Earlier this week, the City of Alameda, CA asked scientists to shut down an ongoing experiment into marine cloud brightening, a form of solar geoengineering (also known as solar radiation management) citing concerns about public health.
Marine cloud brightening is, in theory, a way of cooling the earth by making certain clouds have a greater albedo effect, which describes how light-colored surfaces (like polar ice caps) reflect more solar radiation (and therefore heat) back to space. It mostly has been studied on a certain type of cloud that often comes from ship emissions or volcanic eruptions, which have higher aerosol and cloud droplet concentrations than other clouds and thus reflect more light back to space. The theory underpinning marine cloud brightening is that by creating higher concentrations of droplets using sea spray, the clouds would reflect even more light and therefore heat away from Earth, having local and possibly larger, cooling effects. Additionally, lower temperatures would allow plants, soils, and the oceans to draw up more atmospheric carbon dioxide, helping to slow rising carbon dioxide levels, according to the Intergovernmental Panel on Climate Change.
(There weren’t any actual immediate concerns about public health related to the experiment, which had been going on since April 2 aboard the U.S.S. Hornet, a decommissioned aircraft carrier docked in San Francisco Bay. The University of Washington Marine Cloud Brightening Research Program, which was running the experiment, said the salt particles being sprayed “operate well below established thresholds for environmental or human health impact for emissions.”)
There are larger concerns about marine cloud brightening as a general concept: increasing cloud cover in some places might change rainfall amounts, increasing it in some places and decreasing it in others; it could alter ocean circulation patterns, which could affect fisheries. Similar concerns hold for stratospheric aerosol injection, another kind of solar radiation management, where aerosols like sulfur dioxide are sprayed into the stratosphere to also mimic the albedo effect, but with possibly even greater effects — over land, as opposed to the ocean, changing cloud patterns and precipitation could negatively impact agricultural production and other seasonal occurrences that people, animals, and plants depend on.
More broadly, when it comes to solar geoengineering, some people in the climate and environmental movement worry that pursuing research and experimentation in these kinds of climate interventions will distract attention, funding, and political will away from decarbonization and the existing technologies and abilities we have to reduce emissions. Another worry about purposeful geoengineering (as opposed to the cooling effect that our particle pollution has had, in an unintended way) is that we’d have to keep doing it forever — to have any kind of lasting effect, we’d have to do it for decades, and then were we to stop, rapid warming would follow.
I’m skeptical of the notion that geoengineering at this stage will take meaningful funding and research away from things like decarbonizing electricity, transportation, and industry, since those areas are more likely to generate a profit and are already technologically possible or soon will be. But it’s possible, if not probable or maybe even inevitable, that some company or country will deploy some kind of geoengineering practice in the near future which would certainly change how the global community does or doesn’t address the underlying issue of greenhouse gas emissions and climate change. On the other hand, that’s an argument that more research needs to be done and soon, so that we have a better idea of what will actually happen if large scale solar radiation management does occur.
It’s really easy to argue both sides of this issue: “We’re already geoengineering, basically, with greenhouse gas emissions and particulate pollution, and we had no idea what the consequences would be so we might as well try to make it work for us” goes one side; “We’ve already messed so much with planetary systems that we should be extra careful before screwing with everything in a way that we can’t undo” goes the other.
I’ve been learning a lot about ocean engineering and marine carbon dioxide removal lately for a separate project, which has me thinking about these questions in a slightly different context, more related to carbon dioxide removal than cooling mechanisms, but in the ocean, there’s some overlap. The IPCC has acknowledged in its periodic assessments, including in the Paris agreement, that to keep atmospheric warming to 1.5ºC, we will need to remove somewhere between 100 and 1000 gigatons of carbon dioxide and we will have to use technologies like direct air capture of carbon dioxide, marine carbon dioxide removal, or solar geoengineering to do so.
There are a few kinds of ocean engineering, though they all leverage the inherent power of the ocean to absorb carbon dioxide from the atmosphere, something the ocean does to a planet-saving extent already: oceans have absorbed 30 percent of the excess carbon dioxide we’ve pumped into the atmosphere, and about 90 percent of the excess heat, preventing the Earth from warming by about 36ºF. Some of the approaches I’ve learned about rely on enhancing or accelerating natural mechanisms of carbon storage or removal, such as ocean alkalinity enhancement/enhanced mineral weathering, iron fertilization (mimicking the biological pump of nutrients produced by whales and other animals), biomass sinking, or direct carbon capture through physical processes like electrolysis or electrodialysis.
