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Earth shattered heat records in 2023 and 2024: is global warming speeding up?

2025-01-21  |   Editor : houxue2018  
Category : News

Abstract

Earth's temperature has risen sharply over the past two years, surpassing 1.5 °C above pre-industrial levels in 2024, sparking concerns about whether this is a temporary anomaly or a sign of accelerated climate change. Researchers attribute this temperature surge to factors such as the 2023 El Niño event and reduced air pollution, which affects cloud formation and Earth's cooling mechanisms. However, these factors alone do not fully explain the warming. Some studies suggest global warming might be reducing low-lying cloud cover, creating a feedback loop that exacerbates climate change. The recent warming trend surpasses expectations from prior models, raising questions about the future trajectory of global temperatures. While short-term factors like shipping pollution regulations may play a role, scientists emphasize the need for more data and refined models to understand whether this surge is a one-time event or an indicator of long-term acceleration.

Content

Earth’s temperature has surged in the past two years, and climate scientists will soon announce that it hit a milestone in 2024: rising to more than 1.5 °C above pre-industrial levels. But is this sudden spike just a blip in the climate data, or an early indicator that the planet is heating up at a faster pace than researchers thought?

That question has been at the centre of numerous studies, as well as a session at last month’s meeting of the American Geophysical Union (AGU) in Washington DC. Some scientists argue that the spike can be mostly explained by two factors. One is the El Niño event that began in mid-2023 — a natural weather pattern in which warm water pools in the eastern tropical Pacific Ocean, often leading to hotter temperatures and more-turbulent weather. The other is a reduction over the past few years in air pollution, which can cool the planet by reflecting sunlight back into space and seeding low-lying clouds. Yet neither explanation fully accounts for the temperature surge, other researchers say.

Clouds clearly played a part, according to a study published in Science in December, just before the AGU meeting1. A research team identified a reduction in low-lying cloud cover across parts of the Northern Hemisphere and the tropics that, combined with El Niño, was large enough to explain the temperature spike in 2023. But the cause of this decrease — and whether it can be chalked up to normal climate variations — remains a mystery, the authors say. Decreased air pollution alone doesn’t seem to explain it. They suggest that global warming itself could be causing some reduction in cloud coverage, creating a feedback loop that could accelerate the rate of climate change for decades to come.“I would be very careful about saying this is clear evidence [of acceleration], but there might be something going on,” says co-author Helge Goessling, a climate physicist at the Alfred Wegener Institute in Bremerhaven, Germany.

One reason is that global temperatures were off-the-charts hot in 2023, with an average 1.45 °C of warming above the pre-industrial baseline (see ‘Temperature surge’), shattering previous records. This level of warming is outside the range of what scientists expected on the basis of previous trends and modelling.

Another reason is that last year was also much warmer than expected. Scientists projected that early 2024 would be hot owing to El Niño. But they also anticipated that temperatures would fall after the weather pattern subsided and conditions in the equatorial Pacific returned to normal last June.

“That didn’t happen,” says Zeke Hausfather, a climate scientist at Berkeley Earth, a non-profit organization in California that tracks global temperatures. Instead, global temperatures remained elevated, shattering more records and probably making last year the warmest on record by a sizeable margin. “All of us who made projections at the start of the year underestimated just how warm 2024 would be.”

Some say that the massive temperature spike might end up being a blip in the climate data, owing in large part to new regulations covering air pollution from ocean-going ships. In 2020, the United Nations International Maritime Organization implemented a rule requiring an 80% reduction in sulfur emissions from ships sailing in international waters. One analysis of satellite imagery, published in August, suggests that there has been a clear reduction in ship tracks2, which are formed when sulfur-containing pollution particles seed low-lying mists. The changes seem to correlate with the broader reduction in cloud cover pinpointed by Goessling’s team.

“It’s almost a smoking gun,” says Andrew Gettelman, a climate scientist at the Pacific Northwest National Laboratory in Richland, Washington. If true, Gettelman says, this would indicate that the recent temperature spike could be a one-time phenomenon driven by short-term changes in pollution and a powerful El Niño.

Not everyone is convinced, however. If the pollution reduction was the primary explanation, warmer temperatures should coincide with the areas most frequented by ships, says Yoko Tsushima, a climate scientist at the Met Office in Exeter, UK. “We do not see that pattern,” she says. “The warming is almost everywhere.”

Nor do the numbers necessarily add up. It is clear that shipping regulations have played a part, Goessling says. But his calculations suggest that, to explain the 2023 temperature spike, all forms of air pollution on Earth, rather than just shipping pollution, would need to be almost completely eliminated.

This leaves the possibility that warmer temperatures are somehow driving reductions in low-lying cloud cover, which in turn promotes further warming — a positive feedback loop.

Scientists have already determined that some acceleration is happening, owing in part to the fact that governments are cleaning up their air to improve public health. Climate researchers include this in their models of future global temperatures. But if the climate system is entering a vicious cycle of warming, the severe effects that have long been projected, such as extreme storms and scorching temperatures that could impact migration and food production, will arrive sooner than expected.

Scientists have learnt a lot about Earth’s climate system over the past several decades, but frustrating uncertainties about the extent of future warming this century remain. One potential upside of the recent temperature spike is that it adds to a growing database, helping scientists to improve their models, Goessling says.

“The next couple of years probably will be crunch time in terms of further narrowing down where we are headed,” he adds.

Sources:

NATURE

https://www.nature.com/articles/d41586-024-04242-z .

Provided by the IKCEST Disaster Risk Reduction Knowledge Service System

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