Time to integrate global climate change and biodiversity science-policy agendas

1. There is an increasing recognition that, although the climate change and biodiversity crises are fundamentally connected, they have been primarily addressed independently and a more integrated global approach is essential to tackle these two global challenges. 2. Nature-based Solutions (NbS) are hailed as a pathway for promoting synergies between the climate change and biodiversity agendas. There are, however, uncertainties and difficulties associated with the implementation of NbS, while the evidence regarding their benefits for biodiversity remains limited. 3. We identify five key research areas where incomplete or poor information hinders

Biodiversity is declining globally at unprecedented rates, eroding the very foundations of our economies, livelihoods, food security, health and quality of life world-wide (IPBES, 2019). At the same time, the overwhelming scientific consensus is that humanity is facing a climate emergency (Ripple et al., 2020), with anthropogenic greenhouse gas emissions altering climatic conditions, sea levels and the pH of surface ocean waters. Global strategies to halt these dual crises are often formulated separately within two international conventions (the United Nations Framework Convention on Climate Change (UNFCCC) and the Convention on Biological Diversity (CBD)), yet biodiversity loss and climate change are interdependent issues (Garcia et al., 2018;Pires et al., 2018).
Rapidly changing climatic conditions are threatening the longterm survival of many species (Urban, 2015); they have already led to widespread local extinctions (e.g. Albano et al., 2021) and, in some cases, contributed to the global extinction of species (Cahill et al., 2013). Up to 50% of species could lose most of their suitable climatic conditions by 2100 under the highest greenhouse gas emissions scenario (Warren et al., 2018), while the current global redistribution of biodiversity (Pecl et al., 2017) is expected to escalate. For example, by 2070, 35% of mammals and 29% of birds are projected to have over half of their climatic niche in countries in which they are not currently found (Titley et al., 2021). Climate change is also increasing the frequency and intensity of extreme climatic events (Cai et al., 2014), which are threatening the integrity of many ecosystems across the globe, including two of the world's most diverse ones (coral reefs and humid tropical forests; França et al., 2020). The loss of biodiversity is moreover deepening the climate crisis: reduced species abundance, local extinctions, as well as the rapid degradation and/or loss of ecosystems such as mangroves , tropical forests (Bonan, 2008), peatlands (Loisel et al., 2021) and seagrass (Waycott et al., 2009) are having a major impact on our planet's ability to store carbon, while reducing nature's and people's ability to adapt to and/or cope with changing climatic conditions. Given these linkages, it is not surprising that there is an increasing scientific and political recognition of the need for a more integrated global approach to tackle the climate and biodiversity crises (Pörtner et al., 2021;Turney et al., 2020). How to design and implement solutions that fall under a 'combined' approach are questions likely to be at the centre of the global environmental discussions during meetings of the Conference of the Parties (COP) for the UNFCCC (COP26) and the CBD (COP15). Here, we aim to review the current set of political and scientific propositions for jointly addressing the threats posed by the climate and biodiversity crises, highlighting options with the greatest potential for delivering biodiversity gains.
We then identify research priorities in applied ecology that must be addressed to improve the effectiveness of such options. Finally, we discuss potential systemic barriers to progress environmental efforts that fully integrate the climate and biodiversity agendas.

