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> Toying with ocean chemistry also carries unknown risks. Some environmental groups worry that even early experiments with these techniques could threaten fish and other aquatic life.

>Altering marine environments to cool the planet has been contentious from the moment scientists first suggested it four decades ago.

>This is Part Two of a two-part story. Find Part One here.

> Key Ideas > > - As climate change accelerates, some scientists are calling for more field research into solar geoengineering concepts. However, these ideas are running into opposition from other researchers, some governments and the public. > > - A series of recent setbacks has put solar geoengineering research on the back foot, attempting to figure out a way to navigate the opposition. > > - Proponents of field research say it would help humanity better understand the potential and problems with solar geoengineering, while opponents argue that there are too many risks and it could take our eye off the ball: cutting carbon emissions. > > - The debate has spilled into the international arena, pitting nations that support greater research against those that would like to see a solar geoengineering non-use agreement.

>A combined team of Earth scientists and climate specialists at the University of California San Diego and the National Center for Atmospheric Research has found via modeling that geoengineering projects such as marine cloud brightening can have unexpected and sometimes harmful consequences. > >In their study, published in the journal Nature Climate Change, the group designed models to predict what might happen if large-scale marine cloud brightening projects were undertaken in two major regions in the western United States.

>The researchers found that the artificial clouds would reduce temperatures in the western U.S., primarily California—reducing risk of dangerously high temperatures by as much as 55%. But they also found the same clouds would reduce rainfall amounts, both in the U.S. and other parts of the world. > >The research team also found that if the MCB project continued to the year 2050, its benefits would taper off and heat waves in Europe would become much more common, showing that engineering projects can lead to unforeseen consequences in other parts of the world.

Current mainstream mitigation measures may be insufficient to halt sea-level rise, implying that radical measures may be required. Geoengineering—which can be described as a mechanism to mitigate unprecedented sea-level rise—has garnered scientific interest in line with the present state of climate change. This study investigates traditional and modern geoengineering techniques through a systematic literature review. The results suggest that conventional and pioneering techniques can decrease sea-level rise, and those optimal results would be achieved through the cooperation of methods. Ultimately, findings from this review informed five strategies: tactical application of conventional geoengineering; optimisation through technique alignment; adaptation to receding coastlines; a global platform for project collaboration; and progression of research capabilities. These strategies, in turn, informed a procedural guideline for policymakers who seek to mitigate sea-level rise.

> Precipitation enhancement, commonly called “cloud seeding” or “weather modification” is a scientific method to artificially stimulate clouds to produce more rainfall and snowfall than would be produced naturally. The primary mechanism is to inject substances, such as silver iodide or ice crystals (cloud seeding agents), into the clouds, enabling snowflakes and raindrops to form more easily. Various cloud seeding programs have been operational since the late 1950s. The majority of programs continue for a number of years during winter months and as conditions warrant. The following is a summary on previous cloud seeding programs in California.

> Currently, a U.S. company or citizen with plans to inject aerosols into the atmosphere is required to fill out a one-page form with the Commerce Department 10 days before they do so, thanks to a law from the 1970s that requires reporting of efforts to modify the weather. > > That’s not enough, say academics and researchers who are urging the government to expand their rules governing private firms’ solar radiation modification efforts. It’s part of a broader push to regulate small-scale geoengineering experiments that are already happening.

>Solar Radiation Modification (SRM) describes an array of geoengineering techniques designed to partially block sunlight to mask the heating effect of greenhouse gasses. It does nothing to tackle the root causes of climate change, is inherently unpredictable and risks further destabilizing an already destabilized climate system with more and new extremes. It is neither insurance to ‘buy time’ nor any form of supplement to mitigation. Solar geoengineering is a recipe for disaster that delays climate action and real solutions, and puts our communities and ecosystems at unacceptable risk. > >Widely discussed SRM techniques such as stratospheric aerosol injection (SAI) and marine cloud brightening (MCB) carry the further risk of ‘termination shock’ – the sudden spiraling of global temperatures if such injections were, for whatever reason, ever stopped. For SAI this means injections of chemicals into the stratosphere would need to be continued for several decades if not centuries, in effect requiring policy continuity spanning numerous generations – something that is virtually impossible to assure. In addition to severe environmental, social and political risks – which include serious threats to biodiversity and food security – SRM itself poses a clear ‘moral hazard’, risking delays to meaningful climate action that must occur in the near term. > >The UN Human Rights Council’s Advisory Committee has warned that geoengineering technologies “could seriously interfere with the enjoyment of human rights for millions and perhaps billions of people”. It has also pointed out the disproportionate impact on Indigenous Peoples, peasants, fisherfolk and others living in rural areas. These same groups have been vocal in rejecting geoengineering as a dangerous distraction that would violate their rights.

What do you think?

> On his latest video for the Vlog Brothers, Hank Green spoke about the accidental experiment that cleaning up ship fuel has carried out on the climate, in a video titled "The Biggest Science Story of the Week". Among other things, Hank argues that this could be a crucial opportunity to learn about geoengineering. Geoengineering - according to this Vlog Brother - could be a "giant step forward". So what could geoengineering actually achieve to combat climate change? And why are many climate scientists far more skeptical than Hank lets on?

