- Marine cloud brightening (MCB), the spraying of sea salt aerosols or other fine particles into clouds to artificially brighten them and increase the sun’s reflectivity, is a proposed strategy to ward off the full effects of climate change.
- However, this solar radiation management (SRM) geoengineering technique is highly controversial, and experts say governance of MCB field experiments and deployment is needed now at the national and international levels.
- Ongoing efforts to include marine cloud brightening under an international anti-marine pollution treaty, the London Protocol, could be one effective route to setting standards for research and field experiments.
- But if MCB is deployed on a large scale, some experts say there is the potential for serious negative effects on the global climate system. These impacts could be especially severe if deployment is uncontrolled and lacks science-based governance.
Regional deployment of marine cloud brightening off the U.S. West Coast would be far less effective in the warmer world of 2050, and if implemented, could unleash higher temperatures in Europe and other regions, warns recent research.
The June 2024 modeling study of the controversial geoengineering technique shows “that a regional intervention will have large scale implications. So even though you’re applying [MCB] in a smaller space, the impacts [end up being] global,” says Jessica Wan, first author on the paper and a climate sciences Ph.D. candidate at California’s Scripps Institution of Oceanography.
Marine cloud brightening is a form of solar radiation management. According to the theory, spraying sea salt aerosols, or other tiny particles, into clouds over the world’s oceans could make those clouds brighter, reflecting more of the sun’s rays back into space and leading to a cooling effect on the Earth below.
MCB is viewed as a geoengineering technology that could buy time, while the world drastically slashes its carbon emissions, and as a “painkiller” to ward off the worst impacts of greenhouse gas-induced warming, while those deep cuts are made.
But MCB experimentation and implementation are highly controversial, with opponents calling for an outright ban on marine geoengineering technologies, which they describe as a “dangerous distraction” from tackling climate change emission reductions.
Others argue MCB research is needed now to keep all options on the table, in case aggressive carbon-cutting measures fail to quickly materialize. Adding to the debate, experts warn of the risk posed by the dearth of national and international regulations to guide marine cloud brightening testing and use.
A future fraught with unknowns
Studies like Wan’s highlight the major knowledge gaps that remain in a field that’s been mostly confined thus far to modeling, and point up the vast uncertainties of how MCB should and could be deployed.
For Wan, the “big picture” takeaway is that “the widespread climate impacts of a regional intervention will change under different climate conditions,” meaning that testing and deployment impacts in today’s climate could be very different from those in the more globally warmed future.
“I think the paper shows convincingly that the effectiveness of marine cloud brightening in a certain region can change with continued global warming. [But] I’m not convinced that the change will always be to diminish efficacy,” said Michael Diamond, assistant professor of meteorology and environmental science at Florida State University, who was not involved in the study. “Other work has found that very local deployments (like just over the Great Barrier Reef) don’t seem to have detectable remote effects.”
In Diamond’s view, one conclusion could be that marine cloud brightening may be an option for either large-scale or small-scale deployment to protect fragile ecosystems, but not appropriate at the regional scale.
A tale of two tests
Earlier this year, a small-scale MCB field test led by University of Washington researchers off the Pacific coast of Alameda, California, sputtered to a halt after local officials pulled the plug, a decision welcomed by some campaign organizations.
The incident shed a spotlight on this controversial marine geoengineering technique, raising questions about how small-scale field experiments should be conducted amid the wider lack of global governance.
Scientists involved in the project are currently “exploring next steps,” Kelly Wanser told Mongabay in an email. Wanser is the project co-founder and senior adviser to the University of Washington MCB program.
In Wanser’s view, the Alameda project was not a cloud-brightening experiment at all, as it was too small in scale to “brighten clouds or significantly impact the environment.” It was only intended to gather data on salt spray aerosol distribution and test the basic MCB concept.
“It is extremely important to differentiate between [small-scale field] research — especially basic research on aerosol influences on climate and their impacts on ecosystems and communities — and impact-scale experimentation or activities related to using or marketing climate interventions,” she says.
“One piece of specific learning that emerged [from the Alameda project] is that [researchers have] to provide state and federal agencies with the tools they need for [geoengineering] regulation and enforcement, and for educating and informing the public. These small-scale studies will be important and it may be valuable for the agencies to undertake them directly,” she wrote.