| INTEG R ATING THE B I OD IVER S IT Y AND CLIMATE CHANG E AG ENDA S: THE PROP OS ITI ON SO FAR
The idea that changes in the management of nature could help tackle the climate crisis has been promoted by the UNFCCC for over two decades; for example, the concept of Reducing Emissions from Nature-based Solutions are defined by the International Union for Conservation of Nature (IUCN) as 'actions to protect, sustainably manage, and restore natural or modified ecosystems, that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits'-a definition that clearly positions NbS as being consistent with long-standing natural resource management paradigms (see e.g. Holling & Meffe, 1996;Kellert et al., 2000). NbS have been endorsed in the IPBES Global Assessment (IPBES, 2019), the Climate Change and Land Report of the Intergovernmental Panel on Climate Change (IPCC, 2019) and the Global Adaptation Commission Report .
Although NbS have been defined as actions that have the potential to support multiple interlinked societal challenges (Figure 1), they have been globally hailed as a concept that promotes synergies between the climate change and biodiversity agendas . In comparison to greenhouse gas emissions and carbon stocks, biodiversity is however multifaceted, spatially variable and famously difficult to measure (Pereira et al., 2013). This has led to NbS being rarely differentiated according to their impact on biodiversity, and very little being known about the realised potential for these solutions to deliver positive outcomes for biodiversity (Acreman et al., 2021;Seddon et al., 2020).
NbS specifically addressing the climate change crisis have attracted considerable traction in both governmental and private sectors (Faivre et al., 2017;Seddon et al., 2021); these solutions support climate change mitigation, adaptation or both. Recently, the potential role of NbS for climate change mitigation has been in the limelight (e.g. Girardin et al., 2021), likely due to the difficulties associated with estimating adaptation potential, which is largely reliant on place-based qualitative information that shifts across different K E Y W O R D S ecosystem collapse, environmental legislation, Nature-based Solutions, protected areas, restoration, rewilding, wildlife management societal groups and over time (Morecroft et al., 2019). Acting as an umbrella term, NbS refer to actions that aim to capitalise on existing biodiversity, or to increase biodiversity, to tackle societal challenges.
As such, the setting up of new protected areas, as well as restoration and rewilding projects all have the potential to be NbS for addressing the climate change crisis (Eggermont et al., 2015). for 50% of the terrestrial realm to be conserved to reverse biodiversity loss, prevent CO 2 emissions from land conversion and enhance natural carbon removal. This follows on from calls by scholars over the past decade for half of the Earth to be protected (Noss et al., 2012;Wilson, 2016).

| Protected areas
Protected areas are a key strategy for conserving nature and halting the loss of biodiversity and can mitigate and promote adaptation to climate change (Roberts et al., 2017): a recent study spanning ca. 5.2 million km 2 across 63 countries, for example, showed how protected areas reduced deforestation rates by 41% (Wolf et al., 2021).
Increasing the proportion of landscapes and seascapes being protected, however, comes with several societal, ethical, economic and philosophical challenges (Barnes et al., 2018). Their static boundaries may reduce their potential for protecting biodiversity under climate change (Elsen et al., 2020). As systems of protected areas expand globally, there is a risk that new protected areas will be biased towards places that are remote or unpromising for extractive activities (Devillers et al., 2015). Biodiversity protection in protected areas is not guaranteed: protected areas effectiveness can vary substantially, being likely to be reduced in situations where budgets are limited and governance lacks transparency and fairness (Dawson et al., 2018;Geldmann et al., 2019;Gill et al., 2017).
Protected areas can sometimes negatively impact poor or marginalised people in low-and middle-income countries West et al., 2006), with social tensions and conflicts being on the rise within and around conservation areas in these regions (Duffy, 2014;Lunstrum & Ybarra, 2018). 'Ambitious' targets to protect 30% or 50% of the lands and seas under national jurisdiction may also be insufficient to retain significant portions of the global biodiversity: in the Amazon region, even a 50% target is unlikely to be enough to avoid entire ecosystems being pushed over tipping points (Nobre et al., 2016), pointing out the need for multiple and complementary strategies. Furthermore, retaining existing levels of biodiversity in protected areas is not enough to mitigate and adapt to the climate breakdown we are facing: global carbon sequestration F I G U R E 1 Examples of Nature-based Solutions (NbS) to address the climate crisis. NbS are defined by the International Union for Conservation of Nature (IUCN) as 'actions to protect, sustainably manage, and restore natural or modified ecosystems, that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits'. Current societal challenges include climate change, water security, human health, disaster reduction risk and food security. Examples of NbS are given for each societal challenge. By definition, all NbS should provide biodiversity benefits; only NbS to address the climate change crisis are expected to help reduce greenhouse gas concentrations (GHG) in the atmosphere and/or support climate change adaptation; NbS aimed at addressing other societal challenges may or may not do so

