Global temperature rise is set to exceed 1.5°C, most likely within the next few years, according to a new report from the UN Environment Programme (UNEP).  

The report identifies an ‘overshoot, peak and decline’ pathway as the best remaining option to minimise the magnitude and duration of the overshoot and return to below 1.5°C – which was the global warming target mentioned in the 2015 Paris Agreement arranged in the UN COP climate talks – as soon as possible.

This conclusion is based on the report’s assessment of how the magnitude and duration of warming affect climate risks. It finds that risks increase with every additional fraction of a degree of warming and every year that temperatures remain elevated. Higher warming also increases the likelihood of irreversible impacts and limits to adaptation.

On this basis, UNEP says that keeping the overshoot as small and short as possible would reduce risks and impacts and make adaptation less difficult and expensive.

In UNEP’s most optimistic pathway, global temperatures peak at 1.8°C above pre-industrial levels before subsequently declining. Most other pathways result in higher peak warming.

UNEP says immediate and sustained reductions in greenhouse gas (GHG) emissions, including methane, are needed to minimise the scale of the temperature overshoot on the way to net zero.

It also highlights a rapid transition away from fossil fuels to renewable energy as part of the action needed to reduce emissions. UNEP says this transition would bring benefits including improved air quality and public health, lower energy costs and increased access to electricity.

Once net zero has been reached, temperatures could be brought down through long-term net-negative emissions, with carefully governed CO₂ removal (CDR) forming part of the mix.

CDR involves removing CO₂ from the atmosphere and storing it through approaches including afforestation. UNEP stresses that CDR is needed in addition to, rather than instead of, sustained reductions in GHG emissions.

The report says CDR can only contribute credibly to a return below 1.5°C if peak warming remains well below 2°C and residual emissions are reduced. Strong governance frameworks will also be needed to address environmental integrity, equity and scale, it adds.

Above 1.5°C, risks and impacts will intensify with every additional fraction of a degree and every year. UNEP identifies intensified extreme weather, ecosystem loss and the submersion of small island developing states and low-lying coastal cities among the potential impacts, alongside damage to human health, food security, water supplies, nature, cities, infrastructure and economies.

The report also warns that the likelihood of crossing irreversible tipping points increases with the magnitude and duration of higher temperatures. These include the destabilisation of major ice sheets, degradation of the Amazon rainforest and disruption of the Atlantic Meridional Overturning Circulation.

‘There are no good outcomes if we remain above 1.5°C. Across the globe, extreme heatwaves are already proving that climate impacts will strike faster, hit harder and last longer – costing more lives and causing deeper disruption,’ said Inger Andersen, Executive Director of UNEP.

‘Now is the time we must double down on climate action. We can – and must – get on the right path. By cutting greenhouse gas emissions, strengthening resilience and adaptation, and ensuring exceedance of 1.5°C is as small and short as possible.’

Responding to the UNEP report, David Waskow, Director of the World Resources Institute’s International Climate Initiative, said the extent of the overshoot is not predetermined.

‘How far temperatures rise, how long they stay there and how much damage is done still depends enormously on what countries do now,’ he said.

Waskow pointed to faster progress on clean energy, resilient food and water systems, and adaptation as part of the response. He also said carbon removal would be needed to bring temperatures back down, but could not substitute for deep emissions cuts, including rapid reductions in methane.