In contrast to the study shutdown in California, MCB tests uninhibited by public protest have been underway in Australia for several years, with a first field experiment conducted in 2020 on the Great Barrier Reef.
“There’s only one option for [saving] coral reefs and [that’s] to manage climate change, to reduce emissions, [and] get to net zero as soon as possible and stop this rise in temperature,” says Cedric Robillot, executive director of the Reef Restoration and Adaptation Program. He notes that research shows cloud brightening has the potential to “buy a bit of time” for corals if used in combination with other “coral-centric” interventions.
The Australian MCB research project, unlike the one shut down in California, is subject to an established research permitting protocol enforced within Great Barrier Reef Marine Park. Tests there have thus far been limited in scale, and to scale up, experts say further regulation and oversight will be needed at the national and international levels.
“You’d struggle to find any way to add more governance over this, because of the way the marine park is regulated. That doesn’t mean that is the case everywhere,” says Robillot. “We are highly governed. That doesn’t mean that we are on a crusade to allow global geoengineering to happen.”
Any eventual MCB deployment over the Great Reef would not have transboundary effects according to research, say experts affiliated with the project. If that’s right, decisions of deployment governance could remain within national boundaries — or not.
“That’s the problem with global geoengineering … [O]ne country might think it’s better for them, but the effects are negative for others,” says Robillot. “If it is within your jurisdiction, then I think it’s important to leave these countries to have a choice in terms of the tradeoffs.”
Toward a global marine geoengineering protocol
Because humanity’s climate change and geoengineering crystal balls are murky, there’s no absolute certainty that deployment impacts could be confined to one nation. But the absence of coordinated governance of such tests or potential deployments means no one today is guiding decision-making at the regional or planetary level.
“We don’t currently have any legally binding agreements that directly and specifically address marine geoengineering activities,” says Romany Webb, deputy director of Columbia University’s Sabin Center for Climate Change Law. “But we do have a lot of general international environmental agreements and other international agreements that could impact where and how we engage in marine geoengineering.”
An often-cited 2010 decision by the Convention on Biological Diversity is interpreted by some as a de facto moratorium on any deployment of solar geoengineering that would have negative effects on biodiversity, though this reading is considered a reach by other experts.
A more flexible framework that could offer a means for MCB guidance and governance is the London Protocol, an international agreement to prevent ocean dumping of waste that entered into force in 2006 and was intended to replace the earlier London Convention. In a 2013 amendment, policymakers outlined international restrictions on ocean fertilization that would provoke the growth of algae and thus absorb carbon. But crucially, that amendment has only been accepted by six countries thus far — the United Kingdom, Finland, the Netherlands, Norway, Estonia and Germany — and is yet to come into force; if passed, it would only cover 60 or so nations. Countries including Canada, Germany and Australia have taken cues from it, however, and are in the process of adopting legislation. Among major global powers, China is a party to the protocol but has not accepted this amendment, while the U.S. and Russia have yet to ratify it.
The London Protocol is currently reviewing four other marine geoengineering techniques, including marine cloud brightening, ocean alkalinity enhancement, and biomass sequestration. In 2022, the protocol’s scientific group warned these technologies “have the potential to cause deleterious effects that are widespread, long-lasting or severe.”
Such risks are precisely why there’s an urgency to investigate potential impacts and determine how research should be regulated, says Andrew Birchenough, a technical officer with the International Maritime Organization’s Office for the London Convention/Protocol and Ocean Affairs.
The London Protocol geoengineering regulation process, which lacks a firm timeline, could one day result in the adoption of restrictions to ocean fertilization and/or new assessment guidelines specific to each of the marine geoengineering techniques, he adds.
Birchenough notes the ultimate intention isn’t to ban these activities, but to put a framework in place that enforces responsible research that is “assessed appropriately.” However, governance of potential deployments is a “larger issue” that “can only be answered when you’ve [carried out] some of these activities, experiments and scientific research.”
For Webb, the current international policymaking void is “very problematic,” adding that, “The huge amount of uncertainty associated with governance could be a real barrier to moving forward with needed research.” The dearth of guidance, she notes, “creates opportunities for rogue actors, or others, to pursue projects that shouldn’t be happening at the current time.”
