The world is increasingly likely to temporarily exceed the Paris Agreement’s goal of limiting global warming to 1.5°C above pre-industrial levels. In 2024, average global temperature exceeded this threshold for the first time over a calendar year. Although climate targets are assessed over longer periods, the milestone illustrates how rapidly the planet is warming. Even if current climate commitments and policies are fully implemented, warming is projected to reach at least 1.8°C.
A new UNEP report, *Limiting Overshoot*, argues that governments must therefore prepare for the possibility of exceeding 1.5°C while doing everything possible to minimize how high temperatures rise and how long they remain above the target. The report describes an “overshoot pathway” consisting of four stages: exceeding 1.5°C, reaching peak warming, reducing temperatures and eventually stabilizing the climate. Ideally, peak warming would remain below 2°C before temperatures decline toward 1.5°C or lower.
How damaging this pathway becomes depends heavily on both the height and duration of the overshoot. Higher temperatures increase risks from extreme heat, drought, wildfires and other climate impacts. They could also increase the likelihood of irreversible changes involving ice sheets, permafrost and major ecosystems such as the Amazon rainforest. Exceeding 1.5°C therefore does not mean governments should abandon the target. Instead, UNEP argues that rapid and sustained reductions in greenhouse gas emissions become even more important.
Mitigation and adaptation must also occur simultaneously. Reaching net-zero emissions could halt additional warming, but lowering global temperatures after an overshoot would ultimately require net-negative emissions, meaning humanity removes more carbon dioxide from the atmosphere than it releases. Meanwhile, adaptation measures will be needed to protect societies and ecosystems from worsening climate impacts. Insufficient mitigation could eventually produce conditions where some communities and ecosystems reach limits beyond which effective adaptation becomes impossible.
Carbon dioxide removal (CDR) will consequently become an important part of managing overshoot. Conventional approaches include afforestation and soil management, while newer technologies include direct air capture and chemical removal processes. However, both approaches face major limitations. Land-based methods compete for land and can lose stored carbon through droughts, fires and warming. Technological approaches remain expensive and have yet to operate at the enormous scale that would be required. Climate models indicate that CDR might reverse only a few tenths of a degree of warming this century, meaning it cannot replace aggressive emissions reductions.
The UNEP report also warns that reducing temperatures after peak warming would not simply restore the planet to its previous condition. Oceans, glaciers, ice sheets and ecosystems respond to warming at different speeds, sometimes over decades or centuries. Sea-level rise, biodiversity losses, ecosystem disruption and human displacement could therefore continue even while global temperatures decline.
Ultimately, UNEP emphasizes that every fraction of a degree matters. The goal should be to keep peak warming as low as possible, make the period above 1.5°C as short as possible, accelerate adaptation and emissions reductions, and expand responsible carbon removal. Climate overshoot may increasingly appear unavoidable, but its severity and consequences will still depend heavily on decisions made today.