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We focus on Europe because this is the only continent where NRLs have become recently available, and are regularly updated, for a range of taxonomic groups across more than 20 countries using standard approaches to the listing of threatened species. Red lists provide an objective framework for the classification of the broadest range of species according to their extinction risk based on the current trend in population size, geographic range, and area of occupancy ( 19).

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Here, we provide such an assessment by analyzing national red lists (NRL) of threatened species of seven taxonomic groups (vascular plants, bryophytes, mammals, fish, reptiles, dragonflies, and grasshoppers) from 22 European countries ( Tables S1 and S2) in relation to the magnitude of contemporary as well as historic drivers of environmental degradation.

Given that many conservation policies in Europe (and elsewhere) are developed and implemented at regional to global scales (e.g., Ramsar Convention and Convention on Biological Diversity) and reported at the level of individual countries, assessing extinction debt at this scale would appear to be a crucial step. However, despite the recent increase in interest in the potential for temporal lags in population declines and extinction processes ( 8, 10, 12, 17), evidence for extinction debt has not yet been examined for a broad range of taxa at a spatial scale consistent with national or global decision-making. Thus, red lists describing threatened species at either a national or global scale, which identify species extinction risks using criteria such as a reduction in population size, range size, and perceived rate of recent population or range decline ( 19), might be too optimistic. If time-lags in population decline at the scale of individual habitats are a common phenomenon, the number of species facing extinction risks at larger spatial scales might easily be underestimated because many local populations of extant species might not survive in the long-term even if further environmental degradation is halted.

In long-lived or less-mobile taxa (e.g., vascular plants, bryophytes, reptiles), a delayed response of populations to the deterioration and fragmentation of their habitats is especially likely and might extend over at least several decades. The likelihood and magnitude of extinction debt is still contentious, however ( 12, 13), and seems to vary with the nature of environmental degradation and with the life history traits of the species concerned ( 14– 18). Recent empirical research has shown that, at the scale of individual habitat patches, a delayed response of species to habitat loss and fragmentation is indeed often detectable, particularly among habitat specialists ( 9– 11). Such time-lags between environmental forcing, population decline, and, finally, extinction create a transient disequilibrium between environmental conditions and species’ abundance or range size, which has been conceptualized as “extinction debt” ( 9). However, species populations do not necessarily respond immediately to environmental degradation but might do so with a delay ( 9, 10). The progressive impact of environmental degradation on the loss of global biodiversity ( 1– 4) is strongly linked to key socioeconomic indicators such as human population size ( 5), land use ( 6), and gross domestic product (GDP) ( 7, 8). Mitigating extinction risks might be an even greater challenge if temporal delays mean many threatened species might already be destined toward extinction.

The negative impact of human activities on current biodiversity will not become fully realized until several decades into the future. We conclude that, irrespective of recent conservation actions, large-scale risks to biodiversity lag considerably behind contemporary levels of socioeconomic pressures. Across 22 European countries, the proportions of vascular plants, bryophytes, mammals, reptiles, dragonflies, and grasshoppers facing medium-to-high extinction risks are more closely matched to indicators of socioeconomic pressures (i.e., human population density, per capita gross domestic product, and a measure of land use intensity) from the early or mid-, rather than the late, 20th century. Here, we test for such a delay in impact by relating numbers of threatened species appearing on national red lists to historical and contemporary levels of socioeconomic pressures. However, though the impact of these pressures on biodiversity is substantial, it could be seriously underestimated if population declines of plants and animals lag behind contemporary environmental degradation. Rapid economic development in the past century has translated into severe pressures on species survival as a result of increasing land-use change, environmental pollution, and the spread of invasive alien species.

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