What would happen if Earth had no clouds?
“It’s a very interesting thought experiment,” says Storelvmo, an atmospheric scientist at the University of Oslo in Norway. On one hand, the reflectivity (albedo) of our planet is strongly determined by cloud cover. Removing the clouds would make the planet darker, allowing it to absorb more sunlight and warm up. However, clouds also act like a blanket to trap heat, preventing Earth from cooling down. So removing them would also lead to a cooling effect. Storelvmo says that the loss of reflectivity would likely dominate. “A simple back-of-the-envelope calculation of the net effect of removing clouds from Earth’s energy budget would give a warming of something like 10 degrees Celsius,” she explains. “This, in turn, would lead to a planet drastically different than the present, one almost certainly without any permanent ice sheets or sea ice.” The calculations could be made much more complicated by considering the effects on the hydrological cycle, because without clouds in the atmosphere, there could not be rain or snow. If for some reason clouds could not form, it would lead to a build-up of water vapour in the atmosphere. As water vapour is a potent greenhouse gas, this should lead to a greenhouse effect much stronger than at present – adding further warming. Thankfully, this isn’t something we need to worry about. “While a warmer atmosphere is indeed expected to have fewer clouds, a completely cloud-free Earth in response to warming is not plausible by any stretch of the imagination,” says Storelvmo. In the MC2 project, which was funded by the European Research Council, Storelvmo explored the role of mixed-phase clouds (which contain both liquid and ice) in the climate system. Among other results, Storelvmo’s team showed how microscopic properties, such as aerosol particles, cloud droplets and ice crystals, as well as their interactions, have an outsized influence on cloud feedback processes, and therefore global warming. Could we counteract the expected loss of clouds due to global warming? There are currently several ideas which all fall in the category of solar radiation modification (SRM). For example, cloud seeding is a controversial idea that aims to increase cloud cover and overall reflectivity by spraying particles into the atmosphere. Storelvmo agrees that cloud seeding has the potential to counteract some of the cloud reduction – we already see inadvertent cloud seeding triggered by the exhaust plumes of ships, leading to brighter and more persistent clouds. “However, exactly how much cooling one could get out of such cloud seeding remains an area of active research,” she adds. Click here to find out more about Trude Storelvmo’s research: Unpicking the role of mixed-phase clouds in the climate system
Keywords
MC2, cloud seeding, global warming, ship, exhaust, aerosol, albedo