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Sowing the atmosphere with aerosols would not prevent high concentrations of carbon dioxide in the atmosphere from destabilizing low clouds, opening the door to extreme warming
Pumping aerosols into the atmosphere to reflect sunlight, thereby cooling the Earth, is a next-generation method of dealing with climate change. According to new research from Caltech, however, such solar geoengineering may fail to prevent catastrophic warming in the long term.
Solar geoengineering has received attention because it is feasible with existing technology, says Tapio Schneider, Theodore Y. Wu Professor of environmental science and engineering and senior researcher at JPL, which Caltech manages for NASA.
“Obviously, there are governance and ethical issues about who controls the Earth’s thermostat,” says Schneider, but “beyond that, our research shows that solar geoengineering may ultimately not solve the problem if greenhouse gas emissions high levels continue for more than a century “.
Using high-resolution computer simulations, Schneider and colleagues Colleen M. Kaul and Kyle G. Pressel of the Pacific Northwest National Laboratories in Washington demonstrated that very high concentrations of carbon dioxide (CO2) could still break up low-lying stratocumulus clouds. and this cloud destruction could trigger potentially sudden warming of about 10 degrees Fahrenheit.
A study explaining their findings was published in the journal Proceedings of the National Academy of Sciences on November 16.
Broadly speaking, solar geoengineering works like this: If the Earth is getting too hot due to increasing concentrations of greenhouse gases, which heat the Earth by absorbing infrared radiation, it can cool the Earth by blocking out some sunlight. However, while this could potentially work in the short term, it ignores the bigger picture of how clouds work, Schneider and colleagues say.
Lower stratocumulus clouds cool the Earth by reflecting sunlight back into space. They also radiate infrared radiation upward from their cloud tops, thereby cooling the air in the clouds and guiding it downward to the planet’s surface. This forms a connection between clouds and their moisture supply on the surfaces of the Earth’s oceans.
The researchers’ computer simulations show that the presence of high concentrations of greenhouse gases such as CO2 effectively places an infrared blanket on the clouds that prevents them from radiating upward energy. This can cause clouds to break up, leading to severe warming, which would also occur if incoming sunlight were blocked by geoengineering efforts.
“The findings may also have implications for climates early in Earth’s history, when the sun was weaker but the Earth was relatively warm,” Schneider says. “Most importantly, they show that by continuing to emit greenhouse gases, with or without geoengineering, humans are disrupting an incredibly complex system that could hold us climate surprises.”
The paper is titled “Solar geoengineering may not prevent strong warming from direct effects of CO2 on the cloud cover of stratocumulus.” This research was supported by Eric and Wendy Schmidt on the recommendation of the Schmidt Futures program; the Earthrise Alliance; Mountain philanthropies; the Paul G. Allen Family Foundation; Caltech Senior Trustee Charles Trimble (BS ’63, MS ’64); and the National Science Foundation.
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