Carbon Rise Could Cause Cloud Tipping Point-

The planet’s temperature could zoom in an ever more greenhouse world, as researchers identify a dangerous possible cloud tipping point.

Stratocumulus clouds over the Atlantic: A tipping point ahead? (Image Credit: MAClarke21, via Wikimedia Commons) Click to Enlarge.

Climate scientists have confirmed a high-level hazard, a cloud tipping point, that could send global warming into a dramatic upwards spiral.

If carbon dioxide concentrations in the atmosphere become high enough, the clouds that shade and cool some of the tropical and subtropical oceans could become unstable and disperse.  More radiation would slam into the ocean and the coasts, and surface temperatures could soar as high as 8°C above the levels for most of human history.

And this dramatic spike would be independent of any warming directly linked to the steady rise in carbon dioxide concentrations themselves, the scientists warn.

Avoidance possible
“I think and hope that technological changes will slow carbon emissions so that we do not actually reach such high CO2 concentrations,” said Tapio Schneider, an environmental scientist at the Jet Propulsion Laboratory, the research center managed for the US space agency NASA by the California Institute of Technology.

“But our results show that there are dangerous climate change thresholds that we have been unaware of.”

The role of clouds in the intricate interplay of sunlight, forests, oceans, rocks, and atmosphere that controls the planet’s climate has been the subject of argument.  Do clouds really slow warming?  And if so, by how much, and under what conditions?

There may not be a simple answer, although researchers are fairly confident that the thinning of clouds over the California coasts may have made calamitous wildfires in the state more probable.

So to resolve what Professor Schneider calls “a blind spot” in climate modeling, he and his colleagues worked on a small-scale computer simulation of one representative section of the atmosphere above the subtropical ocean, and then used supercomputers to model the clouds and their turbulent movement over a mathematical representation of the sea.  And then they started to tune up the atmospheric concentrations of carbon dioxide.

Carbon threshold
They found that, once CO2 levels reached 1,200 ppm, the decks of stratocumulus cloud vanished, and did not reappear until CO2 levels dropped to well below this dangerous threshold.

If – and this has yet to happen – other researchers use different approaches to confirm the result, then the US scientists will have established a better understanding of one component of natural climate control.

The research may also illuminate a puzzle of climate history:  50 million or more years ago, during a geological epoch called the Eocene, the Arctic ice cap melted.  Climate models have shown that, for this to happen, atmospheric carbon ratios would need to rise to 4,000 ppm.

These, the Caltech team, suggests, would be “implausibly high” CO2 levels.  The latest study suggests this might be an overestimate:  a mere 1,200 ppm would be enough to set the planetary thermometer soaring. − Climate News Network

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