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Many national and corporate climate targets seek to limit global warming to 1.5°C. Yet, global warming continues to increase. It makes it almost inevitable that 1.5°C of global warming will be exceeded. Scientists, policymakers, and society will increasingly engage in a new discussion about what it now means to “keep 1.5°C alive”: is it possible to exceed 1.5°C but to return to or below this level within a given timeframe? What would be needed to at least keep that option on the table, and what would be its consequences?
A first comprehensive conceptual review explores the implications of such “overshoot” pathways. Authored by an international team of scientists and design experts involved in assessments by the Intergovernmental Panel on Climate Change, the review considers climate-related damages and risks, adaptation and vulnerability, global emission requirements, and issues arising for global and national climate policy. The review sets out evidence and knowledge gaps that illustrate the choices and challenges that decision-makers are now facing.
A key conclusion is that accelerated emission reductions in the near term are critical to limit peak warming and to keep the option of a return to 1.5°C on the table, but that effective and equitable adaptation will remain critical to limit damages along the way. Many more decisions and choices will determine what risks such a return would avoid, what damages would nonetheless be irreversible, and the implications for equity and climate justice.
CMCC is introducing a digital information platform that will grow to inform these discussions.
Understanding “overshoot” and why it matters
Scientific evidence is clear that climate-related risks increase with every fraction of global warming. For this reason, many national targets and political declarations have set a goal of limiting warming to 1.5°C. Yet, as global warming continues to increase, exceeding 1.5°C looks to be increasingly inevitable.
Recent assessments by the IPCC indicate that global temperatures will reach 1.5°C before the mid-2030s. Observations show that 2024 was already the first time warming in a single year exceeded this level.
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This raises the question: once we have exceeded global warming of 1.5°C, do we need to give up on this goal, or is it possible to at least bring global warming back to or below 1.5°C before the end of the century? While exceeding 1.5°C will lead to increased climate risks, could bringing temperatures back down also reverse some of those risks?
This conceptual review focuses on the ‘overshoot’: global warming trajectories that exceed a specified warming limit for some time, but return to or below that limit within a specified time period.
Note to journalists: this meaning of overshoot (exceed-and-decline) in the scientific literature is different from its common English meaning, where overshoot simply means that a given limit has been exceeded, without any plans or promises to get back to the limit at a later point.
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A framework for overshoot: Risks, adaptation, and the path back to 1.5°C
An international team of experts has published the paper “Overshoot: a conceptual review of exceeding and returning to global warming of 1.5°C?”. The paper provides a clear framework for understanding climate risks in the context of overshoot pathways. The paper examines how risks evolve when global temperatures exceed 1.5°C, explores adaptation options, and assesses their feasibility from a geophysical and Earth system response perspective. It also highlights key barriers, challenges, and knowledge gaps that need urgent attention.
The study applies this framework to risks aggregated according to the IPCC’s “reasons for concern”, which include: irreversible losses to ecosystems and cultural heritage, increasing extreme weather events, shifting regional vulnerabilities that could worsen global inequalities, complex global-scale impacts, and the risk of triggering irreversible tipping points like ice sheet collapse or Amazon forest dieback.
A key insight is that a world that exceeds 1.5°C even only temporarily will be a more damaged world than if we had avoided exceeding 1.5°C – but bringing warming back to or below 1.5°C would generally result in lower risks than if warming stabilised and remained permanently above 1.5°C.
To reverse global warming after overshoot, climate policy could pursue different strategies, described in the paper by three illustrative and complementary strategies: further scaling up carbon dioxide removal (CDR), further reducing residual CO2 emissions, and further reducing short-lived climate forcers especially methane. To achieve a reduction in global temperature, these actions would need to go beyond what is currently envisaged in most national climate targets.
The feasibility of returning to 1.5°C depends on how high peak warming reaches – lower peaking reduces environmental, technological, and economic barriers to recovery. Accelerating near-term actions to reduce emissions is shown to be a key prerequisite to keep a return to 1.5°C on the table, at least in principle.