| Restoration
Large-scale ecological restoration projects have gained significant traction in recent years, with research suggesting that the restora- Different projects may impact different dimensions of biodiversity, raising cost-effectiveness and prioritisation issues (e.g. how do you compare a restoration project that improves one dimension of biodiversity over a project that improves another?). Our understanding of how multiple stressors interact to shape biodiversity is limited (Cabral et al., 2019;Schulte to Bühne et al., 2021), and establishing targets for ecosystem restoration remains a significant challenge for most ecosystems (Perring et al., 2015;Pettorelli, Barlow, et al., 2018). Decisions on which site(s) to restore can profoundly affect outcomes and costs and may knowingly or unknowingly favour climate change mitigation/adaptation over biodiversity (or vice and versa; Strassburg et al., 2020). In addition, local increases in biodiversity do not automatically imply global biodiversity benefits, as, for example, restoration may simply increase the distribution of widespread generalist species (e.g. Lennox et al., 2018) not threatened with extinction.

| E VIDEN CE G APS AND RE S E ARCH NEEDS
An important step for nature and people is to significantly improve the integration of the biodiversity and climate change agendas so that win-win situations can be more easily identified; one cannot simply continue to independently manage landscapes, freshwater wetlands and seascapes for biodiversity conservation or climate change mitigation/adaptation, hoping that one will automatically benefit the other. Here, we identify five research areas in applied ecology where incomplete or poor information hinders the development of biodiversity and climate solutions.

Agreeing on a framework to assess how climate change mitigation
and adaptation approaches benefit biodiversity conservation. Our understanding of the short-term and long-term biodiversity benefits and disbenefits associated with the deployment of NbS remains limited. To address this knowledge gap, a framework for comparing biodiversity benefits across climate change mitigation and adaptation projects is required .
Research over the past decade has highlighted the potential importance of functional diversity for ecosystem functioning and resilience (Duncan et al., 2015); similarly, much work has been done to quantify ecosystem collapse risk in a standardised manner (Bland et al., 2017). Admittedly, there remain significant challenges associated with the identification of appropriate metrics of functional diversity (Malaterre et al., 2019) and the practical implementation of ecosystem risk assessments (e.g. Bland et al., 2018). Yet these developments could represent a promising route for identifying biodiversity metrics that can be compared across sites and over time. to identify areas where the restoration of existing ecosystems is likely to fail, but also to identify situations where restoration is the only option to avoid passing tipping points.

Predicting the impacts of climate change on NbS effectiveness.
Changes in climatic conditions are not only a threat to biodiversity but may also jeopardise the effectiveness of management actions aimed at retaining and improving biodiversity. This issue has been highlighted for some time when it comes to factoring in climate change in protected area designation (see e.g. Hannah et al. 2007) and the incorporation of climate change adaptation into protected area planning (see e.g. Wilson et al., 2020). However, our understanding of how climate change may affect the ecological and socio-economic effectiveness of other NbS is much less detailed . Research suggests that the success and pace of restorative actions will be determined partly by local climate trajectories, with, for example, forest regrowth expected to be slower in hotter and drier climates. Similarly, precipitation anomalies are expected to alter greenhouse gas emissions from wetlands, with potential impacts on carbon benefits associated with wetland creation or restoration (Nisbet et al., 2016 (Bellwood et al., 2019). Developing the knowledge and evidence needed to expand activities from local actions to larger scale responses in a manner that effectively and appropriately address the scale of drivers of declines is an important priority for turning the tide on biodiversity loss and climate change. In many situations, this will require improving our understanding of the co-dependencies between ecosystems and adopting approaches that explicitly acknowledge the telecoupled nature of our world.

