World set to breach 1.5°C, but return below it still possible, UN says

The world is on course to exceed the 1.5°C global warming threshold within the next few years, but rapid action could still limit the extent of the overshoot and eventually bring temperatures back below the threshold, according to a new United Nations Environment Programme (UNEP) report.

The report, Limiting Overshoot, says the most optimistic pathway would see global temperatures peak at 1.8°C above pre-industrial levels, while other pathways would produce higher levels of warming.

UNEP says the remaining option is an “overshoot, peak and decline” pathway: temperatures would temporarily exceed 1.5°C, peak at the lowest level possible and subsequently decline as greenhouse gas concentrations are reduced.

The strategy would require immediate and sustained cuts in greenhouse gas emissions, including methane, followed by net-negative emissions to bring temperatures down. Carefully governed carbon dioxide removal, including afforestation and other methods of removing carbon from the atmosphere, would form part of that effort.

But the report warns that overshooting 1.5°C is not a harmless technical detour. Climate risks and impacts would intensify with every additional fraction of a degree and every year temperatures remain elevated.

Expected consequences include more intense extreme weather, ecosystem losses and greater threats to human health, food and water supplies, infrastructure and economies. Low-lying coastal cities and small island states face particular risks.

The likelihood of triggering potentially irreversible climate tipping points would also increase as warming rises and persists. UNEP highlights risks including the destabilisation of major ice sheets, degradation of the Amazon rainforest and disruption of the Atlantic Meridional Overturning Circulation, a major system of ocean currents that helps regulate the climate.

“This summer’s scorching heat, raging wildfires and deadly floods are a warning of what lies ahead,” UN Secretary-General António Guterres said.

“We must make the overshoot above 1.5 degrees as small and short as possible. That demands an overshoot of ambition.”

UNEP Executive Director Inger Andersen said the consequences of warming beyond the threshold were already becoming evident.

“There are no good outcomes if we remain above 1.5°C,” Andersen said. “Across the globe, extreme heatwaves are already proving that climate impacts will strike faster, hit harder, and last longer – costing more lives and causing deeper disruption.”

She called for governments to accelerate emissions reductions, strengthen resilience and adaptation, and ensure that any period above 1.5°C is “as small and short as possible.”

The report says mitigation and adaptation must advance together. Governments need to prepare communities and economies for climate impacts while simultaneously reducing the emissions driving warming.

It also stresses that adaptation cannot rely solely on emergency responses after disasters occur. Planning must anticipate increasingly complex and potentially abrupt climate risks.

Professor Joeri Rogelj, a climate scientist at Imperial College London and one of the report’s authors, said the prospect of overshooting 1.5°C was a consequence of delayed emissions cuts.

“Overshooting 1.5°C is a painful reminder that failing to cut greenhouse gas emissions has consequences we can now no longer avoid, only limit,” Rogelj said.

The report says countries with greater responsibility for climate change should act fastest and with the greatest ambition, while equity and justice should underpin the global response.

Carbon dioxide removal could help return temperatures below 1.5°C, but UNEP cautions that it cannot substitute for emissions reductions. For the strategy to work, peak warming must remain well below 2°C and remaining emissions must continue to fall. Strong governance will also be needed to address the environmental and equity implications of large-scale carbon removal.

The report says a future below 1.5°C remains technically possible, but years of inaction mean some losses and changes will be irreversible even if temperatures eventually decline.

“Every fraction of a degree matters, and every year spent in overshoot increases climate risks and the potential for irreversible losses,” said Murat Kurum, President-Designate of COP31.

He called for accelerated electrification, methane reductions, stronger climate-resilient cities and greater protection of marine and coastal ecosystems.

For vulnerable countries and communities, UNEP says the question is therefore no longer simply whether the world can avoid crossing 1.5°C, but how high temperatures rise, how long they remain there and how quickly humanity can bring them back down.