The summary
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Global temperatures have been even higher than climate scientists expected over the past two years.
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A new study offers a possible reason why: cloud cover has decreased.
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The research suggests the reduction could be a result of global warming, which would mean the planet is warming even faster than scientists thought.
Temperatures around the world have risen much higher than scientists expected in the past two years. The trend has raised a puzzle: Are the hidden dynamics of climate change behind this sudden shift?
Last year was the hottest year on record, and over the summer 2024 was on track to be hotter. Even after taking into account the expected effects of greenhouse gas pollution and El Niño – a natural pattern that typically drives up temperatures – researchers could not account for roughly 0.2 degrees Celsius (0.36 degrees Fahrenheit) of warming which was observed in 2023.
A new study offers a possible explanation: Cloud cover has decreased over the past two years, allowing more light to reach Earth’s surface and heat it, rather than being reflected back into space.
The research, published Thursday in the journal Science, suggests that an overall decrease in the planet’s albedo, as this dynamic is called, is a likely cause of the temperature anomaly observed in 2023.
“This is almost consistent with this most recent additional increase in observed solar radiation,” said Helge Goessling, author of the study and a climate physicist at the Alfred Wegener Institute in Germany.
The expected behavior of clouds in a warmer world is one of the most difficult aspects of the climate system to study and model. Answering questions about this will help scientists better determine how sensitive the planet is to greenhouse gas emissions.
If the decrease in low cloud cover is not due to chance, it likely means that the Earth is warming even faster than scientists thought.
“It’s not really clear yet to what extent some of this could be variability that goes away,” Goessling said. “It shifts the odds toward higher-than-expected warming.”
The new research is based on an analysis of climate models and NASA satellite data on Earth’s reflectivity. It outlines three possible reasons why fewer low clouds develop, but offers no conclusions about how much each factor contributes.
One option is that a natural process temporarily deviates from normal, causing cloud cover to decrease. For example, it’s possible that natural variability is causing the ocean surface to warm more than expected, and that this is changing the physics of how clouds form.
A second possibility is changes in maritime shipping regulations: the International Maritime Organization imposed restrictions on the permitted sulfur content in maritime fuels in 2020. Some scientists think that reducing the number of sulfur particles that pollute the atmosphere could have the unintended effect of dampening the formation of marine clouds.
“Because these act as condensation nuclei for clouds, they can make clouds brighter and also live longer,” Goessling said of the sulfur particles.
The third option is that unidentified feedback loops in the climate system are causing cloud cover to decrease due to global warming.
If the latter two possibilities turn out to be the main contributors, it would mean that the climate is more sensitive to human pollution than many scientists had thought – and that humanity is therefore closer to exceeding the targets that world leaders have set for the limiting emissions than previously achieved. . (The term “climate sensitivity” refers to how warm the planet would be if the concentration of carbon dioxide and other greenhouse gases in the atmosphere were to double.)
Yet many questions remain, says Zeke Hausfather, head of climate research at the funding company Stripe and a research scientist at Berkeley Earth.
“We are still unsure whether these changes in cloud behavior are not due to short-term variability – which would return to more normal conditions over time – or whether they represent a new, ongoing change in the climate system ” he said. an email.
According to the National Oceanic and Atmospheric Administration, average land and ocean surface temperatures in 2023 were about 2.12 degrees Fahrenheit above 20th century averages.
Efforts by world leaders to reduce greenhouse gas emissions remain insufficient. Global temperatures are on track to rise more than 3 degrees Celsius (5.4 degrees Fahrenheit) on average – well above the 1.5 degrees Celsius (2.7 degrees Fahrenheit) target set in the Paris Agreement.
This article was originally published on NBCNews.com
