This article originally appeared in the State of Green Business 2021. You can download the entire report here.

Over the past few years, as companies have come under steadily increasing pressure to tackle climate change, nature-based solutions have emerged as a particularly exciting method for shrinking corporate carbon footprints. Investing in forests can be a win-win that both sequesters carbon and regenerates nature. That’s why one recent survey recorded almost $160 million spent on forest offsets in 2019. And a newer option, soil carbon, also is generating investment from multiple corporate sectors.

Yet another natural sink absorbs about as much carbon dioxide as our planet’s soils and forests combined: the world’s coastal and ocean waters. Until recently, ocean sequestration, also known as blue carbon, attracted little attention outside academic and think-tank circles. We might be at a turning point, however, because a handful of forward-looking corporations, conservation organizations and startups recently have accelerated efforts to store carbon in marine systems. Thanks to their work, companies of all sizes soon may be able invest in ocean sequestration.

One pioneer in this area is Shopify, an e-commerce company that has committed to spending $5 million annually on innovative clean technologies. Shopify’s first round of investments, announced in September, includes Running Tide, a company based on the coast of Maine. Running Tide’s core business is oyster farming, but CEO Marty Odlin is planning on a new revenue stream: growing kelp and sinking his crop in the deep ocean. 

« Once it goes down below 1,000 meters, it’s not coming back up, because the pressures are so great, » Odlin told Fast Company. « So you can get at least 1,000 years of sequestration. More likely, it will turn into oil or sediment and be sequestered on the geologic timescale — millions of years. »

Once it goes down below 1,000 meters, it’s not coming back up, because the pressures are so great.

At Running Tide, engineers will use the Shopify investment to build kelp-growing platforms, which they will launch into ocean current systems selected as having the right temperature and nutrients to support kelp growth. The platforms will be kept afloat by buoys designed to biodegrade once they reach the deep ocean, at which point the kelp will fall to the ocean floor, taking its carbon with it. Running Tide will measure the carbon sequestered in the process and sell credits on the carbon markets.

Shopify also made a bet on Planetary Hydrogen, a startup that aims to produce « green hydrogen » while simultaneously capturing carbon and healing the ocean. The process begins with a twist on existing green hydrogen technology, in which renewable energy is used to power the production of hydrogen from water, a reaction that produces no carbon. The Planetary Hydrogen team adds a mineral salt to the process, leading to the creation of a waste product — a mineral hydroxide — that binds with atmospheric carbon dioxide. The final step involves adding the bicarbonate compound that results from this reaction to the ocean, where, because the substance is alkaline, it helps counter climate-caused ocean acidification.

According to the company’s calculations, the process can capture and store 40 kilograms of carbon dioxide for every kilogram of hydrogen produced. “Our fuel may be the greenest on Earth,” boasted Greg Rau, Planetary Hydrogen’s chief technology officer, at GreenBiz Group’s VERGE Carbon conference last fall. 

The catch? Let’s start with costs. Green hydrogen costs two to three times as much as the conventional alternative, and Planetary Hydrogen’s fuel is even more expensive. In most markets that probably would be the end of the story, but the carbon-negative status of Planet Hydrogen’s product means that it could earn credits from schemes such as California’s Low Carbon Fuel Standard — enough credits, Rau believes, to make it a cheaper option than other forms of hydrogen.

Before that happens, his team will have to scale up the technology, which it plans to do using Shopify’s investment. A pilot plant should come online in 2022, according to Rau.

Another challenge facing both Planetary Hydrogen and Running Tide is the issue of permanence.

For a credit to be traded on carbon markets, an established certification body — Verra and Gold Standard are two leading examples — needs to sign off on the process used to store the carbon. Among other things, the certifier would assess how long the carbon is likely to stay sequestered.

The biology and chemistry of the deep oceans suggest that kelp and bicarbonate could offer a better guarantee of long-term storage than, say, forests. But collecting the data needed to demonstrate that will be challenging given the vastness of the oceans and the fact that this is a new frontier for certification bodies. « We need to rethink the basis for calculating the carbon benefits of these projects, » Carlos Duarte, an expert in marine ecosystems at the King Abdullah University of Science and Technology in Saudi Arabia, said at VERGE Carbon.

Given the uncertainties, many companies will wait before investing in emerging ocean projects. But there are more established blue carbon options that are better understood.

In 2018, for instance, Apple announced that it would back a project to protect and restore 27,000 acres of mangrove forest on Colombia’s Caribbean coast. According to Conservation International, one of the NGOs behind the project, mangroves and other coastal wetlands can store up to 10 times more carbon per unit area than terrestrial forests. Apple will purchase carbon credits generated by the project, generating a new income stream for the 12,000 local people whose livelihoods depend on the mangroves.