Identifying the world's most climate change vulnerable species: a systematic trait-based assessment of all birds, amphibians and corals

Abstract

Climate change will have far-reaching impacts on biodiversity, including increasing extinction rates. Current approaches to quantifying such impacts focus on measuring exposure to climatic change and largely ignore the biological differences between species that may significantly increase or reduce their vulnerability. To address this, we present a framework for assessing three dimensions of climate change vulnerability, namely sensitivity, exposure and adaptive capacity; this draws on species' biological traits and their modeled exposure to projected climatic changes. In the largest such assessment to date, we applied this approach to each of the world's birds, amphibians and corals (16,857 species). The resulting assessments identify the species with greatest relative vulnerability to climate change and the geographic areas in which they are concentrated, including the Amazon basin for amphibians and birds, and the central Indo-west Pacific (Coral Triangle) for corals. We found that high concentration areas for species with traits conferring highest sensitivity and lowest adaptive capacity differ from those of highly exposed species, and we identify areas where exposure-based assessments alone may over or under-estimate climate change impacts. We found that 608-851 bird (6-9%), 670-933 amphibian (11-15%), and 47-73 coral species (6-9%) are both highly climate change vulnerable and already threatened with extinction on the IUCN Red List. The remaining highly climate change vulnerable species represent new priorities for conservation. Fewer species are highly climate change vulnerable under lower IPCC SRES emissions scenarios, indicating that reducing greenhouse emissions will reduce climate change driven extinctions. Our study answers the growing call for a more biologically and ecologically inclusive approach to assessing climate change vulnerability. By facilitating independent assessment of the three dimensions of climate change vulnerability, our approach can be used to devise species and area-specific conservation interventions and indices. The priorities we identify will strengthen global strategies to mitigate climate change impacts.

Figure 1. Framework to assess the impacts of climate change on species.

Combinations of the three dimensions of climate change vulnerability, namely sensitivity, exposure and low adaptive capacity describe four distinct classes of climate change vulnerable species, each with particular implications for conservation prioritisation and strategic planning. Species that are ‘highly climate change vulnerable’ (1), being sensitive, exposed and of low adaptive capacity, are of greatest concern. They are the first priority for monitoring responses to climate change and for assessment of the interventions needed to support them. ‘Potential adapters’ (2) are sensitive and exposed (but high adaptive capacity) species that may be able to mitigate negative climate change impacts by dispersal or microevolution, although close monitoring is needed to verify this. ‘Potential persisters’ (3) have low adaptive capacity and are exposed (but are not sensitive) so may be able to withstand climate change in situ by themselves, but again, monitoring is needed to ensure that the assumptions about insensitivity are realized in practice. Finally, species of ‘high latent risk’ (4) have low adaptive capacity and are sensitive (but are not exposed). Although not of immediate concern if climate change projections and emissions scenarios are accurate, they could become climate change vulnerable if exposed beyond selected time frames (e.g., 2050).

Figure 2. Concentrations of climate change vulnerable species.

Areas with greatest concentrations of species with high sensitivity and low adaptive capacity only are shown in blue, and those with high exposure to climatic change only are in yellow. Areas with high concentrations of species that have high sensitivity and low adaptive capacity species, as well as of highly exposed species, are shown in maroon; they correspond with areas of high overall climate change vulnerability. Total numbers of climate change vulnerable birds, amphibians and corals are shown in A, C and E respectively, while B, D and F show the proportions of species occurring in a region that are climate change vulnerable. Grey areas show where species are present, but concentrations of focal species groups are low; colours increase in intensity as total numbers (for A, C and E) and proportions (for B, D and F) of focal species increase. These results were based on the moderate A1B emissions scenario for 2050 and assume an optimistic scenario for missing trait information.

Figure 3. Concentrations of species that are both climate change vulnerable and threatened by non-climate stressors.

Areas with high concentrations of species that are climate change vulnerable only are in yellow, threatened species (according to the IUCN Red List) only are in blue, and areas with high concentrations of both are shown in maroon. The log of total numbers of these birds, amphibians and corals are represented by A, B and C respectively (see Figure S6 for maps of the proportions of these species relative to species richness). Grey areas show where species are present but concentrations of species that are either climate change vulnerable or threatened are low; colours increase in intensity as species concentrations increase. These results are based on the moderate A1B emissions scenario for 2050 and assume optimistic assumptions for missing trait information.

Figure 4. Climate change vulnerability under different emissions scenarios.

Red, black, and blue lines represent the percentages of highly climate change vulnerable species under high (A2), mid-range (A1B) and low (B1) emissions scenarios for birds (A), amphibians (B) and corals (C) for 1975–2050 and 1975–2090. Optimistic and pessimistic estimates for missing biological trait data are represented by solid and dashed lines respectively.