While warning that breaching the 1.5°C global warming limit would bring irreversible losses that no adaptation initiatives could undo, the United Nations Environment Programme (UNEP) on Wednesday (September 2, 2026), for the first time, set out a detailed “overshoot, peak and decline” pathway.
This is a route under which the world overshoots the 2015 Paris Agreement’s central goal — limiting the rise in average global temperatures to 1.5°C above pre-industrial levels — which a UNEP report said was now unavoidable, but holds the peak as low as possible and then brings temperatures back down below the limit by the end of the century.
The report, Limiting Overshoot, released in Nairobi, said global warming would cross 1.5°C “in the next few years”. Even a scenario in which every country delivers on its national climate plan and net-zero target puts peak warming at 1.8°C, it said. According to the report, current policies point to a rise of about 2.6°C by 2100, with a range of 1.9–3.6°C. The pathway, the report said, “is by no means an acceptable or preferred pathway; it is simply the best remaining option.”
The diplomatic grounds for that framing were laid at the 30th UN Climate Change Conference, COP30, held in 2025 in Brazil’s Belém, where the consensus “Global Mutirão” decision became the first COP text to concede that a temporary overshoot of the 1.5°C limit was likely, given how fast the remaining carbon budget was being spent. At the conference, countries also committed, for the first time, to limiting the size and duration of the overshoot and to closing adaptation gaps, which would require deep, rapid and sustained emission cuts.
Given that cuts alone will no longer suffice, a steep scaling up of nature-based removals such as large reforestation programmes was needed, COP30 CEO Ana Toni said in a statement. UN Secretary-General Antőnio Guterres also released a statement, saying, “This summer’s scorching heat, raging wildfires and deadly floods are a warning of what lies ahead. We must make the overshoot above 1.5 degrees as small and short as possible. That demands an overshoot of ambition.”
Compounding costs
The UNEP report suggested that time spent above 1.5°C carries compounding costs such as faster sea-level rise, coral reef collapse, glacier loss exceeding a quarter of global mass by 2100, declines of up to 14% in global food production by 2050 without effective adaptation, and rising odds of irreversible tipping points in the West Antarctic and Greenland ice sheets, the Atlantic Meridional Overturning Circulation and the Amazon.
Moreover, it gets harder to roll back the effects of a tonne of emitted carbon. The report computed that every five years of continued high emissions adds roughly 0.1°C to peak warming. Reversing that same 0.1°C afterwards means pulling about 220 billion tonnes of carbon dioxide back out of the atmosphere over and above whatever is still being emitted. Very broadly, a single large tree growing for about 30 years can cut out only a tonne of carbon dioxide. Carbon dioxide removal, the report stresses, is needed in addition to, not instead of, emission cuts, and can credibly cool temperatures back to the 1.5°C limit only if peak warming stays well below 2°C. Even the most optimistic scaling up of emission cuts is unlikely to reverse more than a few tenths of a degree this century, the report underlined.
UNEP Executive Director Inger Andersen was explicit that the report is not a concession. “Let’s be very clear, the 1.5 target is still the goal. But now we need to approach it differently from above,” she said.
The report arrives at a moment of uncertainty over whether countries will cut emissions at all. The United States, the world’s largest historical emitter, formally exited the Paris Agreement earlier this year and has also announced its withdrawal from the U.N. Framework Convention on Climate Change, the Intergovernmental Panel on Climate Change and the Green Climate Fund. Separately, the closure of the Strait of Hormuz following the conflict in West Asia has produced what the International Energy Agency calls the largest supply disruption in the history of the global oil market, with output from affected countries down more than 14 million barrels a day. Sustained high energy prices could push governments toward coal and other short-term fossil responses.
Methane targets
The report, in a first for the UN, placed significant stress on methane, which currently contributes about 0.5°C of warming. Cutting it is described as the most effective way to slow warming in the near term. Human activity currently puts out roughly 350–400 million tonnes of methane a year, mostly from fossil fuel operations, livestock, rice paddies, landfills and wastewater. When modellers build the pathways that underpin net-zero targets, they typically assume that about half of this gets cut by mid-century through “cheap, technically easy” interventions such as plugging leaks and venting from oil and gas. But the other half, roughly 150–200 million tonnes a year still being emitted in 2050 from agriculture and waste, is harder to cut; though shaving 60–70 million tonnes from it could reduce temperature rise to the same extent as removing 220 gigatonnes of carbon dioxide from the atmosphere.
Over 155 countries have joined the Global Methane Pledge to cut anthropogenic methane at least 30% below 2020 levels by 2030. India, China, Russia and Iran remain outside it.
The UNEP report co-author Richard Betts of the University of Exeter said, “It is a reality check. We have to live with this warmer world.”
Published – September 02, 2026 12:27 pm IST
