1567. Limiting the Magnitude and Duration of Overshoot Beyond 1.5°C: UNEP’s “Limiting Overshoot” Report

On September 2, 2026, the United Nations Environment Programme (UNEP) released Limiting Overshoot: Navigating Exceedance of 1.5°C and Pathways towards Return. Recognizing that global average temperatures are likely to exceed 1.5°C above pre-industrial levels within the next few years, the report sets out the actions needed to limit the resulting impacts and return warming to below 1.5°C as soon as possible.

UNEP is not arguing that warming beyond 1.5°C should be accepted as inevitable or harmless. Rather, it identifies an “overshoot, peak and decline” pathway—immediate and sustained emissions reductions, the lowest possible temperature peak, the shortest possible period above 1.5°C, and a subsequent decline in temperatures—as the best remaining option.

Overshoot Is a Temperature Pathway, Not a Single-Year Record

In the report, “overshoot” does not simply mean that the global average temperature exceeds 1.5°C in a particular year. It refers to the full temperature pathway in which warming moves above 1.5°C, reaches a peak, then declines and eventually stabilizes.

In 2024, the annual global average temperature was reported to have exceeded 1.5°C above pre-industrial levels for the first time. However, progress against the Paris Agreement’s long-term temperature goal must be assessed using the average state over multiple decades, rather than a single annual value.

The key questions are therefore how high temperatures will rise, how long warming will remain above 1.5°C, and whether temperatures can ultimately be brought down. UNEP stresses that none of these outcomes is predetermined: they will depend heavily on present and future emissions reductions, investment, adaptation measures and international cooperation.

Higher Peaks and Longer Overshoot Increase Risks

UNEP finds that risks to people and nature rise as peak warming increases and the duration above 1.5°C lengthens. Extreme heat, heavy rainfall, drought and ecosystem loss are likely to become more severe. Greater and more prolonged warming also raises the likelihood of crossing thresholds associated with irreversible or extremely difficult-to-reverse changes, including destabilization of large ice sheets, degradation of the Amazon rainforest and changes in the Atlantic Meridional Overturning Circulation (AMOC).

Even if global average temperatures are lowered in the future, impacts such as sea-level rise, biodiversity loss, changes to glaciers and ecosystems, and the loss of homes and livelihoods may not be reversed. UNEP therefore emphasizes that keeping the peak as low as possible and shortening the duration of overshoot are essential to reducing risks to people, societies, economies and ecosystems.

Emissions Reductions, Adaptation and CDR Must Advance in Parallel

To limit the magnitude of overshoot, greenhouse gas emissions—including both carbon dioxide and methane—must be cut immediately and continuously. Reducing methane, a short-lived climate pollutant, is particularly important for slowing near-term warming.

At the same time, adaptation must be strengthened to address climate impacts that are already evident and to prepare for cascading and compounding risks. UNEP’s central message is that mitigation and adaptation are not alternatives; both must move forward together.

Reaching global net-zero carbon dioxide emissions is crucial for halting further warming and moving temperatures toward stabilization. Bringing temperatures down after an overshoot will require sustained net-negative CO₂ emissions, meaning that carbon dioxide removals exceed emissions over an extended period. UNEP identifies carbon dioxide removal (CDR) as one component of this effort.

Responsible Governance Is Essential for the Use of CDR

CDR includes nature-based approaches such as afforestation and reforestation, forest and wetland restoration, and soil carbon management, as well as technological approaches such as direct air carbon capture and storage (DACCS). UNEP regards CDR as important for bringing temperatures down, but makes clear that it must not be treated as a substitute for emissions reductions.

Land- and ecosystem-based CDR options may be deployed relatively early, but they can require large areas of land. Potential competition with food production, livelihoods, land rights, biodiversity and water resources must therefore be carefully considered. Carbon stored in forests and soils may also be released again through warming, drought, wildfire, pests and disease.

In light of these challenges, the report calls for strong governance of CDR deployment, taking account of the permanence of carbon storage, technological maturity, cost, environmental and social impacts, and equity.

Maintaining the 1.5°C Goal and Expanding the Options That Remain

The “overshoot, peak and decline” pathway does not weaken the 1.5°C goal or justify delays in climate action. UNEP frames overshoot not as a reason for resignation, but as a reason for greater urgency.

The report’s message can be summarized as follows: minimizing both the magnitude and duration of warming beyond 1.5°C requires the parallel acceleration of deep and sustained greenhouse gas emissions reductions, stronger adaptation to climate impacts, and responsibly governed CDR that complements—rather than replaces—emissions cuts.

Choices made today on policy, investment and international cooperation will shape the height of future peak warming, the duration of overshoot, and the adaptation and development options available to future generations.

Reference
UNEP (2026). Limiting Overshoot: Navigating Exceedance of 1.5°C and Pathways towards Return. https://doi.org/10.59117/20.500.11822/49857

Contributor: Miyuki Iiyama, Strategic Coordination Office