Over the past two years, temperatures around the world have risen far more than scientists expected. This trend is creating the mystery of whether there are hidden climate change dynamics behind the sudden change.

Last year was the hottest summer on record, 2024 was likely to be even hotter.. Even after accounting for the expected effects of greenhouse gas pollution and El Niño (a natural pattern that generally increases temperatures), the researchers found that the roughly 0.2 degrees Celsius (0.36 degrees Fahrenheit) of warmer temperatures observed in 2023 I couldn’t explain the change.

A new study offers a possible explanation. Cloud cover has decreased over the past two years, meaning more light is now reaching and heating the Earth’s surface, rather than being reflected back into space.

In the research, Published in Science on Thursdaysuggesting that this dynamic, called an overall decrease in the planet’s albedo, is likely the cause of the observed temperature anomaly in 2023.

“This is broadly consistent with the observed recent further increase in solar radiation,” said study author Helge Goessling, a climate physicist at the Alfred Wegener Institute in Germany.

The expected cloud behavior in a warmer world is one of the most difficult aspects of the climate system to study and model. Answering questions about it will help scientists more accurately determine how sensitive the Earth is to greenhouse gas emissions.

If the decrease in low-level cloud cover is not a coincidence, it likely means the Earth is warming even faster than scientists thought.

“It’s not really clear yet how likely it is that some of this variation is variability that disappears again,” Gosling said. “This increases the likelihood of greater-than-expected warming.”

The new study is based on analysis of climate models and NASA satellite data on Earth’s reflectivity. It outlines three possible reasons for the decline in developing low clouds, but provides no conclusions about how much each factor contributes.

One option is that natural processes temporarily deviate from normal, causing a decrease in cloud cover. For example, natural fluctuations may be causing sea surface temperatures to rise more than expected, thereby changing the physics of how clouds form.

The second possibility is a change in maritime transport regulations. In 2020, the International Maritime Organization imposed limits on the sulfur content allowed in marine fuels. Some scientists believe that reducing the number of sulfur particles polluting the atmosphere may have the unintended effect of suppressing ocean cloud formation.

“They act as condensation nuclei for clouds, so they can make clouds brighter and last longer,” Goessling said of the sulfur particles.

A third option is that unidentified feedback loops within the climate system are causing clouds to decrease due to global warming.

If the latter two possibilities turn out to be the main culprits, it would mean that the climate is more sensitive to anthropogenic pollution than many scientists thought, and that humanity is therefore more likely than world leaders to It means we are closer to exceeding the targets set for emissions limits than previously realized. (The term “climate sensitivity” refers to how warm the Earth is. If the concentration of carbon dioxide and other greenhouse gases in the atmosphere doubled.. )

Still, many questions remain, said Zeke Hausfather, director of climate research at financial firm Stripe and a researcher at Berkeley Earth.

“It remains to be seen whether these changes in cloud behavior are due to short-term fluctuations and will return to more normal conditions over time, or whether they represent new and ongoing changes to the climate system. No,” he said. Email.

According to the National Oceanic and Atmospheric Administration, the average surface temperature of land and ocean in 2023 was about 2.12 degrees Fahrenheit above the 20th century average.

Efforts by world leaders to reduce greenhouse gas emissions remain insufficient. Global temperatures are on track to rise by more than 3 degrees Celsius (5.4 degrees Fahrenheit) on average, far exceeding the 1.5 degrees Celsius (2.7 degrees Fahrenheit) goal set by the Paris Agreement.