The ocean is by far the world\u2019s largest carbon sink, capturing about 30% of human-caused CO2 emissions and about 90% of the excess heat energy from said emissions. For about as long as scientists have known these numbers, there\u2019s been intrigue around engineering the ocean to absorb even more. And more recently, a few startups have gotten closer to making this a reality. <\/p>\n
Last week, one of them got a vote of confidence<\/a> from leading carbon removal registry Isometric<\/a>, which for the first time validated \u201cocean alkalinity enhancement\u201d credits sold by the startup Planetary \u2014 625.6 to be exact, representing 625.6 metric tons of carbon removed. No other registry has issued credits for this type of carbon removal. <\/p>\n When the ocean absorbs carbon, the CO2 in the air reacts with the water to form carbonic acid, which quickly breaks down into hydrogen ions and bicarbonate. The excess hydrogen increases the acidity of the ocean, changing its chemistry to make it less effective at absorbing CO2, like a sponge that\u2019s already damp. As levels of atmospheric CO2 increase, the ocean is getting more acidic overall, threatening marine ecosystems. <\/p>\n Planetary is working to make the ocean less acidic, so that it can take in more carbon. At its pilot plant in Nova Scotia, the company adds alkalizing magnesium hydroxide to wastewater after it\u2019s been used to cool a coastal power plant and before it\u2019s discharged back into the ocean. When the alkaline substance (which, if you remember your high school chemistry, is also known as a base) dissolves in the water, it releases hydroxide ions, which combine with and neutralize hydrogen ions. This in turn reduces local acidity and raises the ocean\u2019s pH, thus increasing its capacity to absorb more carbon dioxide. That CO2 is then stored as a stable bicarbonate for thousands of years. <\/p>\n \u201cThe ocean has just got such a vast amount of capacity to store carbon within it,\u201d Will Burt, Planetary\u2019s vice president of science and product, told me. Because ocean alkalinity enhancement mimics a natural process, there are fewer ecosystem concerns than with some other means of ocean-based carbon removal, such as stimulating algae blooms<\/a>. And unlike biomass or soil-related carbon removal methods, it has a very minimal land footprint. For this reason, Burt told me \u201cthe massiveness of the ocean is going to be the key to climate relevance\u201d for the carbon dioxide removal industry as a whole. <\/p>\n But that\u2019s no guarantee. As with any open system where carbon can flow in and out, how much carbon the ocean actually absorbs is tricky to measure and verify. The best oceanography models we have still don\u2019t always align with observational data. <\/p>\n Given this, is it too soon for Planetary to issue credits? It\u2019s just not possible right now for the startup \u2014 or anyone in the field \u2014 to quantify the exact amount of carbon that this process is removing. And while the company incorporates error bars into its calculations and crediting mechanisms, scientists simply aren\u2019t certain about the degree of uncertainty that remains.<\/p>\n \u201cI think we still have a lot of work to do to actually characterize the uncertainty bars and make ourselves confident that there aren\u2019t unknown unknowns that we are not thinking about,\u201d Freya Chay, a program lead at CarbonPlan, told me. The nonprofit aims to analyze the efficacy of various carbon removal pathways, and has worked with Planetary<\/a> to evaluate and inform its approach to ocean alkalinity enhancement. <\/p>\n Planetary\u2019s process for measurement and verification employs a combination of near field observational data and extensive ocean modeling to estimate the rate, efficiency, and permanence of carbon uptake. Close to the point where it releases the magnesium hydroxide, the company uses autonomous sensors at and below the ocean\u2019s surface to measure pH and other variables. This real-time data then feeds into ocean models intended to simulate large-scale processes such as how alkalinity disperses and dissolves, the dynamics of CO2 absorption, and ultimately how much carbon is locked away for the long-term. <\/p>\n But though Planetary\u2019s models are peer-reviewed and best in class, they have their limits. One of the largest remaining unknowns is how natural changes in ocean alkalinity feed into the whole equation \u2014 that is, it\u2019s possible that artificially alkalizing the ocean could prevent the uptake of naturally occurring bases. If this is happening at scale, it would call into question the \u201cenhancement\u201d part of alkalinity enhancement. <\/p>\n There\u2019s