Climate Report: Days with Marine Heatwaves Have More Than Tripled Since 1991

Total global emissions in 2024 corresponded to the effect of roughly 56.8 billion tonnes of CO2. Of this, 38.6 gigatonnes of CO2 (GtCO2) came from fossil fuels and industry. Averaged over the years 2015 to 2024, the figure was 54.6 GtCO2, of which 36.7 came from fossil fuels and industry. While emissions are no longer rising as rapidly as in the 2000s, they are still increasing.

Emissions and Concentrations Continue to Rise

According to the calculations, global warming is continuing at a high speed. In the period from 2010 to 2019, the warming rate was 0.23 degrees per decade. For 2016 to 2025, the researchers calculated 0.27 degrees per decade, matching the rate from 2015 to 2024. Temperatures over land areas have risen by 1.81 degrees from the 1850–1900 period to the decade of 2016–2025.

Humankind is still far from "jetzt auf einem abnehmenden Pfad zu sein," says co-author Sonia Seneviratne of ETH Zurich. She adds: "Man sieht, dass die Emissionen einfach weiter zunehmen, obwohl wir sehr viele Alternativen haben." She pointed to Ethiopia, which has imposed an import ban on combustion engines. "Also wenn Äthiopien das schafft, denke ich, könnten viele Länder in Europa das auch schaffen," she said. She finds the increase in emissions "sehr schwierig zu verstehen, wenn wir wissen, dass es das Pariser Abkommen 2015 gegeben hat."

As a consequence, Earth's energy imbalance is growing: Because more energy enters the Earth system through greenhouse gases than leaves it, the planet stores additional heat. "Und dadurch speichern wir mehr Wärme im Erdsystem und bringen die Welt aus dem Gleichgewicht," the report states. The value has more than doubled, from 0.40 watts per square meter in the period 1976–1995 to 1.04 watts per square meter in the period 2006–2025.

Earth's Energy Imbalance Is Growing

According to the report, the oceans have stored about 90 percent of the excess heat uptake since the 1970s. In the ocean, a robust increase in warming has been observed since the 1990s at depths between 700 and 2,000 meters. Newly included in the report are the days with marine heatwaves, whose number more than tripled from 1991 to 2025. In 2025, there was an average of 65 days of marine heatwaves at every location on the ocean surface.

Combined with the rising sea level, the threat to coastal regions is intensifying. From 1971 to 2018, the sea level rose by about 2.33 millimeters per year according to the report; from 2018 to 2025, it was already 3.84 millimeters per year. This acceleration increases the risks of storm surges and erosion.

Marine Heatwaves and Sea Level

The CO2 emissions budget for the 1.5-degree target will be exhausted in approximately three years at the current rate of emissions. If humanity wishes to limit global warming to 1.5 degrees with a 50 percent probability, it may only produce another 130 GtCO2 according to the IGCC. For a limit of 1.7 degrees, that figure would be 500 GtCO2, corresponding to roughly twelve years.

Shrinking CO2 Budget

For the report, more than 70 researchers evaluated over 40 datasets, many of which, according to the authors, are now at risk due to decisions about public funding. This also puts the scientific basis for future climate policy under pressure.

The report thus paints an overall picture that sets new record marks in several areas: higher emissions, higher concentrations, stronger warming, more frequent marine heatwaves, and a faster-rising sea level. At the same time, the authors point to available alternatives and policy instruments that have so far not been deployed to the necessary extent.

What paths will emerge from this for international climate policy will be shown by the upcoming negotiations and national decisions. The report itself provides the data basis for this — and at the same time an urgent timeframe, because the remaining budget for the 1.5-degree target will be exhausted in a few years according to the IGCC's calculations.