The world failed to stop warming. Can it reverse the rise in temperatures?

The United Nations has not abandoned the goal of limiting global warming to 1.5°C, despite reports that the target is effectively impossible to achieve. A new United Nations Environment Programme report instead examines how the world could move beyond the threshold temporarily and then return to it.

The report, titled “Limiting Overshoot: Navigating exceedance of 1.5°C and pathways towards return,” uses “overshoot” to describe a period when warming exceeds the target. Annual global temperatures have already surpassed 1.5°C above pre-industrial levels since 2024. The Paris Agreement target, however, refers to long-term warming measured over about 20 years, rather than a single year.

The longer-term outlook remains grim. UNEP’s emissions gap assessment last year projected that even if countries fully met their promised emissions-reduction targets, global temperatures could rise by 2.3°C to 2.5°C above pre-industrial levels by the end of this century. The new report formalizes that prospect and sets out what could follow.

It proposes an “overshoot, peak and decline” pathway. The aim would be to keep the period above 1.5°C as short as possible and limit the peak, because climate impacts would grow disproportionately as the overshoot became higher and lasted longer. The report says overshoot should not prompt resignation, but should instead accelerate action.

In its most optimistic scenario, UNEP says warming could peak at about 1.6°C to 1.8°C. Returning to 1.5°C would require more than the carbon neutrality agreed under the Paris Agreement. The world would need net-negative emissions, removing more greenhouse gases from the atmosphere than it emits. UNEP estimates that lowering global warming by 0.1°C would require cutting net cumulative carbon dioxide emissions by 220 gigatonnes, roughly six years of current global emissions. A decline from 1.8°C to 1.5°C would therefore require removing about 660 gigatonnes, equivalent to 17 to 18 years of emissions.

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Overshoot is not a reason for resignation, but rather a reason to act with greater urgency.