The concentration of carbon dioxide in the atmosphere is at its highest point in 800,000 years, according to UN research that found 2024 was likely to have been the hottest year on record and the first to surpass 1.5C above pre-industrial levels. 

In an annual assessment of the climate, the UN’s World Meteorological Organization said signs of human-induced climate change “reached new heights” last year, with record greenhouse gas levels — combined with the El Niño weather phenomenon and other factors — causing record heat. 

“Our planet is issuing more distress signals,” said UN secretary-general António Guterres, urging world leaders to step up climate action. 

His comments came after President Donald Trump launched a sweeping attack on environmental policy, including pulling the US out of the Paris climate agreement for the second time.

The global average surface temperature was 1.55C above the 1850-1900 level, with a 0.13 C margin of uncertainty either way — making last year the warmest in a 175-year observational record, according to the research, which draws together data from member countries and partner agencies.

The record temperatures have led to intensified storms and weather-related disasters, with at least 151 “unprecedented” extreme weather events in 2024.

“Millions of people are increasingly suffering the consequences” of climate change in the form of heatwaves, floods, droughts, storms and rising seas, said Stefan Rahmstorf, head of the research department at the Potsdam Institute for Climate Impact Research.

“We can only stop the warming trend by getting out of fossil fuels, and we must do it fast,” he said. “Ignoring reality, denying the laws of physics and silencing scientists can only lead to harm, and ordinary people will pay the price for that.”

The latest temperature milestone is not a breach of the Paris agreement’s goal of limiting the long-term temperature rise to 1.5C, which measures the average temperature over decades. 

However, the report suggested long-term warming has accelerated rapidly in recent years, and is now 1.34-1.41C above pre-industrial levels. The Intergovernmental Panel on Climate Change said in 2020 that the world had warmed by 1.1C above the 1850-1900 reference period.

“While a single year above 1.5C of warming does not indicate that the long-term temperature goals of the Paris Agreement are out of reach, it is a wake-up call that we are increasing the risks to our lives, economies and to the planet,” said WMO secretary-general Celeste Saulo.

The report also warned of a huge climate impact on the world’s seas, which are warming twice as fast as they were before 2005. The oceans reached a record heat level for the eighth consecutive year in 2024.

Meanwhile, the rate of sea-level rise has doubled over the past three decades. The WMO said it would take hundreds to thousands of years to reverse the this rise and that of ocean warming.

The cryosphere — the frozen parts of the Earth’s surface — is “melting at an alarming rate”, added Saulo, with record glacier loss between 2022 and 2024.

The amount of ice on the world’s seas reached an all-time low early last month and the daily level remained below the previous minimum until mid-March. The Arctic’s sea ice hit a regional record low in the month of February.

The report said carbon dioxide concentration levels were 420 parts per million (ppm) in 2023, the last year for which final data are available — 2.3 ppm more than the year before. The pre-industrial level was 280 ppm, according to the US National Oceanic and Atmospheric Administration.

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