World poised to breach 1.5C warming limit, UN says

The world is likely to cross the Paris Agreement’s 1.5C warming threshold within the next few years, according to a UN report that says even the most optimistic scenario now points to a peak of about 1.8C.

The UN Environment Programme said on Wednesday, 2 September, that temporarily exceeding 1.5C had become unavoidable. Under current policies, warming could reach roughly 2.6C by the end of the century.

The threshold refers to the rise in long-term global average temperature above preindustrial levels. Individual years have already exceeded 1.5C, but the Paris target is assessed over a longer period rather than from a single annual reading.

UNEP’s Limiting Overshoot report argues that the remaining task is to restrict how far and for how long temperatures exceed 1.5C, reach a peak and then bring warming back down.

“There are no good outcomes if we remain above 1.5C,” UNEP Executive Director Inger Andersen said.

Every additional fraction of a degree increases the risk of extreme heat, floods, ecosystem loss, food and water insecurity, and irreversible changes to ice sheets, coral reefs and other natural systems.

Small island states and low-lying coastal cities face particularly acute risks from rising seas. Higher temperatures will also increase the cost and difficulty of adapting infrastructure, agriculture and public-health systems.

UNEP said the best remaining pathway requires immediate and sustained reductions in greenhouse-gas emissions, including methane, followed by net-zero and eventually net-negative emissions.

Removing carbon dioxide from the atmosphere would be necessary to lower temperatures after the peak. Possible methods include restoring forests and using engineered systems such as direct-air capture.

The report warns that carbon removal cannot substitute for emissions cuts. Many technologies remain expensive, energy-intensive or unproven at the scale that would be required.

Delaying action would raise both the temperature peak and the quantity of carbon that must later be removed. Estimates cited by climate researchers suggest that another five years of emissions near current levels could add about 0.1C to peak warming.

The overshoot could also cause losses that are not reversed even if average temperatures later decline. Species extinction, glacier loss and some sea-level rise would continue to affect communities for decades or centuries.

UN Secretary-General António Guterres said the overshoot must be kept “as small and short as possible.” The report reframes the 1.5C goal as a level to which temperatures must return after a period above it.