By Abbas Nazil
The world is likely to breach the 1.5°C global warming threshold within the next few years, according to a new report by the United Nations Environment Programme (UNEP), but the report says the scale and duration of the overshoot will still depend on decisions made now.
UNEP said crossing the threshold would not mean that efforts to limit climate change had failed, stressing that every fraction of a degree of warming avoided would reduce the risks and damage associated with a hotter planet.
The report, titled “Limiting Overshoot,” outlines an “overshoot, peak and decline” pathway in which global temperatures rise above 1.5°C before reaching a peak as greenhouse gas emissions decline towards net zero, followed by a possible reduction in temperatures if humanity achieves sustained net-negative emissions.
Under the most ambitious scenario examined by UNEP, global warming could peak at approximately 1.8°C by the middle of the century.
However, policies currently in place are projected to put the world on a trajectory towards about 2.6°C of warming by 2100, highlighting the importance of rapidly reducing emissions to prevent greater climate impacts.
The report comes as concerns grow over the difficulty of keeping global warming within the temperature limit established as a central objective of international climate action.
For almost a decade, limiting warming to 1.5°C above pre-industrial levels has remained a key goal of global climate policy, particularly under the Paris Agreement.
Although 2024 became the first individual year in which average global temperatures exceeded 1.5°C above pre-industrial levels, this does not mean that the Paris threshold has already been formally breached because the target is assessed over a longer period rather than a single year.
UNEP estimates that sustained warming is currently around 1.4°C, although it now considers a formal breach of the threshold likely within the coming years.
Climate scientists have repeatedly stressed that 1.5°C should not be viewed as a point at which climate action suddenly becomes meaningless.
Instead, climate risks increase progressively with every additional fraction of warming, meaning a world that reaches 1.6°C would face less damage than one reaching 1.7°C, while limiting the amount of time spent above 1.5°C could also reduce the consequences.
Andrew Weaver, a climate scientist at the University of Victoria in Canada who was not involved in the UNEP report, said the 1.5°C limit should not be regarded as a point beyond which climate action is no longer useful.
UNEP said countries should therefore seek to keep any temperature overshoot as small and as brief as possible instead of abandoning the 1.5°C goal once it is exceeded.
Mirey Atallah, chief of UNEP’s adaptation and resilience branch and coordinator of the report, said climate policy, scientific thinking and decision-making would need to adapt to a situation in which the world may approach the 1.5°C target from above rather than below.
Returning global temperatures below 1.5°C would require deep and sustained reductions in fossil fuel emissions, followed by a period in which humanity removes more carbon dioxide from the atmosphere than it emits.
Such carbon removal could involve forests and other natural systems, as well as technological approaches that would need to be deployed at a much greater scale than currently exists.
UNEP, however, cautioned that carbon removal cannot replace the urgent need to cut greenhouse gas emissions.
The report also warns that some consequences of temporarily exceeding 1.5°C could become irreversible, with higher temperatures increasing risks to ice sheets, the Amazon rainforest and the Atlantic circulation system.
Additional warming is also expected to intensify heatwaves, flooding, food insecurity and ecosystem losses, while impacts such as sea-level rise and species extinction cannot simply be reversed even if global temperatures eventually decline.
The report therefore shifts the focus from whether the 1.5°C threshold will be breached to how high temperatures rise, how long they remain above the threshold and whether they can eventually be brought down.
Richard Betts, a climate scientist at the University of Exeter and a co-author of the report, described the findings as a reality check while stressing that significant opportunities remain to limit future warming.
UNEP’s assessment ultimately indicates that the likelihood of temporarily exceeding 1.5°C does not remove the need for urgent climate action, but instead makes rapid emissions reductions even more important.
The extent of future warming will continue to depend heavily on how quickly countries reduce greenhouse gas emissions and transform their energy and economic systems in the years ahead.