Coordinating research, understanding risks
While the London Protocol may eventually create a somewhat limited framework for the study of MCB, earlier this year an international group of experts released a call to deepen research in a coordinated fashion, including small-scale experimentation.
“If we are going to embark on a large-scale marine cloud brightening effort we need to understand the larger scale [atmospheric] circulation changes” that MCB could bring, says Graham Feingold, leader of the Clouds, Aerosol and Climate Program at NOAA’s Chemical Sciences Laboratory. Feingold points to the lack of “well-coordinated” research in this area at both the national and international levels.
Large-scale research is not only essential to understanding if MCB is technically feasible and cost effective, but to shed light on the potential negative consequences of tinkering with global marine cloud formation and atmospheric circulation, both of which remain poorly understood. “If you seed clouds in the Southeast Atlantic, you could have changes to clouds, temperature and precipitation in the Amazon, for example,” Feingold states.
“That’s something that really needs to be brought to the fore because this is not just a local problem, this is a global problem,” Feingold adds. “Sensitive ecosystems may be at risk, like the Amazon. There is a distinct possibility that MCB could benefit certain parts of the world but have deleterious effects in other parts of the world and we need to understand that.”
If, for example, an MCB deployment were to deepen Amazon drought, that would cause tree die-off, weakening the Amazon carbon sink and ultimately worsening climate change — potentially undoing some or all the good MCB might do.
What’s clear is that marine cloud brightening research, and all geoengineering research for that matter, remains in its infancy, and the science will stay contentious and highly debated until studies begin delineating possible real-world impacts. Likewise, policy and governance need to catch up with the international momentum and the billionaire entrepreneurial buzz that’s building behind these activities.
“There needs to be governance at all levels, from the local scale all the way up to global structures,” Wan states. What exactly that will look like, however, is still up in the air.
Banner image: To date, MCB research has mostly taken the form of modeling. One paper published earlier this year suggests that the efficacy of regional cloud brightening on the U.S. West Coast could decline substantially as climate change worsens, with negative knock-on effects, including increased temperatures in Europe and other parts of the world. Image by Joel Hatfield via Flickr (CC BY-ND 2.0).
Citations:
Wan, J. S., Chen, C. J., Tilmes, S., Luongo, M. T., Richter, J. H., & Ricke, K. (2024). Diminished efficacy of regional marine cloud brightening in a warmer world. Nature Climate Change, 14, 808-814. doi:10.1038/s41558-024-02046-7
Chen, Y., Haywood, J., Wang, Y., Malavelle, F., Jordan, G., Peace, A., … Lohmann, U. (2023). Substantial cooling effect from aerosol-induced increase in tropical marine cloud cover. Nature Geoscience, 17(5), 404-410. doi:10.1038/s41561-024-01427-z
Latham, J., Kleypas, J., Hauser, R., Parkes, B., & Gadian, A. (2013). Can marine cloud brightening reduce coral bleaching? Atmospheric Science Letters, 14(4), 214-219. doi:10.1002/asl2.442
Hirasawa, H., Hingmire, D. S., Singh, H. A., Rasch, P. J., & Mitra, P. (2023). Effect of regional marine cloud brightening interventions on climate tipping elements. Geophysical Research Letters, 50(20). doi:10.1029/2023gl104314
Feingold, G., Ghate, V. P., Russell, L. M., Blossey, P., Cantrell, W., Christensen, M. W., … Zheng, X. (2024). Physical science research needed to evaluate the viability and risks of marine cloud brightening. Science Advances, 10(12). doi:10.1126/sciadv.adi8594
Russell, L. M., Sorooshian, A., Seinfeld, J. H., Albrecht, B. A., Nenes, A., Ahlm, L., … Wonaschütz, A. (2013). Eastern Pacific emitted aerosol cloud experiment. Bulletin of the American Meteorological Society, 94(5), 709-729. doi:10.1175/bams-d-12-00015.1
MacMartin, D. G., Kravitz, B., & Goddard, P. B. (2023). Transboundary effects from idealized regional geoengineering. Environmental Research Communications, 5(9), 091004. doi:10.1088/2515-7620/acf441
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