An international, multidisciplinary team of renowned scientists and experts
The team behind this research is composed of high-profile experts from top institutions around the world. Several authors served or are serving as vice-chairs of one of the IPCC’s Working Groups, while others served as authors of a range of IPCC reports. CMCC’s Anna Pirani, one of the paper’s authors, also has an extensive background in the IPCC, including being the Head of the Working Group I Technical Support Unit of AR6 and now the alternate IPCC Focal Point for Italy.
The team includes contributors from prestigious institutions such as CICERO in Norway, the German Institute for International and Security Affairs, the Met Office in the UK, the University of Bristol, the University of Fiji, the Institute for Small Islands, the Alfred Wegener Institute for Polar and Marine Research, the Mountain Research Initiative, the University of Bern, the Global Systems Institute at the University of Exeter, and ETH Zurich.
The paper’s graphical material was co-designed with the team of authors, led by Angela Morelli and Tom Gabriel Johansen of Info Design Lab.
A new platform for science, policy, and public engagement
The CMCC Foundation is proud to launch Overshoot: what does it mean to exceed and return to 1.5 ºC?, a digital platform designed to provide accessible, science-based insight on the concept of overshooting 1.5°C global warming and its implications for climate risks, adaptation, and mitigation. The platform leverages data visualization and storytelling to bridge the gap between scientific research, public awareness, and policy action.
The Overshoot platform is a living environment that provides a series of resources to navigate a complex topic destined to characterize the climate debate of the future, intertwining scientific, political, environmental, social, and economic implications, enabling policymakers, researchers, and the general public to grasp the complexities of overshoot scenarios and their implications.
Looking ahead
The launch of Overshoot aligns with CMCC’s mission to advance climate science for policy and society. As discussions on overshoot evolve, the platform will continue to serve as a living resource, incorporating new research, policy developments, and user engagement features.
The overshoot journey is not a straightforward process but a complex path shaped by multiple competing motivations and pressures. Decision-makers will need to navigate a variety of competing drivers, trade-offs, and synergies when considering whether and how quickly to reduce global temperatures back below 1.5°C after exceeding that threshold.
The journey along an overshoot pathway will require simultaneous, integrated decisions on adaptation, mitigation, and resilience, all while accounting for differing preferences, capacities, and responsibilities for action.
For more information, visit Overshoot: what does it mean to exceed and return to 1.5 ºC?
Author information
Andy Reisinger, Institute for Climate, Energy and Disaster Solutions (ICEDS), Australian National University, Acton, Canberra ACT, Australia
Jan S. Fuglestvedt, CICERO Center for International Climate Research, Oslo, Norway
Anna Pirani, Euro-Mediterranean Center on Climate Change (CMCC Foundation), Italy
Oliver Geden, German Institute for International and Security Affairs, Berlin, Germany
Chris D. Jones, Met Office Hadley Centre, Exeter, United Kingdom, and School of Geographical Sciences, University of Bristol, Bristol, United Kingdom
Shobha Maharaj, Ecological and Climate Crises Legal Institute (ECCLI), University of Fiji, Saweni, Lautoka, Fiji, and Institute for Small Islands, Port of Spain, Trinidad and Tobago
Elvira S. Poloczanska, Integrative Ecophysiology, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
Angela Morelli, InfoDesignLab, Oslo, Norway
Tom Gabriel Johansen, InfoDesignLab, Oslo, Norway
Carolina Adler, Mountain Research Initiative, c/o Centre for Development and Environment (CDE), University of Bern, Bern, Switzerland
Richard A. Betts, Met Office Hadley Centre, Exeter, United Kingdom, and Global Systems Institute, Streatham Campus, University of Exeter, Exeter, United Kingdom
Sonia I. Seneviratne, Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland
About CMCC
The Euro-Mediterranean Center on Climate Change (CMCC) is a leading research institution dedicated to climate science, providing cutting-edge insights and innovative solutions for climate adaptation and mitigation strategies. CMCC plays a pivotal role in global climate research, working closely with international partners to advance climate modeling, forecasting, and policy recommendations.
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