Key climate indicators sound climate warning sign, scientists say
From greenhouse gases to rising sea levels or the +1.5°C warming limit, key climate indicators are in the red, warn 60 renowned researchers in a global study released this Thursday (19).
Human-caused warming “has increased at a rate unprecedented in the record, reaching 0.27°C per decade between 2015 and 2024,” the scientists concluded.
Greenhouse gas emissions, mainly from the use of fossil fuels, hit a record high in 2024, averaging 53 billion tons of CO2 per year over the past decade. In addition, polluting particles in the air, which have a cooling effect, have decreased.
The finding, published in the journal Earth System Science Data, is the result of the work of researchers from 17 countries, who based themselves on the methods of the IPCC, a group of climate experts appointed by the UN, to which the majority belong or have belonged.
The aim of the study is to provide indicators updated annually from the IPCC report, without waiting for the next one, which will be released in a few years.
By 2024, observed warming compared to the pre-industrial era will reach 1.52°C, of which 1.36°C is exclusively attributable to human activity.
This is a record level, but it is predictable, taking into account human-caused warming, to which these natural phenomena are occasionally added, says expert Christophe Cassou of the French National Center for Scientific Research (CNRS). “It is not an exceptional or surprising year for climatologists.”
This does not mean that the planet has already exceeded the most ambitious limit of the Paris Agreement (warming limited to 1.5°C), a phenomenon that is understood to be observed over several decades. But the window is closing more and more.
The residual carbon budget – expressed as the total amount of CO2 that could still be emitted while maintaining a 50% probability of limiting global warming to 1.5°C – is shrinking. It was around 130 billion tonnes at the start of 2025, just over three years of emissions at the current rate, compared with around 200 billion a year ago.
“Exceeding the 1.5°C limit is now inevitable,” says one of the authors, Pierre Friedlingstein of CNRS. “I tend to be an optimist,” says lead author Piers Forster of the University of Leeds. “But if you look at this year’s publication, things are heading in the wrong direction.”
The authors included two new indicators this year, including one on sea level rise, which is expanding due to the effect of warming and receiving significant volumes of fresh water due to the accelerated melting of glaciers.
The annual rate has roughly doubled, with an increase of about 26 mm between 2019 and 2024, when the average had been less than 2 mm per year since the beginning of the 20th century.
In total, sea levels have risen by 22.8 cm since the beginning of the last century, enough to increase the destructive power of storms and threaten the existence of some island countries. This rise, which is due to complex phenomena, is subject to strong inertia and would continue even if emissions were stopped immediately.
Humanity, however, is not helpless. “What can we do to limit the speed and magnitude of sea level rise? Reduce greenhouse gas emissions as quickly as possible,” says climatologist Valérie Masson-Delmotte.
With less than six months to go until COP30, however, climate policies are being weakened by the United States' withdrawal from the Paris Agreement.
“Any change in trajectory or in terms of public policies that could increase or maintain emissions that would otherwise have been reduced will have an impact on the climate and the level of warming in the coming years,” says Aurélien Ribes, from the French National Center for Meteorological Research.
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