Impact of global warming and Greenland ice sheet melting on malaria and Rift Valley Fever

Mosquitoes are climate-sensitive disease vectors. They need an aquatic environment for the development of their immature stages (egg-larva-nymph). The presence and maintenance of these egg-laying sites depends on rainfall. The development period of mosquitoes is reduced when temperature increases, up to a lethal threshold. Global warming will impact vector’s distribution and the diseases they transmit. The last deglaciation taught us that the melting of the ice sheet is highly non-linear and can include acceleration phases corresponding to sea level rise of more than 4 m per century. In addition, glacial instabilities such as iceberg break-ups (Heinrich events) had significant impacts on the North Atlantic Ocean circulation, causing major global climate changes. These melting processes and their feedbacks on climate are not considered in current climate models and their detailed impacts on health have not yet been studied.

To simulate an accelerated partial melting of the Greenland ice sheet, a freshwater flux corresponding to a sea level rise of +1 and +3 m over a 50-year period is superimposed on the standard RCP8.5 radiative forcing scenario. These scenarios are then used as inputs for the IPSL-CM5A climate model to simulate global climate change for the 21^st century. These simulations allow to explore the consequences of such melting on the distribution of two vector-borne diseases which affect the African continent: malaria and Rift Valley Fever (RVF).  Malaria is a parasitic disease that causes more than 200 million cases and more than 600,000 deaths annually worldwide. RVF causes deaths and high abortion rates in herds and poses health risks to humans through contact with infected blood. Former studies have already characterised the evolution of the global distribution of malaria according to standard RCPs. Using the same malaria mathematical models, we study the impact of an accelerated Greenland melting on simulated malaria transmission risk in Africa. Future malaria transmission risk decreases over the Sahel and increases over East African highlands. The decrease over the Sahel is stronger in our simulations with respect to the standard RCP8.5 scenario, while the increase over east Africa is more moderate. Malaria risk strongly increases over southern Africa due to a southern shift of the rain belt which is induced by Greenland ice sheet melting.,. For RVF, the disease model correctly simulates historical epidemics over Somalia, Kenya, Mauritania, Zambia and Senegal.  However, our results show the difficulty to validate continental scale models with available health data. It is essential to develop climate scenarios that consider climate tipping points. Assessing the impact of these tipping point scenarios and the associated uncertainties on critical sectors, such as public health, should be a future research priority.