In face of the Holocene-Anthropocene Mass Extinction conservationists challenge themselves to think of novel biodiversity protection measures. Thinking outside of the box of fenced reserves is literally required, as over 85 percent of Earth’s land does not have nature-protected status, and many stressors, including climate change, also hit home inside nature reserves, decreasing potential refugia in size.

One solution might be to invest in corridors, connecting climate-sturdy refugia, and helping threatened species reach suited habitat.

Comparing the beneficial effects of climate mitigation and ecological climate adaptation for biodiversity conservation in WWF’s ‘Priority Places’. Extirpation defines as local extinction of species. The graph (unlike other global research that suggests exponential relation between temperature and extinction) indicates a linearly increasing extinction risk for increasing temperature, highlighting risks under the 2 degrees target, actual current pledges ((I)NDCs) and warming under a business as usual scenario. Per warming scenario the relative effects of ecological adaptation measures are also illustrated, indicating these can lower extinction risk, but also that mitigation is more important than adaptation.

This we learn from a new publication in Climatic Change, by a group of researchers led by Rachel Warren of the Tyndall Centre of Climate Change Research at the University of East Anglia, joined by specialists of the Centre for Tropical Biodiversity and Climate Change of James Cook University and WWF UK’s Living Planet Centre.

The research group assessed the risks of different climate change scenarios for 33 ‘priority places’ of terrestrial biodiversity, including climate-vulnerable ecoregions like the Miombo Woodlands, Southwest Australia, Amazon-Guianas, Coastal East Africa, Cerrado and African Rift Lakes, using a pre-existing biodiversity model of 80,000 species from five terrestrial taxa (plants, amphibians, reptiles, birds and mammals).

Although metastudies show that usually (global, universal) species extinction risk increases exponentially with warming, the Climatic Change authors find a linear response, from 25 percent local extinction risk under 2 degrees warming, to about 50 percent under a business as usual 4.5 degrees scenario.

Meanwhile biodiversity refugia within these priority places decrease considerably in size and show a sharper response to warming, with overall refugia size declining to 56 percent under 2 degrees warming, going down to just 18 percent remaining under the 4.5C scenario.

A climatic refugium is defined in this study as ‘an area where 75% of the total number of species presently found in a given taxon in a given Priority Place will still be found under a changed climate’. Graph shows average decrease in refugia size for various climate change scenarios, with and without adaptation.

Novel conservation strategies, focussed on helping species disperse, offsets some of the expected biodiversity loss, the study finds. When climate refugia would be connected through corridors, enabling species to migrate, the extinction risk decreases by 5 percent under the 2 degrees scenario, and by 18 percent under the 4.5 degrees scenario. Enabling autonomous adaptation by dispersal increases refugia size by 11 to 15 percent (respectively for 2 and 4.5 degrees scenario).

Take home message: the threat of climate change for terrestrial biodiversity is severe – even under the ‘relatively ambitious’ 2 degrees target 25 percent of priority biodiversity is at risk of local extinction, even without the additional stress of other major extinction drivers. Novel adaptation strategies can be used to support mitigation efforts, but not to replace them, as ambitious adaptation cannot compensate for lacking mitigation. From a conservation standpoint mitigation deserves utmost priority even beyond the three warming scenarios of this study, as the authors end with the following remark:

“The expectation is that further mitigation to limit global temperature rise to well below 2 or 1.5 °C as outlined in the Paris Agreement would further reduce risk of extirpation and increased area of refugia.”

Yes. 1.5 is better than 2. That’s why the world agreed on it, lest we forget.

© Rolf Schuttenhelm | www.bitsofscience.org