Alfred Wegener Institute: Rapid surge in global warming mainly due to reduced planetary albedo

[OKIsItJustMe]

https://www.awi.de/en/about-us/service/press/single-view/sprunghafter-anstieg-der-erderwaermung-ist-massgeblich-auf-geringere-rueckstrahlkraft-des-planeten-zurueckzufuehren.html

05. December 2024
Rapid surge in global warming mainly due to reduced planetary albedo
Researchers find a potential explanation for the unusually sudden temperature rise in 2023: reduced low-level cloud cover limits Earth’s ability to reflect solar radiation

Rising sea levels, melting glaciers, heatwaves at sea – 2023 set a number of alarming new records. The global mean temperature also rose to nearly 1.5 degrees above the preindustrial level, another record. Seeking to identify the causes of this sudden rise has proven a challenge for researchers. After all, factoring in the effects of anthropogenic influences like the accumulation of greenhouse gases in the atmosphere, of the weather phenomenon El Niño, and of natural events like volcanic eruptions, can account for a major portion of the warming. But doing so still leaves a gap of roughly 0.2 degrees Celsius, which has never been satisfactorily explained. In the journal Science, a team led by the Alfred Wegener Institute puts forward a possible explanation for the rise in global mean temperature: our planet has become less reflective because certain types of clouds have declined.

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Decline in lower-altitude clouds reduces Earth’s albedo
The albedo of the surface of the Earth has been in decline since the 1970s – due in part to the decline in Arctic snow and sea ice, which also means fewer white areas to reflect back sunlight. Since 2016, this has been exacerbated by sea-ice decline in the Antarctic. “However, our analysis of the datasets shows that the decline in surface albedo in the polar regions only accounts for roughly 15 percent of the most recent decline in planetary albedo,” Helge Goessling explains. And albedo has also dropped markedly elsewhere. In order to calculate the potential effects of this reduced albedo, the researchers applied an established energy budget model capable of mimicking the temperature response of complex climate models. What they found: without the reduced albedo since December 2020, the mean temperature in 2023 would have been approximately 0.23 degrees Celsius lower.


With higher-level clouds, the warming effect typically predominates due to the interaction with thermal radiation, whereas with low-level clouds the cooling effect dominates due to the reflection of sunlight. (Graphic: Alfred-Wegener-Institut / Yves Nowak)

One trend appears to have significantly affected the reduced planetary albedo: the decline in low-altitude clouds in the northern mid-latitudes and the tropics. In this regard, the Atlantic particularly stands out, i.e., exactly the same region where the most unusual temperature records were observed in 2023. “It’s conspicuous that the eastern North Atlantic, which is one of the main drivers of the latest jump in global mean temperature, was characterised by a substantial decline in low-altitude clouds not just in 2023, but also – like almost all of the Atlantic – in the past ten years.” The data shows that the cloud cover at low altitudes has declined, while declining only slightly, if at all, at moderate and high altitudes.

The fact that mainly low clouds and not higher-altitude clouds are responsible for the reduced albedo has important consequences. Clouds at all altitudes reflect sunlight, producing a cooling effect. But clouds in high, cold atmospheric layers also produce a warming effect because they keep the warmth emitted from the surface in the atmosphere. “Essentially it’s the same effect as greenhouse gases,” says Helge Goessling. But lower clouds don’t have the same effect. “If there are fewer low clouds, we only lose the cooling effect, making things warmer.”

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http://dx.doi.org/10.1126/science.adq7280

[IbogaProject]

1. Vangelis did a song about this in 1976

?si=EoL856hypv6cFo1A

Albedo 0.39

[OKIsItJustMe]

2. Well, yes, the problem of decreasing albedo was identified decades ago

However, this is an unexpectedly rapid change.

…

But why are there fewer low clouds? Lower concentrations of anthropogenic aerosols in the atmosphere, especially due to stricter regulations on marine fuel, are likely a contributing factor. As condensation nuclei, aerosols play an essential part in cloud formation, while also reflecting sunlight themselves. In addition, natural fluctuations and ocean feedbacks may have contributed. Yet Helge Goessling considers it unlikely that these factors alone suffice and suggests a third mechanism: global warming itself is reducing the number of low clouds. “If a large part of the decline in albedo is indeed due to feedbacks between global warming and low clouds, as some climate models indicate, we should expect rather intense warming in the future,” he stresses. “We could see global long-term climate warming exceeding 1.5 degrees Celsius sooner than expected to date. The remaining carbon budgets connected to the limits defined in the Paris Agreement would have to be reduced accordingly, and the need to implement measures to adapt to the effects of future weather extremes would become even more urgent.”

[LastDemocratInSC]

3. "We should expect rather intense warming in the future..."

That's a polite way of describing what happens in a feedback loop when each pass around the loop increases the amplifier gain.

Or not.

[OKIsItJustMe]

4. Well, we've always known about certain albedo feedbacks

Like, warmer temperatures melt the Arctic ice cap, the albedo of snow/ice is roughly 90%, and the albedo of open seawater is like 10%. So, more sunlight is captured, meaning more heat, which melts more ice…

The relationship between clouds and global warming has always been a bit fuzzy, due to its complexity. As the air warms, that leads to more evaporation, which may lead to more clouds, which might warm or cool the planet… Hmmm…

So, we’ve focused primarily on “Greenhouse Gases,” which were better understood.