Assessing the impacts of climate change on biodiversity: is below 2 °C enough?

Large changes in biodiversity are expected to occur if climate change continues at its current pace. Adverse effects include changes in species habitats and compositions, and consequently changes in ecosystem functioning. We assessed the magnitude of expected changes of biodiversity by performing a meta-analysis of the responses of species distributions to climate change. We focused on the proportion of local remaining species and their habitats. We summarized 97 studies and calculated two effect-size metrics from their results to quantify changes in biodiversity. These metrics are the fraction of remaining species (FRS) and the fraction of remaining area (FRA) with suitable climate for each species. Both metrics calculate deviations from the original biodiversity state and together they indicate biodiversity intactness. We found an expected gradual decrease in both FRS and FRA with significant reductions of 14% and 35% between 1 and 2 °C increase in global mean temperatures. Strong impacts are projected for both mammals and plants with FRS reductions of 19%. The climate-change response of biodiversity varies strongly among taxonomic groups and biomes. For some taxonomic groups the FRA declines strongly beyond 3 °C of temperature increase. Although these estimates are conservative, as we assume that species are unable to disperse or adapt, we conclude that already at moderate levels (i.e., 1–2 °C) of temperature increase a significant decrease of original biodiversity is projected. Our research supports the pledge to limit climate change to 1.5 °C and preferably lower to protect biodiversity.