UN warns world is heading past 1.5°C, but window to reverse warming remains

NAIROBI, Kenya, Sep 2—The world is now on course to overshoot the 1.5°C climate threshold within the next few years, with even the most optimistic scenario projecting warming to peak at 1.8°C, the UN Environment Programme (UNEP) warned.

In a new report released Wednesday, UNEP said crossing 1.5°C would expose countries and communities to escalating climate risks, including more extreme weather, ecosystem losses, threats to food and water security and potentially irreversible changes to major climate systems.

The report, Limiting Overshoot, says the most viable remaining pathway is to allow warming to peak and then drive temperatures back down through deep emissions cuts and carefully governed carbon dioxide removal.

The report’s central message, however, is that crossing 1.5°C must not become a new climate normal.

Instead, UNEP is calling for an “overshoot, peak and decline” strategy designed to keep temperatures above 1.5°C for the shortest possible period and return the planet below the threshold as quickly as possible.

The pathway would require immediate and sustained cuts in greenhouse gas emissions, including methane, a rapid transition away from fossil fuels and eventual achievement of net-zero emissions. In the longer term, the world would also need net-negative emissions, supported by carefully governed carbon dioxide removal.

UN Secretary-General António Guterres said recent extreme weather events were a warning of the consequences of continued warming.

“This summer’s scorching heat, raging wildfires and deadly floods are a warning of what lies ahead,” Guterres said, calling for an “overshoot of ambition” to ensure any period above 1.5°C is as small and short as possible.

UNEP says the stakes will rise with every additional fraction of a degree above 1.5°C.

Higher temperatures are expected to intensify extreme weather, accelerate ecosystem losses and increase threats to food and water security, human health, infrastructure and economies.

The risks also extend to some of the planet’s major climate systems.

The report warns that the probability of triggering potentially irreversible tipping points increases as temperatures remain higher for longer.

These include 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 global climate.

For vulnerable nations, particularly small island and low-lying coastal states, the consequences could be existential, with rising seas threatening communities, infrastructure and livelihoods.

UNEP Executive Director Inger Andersen said the world could no longer afford to treat climate impacts as a distant threat.

“There are no good outcomes if we remain above 1.5°C,” Andersen said, warning that extreme heat and other climate impacts are already striking faster and harder.

Cutting emissions

The report stresses that carbon dioxide removal cannot be used as a substitute for cutting emissions.

Instead, UNEP says carbon removal must supplement deep and sustained reductions in greenhouse gases, with credible deployment dependent on keeping peak warming well below 2°C and eliminating remaining emissions as far as possible.

The organisation is also urging countries to pursue climate mitigation and adaptation simultaneously.

Measures such as nature-based cooling can help achieve both objectives, while stronger adaptation is needed to protect communities from climate impacts that are already unavoidable.

But UNEP cautions that adaptation has limits. Some climate-related losses will be irreversible even if global temperatures eventually return below 1.5°C.

Communities could be forced to relocate; livelihoods could disappear and societies may have to adapt to permanently altered environmental conditions.

The report places particular responsibility on countries that have contributed most to historical greenhouse gas emissions.

UNEP says countries with greater responsibility for climate change should move fastest and pursue the greatest level of ambition, while climate action must be underpinned by equity and justice.

Political commitment, effective national policies, international cooperation, inclusive governance and adequate climate finance will all be critical to keeping the overshoot pathway viable.

The warning comes as governments prepare for further international climate negotiations, where pressure is mounting for countries to convert long-standing climate pledges into faster emissions cuts and concrete investments.