Abstract
Biodiversity loss is accelerating under compounding human pressures, yet most conservation tools quantify the pressure species already face, rather than when it will push them beyond the levels they have experienced. This temporal blind spot limits proactive planning, particularly under the Kunming-Montreal Global Biodiversity Framework (GBF), which sets action-oriented targets for 2030 and long-term goals for 2050. We link forecasts of cumulative human modification to 2040, which assume past patterns of change continue, to the area of habitat of 15,924 terrestrial mammal and bird species. Our framework adds species-specific exposure thresholds, aggregation across species or ranges, and an uncertainty envelope. We estimate exceedance under the mean HM forecast and under lower and upper trajectories that bound its 95% prediction interval, giving three estimates of exposure timing. We define the Estimated Time to Act (ETA) as the first year in which at least 30% of species in a local community exceed their exposure threshold. Based on the upper estimates, the community criterion is met on 19.7% of land by 2040, including 11.7% that the mean forecast alone does not flag, mostly land already moderately modified in 2015. On the same basis, almost a quarter of threatened species (24%) have at least half of their habitat exceeding their exposure threshold by 2040, more than twice the share of non-threatened species. Of 822 ecoregions, 338 combine moderate or high naturalness with high exceedance risk, most of them less than 30% protected. ETA complements existing biodiversity metrics by adding the dimensions of time and uncertainty. In doing so, it makes explicit the urgency implied by the GBF’s deadlines, helping decision-makers identify where and when to act before pressure arrives.