Measuring the success of climate change adaptation and mitigation in terrestrial ecosystems

Measuring mitigation and adaptation As more and more carbon dioxide is emitted into the atmosphere, humans and the natural world are beset by the damaging consequences of a rapidly changing climate. Natural and seminatural ecosystems are likely to be the best starting place for immediate adaptation and mitigation solutions. First, though, many natural environments need restoration to maximize their own resilience to climate change. In reviewing our options, Morecroft et al. point out that we can directly observe the success of mitigation strategies by quantifying atmospheric carbon dioxide. Successful adaptation is more challenging because it involves a range of social and biodiversity measures. However, we could make matters worse if we do not constantly monitor the effects of the interventions we devise and react flexibly as changing conditions unfold. Science, this issue p. eaaw9256 BACKGROUND Responding effectively to climate change requires urgent action to halt net greenhouse gas (GHG) emissions and to adapt to changes that cannot be prevented. The Paris Agreement of the United Nations Framework Convention on Climate Change has committed governments to the following: keeping global temperature rise below 2°C, pursuing efforts to limit it to 1.5°C, and adapting to reduce the vulnerability of people and ecosystems to the damaging consequences of a changing climate. When protected, restored, or managed appropriately, natural and seminatural ecosystems make critical contributions to climate change mitigation and to helping people adapt to climate change. Ecosystems themselves are vulnerable to climate change, but by restoring natural ecosystem processes, resilience can be built, and a wide range of adaptation strategies can ameliorate the impacts. Both synergies and conflicts between different objectives can arise, and it is essential to have clarity about what constitutes success across the range of adaptation and mitigation outcomes and to track progress. The success of ecosystem-based mitigation can be measured in terms of falling net emissions and stabilization of atmospheric CO2 concentration. Although this is conceptually straightforward, it can be difficult to measure ecosystem fluxes accurately. Adaptation is more complicated because it encompasses a wide range of objectives, with respect to people and biodiversity, including both reducing vulnerability and managing unavoidable change. ADVANCES Many studies have investigated how nature-based solutions can contribute to climate change mitigation and adaptation. The evidence is now clear that protecting and restoring ecosystems is essential to holding global temperature rise to between 1.5° and 2°C. The value of different interventions for reducing GHG emissions and promoting carbon sequestration can be quantified with varying degrees of confidence. The evidence for the effectiveness, opportunities, and limitations of ecosystem-based adaptation in enabling people to cope with climate change is also growing, and these approaches are starting to be implemented. Adaptation to reduce the vulnerability of biodiversity and ecosystems themselves to climate change has been discussed over many years but proposed measures remain largely untested. This is starting to change, with recent studies gathering empirical evidence of the factors that influence the vulnerability of ecosystems and biodiversity. Nevertheless, evaluation and reporting of adaptation is currently focused on planning and implementation of actions rather than on assessment of whether these programs have successfully reduced vulnerability. OUTLOOK A picture is emerging of what successful adaptation and mitigation in terrestrial ecosystems looks like when it is built around protecting and restoring natural ecosystem processes. To realize the potential of ecosystems to ameliorate climate change requires integrated actions that are consistent with wider biodiversity and sustainable development goals. High-carbon ecosystems, particularly forests and peatlands, are essential, but other ecosystems, such as savannas, are also important elements of wider nature-based solutions and should be protected and restored. Pursuing mitigation objectives alone risks perverse outcomes that increase rather than reduce vulnerability. Further work is required to test the effectiveness of specific ecosystem-based mitigation and adaptation measures and what works best to support biodiversity in a changing climate. More-robust monitoring and evaluation are needed to drive progress. Measuring adaptation for biodiversity is particularly challenging, and monitoring and management will need to develop together as we learn from experience. The role of natural and seminatural ecosystems in adaptation to and mitigation of climate change. The flow diagram shows the relationships between adaptation for biodiversity, ecosystem-based adaptation for people, and ecosystem-based mitigation. Negative impacts of climate change are shown in dark gray, and positive responses are shown in green. Successful ecosystem response to climate change depends on an integrated approach to ensure that synergistic effects are maximized and harms are avoided. Natural and seminatural ecosystems must be at the forefront of efforts to mitigate and adapt to climate change. In the urgency of current circumstances, ecosystem restoration represents a range of available, efficient, and effective solutions to cut net greenhouse gas emissions and adapt to climate change. Although mitigation success can be measured by monitoring changing fluxes of greenhouse gases, adaptation is more complicated to measure, and reductions in a wide range of risks for biodiversity and people must be evaluated. Progress has been made in the monitoring and evaluation of adaptation and mitigation measures, but more emphasis on testing the effectiveness of proposed strategies is necessary. It is essential to take an integrated view of mitigation, adaptation, biodiversity, and the needs of people, to realize potential synergies and avoid conflict between different objectives.