Could bright clouds buy us time to fight climate change?

Brightening Earth’s clouds so they reflect more sunlight could cool the planet—if we can figure out how to do it without causing any unintended harm.To test this theory, a team of more than 30 leading scientists compiled a research roadmap and published it in the journal scientific progress yesterday.

The paper focuses on how the Earth’s surface can be artificially obscured with ocean clouds by spraying salt water from ships into the air, a strategy called ocean cloud brightening (MCB). They need to be very careful about any future experiments, which would fall into the controversial category of solar geoengineering. The idea is to offset some of the effects of climate change by finding ways to reflect solar radiation.

Researchers still don’t know how fruitful these efforts will be, or whether they might inadvertently create new problems by disrupting the planet in such a way. But as climate change triggers growing disasters and countries fall behind on goals to reduce pollution that heats the planet, some scientists see solar geoengineering as a possible emergency plan.

“We need to think about fallback plans for less than ideal conditions to give us enough time.” .

She added that geoengineering – deploying new technologies to manipulate the environment to lower global temperatures – would do nothing to stop the greenhouse gas emissions that drive climate change. It has the potential to slow worsening climate disasters as policymakers work to reduce emissions. But first, it’s important to understand what the possible risks and benefits are.

There is already debate about what role, if any, solar geoengineering should play as a climate solution and how it should be regulated. So far, the drama has centered around a different strategy called stratospheric aerosol injection (SAI), which involves catapulting particles into the Earth’s stratosphere to reflect sunlight back into space.

In 2022, a start-up company caused a global uproar when it effectively suspended large-scale geoengineering around the world but continued to advance its own temporary SAI experiments. You can see the co-founders on YouTube grilling biocide in a parking lot to create sulfur dioxide gas, which is then launched in a weather balloon. Even groups optimistic about solar geoengineering have balked at the experiments, saying they undermine more serious research into how to mimic the way volcanoes spew sulfur dioxide to temporarily cool the Earth during eruptions.

Since then, academics and international agencies including the United Nations and the European Union have been working to develop stronger guidelines for solar geoengineering. Some environmental advocates oppose solar geoengineering outright, saying there are too many uncertainties and that climate solutions need to focus on preventing greenhouse gas emissions from causing climate change.

Scientists are more uncertain about the effects of ocean cloud brightening than stratospheric aerosol injection. So it’s not surprising that the authors of the new MCB paper want to err on the side of caution. A group of 31 scientists from around the world met in 2022 to assess the current scientific understanding of ocean cloud brightening and what knowledge gaps need to be filled. Their paper published this week summarizes their findings and lays out plans to advance MCB research.

Ocean clouds brighten to mimic the effect of a volcanic eruption. But unlike SAI, it sends reflected particles to low-altitude clouds rather than to the higher stratosphere. Sulfur in ship stack pollution has also been shown to have a similar reflective effect, although recent research suggests this may have been overestimated in the past.

Clouds are a climate mystery, which makes them particularly difficult to manipulate. Some types of clouds block sunlight, while others absorb heat. Of course, the goal of ocean cloud brightening is to get more of the former. Inadvertent thinning of clouds and rainfall could lead to higher temperatures. Cloud formation or response to human intervention will depend on a complex, ever-changing set of factors—from weather to how human-borne particles interact with other aerosols already in the air.

“We have to put the right-sized particles into the receiving cloud at the right time of day and season, and over a large enough area to cover a large swath of the ocean… This is a major challenge,” said lead author and U.S. a researcher at NOAA’s Chemical Sciences Laboratory said in a press release.

The real-world feasibility of ocean cloud brightening will depend on whether researchers see positive results in laboratory tests and modeling studies, the new paper says. They also need to see if small field tests can be scaled up to have a global impact. Satellite observations are critical for monitoring the results of such experiments. In addition to the physical science feasibility discussed in this article, there are social and ethical implications that need to be considered. How do you avoid any differences in terms of who benefits or who bears any unforeseen burdens? For example, brightening ocean clouds could trigger changes in rainfall in different areas.

“Interest in MCBs is growing, but policymakers currently do not have the information they need to decide if and when to deploy MCBs,” Feingold said. “The question is whether we can design MCBs using our current modeling and observational tools. Research is planned to determine whether this approach is feasible on a global scale and, if not, what steps are needed to achieve this.”