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Stratocumulus are rather boring. They are not as elegant as clouds of cirrus (these horsetail trails high in the sky) nor as majestic as cumulonimbus (the big scary thunder).
But the stratocumulus clouds, which hover low in the sky and create vast bridges of cloud cover, have supreme value in our warming world: their white peaks reflect a lot of solar radiation in space.
But the vast cloud portfolio of the Earth in 2019 could potentially be modified by extreme climate change. These cloudy layers of stratocumulus could disappear, which would further intensify global warming.
This is the troubling conclusion of a study published Monday in the newspaper Nature Geoscience, based on a computer model that provides a new warning that climate change may offer surprises beyond the already existing and clearly predictable consequences.
Lead researcher Tapio Schneider, a Caltech climatologist, hypothesized that very high levels of carbon dioxide in the atmosphere could suppress the formation of stratocumulus cloud layers. With his colleagues, he modeled the formation of such clouds and, after two years of computer calculations, concluded that the constant increase in atmospheric CO2 could trigger a sudden increase in temperature associated with the disappearance of stratocumulus.
The effect seemed intense if CO2 reached 1,200 parts per million, or three times the current level, which is already much higher than the carbon dioxide level of the pre-industrial era. If CO2 reached 1,300 parts per million, the new report says, the global atmospheric temperature would rise by 8 degrees Celsius (46 degrees Fahrenheit) above the warming that had already been produced from greenhouse gases.
"It's a dramatic effect," said Schneider The Washington Post. The cloud layers of stratocumulus "dissolve completely," he said.
"Once the stratocumulus bridges are broken, they only reform when the CO2 concentrations fall significantly below the level at which instability occurred for the first time", according to the l & # 39; study.
Kerry Emanuel, professor of atmospheric science at MIT, said about Schneider's study: "What he's done is certainly plausible, but these clouds are really hard to simulate …. It provides a plausible route, but not yet proven – could have a tipping point in the climate ".
Climatologists have long been disturbed by clouds. A cloud can amplify or limit global warming, depending on its type, size, location, thickness, duration, and so on. But clouds are hard to pin down in a computer model.
These are remarkably insubstantial elements of the natural world. If you could bring all the clouds and vapor of the water to the surface of the atmosphere, it would form a liquid layer less than an inch thick, said Schneider. and the clouds alone would create a layer no deeper than a layer of paint.
"You have to predict what little fraction of this water vapor will condense into clouds," Schneider said.
There is no easy way to check whether clouds would behave this way in a world where carbon dioxide levels are so alarming. What is certain is that an increase of 8 degrees Celsius, in addition to the warming already caused by greenhouse gas emissions, would be catastrophic, not only for human civilization, but also for countless species and ecosystems shaken by rapid climate change.
Since the beginning of the industrial revolution, when people started burning fossil fuels on a large scale, global temperatures have risen by about 1 degree Celsius, or about 1.8 degrees Fahrenheit, with the Warming caused by rising carbon dioxide emissions in the atmosphere to more than 400 ppm, a level exceeded in 2013 for the first time in recorded history.
It's hard to imagine a world with nearly 1,300 ppm of CO2.
Schneider, for one, does not think that such extreme levels of CO2 will materialize, simply because it assumes that human civilization will find a way to avoid rejecting all that carbon in the world. atmosphere.
"I hope there will be enough technological progress to not get there, but it's not out of the way," Schneider said.
Matt Huber, a Purdue climatologist who has studied the effects of clouds on the climate, presented a careful assessment of the new document.
"Whenever you see a surprising result in a climate model, you worry that the model itself is too superficial, that there is something that should stabilize the model," he said. declared.
But Huber noted that Schneider paper offers a potential answer to a long-standing riddle. Scientists have known for decades that there are 55 million years ago, the Earth was subjected to a strangely hot phase, called the Paleocene Eocene Thermal Maximum (PETM). These are the famous "crocodiles of the Arctic".
How has the Earth become so hot? Carbon dioxide is an obvious part of the mystery, but climate models do not seem to be able to push the planet to such high temperatures without extraordinary levels of CO2, such as 4000 ppm or more. And the geological record does not show CO2 greater than 2,000 ppm.
So there must be another factor.
One possibility is that a massive leak of methane from the ocean floor has turned the climate into a new greenhouse regime. But Schneider's paper offers another hypothesis: the cloud cover in danger of extinction could lead to a climatic tipping point.
Stratocumulus are produced when warm air rises from the surface and cools, causing condensation of water vapor. In California, these layers of clouds are known as marine layers and are known to sneak into coastal towns and warm up on hot days.
These clouds cover vast expanses of the tropical ocean.
Cloud formation depends on the cooling process at the top of the clouds. This occurs on a physical scale that traditional climate models can not easily grasp.
"They simply fall into the computer network," Schneider said.
He and his colleagues have developed a new model that uses what is known as a large swirl simulation. The model indicates that the cooling process required for these cloud layers will be removed if the planet becomes too hot.
2019 © The Washington Post
This article was originally published by The Washington Post.
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