: cyclones, floods, and droughts that destroy healthcare infrastructure, displace populations, and create mosquito breeding sites.
“Climate change is a threat multiplier,” notes Thomson’s work on climate impacts. “It makes escaping poverty and accessing healthcare harder and widens existing inequality gaps, for example for women and children.”
The mechanism by which climate change redraws malaria maps is straightforward in principle, complex in practice. Malaria transmission requires temperatures warm enough for both mosquitoes and Plasmodium parasites to complete their life cycles. Below roughly 18°C, transmission essentially stops. Between 25-28°C, transmission accelerates dramatically as mosquitoes bite more frequently, reproduce faster, and parasites mature more quickly inside the mosquito’s gut. Above 32°C, mosquito mortality increases and transmission efficiency drops.
As global temperatures rise, the altitudinal and latitudinal boundaries of suitable malaria habitat shift. The East African highlands provide the clearest example. Regions above 2,000 meters were historically too cold for sustained malaria transmission. Now, as temperatures climb, mosquitoes are colonizing these highlands. Populations living there have little immunity and health systems lack experience managing the disease, creating conditions for explosive epidemics.
But temperature tells only part of the story. Rainfall patterns matter enormously. Mosquitoes need standing water to breed—puddles, tire tracks, discarded containers, irrigation channels. Too little rain means no breeding sites. Too much rain can flush out larvae, temporarily reducing transmission. The sweet spot for Anopheles mosquitoes tends to be moderate, consistent rainfall that maintains breeding sites without washing them away.
This is where El Niño and La Niña events enter the picture. Thomson’s research documented how these climate oscillations drive epidemic malaria. In the 1990s, western India saw significantly more malaria cases with higher rainfall during La Niña in 1996, while El Niño’s drier conditions in 1998 corresponded with fewer cases in the same region. Sri Lanka, before widespread use of mosquito control measures, experienced a three-fold increase in malaria risk following monsoon failures associated with El Niño. Southern African countries have seen malaria epidemics follow unusual rainfall patterns.
The challenge for early warning systems is translating these climate signals into health interventions. Thomson helped pioneer this approach during her Columbia years, developing methodologies that integrated seasonal climate forecasts with epidemiological models. The goal was simple but revolutionary: instead of reacting to malaria outbreaks after they occurred, health systems could prepare weeks or months in advance.
A functional early warning system operates on multiple timescales. Seasonal forecasts—predictions of rainfall and temperature for the coming 3-6 months—allow health ministries to pre-position supplies, train healthcare workers in high-risk areas, and intensify vector control before transmission accelerates. Weekly weather monitoring during malaria season helps target interventions geographically, concentrating limited resources where they’re most needed. And longer-term climate projections inform strategic planning: where should countries build health infrastructure? Which regions will need enhanced surveillance as malaria risk increases?
Vietnam offers a concrete example of this approach in action. A research team is developing E-DENGUE, a digital tool that uses climate data to predict dengue outbreaks up to two months in advance for the Mekong Delta region. While focused on dengue rather than malaria, the methodology is similar: integrate weather forecasts with disease surveillance data to give health practitioners time to mobilize resources before outbreaks peak.
The effectiveness of early warning depends critically on trust and communication between climate scientists and health officials. “Climate scientists have to be interested in how their science can benefit society in a practical way,” Thomson emphasized. “Then they have to really look at the timeframe of decisions.” A malaria control officer needs to know whether to expect high transmission next month, not theoretical risk projections for 2050. Early warning systems must deliver actionable information at the right temporal and spatial scales.
Yet significant challenges remain. Many countries lack the basic surveillance infrastructure needed to detect disease outbreaks quickly. Laboratory capacity is limited, making it difficult to distinguish malaria from other febrile illnesses. Climate data may not be available at fine enough resolution to predict local outbreak risk. And even when early warnings are issued, weak health systems may lack the resources to respond effectively.
Drug and insecticide resistance compound these difficulties. Pyrethroid resistance—the most common insecticide used in bed nets—has been confirmed in 55 of 64 countries monitored between 2018 and 2023. Partial resistance to artemisinin, the frontline antimalarial treatment, has emerged in East Africa. These biological threats mean that even with perfect climate forecasts and robust early warning, health systems need new tools to combat evolving malaria parasites and mosquitoes.
Thomson’s recent position at Wellcome reflects the evolution of this work from pure research toward implementation and adaptation strategy. Wellcome is funding 24 research teams across 12 countries to develop new digital tools for climate-sensitive infectious diseases, recognizing that early warning systems need continuous refinement and local adaptation.
The stakes are enormous. Climate models project that by mid-century, regions currently malaria-free could become suitable for transmission. Conversely, some areas may become too hot for mosquitoes, potentially reducing transmission. The net effect is uncertain but concerning, particularly for highland regions in Africa and Asia where populations lack immunity.
Early warning systems represent our best tool for staying ahead of these shifting disease geographies. They can’t stop climate change or eliminate malaria entirely, but they can buy precious time—weeks or months—for health systems to prepare, protect vulnerable populations, and prevent deaths. For Thomson, who has dedicated her career to building these systems, the work has never been more urgent. The malaria map is being redrawn. The question is whether our early warning systems can keep pace with the redrawing.