The Earth could be on course to exceed the symbolic 1.5°C global warming threshold in as little as three years if current carbon dioxide emissions continue unchecked.

That’s the stark warning from more than 60 of the world’s leading climate scientists in the most up-to-date assessment of global warming to date.

In 2015, nearly 200 countries agreed to work towards limiting global temperature rises to 1.5°C above pre-industrial levels – temperatures recorded in the late 19th century – in an effort to avoid the most severe consequences of climate change.

However, nations have continued to burn record amounts of coal, oil and gas, while also clearing vast areas of carbon-rich forests – placing that international target in jeopardy.

Climate change has already intensified many extreme weather events – including the UK’s 40°C heatwave in July 2022 – and has driven rapid sea level rise, posing a threat to coastal communities.

“Things are all moving in the wrong direction,” said lead author Prof Piers Forster, director of the Priestley Centre for Climate Futures at the University of Leeds.

“We’re seeing some unprecedented changes and we’re also seeing the heating of the Earth and sea-level rise accelerating as well.”

These changes “have been predicted for some time and we can directly place them back to the very high level of emissions”, he added.

At the start of 2020, scientists estimated that humanity had a remaining “carbon budget” of 500 billion tonnes of carbon dioxide (CO₂) – the principal planet-warming gas – to retain a 50% chance of staying below the 1.5°C threshold.

By early 2025, that budget had been slashed to 130 billion tonnes, according to the new study.

This sharp decline is largely attributed to continued record emissions of CO₂ and other greenhouse gases such as methane, alongside more refined scientific modelling.

At the current rate of around 40 billion tonnes of CO₂ emissions per year, that remaining budget would be exhausted in roughly three years.

This would effectively lock the planet into overshooting the Paris Agreement’s target – though the 1.5°C mark is unlikely to be officially breached for a few years after the budget is used up.

Last year marked the first time on record that the global average air temperature exceeded 1.5°C above pre-industrial levels over a 12-month period.

However, a single year above the threshold does not constitute a formal breach of the Paris Agreement. The exceptional heat of 2024 was partly boosted by natural climate variations.

Nonetheless, researchers estimate that human-induced warming was by far the main driver, reaching 1.36°C above pre-industrial levels.

The current rate of warming – around 0.27°C per decade – is unprecedented in the geological record.

If emissions remain at today’s levels, the planet is expected to cross the 1.5°C threshold around 2030 on this measure.

Beyond that point, it may be theoretically possible to reduce long-term warming by removing large volumes of CO₂ from the atmosphere.

But the authors caution against relying on such unproven and ambitious technologies as a “get-out-of-jail-free card”.

“For larger exceedance [of 1.5C], it becomes less likely that removals [of CO2] will perfectly reverse the warming caused by today’s emissions,” warned Joeri Rogelj, professor of climate science and policy at Imperial College London.

The study is packed with stark statistics that underline the extent of the climate crisis already under way.

Perhaps most striking is the speed at which excess heat is accumulating in the Earth’s climate system – a process known in scientific terms as the “Earth’s energy imbalance”.

Over the past decade, this rate of warming has been more than twice as high as in the 1970s and 1980s, and around 25% greater than in the late 2000s and 2010s.

“That’s a really large number, a very worrying number” over such a short period, said Dr Matthew Palmer of the UK Met Office, and associate professor at the University of Bristol.

This surge is primarily due to greenhouse gas emissions, though a reduction in the cooling effect of aerosols (tiny atmospheric particles) has also played a role.

All of this extra energy must go somewhere. Some of it warms the land and air, or melts glaciers and ice sheets – but about 90% is absorbed by the oceans.

This not only disrupts marine ecosystems but also leads to sea-level rise: warmer waters expand in volume, and melting glaciers add yet more water to the seas.

As a result, the pace of global sea-level rise has doubled since the 1990s, increasing the flood risk for millions of people living in coastal regions.

While the overall picture is sobering, the researchers highlight one note of hope: the rate of growth in emissions does appear to be slowing, thanks to the global rollout of cleaner technologies.

They stress, however, that “rapid and stringent” emissions cuts are more vital than ever.

The Paris target is grounded in robust scientific evidence showing that the impacts of climate change become significantly more severe at 2°C of warming compared to 1.5°C.

That distinction is often over-simplified – suggesting that staying below 1.5°C is “safe” while going above it is “dangerous”.

In truth, every additional fraction of warming worsens the severity of extreme weather, accelerates ice loss, and raises sea levels further.

“Reductions in emissions over the next decade can critically change the rate of warming,” said Prof Rogelj.

“Every fraction of warming that we can avoid will result in less harm and less suffering of particularly poor and vulnerable populations and less challenges for our societies to live the lives that we desire,” he added.

 

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