Can glowing clouds buy us time to fight climate change?

Making Earth’s clouds brighter so they reflect more sunlight might just cool the planet – if we can figure out how to do that without causing unintended damage. To test the theory, a group of more than thirty leading scientists wrote a research roadmap that was published in the journal. Scientific progress yesterday.

The article focuses on how to tackle attempts to artificially darken the Earth’s surface with marine clouds by spraying salt water into the air from ships, a strategy called marine cloud brightening (MCB). They will have to be very careful with future experiments, which would fall into the controversial category of solar geoengineering. The idea is to counter some of the effects of climate change by finding ways to reflect solar radiation.

Researchers still don’t understand how fruitful these efforts would be, nor whether they could inadvertently create new problems by tampering with the planet in this way. But as climate change causes ever-greater disasters and countries fall behind on targets to reduce global warming pollution, some scientists see solar geoengineering as a possible fallback plan.

“We have to consider less than ideal backup plans just to buy enough time.”

“We need to consider less than ideal backup plans just to buy enough time,” Lynn Russell, co-author of the paper and a climate scientist at the Scripps Institution of Oceanography at the University of California San Diego, said in a press release . .

Geoengineering – deploying new technologies to manipulate the environment in ways that could lower global temperatures – does nothing to stop the greenhouse gas emissions that cause climate change, she added. It could have the potential to slow worsening climate disasters as policymakers work to reduce emissions. But first, it’s important to know what the potential risks and benefits are.

There have already been battles over what role solar geoengineering should play as a climate solution and how to regulate it. So far, the drama has mainly involved another strategy called stratospheric aerosol injection (SAI), which involves catapulting particles into Earth’s stratosphere to reflect sunlight back into space.

One startup caused a global stir in 2022 when it pushed ahead with its own makeshift SAI experiments despite a de facto global moratorium on large-scale geoengineering. You can watch the co-founders on YouTube grilling fungicide in a parking lot to create sulfur dioxide gas, which they then launch aboard a weather balloon. Even groups optimistic about solar geoengineering opposed the experiments, saying it undermined more serious research into how to mimic the way volcanoes temporarily cooled the planet by spewing sulfur dioxide during eruptions.

Since then, there has been pressure within academia and international institutions, including the United Nations and the European Union, to establish stronger guidelines for solar geoengineering. Some environmental advocates are against solar geoengineering altogether, saying the uncertainties are too great and that climate solutions should focus on preventing the greenhouse gas emissions that cause climate change.

Scientists are even more uncertain about the effects of brightening marine clouds than they are about injecting aerosols into the stratosphere. So it’s no surprise that the authors of the new MCB article want to proceed with caution. The group of 31 scientists from around the world met in 2022 to assess where the current scientific understanding of marine cloud brightening stands and what knowledge gaps need to be filled. The paper they published this week summarizes their findings and proposes a plan to advance MCB research.

The lighting of marine clouds mimics the effects of volcanic eruptions. But unlike SAI, this involves sending reflective particles toward low-lying clouds rather than higher up in the 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, making them particularly difficult to manipulate. Some types of clouds block sunlight, while others can trap heat. The goal of brightening marine clouds is obviously to achieve more of the former. If cloud cover unintentionally thins and rain falls, this could lead to more warming. The way a cloud forms or responds to human intervention will depend on a range of complex, changing factors – from the weather to the way particles spread by humans interact with other aerosols already in the air.

“We would have to get the right size particles into receptive clouds at the right times of day and in the right seasons, and over areas large enough to cover large parts of the ocean… It’s a big challenge,” Graham Feingold, lead author and a researcher at NOAA’s Chemical Sciences Laboratory, said in a press release.

How feasible brightening marine clouds is in the real world will depend on whether researchers see positive results in laboratory tests and modeling studies, the new paper says. They will also have to see if small field tests can be scaled up to have a global impact. Satellite observations would be crucial for monitoring the results of such experiments. In addition to the scientific feasibility discussed in this article, societal and ethical implications will also need to be considered. How do you prevent differences when it comes to who benefits from this or who bears unforeseen burdens? For example, brightening marine clouds could cause changes in rainfall from region to region.

“Interest in MCB is growing, but policymakers currently do not have the information they need to decide if and when to deploy MCB,” Feingold said. “The question is whether we can design an MCB research program using our current modeling and observation tools to determine the feasibility of this approach on a global scale, and if not, what needs to be done to position ourselves to do this.”

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