also the issue of regional and seasonal variability in the efficiency of CO2 uptake, which makes it difficult to put any hard numbers to the efficacy of this solution overall. To this end, CarbonPlan has worked with the marine carbon removal research organization [C]Worthy to develop an interactive tool<\/a> that allows companies to explore how alkalinity moves through the ocean and removes carbon in various regions over time. <\/p>\n As Chay explained, though, not all the models agree on just how much carbon is removed by a given base in a given location at a given time. \u201cYou can characterize how different the models are from each other, but then you also have to figure out which ones best represent the real world,\u201d she told me. \u201cAnd I think we have a lot of work to do on that front.\u201d<\/p>\n From Chay\u2019s perspective, whether or not Planetary is \u201cready\u201d to start selling carbon removal credits largely depends on the claims that its buyers are trying to make. One way to think about it, she told me, is to imagine how these credits would stand up in a hypothetical compliance carbon market, in which a polluter could buy a certain amount of ocean alkalinity credits that would then allow them to release an equivalent amount of emissions under a legally mandated cap. <\/p>\n \u201cWhen I think about that, I have a very clear instinctual reaction, which is, No, we are far from ready,\u201dChay told me. <\/p>\n Of course, we don\u2019t live in a world with a compliance carbon market, and most of Planetary\u2019s customers thus far \u2014 Stripe, Shopify, and the larger carbon removal coalition, Frontier, that they\u2019re members of \u2014 have refrained from<\/a> making concrete claims about how their voluntary carbon removal purchases impact broader emissions goals. But another customer, British Airways, does appear to tout<\/a> its purchases from Planetary and others as one of many pathways it\u2019s pursuing to reach net zero. Much like the carbon market itself, such claims are not formally regulated. <\/p>\n All of this, Chay told me, makes trying to discern the most responsible way to support nascent solutions all the more \u201csquishy.\u201d<\/p>\n Matt Long, CEO and co-founder of [C]Worthy, told me that he thinks it\u2019s both appropriate and important to start issuing credits for ocean alkalinity enhancement \u2014 while also acknowledging that \u201cwe have robust reason to believe that we can do a lot better\u201d when it comes to assessing these removals. <\/p>\n For the time being, he calls Planetary\u2019s approach to measurement \u201clargely credible.\u201d <\/p>\n \u201cWhat we need to adopt is a permissive stance towards uncertainty in the early days, such that the industry can get off the ground and we can leverage commercial pilot deployments, like the one that Planetary has engaged in, as opportunities to advance the science and practice of removal quantification,\u201d Long told me. <\/p>\n Indeed, for these early-stage removal technologies there are virtually no other viable paths to market beyond selling credits on the voluntary market. This, of course, is the very raison d\u2019etre of the Frontier coalition, which was formed to help emerging CO2 removal technologies by pre-purchasing significant quantities of carbon removal. Today\u2019s investors are banking on the hope that one day, the federal government will establish a domestic compliance market that allows companies to offset emissions by purchasing removal credits. But until then, there\u2019s not really a pool of buyers willing to fund no-strings-attached CO2 removal.<\/p>\n Isometric \u2014 an early-stage startup<\/a> itself \u2014 says its goal is to restore trust in the voluntary carbon market, which has a history of issuing bogus offset credits<\/a>. By contrast, Isometric only issues \u201ccarbon removal\u201d credits, which \u2014 unlike offsets \u2014 are intended to represent a permanent drawdown of CO2 from the atmosphere, which the company defines as 1,000 years or longer. Isometric\u2019s credits also must align with the registry\u2019s peer-reviewed carbon removal protocols<\/a>, though these are often written in collaboration<\/a> with startups such as Planetary that are looking to get their methodologies approved. <\/p>\n The initial carbon removal methods that Isometric dove into \u2014 bio-oil geological storage<\/a>, biomass geological storage<\/a>, direct air capture<\/a> \u2014 are very measurable. But Isometric has since branched beyond the easy wins to develop protocols for potentially less permanent and more difficult to quantify carbon removal methods, including enhanced weathering<\/a>, biochar production<\/a>, and reforestation<\/a>. <\/p>\n