The world is likely to cross the 1.5°C global warming threshold within the next few years, exposing communities and ecosystems to increasingly severe climate risks, according to a new report by the United Nations Environment Programme (UNEP).
The report, Limiting Overshoot: Navigating Exceedance, however, says the world can still limit the duration and magnitude of warming above 1.5°C and eventually return temperatures below the threshold if countries urgently intensify climate action.
It identifies an “overshoot, peak and decline” pathway as the best remaining option for minimizing the period of excessive warming.
UN Secretary-General António Guterres said recent extreme weather events, including scorching heat, wildfires and deadly floods, were warnings of what could lie ahead.
“We must make the overshoot above 1.5 degrees as small and short as possible. That demands an overshoot of ambition,” Guterres said.
According to the report, achieving this would require immediate and sustained reductions in greenhouse gas emissions, particularly methane, as countries move towards net-zero emissions.
It also calls for long-term net-negative emissions supported by carefully governed carbon dioxide removal, including afforestation and other methods of removing carbon dioxide from the atmosphere and storing it.
At the same time, UNEP said countries must strengthen adaptation measures to reduce the vulnerability of communities, economies and ecosystems to both expected and unexpected climate impacts.
However, it warned that adaptation has limits and that some losses could become irreversible, particularly if global temperatures are allowed to peak at higher levels.
Climate risks to intensify
UNEP said the most optimistic scenario would see global temperatures peak at around 1.8°C above pre-industrial levels, while most other scenarios project higher warming.
Above 1.5°C, the report said, climate risks would increase with every additional fraction of a degree and every year temperatures remain elevated.
Expected consequences include more intense extreme weather events, ecosystem degradation and increased threats to small island developing states and low-lying coastal cities.
The impacts are also expected to affect human health, food security, water supplies, infrastructure, economies and nature.
The report warned that higher and prolonged temperatures would increase the likelihood of triggering irreversible climate tipping points.
These include destabilisation of major ice sheets, degradation of the Amazon rainforest and disruption of the Atlantic Meridional Overturning Circulation, a major ocean-current system that helps regulate the global climate.
Some consequences, UNEP said, could occur abruptly, while others would accumulate gradually over time.
UNEP Executive Director Inger Andersen said there were “no good outcomes” if global temperatures remained 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,” Andersen said.
She urged countries to accelerate emissions reductions, strengthen resilience and adaptation, and ensure that any period above 1.5°C is “as small and short as possible.”
UNEP calls for stronger global action
The report highlights the potential benefits of rapidly transitioning away from fossil fuels towards renewable energy, including improved air quality and public health, lower energy costs and greater access to electricity.
It calls for stronger political commitment, effective climate policies, inclusive governance and increased financing, while stressing that equity and justice must underpin climate responses.
UNEP said countries with greater responsibility for climate change should move faster and adopt more ambitious measures.
It also stressed that mitigation and adaptation must advance together, with priority given to measures that can achieve both objectives, including nature-based cooling solutions.
The report further cautions that carbon dioxide removal should complement, rather than replace, deep and sustained cuts in greenhouse gas emissions.
It said carbon dioxide removal could credibly contribute to bringing temperatures below 1.5°C only if peak warming remains well below 2°C and residual emissions are reduced.
Irreversible losses likely even after recovery
UNEP said years of delayed climate action mean that even a successful return to below 1.5°C would not restore the world entirely to previous conditions.
Some communities could be forced to relocate or change their livelihoods, while societies would have to adapt to permanently altered environmental conditions.
The report said such changes would raise difficult questions about justice, political legitimacy and the distribution of power, requiring new and inclusive governance arrangements.
UNEP said the “overshoot, peak and decline” pathway represents a new frontier in global climate action but warned that it cannot be postponed for future generations.
“Immediate action is required for such a pathway to remain possible,” the report said.
