The United Nations Environment Programme (UNEP) warned on Wednesday that global warming is set to exceed the 1.5°C limit within the next few years, exposing people and ecosystems to more severe climate damage. In its latest report, UNEP said average global temperatures have already risen by about 1.4°C above pre-industrial levels, largely due to greenhouse gas emissions from fossil fuels such as oil, gas, and coal. These gases trap heat in the atmosphere and contribute to climate change, with effects already felt worldwide through worsening heat waves, droughts, floods, and wildfires, among other risks to humans and biodiversity.
The 1.5°C threshold is the more ambitious goal countries agreed to pursue under the 2015 Paris climate agreement, alongside a commitment to keep warming well below 2°C. However, current national climate policies and trends would put the planet on course for around 2.6°C of warming by the end of the century, according to the report.
UNEP executive director Inger Andersen told journalists that once warming exceeds 1.5°C, "there are no good outcomes." Despite the expected breach, she said the target "is still the goal."
The UN is calling for an "overshoot, peak and decline" pathway, aiming to limit how far temperatures rise above 1.5°C and to keep the period above that level as short as possible. "We must make the overshoot as small and short as possible," UN Secretary-General Antonio Guterres said in a statement. He emphasised that every fraction of a degree and every year above 1.5°C would increase exposure to climate hazards and the risk of irreversible damage. The report warns that heatwaves, floods, and wildfires would become more frequent and extreme, while glaciers and polar ice would melt faster and sea levels would rise.
"What we need to do is limit the peak of warming and shorten the period of overshoot," said Debra Roberts, one of the report's lead authors. That would require drastically cutting greenhouse gas emissions. Roberts said the authors considered 1.8°C "the kind of maximum" from which temperatures could be brought back to 1.5°C. Beyond that, the feasibility of returning to 1.5°C becomes "really, really questionable," she added, warning that warming at 1.8°C would cause "irreversible cascading changes."
Even under optimistic scenarios, reversing a single decade of warming could take about 50 years. Some changes, including polar ice loss and sea-level rise, would be irreversible, according to the report. The UN's proposed pathway is "by no means an acceptable or preferred pathway," but "is simply the best remaining option."
The report proposes a daunting task: reversing climate change by removing carbon dioxide from the atmosphere on an unprecedented scale. This could involve covering large parts of the world with forests or using innovative technologies to extract carbon from the air. However, current industrial capacity for carbon removal is extremely limited, the report notes. It stresses that carbon removal measures must be used "in addition to, not instead of, sustained reductions in residual greenhouse gas emissions." Even if these measures are implemented, global temperatures would continue to rise for the foreseeable future and wouldn't return to today's levels for decades or even centuries.
Joeri Rogelj, a professor at Imperial College London and one of the report's authors, said: "Inadequate mitigation will push communities and ecosystems beyond their ability to adapt." He added that near-term emissions reductions can limit overshoot and reduce harm.
Shobha Maharaj, an adjunct professor at the University of Fiji and another co-author, said: "Adaptation takes decades to build, so overshoot-calibrated plans must be designed and implemented now, ahead of impacts."