‘Blue Carbon’ Can Boost Global Climate Change Reduction Efforts, Expert Says

A critical first step is including coastal wetlands in greenhouse gas inventories

‘Blue Carbon’ Can Boost Global Climate Change Reduction Efforts, Expert Says
Steve Crooks holding equipment in water in Khor Kalba
Global blue carbon expert Steve Crooks stands in Khor Kalba, a nature reserve and mangrove swamp near Kalba, United Arab Emirates. Mangroves accumulate the most carbon of all tropical forest types because they continuously remove carbon dioxide from the atmosphere over thousands of years.
Rob Barnes under license from AGEDI

With national and international momentum building for protecting and enhancing coastal habitats to help combat climate change, countries around the world—and U.S. states—are exploring ways to expand and account for “blue carbon,” that is, atmospheric carbon that’s captured in the world’s coastal ecosystems. Tidal wetlands, mangroves, and seagrass beds remove carbon dioxide from the air via photosynthesis and store the resulting carbon in their branches, leaves, roots, and soil. Because they take more carbon out of the atmosphere than they release into it, these ecosystems are known as “carbon sinks” and can play an important role in efforts to slow climate change.

World-renowned blue carbon expert Steve Crooks, a consultant to The Pew Charitable Trusts’ conserving marine life in the United States and protecting coastal wetlands and coral reefs projects, holds a Ph.D. in sedimentology with a focus on coastal systems and wetlands and has over 25 years of experience assessing how coastal wetlands react to human activity, including development and climate change. He worked with the United Nations’ Intergovernmental Panel on Climate Change (IPCC), several U.S. government agencies and departments, and the Verified Carbon Standard, a program that certifies reductions in carbon emissions, to develop methods for assessing the types and quantities of greenhouse gases that naturally flow in and out of coastal blue carbon habitats.

Originally from northern England, Crooks has lived in the San Francisco Bay Area for over two decades. This interview has been edited for clarity and length.

Q: Your interest in oceanography and sedimentology extends at least back to your college years. What piqued your interest initially?

A: My earliest memories of the ocean actually are from when I was about 2 years old, playing on a beach near where we lived in England. We were lucky to have beautiful beaches. The people from our town, South Shields, are known as “Sandies” or “Sand Dancers” because of their love for the shore. But I never intended to be an oceanographer. When I first went to university, I was studying biochemistry and biology, and at Bangor University, in the U.K., in addition to a major and minor, you can do a third subject of interest in your first year. So, I chose earth sciences, and I was hooked. Then I realized I could actually study oceanography, and so I switched my major. I remember my mother saying, “Why are you giving up biochemistry? It's a good income. Who hires oceanographers?”  

Q: Let’s fast-forward to what you’re doing now. Can you talk about how a nature-based solution like blue carbon ecosystems can help meet the challenge of climate change?

A: Blue carbon ecosystems are an important part of the global carbon cycle, and the Paris climate agreement has opened the door to including coastal wetlands in climate mitigation strategies. But to meet the commitments of the agreement, we need to decarbonize—or remove carbon from—the atmosphere and ocean and re-carbonize—or sequester it—into the biosphere, which includes soils and the seabed. Coastal wetlands are important carbon sinks, storing more carbon per acre than tropical forests.

We’ve been destroying these ecosystems for centuries, and that’s really accelerated over the last 50 years. And those devastated habitats can release thousands of years’ worth of carbon back into the atmosphere within just a few decades. Now, with new awareness, there’s an opportunity to try and slow or reverse that.

Q: In addition to being able to store and sequester carbon, what other benefits do these coastal wetlands provide?

A:  There are so many: food provision, water quality, biodiversity, shoreline stabilization, and some that are difficult to quantify, such as emotional well-being. They provide huge benefits in terms of fisheries, because part of the life cycle of many marine fish species relates to coastal ecosystems. The coastal peatlands in Alaska, for example, provide habitat for spawning salmon. Mangroves in Florida and across the tropics provide similar benefits, helping to support a billion-dollar fishing industry. Coastal habitats also attenuate wave energy and provide meaningful storm protection. And though wetlands can never fully protect against a hurricane’s storm surge, they can certainly take some of the bite out of it. And in the Pacific Northwest, restoring tidal forests brings back really big trees with extensive root networks that provide shelter for salmon and improve water quality.