5.
Risk assessment. Actions labelled as NbS do not automatically deliver biodiversity benefits, and, in some instances, their poor design and implementation can have catastrophic direct and indirect consequences for biodiversity and local communities (e.g. Townsend et al., 2020). Risks posed by NbS have been highlighted on an ad hoc basis, but never presented in a comprehensive and systematic manner. We need research that facilitates the emergence of improved risk assessment processes associated with NbS implementation, through, for example, the clear identification of direct and indirect ecological and social risks posed by these solutions to other aspects of the land, wetland or seascape, or the external risks that could undermine the permanence of NbS. The quantification of these risks will require the collection of information on the local socio-ecological context .
Adaptive management approaches (Walters, 1986)   Facility (GEF) is the major financial entity that receives and distributes funding to assist countries in meeting the objectives set by UN conventions; however, each convention is allocated a specific budget, and GEF is accountable to each COP, which decides on its program priorities ( Figure 2). Furthermore, GEF funding in priority areas such as the tropics seems to be related to governance and political considerations rather than biodiversity (Reed et al., 2020). For the moment, there is thus no global, legally binding, platform dedicated to advancing an environmental agenda that equally supports biodiversity conservation and climate change mitigation and adaptation;

| RE S HAPING THE CURRENT P OLI C Y CONTE X T
nor is there a nominated scientific platform dedicated to assessing the evidence and issues around NbS and their implementation, or a clear, major funding mechanism that univocally enables countries to choose to invest in projects that equally support biodiversity con- Finally, there is a need for an overhaul of current environmental legislation to better support biodiversity conservation in times of rapid changes in climatic conditions. In many countries, legislative frameworks relevant to environmental management indeed focus on in situ conservation and the preservation of historical conditions, which have favoured the implementation of conservation projects aiming to restore previously observed benchmarks. However, global environmental change is driving some species far beyond their traditional ranges and some ecosystems far beyond their limits: in such situations, restoring historical conditions may not be a realistic objective, and the facilitation of the emergence of novel ecosystems may prove a more sensible and cost-effective alternative to jointly address the biodiversity and climate change crises. Policy based on a 'compositionalist' paradigm, predicated on the preservation of particular species assemblages and habitat types, thus need to evolve to also consider the benefits of a 'functionalist' paradigm, where the emergence and protection of resilient, resistant ecosystems is also valued (Pettorelli, Barlow, et al., 2018).

| CON CLUS IONS
Climate change can interact with other pressures to reduce biodiversity (see e.g. Cabral et al., 2019;Schulte to Bühne et al., 2021): a cohesive, multi-pronged approach to conserving biodiversity is therefore necessary. NbS can represent an additional, complementary, valuable way to address societal challenges, but broad joinedup thinking among scientific and practitioner communities involved in natural resource management is required to establish where and how NbS potential is best realised. Without it, some societal challenges may be inadvertently prioritised over others; opportunities to jointly and efficiently address these challenges using NbS may be missed; and the biodiversity benefits promised by NbS may seldom materialise. The current institutional set up is, however, not favouring integrated thinking, thereby hampering the rapid identification, prioritisation and implementation of solutions that deliver benefits on multiple fronts without biodiversity costs; it needs reforming.
The first priority to tackle the current global environmental crisis is to transition economies around the world to a sustainable, lowcarbon future. The upcoming COPs present a clear policy window for addressing this priority, but also for addressing many of the issues and challenges detailed in this contribution. To progress environmental efforts that fully integrate the climate and biodiversity agendas, we argue this window should be used to (a) address the substantial and chronic underfunding of global biodiversity conservation, (b) remove financial incentives that negatively impact biodiversity and/or climate change, (c) develop higher levels of integration between the biodiversity and climate change agendas, (d) agree on a monitoring framework that enables the standardised quantification and comparison of biodiversity gains associated with NbS across ecosystems and over time and (e) rethink environmental legislation to better support biodiversity conservation in times of rapid climatic change.

ACK N OWLED G EM ENTS
The authors thank two anonymous reviewers and the Editors for their comments on earlier versions of our manuscript. N.P. is funded by Research England and H.J.K. is funded by the Bertarelli Foundation.

AUTH O R S ' CO NTR I B UTI O N S
N.P. led the writing of the manuscript; all authors contributed critically to the drafts and gave final approval for publication.

DATA AVA I L A B I L I T Y S TAT E M E N T
This article does not contain data.