The impact of climate change and natural climate variability on the global distribution of Aedes aegypti

Aedes aegypti spread pathogens affecting humans, including the dengue, Zika and yellow fever viruses. Anthropogenic climate change is altering the spatial distribution of Ae. aegypti and therefore the locations at risk of vector-borne disease. In addition to climate change, natural climate variability, resulting from internal atmospheric processes and interactions between climate system components (e.g. atmosphere-land, atmosphere-ocean) determines climate outcomes. However, the combined effects of climate change and natural climate variability on future Ae. aegypti spread have not been assessed fully. We developed an ecological model in which Ae. aegypti population dynamics depend on climate variables (temperature and rainfall). We used 100 projections from the Community Earth System Model, a comprehensive climate model that simulates natural climate variability as well as anthropogenic climate change, in combination with our ecological model to generate a range of equally plausible scenarios describing the global distribution of suitable conditions for Ae. aegypti up to 2100. Like other studies, we project the poleward expansion of Ae. aegypti under climate change. However, the extent of spread varies considerably between projections, each under the same Shared Socioeconomic Pathway scenario (SSP3-7.0). For example, by 2100, climatic conditions in London may be suitable for Ae. aegypti for between one and five months in the year, depending on natural climate variability. Our results demonstrate that natural climate variability yields different possible future Ae. aegypti spread scenarios. This affects vector-borne disease risks, including the potential for some regions to experience outbreaks earlier than expected under climate change alone.