The Earth has been warming for decades, but the sudden and extreme increase in temperature has pushed the climate deep into uncharted territory, and scientists are still trying to figure out why. Over the past two years, temperature records have been broken repeatedly in a streak so persistent and mysterious that it has defied the best available scientific predictions of how the climate works.

Scientists agree that burning fossil fuels is causing significant long-term global warming, and natural climate variability can also affect temperatures from year to year. But they are still debating what could be contributing to this extraordinary temperature rise.

Experts believe changes in cloud structure, air pollution and the Earth’s ability to store carbon may be factors, but it will take another year or two to get a clearer picture.

“The warming in 2023 was greater than in any other year and will continue to be so in 2024,” Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, said in November. “I wish I knew why, but I don’t,” he added. “We’re still in the process of assessing what’s happening and whether we’re seeing changes in the way the climate system works.”

“Unknown Territory”

Burning fossil fuels releases greenhouse gases, such as carbon dioxide, that trap heat close to the Earth’s surface. While fossil fuel emissions will rise to record levels in 2023, average sea and air surface temperatures have also trended upward following a decade-long warming trend.

But during an unprecedented period between June 2023 and September 2024, global temperatures were unlike anything seen before, sometimes with significant differences, according to the World Meteorological Organization.

The heat was so intense that 2023 and then 2024 became the hottest years on record.

“Record global warming over the past two years has pushed the planet into uncharted territory,” Richard Allan, a climate scientist at Britain’s University of Reading, told AFP.

What happened was “at the limit of what we could expect based on current climate models,” Sonia Seneviratne, a climate scientist at ETH Zurich in Switzerland, told AFP.

“But overall the long-term warming trend is not unexpected,” he added, given the amount of fossil fuels being burned.

“It’s hard to explain this”

Climate variability may partly explain what happened, scientists said. Before 2023, there was a rare three-year La Niña phenomenon that created a strong cooling effect on the planet and pushed excess heat into the deep oceans. This energy bounces back to the surface in mid-2023 as El Niño warming begins in reverse and global temperatures rise.

But even after El Niño peaked in January, the heat persisted. Temperatures did not fall as fast as they rose, making November the second warmest month on record.

“It’s hard to explain right now,” said Robert Vautard, a member of the UN’s IPCC climate panel. “We lack perspective.

“If temperatures don’t fall more sharply in 2025, we really need to ask ourselves why,” he told AFP.

jury exit

Scientists are looking for clues elsewhere. One theory is that the global switch to cleaner transportation fuels in 2020 accelerated warming by reducing sulfur emissions, which make clouds more specular and reflect sunlight.

In December, another peer-reviewed paper examined whether the amount of low-lying clouds decreased, resulting in more heat reaching the Earth’s surface. At the American Geophysical Union conference this month, Schmidt brought together scientists to explore these and other theories, including whether solar cycles or volcanic activity provide any clues. There are concerns that without a more complete picture, scientists may miss deeper, transformative changes in climate.

“We cannot rule out that other factors also raise the temperature further… the decision is still not valid,” Seneviratne said.

This year, scientists warned that by 2023, Earth’s carbon sinks such as forests and oceans will absorb CO2. _with the atmosphere suffered “unprecedented weakening”. The Arctic tundra has become a net source of emissions after trapping CO2 for millennia, the US National Oceanic and Atmospheric Administration said this month.

Johan Rockström of the Potsdam Institute for Climate Impact Research said the oceans, which act as a huge carbon sink and climate regulator, are warming at a rate that scientists “cannot fully explain”.

“Could this be the first sign that the planet is beginning to lose resilience? We can’t ignore this,” he said last month.