The global warming that the world has been facing for decades due to greenhouse gases emitted by human activities is a known issue, but global temperatures that broke records in 2023 and again in 2024 make it difficult for scientists to understand what is happening.
Scientific circles have proven that burning fossil fuels and destroying natural areas are responsible for long-term climate warming, the natural variation of which also affects temperatures from one year to the next.
However, the reasons for the significant warming witnessed in 2023 and 2024 remain a subject of considerable controversy among climate scientists, as some talk about the possibility that the warming occurred differently or faster than expected.
According to "Agence France-Presse," the research is fueled by several hypotheses. Some suggest a decrease in air pollution and natural carbon sinks such as oceans and forests, which are now absorbing less carbon dioxide.
Studies abound, but it will take a year or two to pinpoint the exact impact of each factor.
“I would like to know what is behind” the record temperatures of 2023 and 2024, said Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, in an interview in November. “We are still assessing whether we are seeing a change in how the climate system works,” he added.
“The record global temperatures of the past two years have pushed the planet into uncharted territory,” climate scientist Richard Allen of the University of Reading told AFP.
Sonia Seneviratne of the Swiss Federal Institute of Technology in Zurich said the record temperatures were “exceptional, within the range of what can be expected based on current climate models.”
However, given the amount of fossil fuels we are burning, we should expect a general trend of warming in the long term, the climate scientist told AFP. Humanity has not yet begun to reduce emissions, despite approaching the peak.
Natural climate variability partly explains this observation. In fact, 2023 was preceded by a rare run of three consecutive years of La Niña, a natural phenomenon that masked some of the warming by intensifying the oceans’ absorption of excess heat.
When La Niña, the opposite phenomenon, took hold with enormous intensity in 2023, that energy returned, pushing global temperatures to levels not seen in 100,000 years, according to paleoclimatologists.
While the peak of La Niña in January 2023 has passed, the heat waves are still ongoing.
“The cooling is very slow,” says climate scientist Robert Vautard, adding that “we are still within the relative margins” of the forecasts, but if “temperatures do not cool even more in 2025, we will have to ask some questions.”
The 2020 commitment to switch to cleaner fuels in shipping provides one explanation. This has reduced sulfur emissions, which has increased the reflection of sunlight by the sea and clouds and helped cool the climate.
In December, a study suggested that the decline in low-altitude clouds allowed more heat to reach the Earth’s surface.
Volcanic activity or solar cycles may also have played a role. Gavin Schmidt organized a conference at the American Geophysical Union in December to discuss all these hypotheses.
Some fear that scientists are not paying attention to other factors.
“We cannot rule out other factors that may have caused the warming,” says Sonia Seneviratne.
In 2023, carbon sinks suffered “unprecedented weakness,” according to a major preliminary study published in the summer. The US National Oceanic and Atmospheric Administration (NOAA) reported in December that the Arctic tundra was now emitting more carbon dioxide than it was storing.
The oceans, a major carbon sink and the main regulator of the climate, are warming at a rate that “scientists cannot fully explain,” says Johan Rockström of the Potsdam Institute for Climate Impact Research. “Is ocean warming a sign of a loss of resilience on this planet? We cannot rule it out,” he said last month.