Tidal forests at Otter Island in Washington state
The tidal forests at Otter Island in Washington state are one of the few remaining intact sites of a once-expansive coastal carbon sink. Crooks counts the Pacific Northwest’s coastal forests among his favorite “blue carbon spots.”
Steve Crooks

Q: What can a large coastal state like your adopted home of California do to protect and restore its blue carbon habitats?

A: California has lost over 90% of its coastal wetlands but is on a path to recover some of them. Enormous progress has been made in San Francisco Bay, and I’ve been lucky to work with restoration engineers, including my wife, Michelle, on several projects there. Some of the state’s lost wetlands have been huge sources of carbon emissions. The Sacramento Delta was once an enormous freshwater tidal wetland that has been turned into agricultural land, and the drained peat soils have released 4,000 years of stored carbon in the last 150 years, the equivalent of around 1 billion tons of carbon dioxide. And those emissions continue. Bringing back wetlands in this region could help the state keep carbon in the ground, as would restoring wetlands around the Eel River, Humboldt Bay, and pocket estuaries in Southern California.

Q: What are some of the challenges U.S. states face in including these habitats in their greenhouse gas emission reduction plans?

A: The U.S. has actually done a relatively good job at protecting its remaining coastal wetlands over the last 50 years, thanks to the enactment of the Clean Water Act in 1972 and related legislation. These protective measures were not enacted with carbon benefits in mind, but the ecosystem gains point to two key lessons: First, we should not weaken the legislative protections we have because they have kept well over 1 billion tons—maybe double that—of carbon dioxide from going back into the atmosphere. And second, we should try to restore wetland ecosystems and recover as much habitat as we can, to support more decarbonization.

Q: So how can states begin to include blue carbon in their greenhouse gas reduction plans?

A: Very few states include wetlands in their greenhouse gas reduction plans, so one of the first challenges is recognizing that there’s an opportunity here. Each coastal region can take some measures to enhance carbon storage or reduce emissions. Including coastal wetlands in state-level greenhouse gas inventories is helpful because if you track something, you’re more likely to improve the management of it.

Q: Are there resources to help them do that?

A: Yes, there’s lots of data and support available to help states measure blue carbon for the purposes of inventorying greenhouse gas emissions and reduction. Luckily, information on blue carbon is now being gathered at the federal level and included in the Environmental Protection Agency’s annual National Inventory of Greenhouse Gas Emissions and Sinks report. The IPCC and NOAA [the National Oceanic and Atmospheric Administration] also provide guidance and data. And the Smithsonian’s Environmental Research Center has built a fabulous global data atlas that anyone can use. For states—and countries, too—the most important thing is to begin including wetlands in inventories, using either regional or IPCC datasets. This first step will get you 90% of the way, so take it.

Crooks, center, leads an international team of volunteers and scientists quantifying carbon stocks in mangroves, marshes, and sabkha—flat, salt-encrusted desert—in Abu Dhabi, UAE
Crooks, center, leads an international team of volunteers and scientists quantifying carbon stocks in mangroves, marshes, and sabkha—flat, salt-encrusted desert—in Abu Dhabi, UAE.
Rob Barnes under license from AGEDI

Q: Looking more globally, what key policy measures are helping individual countries meet the challenge of including blue carbon ecosystems into their greenhouse gas inventories?

A: Around the world, we’re seeing a lot more activity with marine systems and coastal wetlands, from small-scale restoration projects to large-scale blue carbon ecosystem restoration actions.

Countries that are part of the Paris climate agreement now can include coastal wetlands within their nationally determined contributions, the plans each country puts forward to meet the goals of the agreement. More than 70 countries, including many with extensive coastal habitats, such as Seychelles and Belize, are moving to do that.

Q: You travel all over the world for your work. Do you have a favorite blue carbon spot?

A: Oh, goodness. There are so many beautiful wetlands to pick from. The coastal forests of the Pacific Northwest, or at least what remains of them, are particularly beautiful. But I’ve lived on the San Francisco Bay for 20 years, so I've got a great affinity for this area. Within San Francisco Bay, I feel a great affinity for the wetlands that are the focus of my work and have felt personally moved by seeing the benefits of restoration activities in coastal communities of Madagascar and Pakistan. Closer to home, many groups bring at-risk youth into the bay’s wetlands to help with restoration projects, and I’ve seen how this work resonates with these kids. It can really help to restore them emotionally.

Photo credits:

Rob Barnes under license from AGEDI. The first and second photographs.

The front facade of the Supreme Court of the United States in Washington, DC.

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