Scientists say the most extreme climate change scenarios once used in global projections are becoming less realistic, with both the worst and best-case futures now largely ruled out, reflecting how global emissions trends have shifted over time.
A new set of seven climate scenarios suggests that while the most catastrophic warming outcomes are now less likely due to the gradual rise of renewable energy, the world is also no longer on track to meet the Paris Agreement’s most ambitious target of limiting warming to 1.5°C above pre-industrial levels.
Carbon dioxide emissions from fossil fuels such as coal, oil and gas remain the primary driver of global warming. Although the growing use of cleaner energy sources like solar and wind has reduced the probability of the most extreme warming pathways, scientists say the transition has not been fast enough to prevent significant long-term temperature rise.
The updated scenarios replace earlier projections that included both very high-emission futures and highly optimistic pathways. Researchers now say the upper-end projection has been revised downward to about 3.5°C of warming by the end of the century, compared to earlier estimates of around 4.5°C. However, even the most optimistic scenario now exceeds the 1.5°C threshold set in 2015 under the Paris climate accord.
Scientists say the planet is currently about 1.3°C warmer than pre-industrial levels and is warming at a rate of roughly 0.1°C every five years. Even small increases, they warn, are intensifying extreme weather, water shortages and biodiversity loss.
“There is kind of a narrowing of the futures. It cannot be as bad as we thought, but it cannot be as good as we hoped,” said Johan Rockström of the Potsdam Institute for Climate Impact Research.
Researchers say the world is now likely headed toward a “middle” pathway of around 3°C warming by 2100 if current policies continue.
Experts also warn that even the best-case scenario would likely see temperatures overshoot 1.5°C for decades before any potential decline, assuming future carbon-removal technologies become viable at scale.
“This is just physics,” said climate scientist Bill Hare. “We are losing the ability to limit warming even by two degrees without strong action.”
Others stress that exceeding 1.5°C carries serious consequences, particularly for vulnerable nations such as small island states facing rising sea levels.
The revision of older high-end scenarios, once widely used in climate research, has also sparked debate. Some scientists argue that extreme coal-heavy projections were never realistic, while others say they were useful as upper-bound possibilities for planning.
Despite improvements in renewable energy costs and adoption, scientists caution that emissions are still high enough to lock in significant long-term warming. They also warn that natural climate feedbacks—such as carbon released from oceans, forests and permafrost—could add additional warming beyond human control.
“The risks of climate change have not disappeared,” said study author Detlef van Vuuren. “We are still heading towards a future with significant climate impacts that we should avoid.”