Assessing the impacts of climate tipping points on global biodiversity

Crossing global climate tipping points (that is, the persistent collapse of climate subsystems like the melting of ice sheets or the modification of ocean circulation patterns) are expected to have dramatic effects on ecosystems worldwide. One such dramatic effect is the potential exposure of species to stressful climatic conditions outside their physiological limits without time for adaptation, increasing their risk of extinction. However, the extent to which climate tipping points may expose species outside the climatic limits of their existence (i.e. their climate niche) remains an open question.  

In this study, we estimate the risk of extinction to projected climate tipping points for worldwide terrestrial biodiversity. We do this by first evaluating the historical realized climate niche for 80967 terrestrial and freshwater populations, representing 54850 species. We define the realised climate niche as the boundaries in historical climatic conditions experienced by each species from 1940-2020 that we quantify in 15 dimensions related to temperature, rainfall, climate variability, and extreme events (heatwaves, cold spells, and droughts). 

We then use novel and unique global climate projections that simulate two highly likely climate tipping points, the removal of the Amazon rainforest and the shutdown of the Atlantic Meridional Overturning Circulation (AMOC), to investigate the extent of exposure in different climate dimensions for worldwide biodiversity. Defining exposure as when species experience conditions above the historical threshold for a prolonged period in each of the 15 climate dimensions, we explore how habitat suitability is affected in different dimensions for different species, identifying potential climate refugia, and dimensions of maximum exposure for different taxa and regions that we translate to a measure of species extinction risk. We find that biodiversity exposure and potential extinction risk arising from the loss of the Amazon rainforest is highly localized to the Amazon; while the AMOC shutdown scenario has much greater global impact, its typical effect is global cooling, stymieing large-scale biodiversity exposure. 

Our results suggest that we might underestimate the impact of future climate change if we do not account for the possibility of long-lasting and irreversible climate tipping point events.