Synergistic impacts of global warming and thermohaline circulation collapse on amphibians

Abstract

Impacts on ecosystems and biodiversity are a prominent area of research in climate change. However, little is known about the effects of abrupt climate change and climate catastrophes on them. The probability of occurrence of such events is largely unknown but the associated risks could be large enough to influence global climate policy. Amphibians are indicators of ecosystems’ health and particularly sensitive to novel climate conditions. Using state-of-the-art climate model simulations, we present a global assessment of the effects of unabated global warming and a collapse of the Atlantic meridional overturning circulation (AMOC) on the distribution of 2509 amphibian species across six biogeographical realms and extinction risk categories. Global warming impacts are severe and strongly enhanced by additional and substantial AMOC weakening, showing tipping point behavior for many amphibian species. Further declines in climatically suitable areas are projected across multiple clades, and biogeographical regions. Species loss in regional assemblages is extensive across regions, with Neotropical, Nearctic and Palearctic regions being most affected. Results underline the need to expand existing knowledge about the consequences of climate catastrophes on human and natural systems to properly assess the risks of unabated warming and the benefits of active mitigation strategies.

Greenland’s thaw pushes the biodiversity crisis

“…Thus, although our modeled species represent a small fraction of global diversity, the alterations to geographic extent of PSHs and the alteration of species composition is an alarming possibility. Based on our models, we suggest a dramatic decline and alteration of biodiversity across hotspots within a relatively short period of time (10-40 years; see figure S2 in Velasco et al 15 ) after the onset of Greenland's melting, and the ensuing weakening of the AMOC. More than twenty years ago, Myers et al 10 estimated that effectively protecting these biodiversity hotspots, collectively encompassing less than 2% of the Earth's surface, would translate into the protection of 44% of vascular plants and 35% tetrapods.…”

“…The estimated changes in our evaluated variables of mean annual temperature and annual precipitation under the different climate models cannot account for the spatial and temporal heterogeneity observed in species responses across countries (Supplementary figures S9-S11); this despite that these variables (mean annual temperature and annual precipitation) are two of the most important contributors to our species distribution models (Supplementary figure S12-S13). This highlights the idiosyncratic response of species to climate change, yet our results suggest that high global warming and ice sheet melt can have an overarching impact on biodiversity and the climate system 15,22 , leading to worldwide drastic alterations to climate and biodiversity loss.…”

“…The projected reduction in species richness and alteration to species composition highlight the threat for biodiversity posed by global warming and the additional contribution of Greenland's melting 15 . Furthermore, the declines in species richness and alteration to species composition are associated with projected reductions of the geographic ranges of individual species, which are magnified under melting scenarios (figure 3).…”

“…By selecting this representative sample of species, we provide a general snapshot of the ecological impacts of unabated global warming and the melting of Greenland's ice sheets. We quantify biodiversity loss and species' vulnerability across countries and taxonomic groups through predicted changes in species diversity under five climate change scenarios: an unabated high-emission global warming scenario (RCP 8.5), and four variations of the RCP 8.5 generated by simulating different levels of freshwater release into the North Atlantic, starting in 2020 15,22 .…”

A 1150-year-long AMV reconstruction suggests early warning for a North Atlantic climate tipping point

“…This assumption based on our real-data reconstruction has previously been proposed using CMIP5 models, among which such an abrupt change happens in projections of nearly half of the best ones in representing ocean convection in the northern North Atlantic 15 , even under scenarios with low anthropogenic emissions of greenhouse gases. It thus raises serious concerns, while more and more evidence seem to indicate an on-going long-term slowdown in the Atlantic current 56 and that the impacts of such a change are numerous 16,57,58…”