Mostly, they all come to the same thing, which is removing some carbon dioxide from the ocean or converting it to a different form so that the ocean can draw down more atmospheric carbon dioxide. In the ocean, there’s also the added benefit of reducing ocean acidification — all of the carbon the ocean has absorbed over time has changed its pH balance, which has made it harder for some animals, like corals and shellfish to grow their skeletons and shells.
What’s cooler than a kelp forest?!
There are also natural/nature-based solutions which achieve these same or similar outcomes, albeit on a smaller scale, and can be actively helped along by people with some interventions, or can be the product of more laid-back management, just through conservation measures: kelp reforestation, coastal restoration of shellfish beds, seagrass meadow and mangrove replanting, coral reef restoration, or simple things like saving the whales or creating marine protected areas. All of these plants and animals natural take up carbon dioxide from the ocean, and when they die, that carbon sinks to the ocean bottom where, if undisturbed, it will be stored more or less permanently. Plus, they help restore ecosystems or protect species that have been harmed by development, exploitation, or the effects of climate change. None of those can happen at the scale required to keep warming to 1.5ºC, but they also shouldn’t be overlooked — just because something doesn’t require manmade hardware doesn’t mean it’s a technology not worth pursuing.
Having learned about this — the basic science research part of it and the emerging commercial sector — I’m not sure exactly where I net out on the whole thing. The technology that is enabling decarbonization of electricity, transportation and industry basically didn’t exist a decade ago (in an economically logical form), and has been taken up pretty quickly, in the scheme of things. The rapid adoption thus far of clean energy, and, to a lesser extent, electric vehicles, has made a really big difference in the global trajectory since 2015, when the Paris agreement was signed. Even though energy-related carbon dioxide emissions grew in 2023, without the growth of five clean energy technologies — solar, wind, nuclear, heat pumps, and electric cars — emissions growth would have been three times larger, according to the International Energy Agency’s most recent report on carbon dioxide emissions.
Ocean engineering has a very large potential to reduce atmospheric carbon and provide other benefits, so when I’ve spoken to people working to start or grow companies in this area, it’s really exciting! I know there’s some hype inherent in a conversation between a start-up founder and a journalist, but I was also impressed by the methodical way in which many of the companies seemed to approach their work, scaling up only when the results indicated that it would work; using existing infrastructure (desalination plants, utilities, aquaculture facilities, etc.) and their energy supply, or relying only on clean energy; imagining new applications of simple strategies (antacids for the ocean!) or accelerating biological processes with a minimum of harm. I’m excited that people are dreaming up new ways to solve this thorny set of problems, and trying to make it attractive to investors and ready to go when/if a carbon tax is imposed or the offset market becomes mandatory.
Satellite imagery of nutrient pollution in the Baltic Sea. Credit Copernicus Program via Puget Sound Institute
But, part of me is wary of further commercialization of the ocean and what might happen to local and regional ecosystems that depend on them if the chemistry is messed with too much. I worry less (right now anyway) that this will give people license to emit more polluting carbon dioxide than that there will be some unanticipated local effect on particular biological processes or important species, either because the swings in the chemistry are too big or happen too quickly, whose effects are irreversible and cascading. I’m imaging the unintended consequences that have accompanied other changes we’ve made — ones that are not deliberate or are unmeasured but still serve to upend the ways things work in the ocean, like nutrient pollution from fertilizer or wastewater runoff. That change to ocean chemistry wasn’t intended or assumed to be beneficial, but it still affects ecosystem function in ways that we struggle to undo or even contain. Changing ocean chemistry locally or on a large scale with industrial or commercial pressures could also be hard to reverse if the consequences aren’t what scientists anticipate or what company founders promise.
But things aren’t happening fast enough and big enough, and I want ocean CDR to work and direct air capture to work because they scare me so much less than doing nothing or even less than solar geoengineering (rationally or not), and I try to remain hopeful that there are enough people taking enough different approaches with enough care and due diligence to make things happen in a responsible and safe way.
This was originally posted on Tatiana’s Substack News from a Changing Planet, a free twice-monthly newsletter about what on Earth is happening, with articles and essays about climate change and the environment.
Header photo by Shane Stagner on Unsplash.