> One proposed side effect of geoengineering with stratospheric sulfate aerosols is sky whitening during the day and afterglows near sunset, as is seen after large volcanic eruptions. Sulfate aerosols in the stratosphere would increase diffuse light received at the surface, but with a non-uniform spectral distribution. We use a radiative transfer model to calculate spectral irradiance for idealized size distributions of sulfate aerosols. A 2% reduction in total irradiance, approximately enough to offset anthropogenic warming for a doubling of CO2 concentrations, brightens the sky (increase in diffuse light) by 3 to 5 times, depending on the aerosol size distribution. The relative increase is less when optically thin cirrus clouds are included in our simulations. Particles with small radii have little influence on the shape of the spectra. Particles of radius ∼0.5 μm preferentially increase diffuse irradiance in red wavelengths, whereas large particles (∼0.9 μm) preferentially increase diffuse irradiance in blue wavelengths. Spectra show little change in dominant wavelength, indicating little change in sky hue, but all particle size distributions produce an increase in white light relative to clear sky conditions. Diffuse sky spectra in our simulations of geoengineering with stratospheric aerosols are similar to those of average conditions in urban areas today.

> Planetary Technology, a Canadian company, plans to dump 450 tonnes magnesium hydroxide into the sea in St. Ives Bay, Cornwall UK as part of an ocean alkalinity enhancement scheme, which raises concerns for the ‘Hands Off Mother Earth! Alliance. The experiment poses a potential serious risk to marine ecosystems and the Celtic Sea grey seal population.

> Planetary Technology claims that the Ocean Alkalinity Enhancement (OAE) experiment will decrease the acidity of seawater and remove carbon. In theory, this would happen by adding magnesium hydroxide to the water in the bay, however this approach has not been proven.

> Other concerns about the experiments by Planetary Technology raised by civil society include: > - The company has commercial interests, for example Planetary has sold CO2 credits to Shopify and Stripe without yet removing any CO2. > - Magnesium hydroxide occurs naturally as brucite, but the deposits are small. For industrial use, therefore, it is usually precipitated from sea water and then dried at high temperatures. > - This process requires so much energy that producing magnesium hydroxide may use more carbon dioxide than is captured through the enhanced weathering process. > - There are a number of concerns about the technical approach and safety of OAE. A recent article in Nature highlights the technical challenges around the technology.

> The central tragedy in aquatic geoengineering is its superfluousness and cost. We already know how to combat climate change. Investing in alternative renewable energies, nuclear power including fusion, sensible environmental regulations and protections, and investments in public transit all work. > > These all require sacrifice and political will. Geoengineering is a pie in the sky. It is a pipe dream, a perennial and seductive concept because it allows humanity to solve the problems of decarbonization, and energy transformation, without fundamentally altering the technology, behaviors, or structures which caused the problems in the first place.

> Scientists are debating whether iron fertilisation can lock carbon into the deep ocean over the long term, and have raised concerns that it can irreparably harm ocean ecosystems, produce toxic tides and lifeless waters, and worsen ocean acidification and global warming.

> The Saami Council’s opposition stems from a belief that geoengineering is the wrong way to approach climate change. “The way of thinking that humans are entitled to change and manipulate our surroundings has actually brought us into the climate crisis in the first place,” Larsson Blind said.

> IT DOESN’T WORK: None of the technologies have a track record, all of them come with major risks and unknowns, and in some cases the effects would be obviously catastrophic. > > WEAPONIZATION: Computer models show that geoengineering interventions can have regional winners and losers; to the extent that geoengineering successfully changes climate patterns in a predictable way, it will inevitably be weaponized. > > DETRACTS FROM REAL SOLUTIONS: By promising a quick fix, geoengineering threatens to delay the implementation of a transition away from fossil fuels, and could redirect funding and investments away from real climate solutions. Some geoengineering proposals require vast amounts of energy, which means less climate-friendly energy for everyone else. > > HUMAN RIGHTS AND BIODIVERSITY: Many geoengineering proposals require the intensive exploitation of vast amounts of land (in the case of BECCS, twice the size of India!). Those projects would inevitably displace millions of people and potentially wipe out entire ecosystems.

> So you see, I’m not quite sanguine about our ability to engineer solutions to the many-headed hydra of a problem that is biophysical breakdown on this planet. Humans barely understand how nature works in many fundamental ways, including our own biology. We can’t engineer what we can’t understand. We probably can’t engineer biological systems at all. No, I have more confidence in nature fixing itself than in humans fixing nature.

The International Non-Use Agreement on Solar Geoengineering should commit governments to five core prohibitions and measures:

1. The commitment to prohibit their national funding agencies from supporting the development of technologies for solar geoengineering, domestically and through international institutions.
2. The commitment to ban outdoor experiments of solar geoengineering technologies in areas under their jurisdiction.
3. The commitment to not grant patent rights for technologies for solar geoengineering, including supporting technologies such as for the retrofitting of airplanes for aerosol injections.
4. The commitment to not deploy technologies for solar geoengineering if developed by third parties.
5. The commitment to object to future institutionalization of planetary solar geoengineering as a policy option in relevant international institutions, including assessments by the Intergovernmental Panel on Climate Change.