Earth nearing climate red line: World set to cross 1.5°C warming threshold, warns UN body

The world is likely to cross the critical 1.5°C global warming threshold within the next few years, putting communities, ecosystems and economies at greater risk. But the United Nations Environment Programme (UNEP) says crossing the line does not mean the climate battle is lost.

In its new report, “Limiting Overshoot – Navigating exceedance of 1.5°C and pathways towards return,” UNEP says the most realistic remaining strategy is to limit how far temperatures rise above 1.5°C, reach a peak and then bring global temperatures back down.

The report's most optimistic scenario sees global warming peaking at around 1.8°C above pre-industrial levels. Other pathways result in substantially higher temperatures, underscoring how quickly today's climate decisions could reshape the planet's future.

What happens when 1.5°C is breached?  

The 1.5°C threshold, established as a key ambition under the Paris Agreement, is not a cliff beyond which the planet suddenly becomes uninhabitable. Instead, climate risks increase progressively with every additional fraction of a degree.

UNEP warns that warming beyond 1.5°C will intensify extreme weather, ecosystem destruction and risks to human health, food security, water supplies, infrastructure and economies.

Small island nations and low-lying coastal cities face particularly severe threats from rising seas and other climate impacts. The longer temperatures remain elevated, the greater the potential for damage that cannot easily be reversed.

The report also highlights growing risks around climate tipping points. These include destabilisation of major ice sheets, degradation of the Amazon rainforest and disruption of the Atlantic Meridional Overturning Circulation (AMOC), a major ocean-current system that helps regulate the climate.

Some changes could occur abruptly, while others would build gradually over decades.

'Overshoot, peak & decline' strategy  

UNEP's message is that the world must avoid treating a temporary breach of 1.5°C as a reason to abandon the target.

Instead, governments should pursue an “overshoot, peak and decline” pathway: rapidly reduce greenhouse gas emissions, limit the temperature peak and eventually bring global temperatures below 1.5°C.

That requires immediate and sustained cuts in emissions, including methane, alongside the transition towards net-zero greenhouse gas emissions.

Longer term, UNEP says net-negative emissions will also be required. This means removing more carbon dioxide from the atmosphere than is being emitted.

Carbon dioxide removal could involve approaches such as restoring forests and other ecosystems, as well as technological methods. But UNEP stresses that such removal must be carefully governed and cannot substitute for deep emissions cuts.

Why every fraction of a degree matters  

The difference between 1.5°C and 1.8°C may appear small on paper, but its consequences are not.

UNEP says higher peak warming and longer periods above 1.5°C increase risks for people and nature. Keeping the peak as low as possible also reduces the likelihood of crossing irreversible climate thresholds.

That makes the duration of the overshoot almost as important as its size.

A world that briefly moves above 1.5°C and then begins cooling faces fewer risks than one that remains at substantially higher temperatures for decades.

Adaptation becomes more difficult  

Even if emissions are rapidly reduced, some climate impacts are already locked in. Communities therefore need to adapt to heatwaves, floods, droughts, rising seas and other hazards.

But UNEP warns that adaptation has limits.

The higher the temperature peak, and the longer warming remains elevated, the more difficult and expensive adaptation becomes. Some losses and damages could ultimately become unavoidable or irreversible.

The report therefore argues that mitigation and adaptation cannot be treated as separate agendas. Cutting emissions reduces future risks, while adaptation helps societies cope with the impacts already unfolding.

UNEP's assessment comes after years of warnings that the 1.5°C goal is slipping out of reach under current policies.

The organisation's 2025 Emissions Gap Report had already warned that even full implementation of existing national climate pledges would put the world on a trajectory for around 2.3°C to 2.5°C of warming this century.