1240. Discussion on overshoot

Many countries and companies have climate goals aimed at limiting global warming to 1.5°C, in line with the Paris Agreement targets. However, it is considered almost inevitable that global warming will exceed 1.5°C, as global warming is still progressing and global emissions have not yet decreased. It is necessary to consider the impact of "overshoot", i.e., a trajectory of global warming that exceeds the 1.5°C warming limit for a certain period of time but returns to below that limit within a certain period of time.

A review paper written by an international team of scientists and design experts involved in the Intergovernmental Panel on Climate Change (IPCC) assessments has highlighted the key challenges that need to be addressed urgently, with a focus on overshoot.

"Overshoot" is used in different ways in the scientific community, in policy and in popular jargon, which can sometimes be confusing. In common English, overshoot simply means failure to stay within the limits, but the IPCC definition implies both failure to stay within the limits and subsequent corrective actions. Corrective actions (reversing and lowering below the limits) do not compensate for failure to stay within the limits, because overshooting 1.5°C implies greater climate change impacts than if global warming had stayed below the limits. However, overshooting implies less climate change impacts and lesser impacts than if global warming had exceeded 1.5°C and remained permanently above that level.

However, a world that exceeds 1.5°C, even temporarily, would be more damaging than if we had avoided exceeding 1.5°C. The risks of concern here include irreversible loss to ecosystems and cultural heritage, increased extreme weather events, changes in local vulnerability that could exacerbate global inequalities, complex global impacts, and risks of triggering irreversible tipping points such as ice sheet collapse and Amazon forest dieback.

To reverse global warming after it overshoots, a range of mitigation strategies must be pursued. Specific and complementary strategies include further expansion of carbon dioxide removal (CDR), further reduction of residual CO2 emissions, and further reduction of short-lived climate forcing, particularly methane. Acceleration of near-term emission reduction measures is considered an important prerequisite, since a lower peak would reduce environmental, technical, and economic barriers to returning to 1.5°C.

While accelerating emission reductions is essential to limit the peak of temperature rise, effective and equitable adaptation measures remain important to minimize damages along the way. Preparing for overshoot requires simultaneous and integrated decision-making on adaptation, mitigation, and resilience, taking into account different preferences, capacities, and responsibilities for action.

(References)
Andy Reisinger et al, Overshoot: A Conceptual Review of Exceeding and Returning to Global Warming of 1.5°C, Annual Review of Environment and Resources (2025) https://www.annualreviews.org/content/journals/10.1146/annurev-environ-…

Contributor: IIYAMA Miyuki, Information Program