Climate overshoot implications for local adaptation planning

As global warming increases, the topic of overshoot, understood as the temporary exceedance of the 1.5°C limit of the Paris Agreement, is gaining prominence both in scientific and political spheres. However, overshoot and its implications for adaptation in the short – and long-term remain unexplored. In this Perspective, we reflect on the current use of global climate scenarios and local impact projections in science-based adaptation planning. The risks arising from overshoot scenarios in relation to the transgression of limits to adaptation and impact irreversibility are highlighted. We find that the prospects of potential long-term impact reversibility may have limited relevance in most adaptation decision-making contexts, indicating that it might be peak warming, rather than a long-term outcome, that determines adaptation needs and costs. While overshoot may not be relevant for short-term planning, it should be considered for long-term plans and policies, for example for infrastructure-based measures and for irreversible impacts such as sea-level rise. Key insights from adaptation practitioners in four diverse urban vulnerability contexts (Bodø, Lisbon, Nassau, Islamabad) are presented on how these risks are perceived and integrated (or not) into local planning and policy-making. We find that current adaptation planning must be extensively evaluated against a wider set of future global climate outcomes to incorporate risks of transgression of local limits to adaptation and overshoot. To this end, data gaps on adaptation limits and impact reversibility need to be filled and capacity building needs on climate scenarios, overshoot and related concepts for local adaptation practitioners should be addressed.The topic of overshoot has yet to become well-established and widely considered by the adaptation community.Overshoot scenarios unfold on long time horizons making them most relevant for long-term adaptation planning, such as infrastructure-based measures.A strengthened science-policy interface and capacity-building at the local level are needed to support the design of adaptation plans that remain effective in the long-term.Limits to adaptation and impact reversibility resulting from overshoot must be further researched to provide essential science-based inputs in forward-looking adaptation plans.Flexible designs of adaptation measures can be considered to allow the adjustment of the level of risk reduction/protection provided by the measures over time.