The study, led by the London School of Hygiene & Tropical Medicine (LSHTM), estimates that this worst-case scenario would mean the population at risk of the diseases might increase by up to 4.7 additional billion people (relative to the period 1970-1999), particularly in lowlands and urban areas, if temperatures rise by about 3.7° Celsius by 2100 compared to pre-industrial levels.
For malaria, the modelling for the worst-case scenario estimated a total of 8.4 billion people being at risk in 2078 (89.3 per cent of an estimated global population of 9.4 billion) compared with an average of 3.7 billion over the period 1970-1999 (75.6 per cent of an estimated global population of 4.9 billion). For dengue, the modelling estimated a total of 8.5 billion people at risk in 2080 compared with an average of 3.8 billion in 1970-1999.
Malaria suitability is estimated to gradually increase as a consequence of a warming climate in most tropical regions, especially highland areas in the African region (Ethiopia, Kenya, and South Africa), the Eastern Mediterranean region (Somalia, Saudi Arabia, and Yemen), and the Americas (Peru, Mexico, and Venezuela). Dengue suitability is predicted to increase mostly in lowland areas in the Western Pacific region (Guam, Vanuatu, Palau) and the Eastern Mediterranean region (Somalia and Djibouti), and in highland areas in the Americas (Guatemala, Venezuela, and Costa Rica).
A northward shift of malaria
The research predicts there will be a northward shift of the malaria-epidemic belt in North America, central northern Europe, and northern Asia, and a northward shift of the dengue-epidemic belt over central northern Europe and northern USA because of increases in suitability.
First author Dr Felipe J Colón-González, Assistant Professor at LSHTM, said: “Our results highlight why we must act to reduce emissions to limit climate change. Policymakers and public health officials should get ready for all scenarios, including those where emissions remain at high levels. This is particularly important in areas that are currently disease-free and where the health systems are likely to be unprepared for major outbreaks.”
While differential effects of climate change with altitude and urbanisation have been previously discussed, they have not been quantified globally for different levels of altitude and urbanisation, until now.
Climatic conditions could allow malaria to thrive
Although the worst-case scenario models indicated that some areas could become too hot for some mosquito species, that situation would likely cause other health effects such as heat-related mortality, reduced labour productivity, and reduced food production. Moreover, mosquito-borne diseases could become a bigger problem elsewhere, including expanding further north and into higher altitude and temperate regions, as climatic conditions such as temperature and rainfall enable malaria and dengue to thrive in different parts of the world.
Senior Author Dr Rachel Lowe, Associate Professor and Royal Society Dorothy Hodgkin Fellow at LSHTM, concluded: “A number of interventions will be needed to adapt to the health effects of a warmer and more urbanised world and to prepare for all scenarios. Our findings stress the importance of increased surveillance in potential hotspot areas to monitor the emergence of diseases, especially in places without previous experience of dengue or malaria.
“Public health action will be particularly important in areas where transmission is occasional because public health systems might be unprepared to control and prevent these diseases.”