Brightening the clouds on Earth to reflect more sunlight could help cool down the planet. But we need to make sure it won’t cause any other problems. To test this idea, a group of more than 30 top scientists wrote a plan published in the journal Science Advances.
Their plan focuses on how to try to make marine clouds over the ocean brighter by spraying saltwater into the air from ships. This idea is called marine cloud brightening (MCB). But they have to be really careful with these experiments because they fall into a controversial area called solar geoengineering. Solar geoengineering means trying to change the Earth’s environment to fight climate change by reflecting more sunlight.
Scientists are still not sure if this idea will work or if it could cause other problems. But with climate change causing more disasters and countries struggling to reduce pollution, some scientists see solar geoengineering as a backup plan.
“We have to think about backup plans, even if they’re not perfect,” said Lynn Russell, one of the authors of the paper and a climate scientist at the Scripps Institution of Oceanography at the University of California San Diego.
She explained that geoengineering, which means using new technologies to change the environment and possibly lower global temperatures, won’t stop the greenhouse gas emissions causing climate change. But it could help slow down the worsening climate disasters while policymakers work on reducing emissions. However, we need to understand the risks and benefits first.
There’s been debate over whether solar geoengineering should be used as a climate solution and how it should be regulated. Most of the debate has been about a different method called stratospheric aerosol injection (SAI), where particles are shot into the Earth’s stratosphere to reflect sunlight back into space.
In 2022, a startup caused a big fuss when it went ahead with its own experiments for solar geoengineering, despite a global agreement to stop large-scale projects like this. You can find videos of the founders on YouTube, where they’re experimenting with fungicide in a parking lot to make sulfur dioxide gas, which they then send up into the sky using a weather balloon. Even groups that were hopeful about solar geoengineering didn’t like these experiments because they thought it was taking attention away from more serious research into how to cool the planet, like what happens when volcanoes erupt and release sulfur dioxide.
Since then, there’s been a push from universities and international groups like the United Nations and European Union to make stricter rules for solar geoengineering. Some environmentalists are against solar geoengineering altogether, saying there’s too much we don’t know about it, and that we should focus on stopping the greenhouse gas emissions causing climate change.
Scientists aren’t as sure about marine cloud brightening as they are about other methods like stratospheric aerosol injection. So it’s no surprise that the authors of a new paper about marine cloud brightening want to be careful. A group of 31 scientists from different countries got together in 2022 to talk about what we already know about marine cloud brightening and what we still need to find out. Their paper, published this week, summarizes what they found and suggests a plan for more research.
Marine cloud brightening is kind of like what happens when volcanoes erupt. But instead of sending particles up high into the atmosphere like with stratospheric aerosol injection, it involves putting reflective particles into low-lying clouds. Pollution from ships also releases sulfur, which can have a similar cooling effect, although recent studies suggest we might have been overestimating how much it helps in the past.
Clouds are a bit of a puzzle for scientists studying climate, which makes trying to control them tricky. Some clouds block sunlight, while others trap heat. The idea with marine cloud brightening is to have more of the sun-blocking kind. But if we accidentally make clouds thinner and cause them to rain more, it could end up making things hotter. How a cloud behaves when humans try to change it depends on many complicated things, like the weather and how the particles we put into the air mix with other tiny particles already there.
Graham Feingold, who works at NOAA’s Chemical Sciences Laboratory, says it’s a big challenge to get the right-sized particles into the right clouds at the right times and places to cover large areas of the ocean with shade.
Whether marine cloud brightening could really work in the real world depends on if lab tests and computer models show it could be helpful. Scientists also need to see if small tests outside can be made big enough to make a difference all over the world. Using satellites to watch what happens would be really important. Besides the science part, there are also social and ethical questions to think about. How can we make sure everyone is treated fairly if we start doing this? Changing clouds might bring more rain to some places and less to others.
Feingold says that even though more people are interested in marine cloud brightening, policymakers don’t have enough information yet to decide if or when to use it. The big question is whether we can use what we already know to figure out if this idea could really work on a global scale, and if not, what we need to do to make it happen.
