The United Nations Environment Programme has acknowledged that the world is on course to exceed the 1.5°C limit established as a key ambition of the Paris climate accord, with the planet now expected to reach at least about 1.8°C of warming above pre-industrial levels this century even under the most optimistic emissions scenario.
The assessment, contained in a new UNEP report titled Limiting Overshoot, marks a significant shift in the international climate debate. The report recognises that countries are likely to cross the 1.5°C threshold because emissions reductions have not happened quickly enough.
“Obviously, yes, we have climate procrastinated,” Inger Anderson, UNEP’s executive director, said during a briefing on 1 September. “And obviously yes, when we started UNFCCC [the United Nations Framework Convention on Climate Change] we knew what action had to be taken. And we have not taken it at the speed that we could have.”
Nearly 200 countries agreed in the 2015 Paris climate accord to reduce greenhouse gas emissions sufficiently to keep the increase in global average temperatures “well below” 2°C above the pre-industrial average, while pursuing efforts to limit the increase to 1.5°C.
The 1.5°C threshold has remained a central objective of international climate negotiations despite repeated failures to deliver the steep emissions reductions required to achieve it. The 2021 UN climate summit in Glasgow adopted the theme “keep 1.5°C alive”, while the UN climate meeting in Brazil last year ended with a resolution “to keep 1.5°C in reach”.
Scientists had already warned that the threshold was becoming increasingly difficult to maintain. Global average temperatures in 2024 surpassed 1.5°C above pre-industrial levels for the first time, although the long-term average used to define the climate target is expected to cross the threshold by the end of the decade.
Andy Reisinger, a climate researcher at Australian National University in Canberra and an author of the UNEP report, described the assessment as a first for a UN agency. “This is the first report by a United Nations agency that says unambiguously that we will cross 1.5°C in the next few years, given insufficient actions to reduce greenhouse gas emissions,” he said.
The report concludes that all available pathways now involve some degree of temperature overshoot. Even its most optimistic scenario would see warming reach a minimum of about 1.8°C this century. That pathway would require global emissions to fall by half over the next decade and reach net-zero by mid-century, a substantially more ambitious outcome than current formal emissions pledges.
“All of our pathways forward are overshoot pathways,” Debra Roberts, a climate scientist at the University of KwaZulu-Natal in South Africa and a co-author of the report, said during the briefing.
The report nevertheless indicates that exceeding 1.5°C would not necessarily make a return below the threshold impossible. If warming were to plateau at around 1.8°C, the world could potentially return below 1.5°C by the end of the century if the most ambitious emissions reductions were accompanied by a rapid expansion of carbon dioxide removal.
Such efforts could include expanding forests and deploying technologies capable of capturing carbon dioxide directly from the air and storing it permanently. The approach has attracted increasing attention since the IPCC identified carbon removal as necessary for meeting climate targets.
But the scale required would be extraordinary. According to the report, returning to 1.5°C would require removing tens of billions of tonnes of carbon dioxide from the atmosphere every year for decades — thousands of times more than carbon dioxide removal technologies have delivered so far.
The UN assessment therefore presents the 1.5°C target not simply as a threshold the world is approaching, but as one it is now expected to cross, with the possibility of returning below it dependent on emissions cuts and an unprecedented expansion of carbon removal.
