21 Geoengineering
Harvey
Climate Overshoot Commision Report
The Climate Overshoot Commission, a group of senior former diplomats, policy experts and scientists including Laurence Tubiana, the former French diplomat who was one of the main architects of the Paris agreement, focused on solar radiation management because that is one of the most controversial and dangerous ideas.
While regrowing trees is usually regarded as safe, putting mirrors in space to reflect sunlight or seeding clouds to reflect more rays into space could have huge impacts that would be hard to control, and would be impossible to confine within country borders. As well as the risks inherent to changing the climate in one place, there could be a “termination shock” – the concern that if emissions continued to pour into the atmosphere while geo engineering was used, stopping use of the technology would cause severe disruption to the climate as the underlying heating effect took hold again.
Harvey (2023) Experts call for global moratorium on efforts to geoengineer climate
21.1 Ocean Geoengineering
Mehta
Carbon dioxide makes seawater more acidic while warmer seas bleach corals and absorb less CO2
Nascent technologies aim to remove CO2 by tapping into the ocean’s natural carbon cycles
Ocean alkalinity enhancement decreases acidity encouraging absorption of more CO2
Estimates suggest the technology could reach 2 gigatons of removals across the world’s coastlines
Other systems use membranes to filter CO2 from seawater and convert it for capture and storage
Carbon dioxide makes seawater more acidic, so it’s harder for sea creatures to grow shells, while the heat bleaches corals and destroys breeding grounds for fish and marine mammals. Warmer waters also absorb less CO2.
Finding ways to increase the carbon sink at the depths of the ocean, where it can be stored for millennia, and to extract carbon dioxide from surface water offer opportunities to remove CO2 at scale.
Summary
Carbon dioxide makes seawater more acidic while warmer seas bleach corals and absorb less CO2
Nascent technologies aim to remove CO2 by tapping into the ocean’s natural carbon cycles
Ocean alkalinity enhancement decreases acidity encouraging absorption of more CO2 Estimates suggest the technology could reach 2 gigatons of removals across the world’s coastlines
Other systems use membranes to filter CO2 from seawater and convert it for capture and storage
Much of our planet is covered by oceans, which protect us from the worst ravages of global heating. Water and air are constantly exchanging carbon dioxide, and the seas around us have absorbed about a third of the CO2 we’ve pumped into the air, as well as the bulk of the warming it has caused. This has come at a huge cost to marine ecosystems. Carbon dioxide makes seawater more acidic, so it’s harder for sea creatures to grow shells, while the heat bleaches corals and destroys breeding grounds for fish and marine mammals. Warmer waters also absorb less CO2. Over a year. 02:00 02:28
Now a clutch of startups are trying to open up new avenues to remove even more carbon dioxide from our atmosphere by tapping into the ocean’s natural carbon cycles.
Proponents say finding ways to increase the carbon sink at the depths of the ocean, where it can be stored for millennia, and to extract carbon dioxide from surface water offer opportunities to remove CO2 at the scale required to meet the goals of the Paris Agreement. While the chemistry and modelling may stack up, these are nascent technologies. How can we be sure they’ll work in practice and won’t ultimately cause even more damage to the delicate ecosystems on which we rely? Advertisement · Scroll to continue
Some startups want to speed up the natural process by which biomass from land reaches the depths of the ocean. Israel-based Rewind plans to transport forest and agriculture residues to the bottom of the Black Sea. This is an ideal environment, the company says, because it lacks oxygen, so the residues will decompose only very slowly.
U.S. startup Running Tide is designing “carbon buoys”, combinations of biomass and alkaline minerals which could help reduce the acidity of ocean surface waters or provide a growth medium for macroalgae. Later these would be sunk to take carbon to the bottom of the ocean.
Another pathway is to speed up the natural weathering of rock that washes carbonate and bicarbonate minerals into the sea through adding alkaline minerals. So called ocean alkalinity enhancement decreases acidity, so encouraging the absorption of more CO2 from the atmosphere.
David Keller, a scientist at the GEOMAR Helmholtz Centre for Ocean Research in Germany, is coordinating a pan-European project to assess the feasibility of using the ocean to stabilise the climate. Experiments where an alkaline mineral is added to closed tanks floating out at sea suggest it’s safe to do field trials of ocean alkalinity enhancement. There are upper limits because too much alkalinity can cause the release of CO2.
By volume, the ocean holds 150 times more CO2 than the atmosphere, requiring less water to be processed for the same impact. But water is heavier so takes more energy to move. Co-locating Captura’s systems with desalination plants or harnessing ocean currents could cut energy needs. Energy consumption will be about 20-25% of DAC systems today.
Technology developed at UCLA is being exploited by spin-out, Equatic, to both produce clean hydrogen and capture CO2 from air and seawater. In its process, electrolysis of seawater produces hydrogen and creates an alkaline and acid stream of water. In the alkaline stream, the dissolved carbon dioxide forms solid calcium carbonate which can be stored, used to make cement or put back into the sea, where it’s already prevalent. Bubbling air through this (now CO2 depleted) seawater captures more CO2, which gets locked up for thousands of years as a bicarbonate. On the other side of the equation, the addition of olivine (one of the most common minerals on the planet) neutralises the acidic seawater. In turn it too should take up more CO2 from the atmosphere, when returned to the sea.
Ebb Carbon’s solution would take the water flowing out of a desalination plant or cooling water from a power plant and put it through a series of membranes to remove acidity, in the form of hydrochloric acid. The less acidic water that goes back into the sea will draw down atmospheric CO2, to be converted to bicarbonate ions and held in that form for thousands of years. There’s enough existing desalination and power-plant infrastructure to reach the two gigaton scale soon.
For now, the challenge is accurately measuring and verifying how much CO2 is being locked away, and that’s where Ebb’s emphasis is. “There’s a lot of rigour, a lot of science behind the detailed measurements and modelling that enable us to say, with a high degree of certainty, how much CO2 is pulled out of the air,” says Tarbell. That monitoring, reporting and verification is going to be critical to provide faith in the removals companies hope to claim. Nor is it cheap, suggests GEOMAR’s Keller. There are no standard approaches to do this.
As the entrepreneurs press on with modelling and experiments, they argue there’s no choice but to recruit the ocean’s natural systems if we’re to limit further warming. Our carbon emissions are already destroying the marine biodiversity upon which we depend, so we have to try everything to prevent things getting far worse.