Some of the consequences of man-made climate change will not be reversible for hundreds if not thousands of years according to a new report from the World Meteorological Organization (WMO), which also underlined the massive economic and social upheavals from extreme weather.

WMO’s State of the Global Climate report confirmed that 2024 was likely the first calendar year to be more than 1.5C above the pre-industrial era, with a global mean near-surface temperature of 1.55 ± 0.13C above the 1850-1900 average. This is the warmest year in the 175-year observational record and atmospheric concentration of carbon dioxide is now at the highest level in the last 800,000 years.

“While a single year above 1.5 C 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 said that long-term global warming is currently estimated to be between 1.34 and 1.41C compared to the 1850-1900 baseline based on a range of methods, although it noted the uncertainty ranges in global temperature statistics.

The record global temperatures seen in 2023 and broken in 2024 were mainly due to the ongoing rise in greenhouse gas emissions, coupled with a shift from a cooling La Niña to warming El Niño event. Several other factors may have contributed to the unexpectedly unusual temperature jumps, including changes in the solar cycle, a massive volcanic eruption and a decrease in cooling aerosols, according to the report.

Atmospheric concentration of carbon dioxide, as well as methane and nitrous oxide, are at the highest levels in the last 800,000 years and real-time data from specific locations show that levels of these three main greenhouse gases continued to increase in 2024.

In addition to 2024 setting a new heat record, each of the past ten years, 2015-2024, were individually the ten warmest years on record.

Around 90 per cent of the energy trapped by greenhouse gases in the Earth system is stored in the ocean, and in 2024, ocean heat content reached its highest level in the 65-year observational record. Each of the past eight years has set a new record too. The rate of ocean warming over the past two decades, 2005-2024, is more than twice that in the period 1960-2005.

Ocean warming leads to degradation of marine ecosystems, biodiversity loss, and reduction of the ocean carbon sink. It fuels tropical storms and contributes to sea-level rise. In 2024, global mean sea level was the highest since the start of the satellite record in 1993 and the rate of increase from 2015-2024 was double that from 1993–2002, increasing from 2.1 mm per year to 4.7 mm per year.

Ocen warming is also irreversible on centennial to millennial time scales. Climate projections show that ocean warming will continue for at least the rest of the 21st century, even for low carbon emission scenarios.

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