Extreme heat events rise in decade since Paris accord as CO₂ stays at record, studies say

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More than 100 countries now experience at least 10 more “hot days” a year than a decade ago when the Paris climate accord was drawn up, scientists have said, as greenhouse gas emissions failed to be reduced.

The global average temperature rise to 1.3C above the pre-industrial levels from 1C in 2015, as emissions continued to rise, meant almost every country in the world had hotter days, the Climate Central and World Weather Attribution groups of international scientists concluded.

The warming over the decade resulted in an average of at least 30 more “hot days” annually in 10 countries, defined as being where temperatures are warmer for more than 90 per cent of days for the area compared with 1991-2020.

Under the 2015 Paris agreement, almost 200 countries agreed to limit the temperature rise to well below 2C and ideally to 1.5C above the pre-industrial level. This is measured over a period of two decades.

The World Meteorological Organization estimates the long-term global temperature rise by 2024 was about 1.3C above the 1850-1900 baseline.

The researchers noted that the Paris agreement had helped reduce projections for global warming from the baseline of 4C by 2100 before the accord was signed.

If countries successfully delivered on promised climate plans that could limit global warming to 2.6C, the world could experience 57 fewer hot days annually than it would have at 4C, the scientists said.

But Friederike Otto, professor in climate science at Imperial College London, called for greater urgency to limit the consequences further. “The difference between the 1.3C of global warming and the 2.6C means the difference between life and death of thousands of people, and of course, also ecosystems.”

The scientists also warned that extreme heat events had become more likely over the past decade. A weeklong heatwave in southern Europe, as the region experienced in 2023, was now 70 per cent more likely at a temperature that was 0.6C hotter than a decade ago, the research found.

The study was among several reports and papers released this week quantifying the implications of long-term global warming.

The WMO reported that the level of carbon dioxide in the atmosphere reached a record high in 2024, increasing by 3.5 parts per million to 423.9 ppm. It was the largest one-year increase since measurements began in 1957, it said.

The rate of growth had also increased from an average of 0.8 ppm per year in the 1960s to 2.4 ppm per year in the decade from 2011 to 2020.

Phil Williamson at the University of East Anglia said while it was expected that CO₂ levels in 2024 would reach a record high, “what’s new — and scary even for climate scientists” was the rate of increase had sped up when annual fossil fuel emissions had stayed much the same.

“That means that the balance of removals and additions in the natural climate system is also changing, with worldwide forest fires and warming seas now providing a positive feedback to global heating.”

Climate change had also made this year’s wildfires in Los Angeles about two to three times more likely and 25 times larger, in terms of burnt area, according to an annual assessment by scientists, including those from the European Centre for Medium-Range Weather Forecasts and the UK Centre for Ecology & Hydrology.

This came at the same time as a warning of “new reality” in the breach of the first so-called tipping point, where a small change in the Earth’s system can trigger a significant, sudden and potentially irreversible transformation.

The research, led by scientists from Exeter university, said warm-water coral reefs, experiencing widespread dieback, were passing their tipping point and the world was “dangerously close” to other tipping points.

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