My colleagues and I overlaid the projections of climate models with data on the geographic distributions of more than 35,000 species on land and in the ocean.
We found that limiting global warming to 1.5°C (the ambition of the 2015 Paris agreement) would leave 15% of species at risk of abruptly losing at least one third of their current geographic range. However, this doubles to 30% of species on our present trajectory of 2.5°C of warming.
Of the populations within a species projected to be at risk this century, we found that, on average, more than half will switch from being relatively safe to facing dangerous heat in as little as a single decade.
Most populations may initially appear safe. But then, suddenly, a threshold of global warming is crossed beyond which multiple populations across widespread areas face intolerable conditions in rapid succession.
This scenario is already playing out on coral reefs. Just a few decades ago, coral bleaching events driven by extreme sea surface temperatures were rare and localized. Today, these events degrade reefs globally on an almost annual basis.