Stéphane Hallegatte, Katharine J. Mach and colleagues urge researchers to gear their studies, and the way they present their results, to the needs of policymakers.
With the ink just dry on the Paris climate agreement, policymakers want to know how they can act most effectively. Ambition is high: the long-term goal is to keep the average warming of the planet to well below 2 °C, and even to 1.5 °C. …
No single approach will work for all. The risks and impacts of climate change differ by place and time. Local values and contexts matter. Small islands are vulnerable to sea-level rise, for example, and fossil-fuel exporters will lose profits from the transition to low-carbon energy. We must consider value judgements, such as the relative importance of economic damage versus biodiversity loss, as well as inequality and fairness.
And the relevant climate and social sciences are themselves diverse, from studies of the physics of storm formation to investigations of the role of heritage in cultural identity. The challenge for those who assess such scientific knowledge, such as the Intergovernmental Panel on Climate Change (IPCC), is to summarize results in ways that are true to the original research, explicit about the values and judgements in the analysis, and digestible by and useful to policymakers and the public.…..In the IPCC’s sixth cycle of assessment, the climate-science community needs to supply the right sorts of information to help decision-makers to construct policies from myriad mitigation and adaptation options.
Producing this information will require more multidisciplinary research, updated strategies for communicating uncertainty and studies of a broader range of climate and risk projections that include the impacts of policy responses.
Here, we set out four steps to putting policy relevance at the core of both research and assessment.
Integrate disciplines from the start. …The range of risks summarized in the IPCC’s 2014 Synthesis Report was limited by the research available. For example, the assessment highlighted increasing risks of climate extremes but said little about how climatic hazards interact with societal vulnerability. Sparse information on how risks evolve at specific warming levels resulted in the reporting of broad, qualitative levels of risk — for example, ‘undetectable’ to ‘very high’, as judged by experts. But comparison across risks was difficult.
Climate scientists need to close these gaps by scrutinizing the feedbacks between development pathways, climate change and its impacts and risks, and policies and responses.
..But covering many climatic and societal futures, globally to locally, is a monumental task. Projects that compare assumptions and results between different models are a start, but need to include more evidence and expert judgements across disciplines.
….… Research and assessments must be designed to solicit and answer questions crucial to decision-making. For example, how do risks and requirements compare for a climate goal at 1.5 °C, 2 °C or more? How can we avoid locking in to carbon-intensive development pathways and keep open options for rapid decarbonization? How can the effectiveness of adaptation actions be ensured? And how can emissions be reduced without slowing the pace of poverty reduction?
Explore multiple dimensions. More research is needed on regional challenges and opportunities that go beyond the use of a single metric — global mean warming — as a proxy for climate change and its impacts4. For example, ocean acidification and sea-level rise are not linearly related to peak temperature, and the risks that they create require more detailed investigation. And reducing emissions of short-lived climate pollutants such as soot and tropospheric ozone precursors might not change peak warming, but would slow the rate of warming globally5; this would allow more time for ecosystems and societies to adapt, as well as provide local health benefits….
Consider uncertainty. Decision-makers need to appreciate a wide range of possible outcomes, including uncertainty in the consequences of global climate policies. Four aspects of uncertainty must be evaluated and communicated: probability ranges that can be narrowed with future research; unknowns that are linked to a deep lack of knowledge; uncertain reactions that depend on societal decisions and geopolitical events; and other areas of uncertainty that reflect random or chaotic features of the climate system…..Researchers need to assess how different sources of uncertainty affect decision-making, especially in worst-case scenarios. What should we do if temperatures start to rise more rapidly or the impacts are more dangerous than we expect? How can we detect such departures and how should we alter course? Climate policies might prove to be harmful and need revising; technology costs might not fall; carbon capture and sequestration might not work….
Inform holistic solutions.
A fuller evaluation of risks and options is needed that includes those created by climate-change responses for other policy goals. For example, the assessment of climate-change risks at 1.5 °C in the IPCC’s 2014 Synthesis Report foresaw impacts on coral reefs, Arctic sea ice, water availability, food production and sea-level rise. But the bigger picture should also include issues related to climate mitigation, such as economic duress, land- and water-use trade-offs and calls for high-risk geoengineering methods.
The impacts of climate changes and climate policies will interact if, for instance, a slower reduction in poverty owing to higher energy costs increases vulnerability. Synergies and trade-offs must be evaluated, including risks arising from mitigation actions — not just inactions. Social and climate scientists must investigate the political and socio-economic impacts of climate policies (short- as well as long-term), the distribution of those who benefit and those who are adversely affected, and the influences of powerful interest groups.
It is important to explore how climate responses can advance the Sustainable Development Goals and especially poverty reduction10. For instance, improving access to clean energy and decreasing the economic impacts of extreme weather events can accelerate development progress while protecting poorer nations against climate change. Climate action and protection will never be the sole priorities for decision-makers, but they will be integral to the full policy landscape. Research and assessment can create a powerful foundation for these interactions, and empower decisions in the years ahead.