Opinion
Using Climatic Credits to Pay the Climatic Debt

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Highlights

  • Many taxa respond relatively slowly to rising global temperatures, resulting in a disequilibrium between observed and expected biodiversity known as the ‘climatic debt’.

  • Recent empirical work has demonstrated how local-scale climate adaptation options can be conceptualised as climatic credits that pay part of the debt.

  • Other adaptation options focus on adjusting the rate at which debt is repaid (allowing equilibrium to be restored), attempting to make ecosystems more or less responsive to climatic change.

  • A climatic budget can be assembled by uniting climatic debt with options to supply credit and alter the repayment rate, providing a simple way to capture transient dynamics and communicate different management scenarios.

Many organisms are accumulating climatic debt as they respond more slowly than expected to rising global temperatures, leading to disequilibrium of species diversity with contemporary climate. The resulting transient dynamics are complex and may cause overoptimistic biodiversity assessments. We propose a simple budget framework to integrate climatic debt with two classes of intervention: (i) climatic credits that pay some of the debt, reducing the overall biological change required to reach a new equilibrium; and (ii) options to adjust the debt repayment rate, either making a system more responsive by increasing the rate or temporarily reducing the rate to buy more time for local adaptation and credit implementation. We illustrate how this budget can be created and highlight limitations and challenges.

Section snippets

Climatic Debt and Credit and the Value of Budgeting

In response to climate change, organisms must migrate, adapt via phenotypic or evolutionary mechanisms, or face extinction [1]. Across many parts of the world and a range of taxa, changes in species’ distributions following recent decades of climate change have been smaller than expected. The difference between observed and expected changes is described as climatic debt (see Glossary) (Figure 1), which is ‘repaid’ when biodiversity reaches equilibrium with the new climate. The prime focus of

Estimating Climatic Debts and Credits

Estimation of climatic debt begins with the quantification of the relationship between community structure and temperature, so that temperature can be inferred from the observed species composition (Figure 1, Figure 2). The most common approach is to calculate the community temperature index (CTI) from the species temperature indices (STIs) of the species present (e.g., [3,6,7,23,24]). To calculate the current climatic debt, the inferred temperature (e.g., CTI) is subtracted from the observed

Climate Accounting

The magnitude of ongoing climate change has precipitated a paradigm shift from trying to conserve current or historical conditions to managing ecosystem change [45,46] (Box 1). Climatic debts are likely to grow until a system converges to a new equilibrium state, perhaps involving catastrophic changes such as ecosystem collapse. Climatic credits could permanently offset portions of the debt by reducing the extent to which the equilibrium point moves, minimising biological change and risks of

Concluding Remarks

Transient dynamics, such as climatic debt, are challenging to quantify and understand [21]. We propose a climatic credit–debt framework that builds on established concepts to assess impacts of warming and provide intuitive tools to evaluate adaptation options. Although this framework addresses the symptoms rather than the causes of climate warming, credits have the potential to reduce the magnitude of biodiversity changes at local or regional scales and increase the scope for adaptation.

Acknowledgments

Our thanks to Pieter De Frenne, two anonymous referees, and the editor for helpful comments on a previous version.

Glossary

Climatic credit
a change in the environment that offsets part or all of a climatic debt and can be quantified in the same units as the debt (e.g., °C or mm year−1). Typically relates to management interventions that could reduce the debt.
Climatic debt
usually defined as the difference between the observed environmental temperature and the temperature at which the observed community would be at equilibrium with the environment (see ‘inferred temperature’), in degrees Celsius; equally applicable to

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      Although land use pattern is an important factor affecting species richness, other factors, such as climate, cannot be ignored. Many studies on climate extinction debt have confirmed its presence in different biological groups and geographical regions (Devictor et al., 2012; Garcia et al., 2011; Vaughan and Gotelli, 2021). In this study, only land use pattern was selected as the basis on which to demonstrate the existence of extinction debt, without considering the role of other factors.

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    @

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