Last year was the hottest on record, oceans boiled, glaciers melted at alarming rates, and scientists couldn’t pinpoint the cause, reports CNN.
The planet is warming at an accelerated rate PHOTO SHUTTERSTOCK
Certain factors determining the high temperatures were well known, mainly carbon dioxide emissions resulting from the burning of fossil fuels, respectively the natural phenomenon El Niño.
However, these are not enough to explain the temperature records observed in 2023, according to several studies, reports AFP.
In an article published Thursday in the journal Science, scientists point to another potential factor responsible, namely the decreased reflection of the sun’s rays by low-altitude clouds.
In simple terms, fewer bright low-lying clouds mean the planet has “darkened,” allowing it to absorb more sunlight, explained Helge Goessling, author of the report and a climate physicist at the Alfred Wegener Institute in Germany.
This phenomenon is called “albedo” and refers to the ability of surfaces to reflect solar energy back into space.
The three researchers who worked on the study pointed out that the 0.2°C of warming of nearly 1.5°C observed in 2023 relative to the pre-industrial era is not a direct consequence of human-made greenhouse gas emissions or of the triggering of the El Nino phenomenon.
Using data provided by satellites, they concluded that the main factor responsible for this difference is “a historically low level of planetary albedo”, i.e. the percentage of sunlight reflected into outer space by a surface, and which lies “probably at the lowest level since 1940”.
This albedo has been “declining since the 1970s” due to the melting of the Arctic sea ice, then the Antarctic ice sheet “since 2016”, explained Helge Goessling, Thomas Rackow and Thomas Jung.
But in 2023, the decrease in cloud cover and, mainly, in the low altitude accentuated this trend, especially between the Tropic of Cancer and the Arctic Circle, as well as over tropical waters, especially in the Atlantic, where temperature levels were recorded record.
The vital role of clouds
Low-altitude clouds, less than 2,000 meters above Earth, are essential for cooling the air, while high-altitude clouds store the heat emitted by our planet.
“Three fundamental mechanisms could have contributed to this record”, estimated the authors of the study, including natural climatic “internal variability”, a decrease in aerosols – which participate in the formation of clouds and which also reflect the sun’s rays – but also, more worryingly , the very effect of climate change on the phenomenon of decreasing cloud cover.
Low-altitude clouds tend to develop in a cool, moist atmosphere. But as the planet’s surface warms, this can cause them to thin out or dissipate altogether, creating a complicated feedback loop in which low clouds disappear due to global warming, and their disappearance causes further warming.
If this happens, predictions of future warming could be underestimated, and “we should expect quite intense warming in the future,” Goessling pointed out.
The researchers pointed out that further studies and a better understanding of the role played by each of these factors “will be crucial to measuring current and expected future warming”.
Mark Zalinka, an atmospheric scientist at Lawrence Livermore National Laboratory who was not involved in the study, explained that “the fact that clouds play a key role in the story makes sense because they essentially act as a sunscreen of Earth”.
Small changes in cloud cover can “drastically change the albedo of the Earth,” he told CNN.
