Geneva: The UN has warned that global temperatures are likely to exceed the 1.5°C limit set under the Paris climate agreement, urging governments to limit the scale and duration of the expected overshoot.

A new report by the UN Environment Programme (UNEP) says the world is likely to cross the 1.5°C threshold within the next few years as greenhouse gas emissions from fossil fuels continue to drive global warming.

The threshold refers to the long term average temperature above pre industrial levels rather than temperatures recorded in a single year.

The 1.5°C target was established under the 2015 Paris Agreement as an effort to limit the most severe effects of climate change. The report now acknowledges that keeping warming permanently below the threshold is increasingly unlikely, while stressing that every reduction in additional warming would limit climate related damage.

Under the most optimistic scenario assessed in the report, global temperatures could peak at around 1.8°C above pre industrial levels by the middle of the century if countries pursue ambitious climate policies. Current policies, however, could result in warming of about 2.6°C by 2100.

The report describes a potential period of ‘overshoot’, in which temperatures rise above 1.5°C before gradually declining. Scientists and UN officials said the priority should be to keep the peak as low as possible, reduce the time spent above the threshold and eventually return below it.

Such an overshoot would have significant consequences. The report warns of more extreme weather, rising sea levels, melting glaciers and ice sheets, declining food production, water shortages and biodiversity loss.

It also highlights the risk of irreversible changes, including the loss of major ice sheets, damage to the Amazon rainforest and disruption of Atlantic Ocean circulation.

UNEP Executive Director Inger Andersen said the 1.5°C target remained the goal but that governments now needed to approach it differently. The report also calls for greater investment in climate adaptation because some impacts of warming can no longer be avoided.

Returning temperatures below 1.5°C would require substantial reductions in greenhouse gas emissions, followed by the removal of carbon dioxide from the atmosphere. The report identifies reforestation as one option but says it would not be sufficient on its own, increasing the need for other carbon removal technologies.

The report does not suggest that crossing 1.5°C represents a single point beyond which climate action becomes ineffective. Instead, scientists emphasise that limiting every additional fraction of warming can reduce risks and damage.

The findings underline a shift in climate policy from preventing an overshoot at all costs to limiting its scale, managing unavoidable impacts and ultimately reversing warming.

How far and how quickly temperatures can be brought back down will depend largely on the pace of global emissions reductions and the effectiveness of carbon removal efforts.