Their role is fundamental: they shade the planet, reflecting much of the sun's heat back into space. Without them, scientists calculate, the Earth could be absorbing twice as much warmth.
But after three decades of research, how and where clouds move the way they do and how that will change as the climate warms and as the atmosphere becomes either more or less polluted remain among the biggest unanswered questions. These are major concerns for scientists who have spent their careers studying clouds.
They see time running out for solutions. While the world's nations are planning to mitigate enough carbon emissions to contain the rise in the world's warming to a global average of 2 degrees Celsius by midcentury, the risks of missing this target may be severe.
V. "Ram" Ramanathan, a professor of atmospheric and climate sciences at the Scripps Institution of Oceanography in San Diego, is the co-author of a recent study predicting that without more action, there could be "catastrophic" and even "existential" results for mankind and other living species by the end of the century.
"We are now predicting in the study that there could be warming from 5 to 7 degrees," Ramanathan said in an interview. "You can't rule it out. It is a 5 to 10 percent [chance] that it could happen. In such an incident, we need to do something."
But what?
He was one of the leaders of a group of 33 scientists and other experts who unveiled the study at the United Nations in September. It says that besides containing the rise of CO2 emissions, nations must also take "fast and aggressive steps" to restrict other pollutants, such as soot or black carbon, and apply methods to extract more CO2 from the atmosphere.
Otherwise, the group predicted, billions of people could be exposed to potentially "deadly heat stress" and 20 percent of animal species could face "dangers of extinction" by the end of this century.
The level of support that his grim predictions earned surprised Ramanathan, who is cautious with his words and was a recent climate change adviser to Pope Francis. Ramanathan said he never expected to connect the word "existential" with climate threats until two recent cloud experiments helped change his mind. Even then, he was sure that other climate experts — often a contentious group — would disagree.
"I thought they would push back," he recalled. But they didn't. "So silently everyone has come to the conclusion that the problem is drifting away from us."
The signatories of the study suggesting that global warming threatens the human race included policymakers and scientists from China, India, Europe, Australia and leading U.S. universities. Mario Molina, a Nobel Prize winner who co-authored it, predicted that "we have less than a decade to put these solutions in place." Durwood Zaelke, a lawyer who is president of the Institute for Governance and Sustainable Development — a major promoter of the Montreal Protocol to protect the ozone layer — also signed it, even though he said the conclusion scared him.
"I'm an inveterate optimist about our power to control the future, but I am more frightened than I have ever been about this latest analysis," said Zaelke. Ramanathan "is one of our true geniuses in this. It doesn't always make him more popular, but he's always a step or two ahead."
Among the mechanisms named by the report that could trigger runaway warming are the loss of solar-reflecting sea ice from the poles, faster glacial melt caused by black carbon, and the release of methane and CO2 from thawing permafrost.
But experiments probing the behavior of clouds pushed Ramanathan to be even more concerned. One showed that low-level cloud systems including wispy stratocumulus clouds that shade much of the oceans in the midsection of the planet appear to be moving from the warmest part of the Earth toward the poles. "That is a big worry. It's amplifying the heat, moving in the wrong direction," he said.
A second experiment, where he used overhead satellite coverage and Earth-based drones to fly through, over and under soot-laden clouds in the Indian Ocean, suggested that one of the threats of what is sometimes called the "Asian brown cloud" of pollutants is that clouds laden with it absorb more heat that changes air movement or turbulence. This cuts their size and Earth-shading capabilities. The fact that aerosols, such as black carbon, can do that "is not in any model," Ramanathan noted.
Read more at Clouds' Warming Potential Is Frightening Researchers
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