Climate change affects wildlife primarily by altering temperature and precipitation patterns beyond what species and ecosystems evolved to tolerate, shifting viable habitat ranges faster than many species can track or adapt to. Extinction risk is not linear — it increases sharply as specific warming thresholds are crossed.
Per the IPCC Sixth Assessment Report, an estimated 9% of terrestrial and freshwater species face high extinction risk at 1.5°C of warming, rising to 18% at 2°C — a doubling of risk from a 0.5°C difference in warming.
Source: IPCC AR6 Working Group IIUnder a high-warming scenario (roughly 4°C), realistic dispersal-rate models project that 67% of plants, 68% of invertebrates and 44% of chordates would lose over half their geographic range.
A major 2024 review projects likely vertebrate extinctions of 19–34% by 2070 under a moderate-emissions scenario (RCP4.5), rising to 36–44% under a high-emissions scenario (RCP8.5). Insect extinction projections for the same period range from 14–27% and 23–31% respectively.
Source: Wiens & Zelinka, Global Change Biology, 2024The non-linear relationship between warming and extinction risk is the most important framing point here: the difference between 1.5°C and 2°C is not "slightly worse," it's roughly double the share of species at high risk. That makes each fraction of a degree of avoided warming disproportionately valuable, and it's why climate targets are expressed as thresholds rather than a smooth dial.
Extinction risk projections depend heavily on emissions-scenario assumptions and species' dispersal ability, both of which carry real uncertainty — actual outcomes could be better or worse than central estimates. Some research suggests current Red List assessment criteria may underestimate climate-related extinction risk for range-shifting species specifically, meaning today's official threat classifications could be conservative relative to the underlying risk.