Global Warming Could Accelerate Substantially If High CO2 Levels Destabilize Marine Stratus Clouds

A new study suggests that carbon dioxide concentrations could reach a certain level that would destabilize the stratus cloud decks that help cool our planet, causing them to disappear and significantly pushing global temperatures upward.

In a study scheduled to be published by the journal Nature Geoscience on Monday, a team of researchers revealed that surface temperatures could rise by approximately 8 Kelvin (14 degrees Fahrenheit) if carbon dioxide concentrations exceed 1,200 parts per million (ppm). As noted on a Phys.org news release, concentration levels are now at 410 ppm, but are progressively increasing. Concentration levels of carbon dioxide in the atmosphere could break the 1,200 ppm mark by the next century if fossil fuel burning continues at its present rate. This threshold, however, is merely an estimate of the greenhouse gas concentrations that need to be present in order for the event to take place.

“I think and hope that technological changes will slow carbon emissions so that we do not actually reach such high CO2 concentrations. But our results show that there are dangerous climate change thresholds that we had been unaware of,” read a statement from study lead author Tapio Schneider, a professor at the California Institute of Technology and senior research scientist at NASA’s Jet Propulsion Laboratory.

According to Phys.org, stratus cloud decks are usually found in the eastern regions of subtropical oceans, and are responsible for “cooling and shading” the earth by reflecting sunlight. This process is essential in keeping Earth’s surface temperatures more manageable. However, the researchers pointed out that the “turbulent” air motions that allow these marine clouds to cover about one-fifth of all subtropical oceans cannot be resolved on a global level, because of how small they are.

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After creating a “small-scale” model of stratus clouds as they should appear above a typical subtropical ocean patch, the researchers tested the model through a series of computer simulations. There, it was shown that the cloud decks started becoming unstable once carbon dioxide levels went past the 1,200 ppm threshold — and ultimately began to disappear. The simulations also revealed that the clouds only returned when carbon dioxide concentration dropped back down to significantly lower levels.

In addition to showing the potentially dangerous effects of continued fossil fuel burning into the next century, the study could also explain why global temperatures had become so warm about 50 million years ago during the Eocene Epoch. Per Phys.org, existing climate models suggest that carbon dioxide levels should have been in the 4,000 ppm range in order to allow the Arctic to be free of ice, and warm enough to allow crocodiles and other animals to live in the region.

While the actual concentration levels might have been less than half of what those models indicate, the new study hints that the so-called “hothouse climate” of the Eocene might have resulted from the disappearance of stratus cloud decks, and an ensuing global temperature spike.