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Particles in ships\u2019 exhaust inadvertently cause cloud brightening, and a similar effect could be employed to engineer the climate<\/p>\n
NASA\u2019s Earth Obervatory<\/p>\n<\/p>\n
Short-term geoengineering to brighten clouds over the eastern Pacific Ocean could limit the damage caused by El Ni\u00f1o and save the global economy trillions of dollars, although there could be winners and losers from the disruption of natural cycles.<\/p>\n
The El Ni\u00f1o climate phase occurs when easterly winds weaken, allowing warm water built up in the western Pacific to slosh back across the central and eastern parts of the ocean. That heats the atmosphere and raises global temperatures, with losses to economic growth estimated in the trillions of dollars.<\/a><\/p>\n What could become a very strong or \u201csuper\u201d El Ni\u00f1o is now developing in the eastern Pacific.<\/a> But climate modelling has suggested that, in the future, a geoengineering method called marine cloud brightening<\/a> might be able to cut this warming short.<\/p>\n The technique involves spraying tiny droplets of seawater into the air below low-lying stratocumulus clouds, where moisture condenses onto them. The clouds become whiter thanks to the increase in the number of droplets, reflecting more sunlight back to space.<\/p>\n Shading part of the eastern Pacific called the Ni\u00f1o 3.4 region via cloud brightening could interrupt the feedback loops that cause an El Ni\u00f1o to develop. Cooler sea surface temperatures would strengthen the trade winds to again blow warm water back into the western Pacific. More cool water would then well up from the depths of the eastern Pacific, further cooling surface temperatures, and so on.<\/p>\n \u201cYou can basically stop the dominoes from falling early when you do marine cloud brightening,\u201d says Jessica Wan<\/a> at the University of California, San Diego, who worked on the study. \u201cWe\u2019re kicking the cycle in the other direction.\u201d<\/p>\n Wan and her colleagues got the idea from the \u201cblack summer\u201d of catastrophic bush fires in Australia in 2019-2020, which were followed by La Ni\u00f1a, the opposite phase of El Ni\u00f1o that lowers global temperatures. Research has suggested<\/a> that drifting smoke particles brightened clouds and cooled the eastern Pacific, intensifying and prolonging the \u201ctriple dip\u201d La Ni\u00f1a<\/a> that began in 2020 and persisted through three winters, rather than just one or two.<\/p>\n The study modelled what cloud brightening could have done to the super El Ni\u00f1o events of 1997-1998 and 2015-2016. It found that nine months of spraying seawater would have nearly halved warming of the Ni\u00f1o 3.4 region, from 2\u00b0C or more to a little over 1\u00b0C. It would have ended the El Ni\u00f1o by January, shaving several months off the events.<\/p>\n The hypothetical cloud-brightening mission would have been massive, involving an estimated 2400 ships and delivering an amount of seawater spray that isn\u2019t possible with current nozzle technology. But it would have turned a super El Ni\u00f1o into a moderate one.<\/p>\n Wan says she was surprised how well it seemed to work, given that it could only be started in June, once El Ni\u00f1o had clearly begun developing.<\/p>\n Mat Collins<\/a> at the University of Exeter, UK, warns that these results might not translate to the real world, where warming seas typically start dissipating low-level clouds, leading to further warming and dissipation through a feedback loop.<\/p>\n \u201cIn a model with a stronger cloud feedback, you would have to do more aerosol injection,\u201d he says. \u201cThe experiments seem to be at the limit of what can be done.\u201d<\/p>\n Wan admits this approach could have unexpected consequences, since the model only projected the impact over two-year periods. In both simulations, La Ni\u00f1a started earlier after El Ni\u00f1o subsided, and in the 2015-2016 case, this subsequent cooler phase became stronger. That could be bad news for regions like the Horn of Africa, where strong La Ni\u00f1as have, in the past, disrupted rainfall and contributed to widespread famine<\/a>.<\/p>\n