Global change refugia could shelter species from multiple threats

Both pathways towards integrating global change factors with climate refugia require maps of global change variables at sufficiently high resolution. Such global maps at 100-km² grid level or coarser resolution already exist, for example, for light pollution, nitrogen deposition and land use⁶. Progress is being made towards improving spatial resolution of existing maps and mapping an increasing number of global change factors, or at least suitable proxies (for example, transport infrastructure as a proxy for invasive species potential⁶).

The next step in evaluating the viability of climate change refugia or designating global change refugia is to identify areas that are exposed to a relatively low number of global change factors. Normalized ranking⁶ or threshold-based approaches⁷ can be used to establish which factors, including climate variables, exceed a certain threshold level to be considered a likely threat. In some cases, direct evidence from dose–response studies could inform the designation of threat levels, but these response–surface studies are generally rare in ecology. The number of factors that exceed designated thresholds (hereafter, ‘factor number’) can then be compared across locations; for example, a site with a factor number of two has relatively less exposure to global change factors as compared to a site with a factor number of six.

Considerable effort has already gone into identifying areas buffered from critical climate threats. Whether or not these climate refugia are viable under other forms of global change can be assessed by evaluating the overlap with the count of global change factors (Fig. 1, left).

There are two extreme outcomes: the ideal scenario and the worst-case scenario. In the ideal scenario (Fig. 1a), climate refugia could have a low factor number. Such areas should be considered priority conservation areas; substantial effort should be made to keep these exceptionally valuable areas as free from additional pressures as possible. In the worst-case scenario, climate change refugia could have a high factor number. Such areas might need to be deprioritized for further conservation action, because they are unlikely to protect species and ecosystems from the range of global change effects beyond climate.

Even if conservation decision-makers prefer to focus on protecting existing climate refugia regardless of other global change threats, perhaps this insight about other global change factors can at least serve to motivate careful monitoring of the development of these other threats and to implement management interventions to counter effects of threats beyond climate, to the extent that this is possible.

I now argue that global change refugia could be identified de novo, in locations that have not previously been designated as climate refugia (Fig. 1b). Pristine and promising locations for protection might exist that are not currently identified as climate change refugia.

Designating global change refugia on the basis of the factor count described here is preferable because it would shelter species and ecosystems from the whole palette of anthropogenic stressors. However, this approach is the most data-intensive because, ideally, data for all global change factors should be mapped out to identify contiguous areas with the lowest factor number. Although the concept is relatively new and has not yet been attempted at the global scale, an assessment of multiple stressors in southern California, USA, identified ‘super-refugia’ as sites with relatively few extremely warm summers, fires, altered river channels and human-affected trails, and argued that these sites should be priority locations for protected area expansion⁸.

A less data-intensive option would be to identify specialized global change refugia, or locations with low exposure to a particular global change factor. One example is the designation of ‘dark sky places’, areas that have been spared the influence of artificial light at night⁹. Similar areas could be established as microplastic refugia, antibiotic resistance gene refugia or chemical pollution refugia, depending on the particular conservation goal.

Given the imperative under the Kunming-Montreal Global Biodiversity Framework to protect 30% of land area by 2030, ensuring that protected land is resilient to climate change and other global change factors is critically important. Identifying and protecting global change refugia would be a powerful step to help to safeguard biodiversity and ecosystems, and to prevent losses of species due to the full range of global change factors beyond climate change. Climate change refugia have occasionally been considered in conservation planning efforts under the 30×30 framework¹⁰ and preliminary examples suggest that including multiple factors in such prioritizations is possible⁸. Global change refugia should become part of the conversation in the Convention on Biological Diversity, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, and the potential new Intergovernmental Science-Policy panel on chemicals, waste and pollution prevention, which could be established by the UN Environment Programme in 2025.

Making progress on the establishment of global change refugia as a conservation tool requires attention to several fundamental knowledge gaps. Further research is needed to identify what number of global change factors is critical for species and ecosystems, and whether all factors should be weighted equally or whether some should receive higher weights in calculations of cumulative threats. Finally, whether a site is exposed to two divergent factors (for example, invasive species and synthetic organic chemicals) versus two highly similar factors (for example, two different heavy metals) might need to be considered beyond simple factor counts.

In addition to informing area-based conservation, global change refugia could inform restoration priorities, and contribute to progress on goals related to the UN Decade on Ecosystem Restoration. Biological material (for example, seeds or soil inoculum) from global change refugia could be useful for initiating restoration efforts elsewhere, where certain species have been lost. Likewise, global change refugia could be considered as reference sites to guide the trajectory of restoration efforts. Safeguarding such sites by designating them as global change refugia would ensure their continued conservation and restoration value in the future.