New UN report lays out emissions cuts needed for return to 1.5°C

With global temperature rise set to exceed 1.5°C above pre-industrial levels, the report examines a 'lowest possible' 1.5°C overshoot scenario, in which peak warming around the middle of the century is limited to 1.7–1.8°C, with approximately a 50% chance of returning to or below 1.5°C by 2100.

To get onto this pathway, global greenhouse gas emissions would have to be reduced by 18% by 2030, 45% by 2035, and 69% by 2040, relative to 2025 levels. By contrast, full implementation of nationally determined contributions (NDCs) would only reduce emissions by 5–8% by 2030 and 11–15% by 2035. The IIASA-led Scenario Compass Initiative provided the scenario data used in the analyses in the report. The initiative is described in more detail in an upcoming publication.

“If current policies continue, warming could reach 2.8°C this century and increase thereafter, compared with 2.6°C if all NDCs are delivered and similar efforts continue,” notes IIASA Senior Research Scholar Joeri Rogelj. Even achieving additional net-zero targets would only limit warming to 2.1°C. These projections are worse than last year's, reflecting changes in participation in the Paris Agreement and revised estimates of historical emissions. New NDCs have made a negligible difference. Every five years of CO₂ emissions at current levels push peak warming up by around 0.1°C.

IIASA researchers contributed to several chapters of the report. Transformative Institutional and Social Solutions Research Group Leader, Shonali Pachauri, coauthored Chapter 1 and remains a member of the Steering Committee. Energy, Climate, and Environment Program Director, Keywan Riahi and Rogelj, were Lead Authors of Chapter 4, while Research Scholar Setu Pelz co-led Chapter 5 alongside Sophie Boehm of World Resources Institute and Louise Jeffery of New Climate Institute.

"Every additional fraction of a degree and every additional year spent above 1.5°C increases climate risks and narrows the options for a safe future," notes Pachauri. "The Emissions Gap Report 2026 makes clear that the window to limit overshoot is narrowing, but we still have opportunities to act. Immediate and sustained emissions reductions can limit the peak and duration of warming and keep a return to 1.5°C by the end of the century within reach."

Accelerating implementation of Global Stocktake goals

At the first Global Stocktake under the Paris Agreement, nations agreed to triple renewable energy capacity and double the annual rate of energy efficiency improvements by 2030, transition away from fossil fuels in energy systems, reduce non-CO₂ emissions, and halt and reverse deforestation and forest degradation.

Since the Paris Agreement, global renewable electricity capacity has grown three times faster than anticipated, however, progress in other areas has been insufficient.

“Renewables are already a gamechanger and the only area of climate action that we find is already on track for 2030," explains Boehm. "But their remarkable progress alone won't close the gap. Combatting the climate crisis demands that these clean energy additions go hand-in-hand with a deliberate and just transition away from coal, oil, and gas. Although we've hit the accelerator on renewables, we haven't yet pressed the brakes on fossil fuels."

Jeffery notes that over the past decade, coal and oil use grew far less than was expected in 2015, while gas grew broadly as projected. She says we now need a U-turn across all fossil fuels and especially quickly for electricity supply. Coal-fired electricity generation would need to be effectively phased out globally by 2040, while electricity from solar and wind grows at least five and a half times.

"Meeting the minimum effort levels to minimize 1.5°C overshoot will require cooperation," adds Pelz. "That cooperation should reflect differences in responsibility and capability, and our work shows where it should focus, for example, by 2035 electricity from solar and wind must at least triple from today's levels, while CO₂ emissions from energy systems must fall by at least 35%."

Successful climate policies need to be scaled up

The report also finds growing evidence that climate policies can and have reduced emissions. Policy changes have contributed to structural shifts and significant emissions reductions in developed and developing countries. More than 220 evaluations provide evidence of what works across sectors and country contexts.

Evaluated electricity-sector policies resulted in average emissions reductions of 9%, while economic instruments, including carbon taxes and cap-and-trade schemes, achieved reductions of 5–13% over the periods considered. However, these successes remain concentrated in specific sectors, countries and periods and must be replicated, extended and sustained.

"Climate policies have already demonstrated that emissions can be reduced across countries and sectors," notes Riahi. "The challenge now is to scale up these successes through fast, deep and sustained emissions reductions, while limiting the need for large-scale carbon dioxide removal later this century."

The lowest possible overshoot scenario would also require removing and permanently storing roughly 320 gigatonnes of CO₂ over this century, equivalent to around eight years of 2024's global CO₂ emissions. However, socioeconomic and technological challenges make achieving this uncertain.

The authors conclude that the world can still reach the goals of the Paris Agreement, but this will require fast, deep, and sustained emissions reductions, backed by greater efforts to meet the calls for action in the first Global Stocktake.

Further information 
Read the full report. 
Read the original UNEP press release.