Can the Ocean Save the Planet? The idea ofocean-based climate solutions is appealing, but the challenges are formidable.

• Author: Helvarg, David

Marine Technicians Margot Buchbinder and Luis Hernandez unlock a chain-link gate at Point Molate, a natural headland on San Francisco Bay, and drive to the waters edge along a degraded road, part of what was once a World War II Navy fuel depot. From here, they climb down concrete blocks and boulders in the fading light of dusk.

Wearing full wetsuits and booties, they shuffle through the mud and shallow water of low tide; the shuffling helps warn bat rays to get out of their way. Using a marine GPS finder, they quickly locate and retrieve a couple of remote sensors about the size of nine-volt batteries that measure the water's temperature and salinity around local eelgrass beds. Slogging back toward shore, they are backlit by the lights of an oil tanker docked at the local Chevron refinery's "Long Wharf."

The pair's work is part of research being conducted by San Francisco State University's Katharyn Boyer on the ecology and restoration of coastal habitats, including San Francisco Bay's approximately 3,000 acres of eelgrass. Eelgrass, a species of seagrass, along with kelp, coastal salt marshes, mangroves, and other marine plants and animals (including whales) have long been acknowledged as essential for ocean health. They are now also being recognized as "Blue Carbon" sinks--sequesterers of excess carbon dioxide in the atmosphere generated from the burning of fossil fuels and other sources.

"I suspect, but don't know yet, that natural eelgrass beds will have more carbon sequestration in the sediment than restored beds but restoration will also put you somewhere along that trajectory," says Boyer, whose team uses the historic eelgrass at Point Molate as a seedling bed for restoration elsewhere in the bay. "It's all part of the solution," she offers, "but we've got to deal with emissions or we don't solve the problem."

In promoting carbon dioxide removal--both "nature-based" and geo-engineered, as described in a recent National Academies of Sciences report--the United States, United Nations, and others are admitting failure.

Despite commitments by the world's leaders, the goal set forth in the 2015 Paris Agreement and the 2021 Glasgow Climate Pact, to limit global warming to 1.5 degrees Celsius above preindustrial levels (marking the difference between a dangerous climate shift and a catastrophic one), now appears unattainable unless carbon dioxide is also taken out of the atmosphere.

And so, in addition to efforts to reverse deforestation...