Backside Trawling May Unleash Carbon Dioxide, Worsening World Warming

A Controversial Fishing Technique Might Dredge Up a Local weather Time Bomb

By Kate McMahon edited by Andrea Thompson

A heavy steel web is dragged throughout the seafloor at breakneck pace, churning up darkish clouds of sediment and swallowing every part in its path. A blue-spotted stingray tries to flee, flailing its winglike pectoral fins because the trawl closes in from behind, however its efforts are in useless. This unprecedented footage—a scene in David Attenborough’s newest documentary Ocean—is the primary time backside trawling has been captured in excessive definition, exposing a observe not often seen by the general public.

Backside trawling is a extremely controversial fishing technique, nevertheless it gives 1 / 4 of the world’s seafood. It entails a vessel pulling a weighted web and different heavy gear, blindly and quick, alongside huge stretches of seabed—usually in pursuit of just one or two commercially worthwhile species. It traps big numbers of different organisms and bulldozes over fragile habitats, destroying centuries-old coral, scallop gardens and seagrass beds. “It’s exhausting to think about a extra wasteful approach to catch fish,” Attenborough narrates somberly as viewers watch a pile of useless juvenile sharks and rays get swept off the deck of the fishing vessel in Ocean.

However ecological destruction is just not the one concern. Rising analysis factors to a different lesser-known drawback with backside trawling: its potential to unleash climate-warming gases by disturbing carbon saved in seafloor sediments.

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The ocean is the world’s largest single carbon sink, absorbing round 30 % of the carbon dioxide that human exercise pumps into the environment. Phytoplankton—microscopic crops and algae drifting close to the ocean’s floor—soak up CO₂ throughout photosynthesis, changing it into natural carbon that will get saved of their tissues. Many sink to the seafloor after they die; sediments finally bury them and the carbon they include, successfully locking it away.

Backside trawling stirs large clouds of this carbon-rich sediment again into the water column. There the natural matter is uncovered to oxygen and microbial exercise that converts a number of the carbon into different chemical kinds, which may worsen ocean acidification or escape into the environment as CO₂.

However how a lot of this dredged-up carbon is definitely launched into the environment by backside trawling—and the way rapidly—stays a matter of debate.

Some scientists argue that a good portion of the carbon launched by backside trawling makes its means into the environment—at ranges that rival a number of the world’s worst emitters. “If all of the disturbed carbon entered the environment, it could rival aviation’s emissions,” says Utah State College ecologist Trisha Atwood, who co-authored a 2021 research and a 2024 follow-up that quantified trawling emissions through the use of statistical fashions. “Our newest analysis reveals that 55 to 60 % of the resuspended carbon is definitely launched into the environment over seven to 9 years, which is round 340 [million] to 370 million metric tons of CO₂ yearly.” That’s greater than the complete annual emissions of nations reminiscent of Italy or Spain.

However different consultants disagree with such excessive estimates, explaining that the ocean’s carbon cycle is ruled by complicated biogeochemical processes that naturally soak up, convert or sequester a lot of the carbon that will get resuspended within the water column. “You will need to notice that a number of the CO₂ launched from natural matter mineralization [microbial decomposition] finally ends up as bicarbonate, which is dissolved in seawater and doesn’t change with the environment,” says Volker Brüchert, an affiliate professor of biogeochemistry at Stockholm College. This enter of bicarbonate contributes to acidification and hinders a number of the ocean’s capacity to soak up extra CO₂, he says—“however direct corresponding knowledge for such a big CO₂ emission from oceanic cabinets into the environment has not been demonstrated.”

There’s, nevertheless, normal consensus that frequent trawling makes it tougher for carbon to stay sequestered in seafloor sediments. “It’s troublesome to measure the precise scale of greenhouse fuel emissions, however we all know carbon on the seabed is extra more likely to be preserved if it’s not frequently resuspended by backside trawling exercise. There’s rising proof to assist this,” says William Austin, a paleooceanographer on the College of St. Andrews in Scotland and chair of the United Nations Ocean Decade Program for Blue Carbon.

Methane, a greenhouse fuel way more potent than CO₂, provides one other variable that’s troublesome to account for in seafloor disturbance. Most oceanic methane is saved as methane hydrates—icelike compounds shaped beneath excessive strain and low temperatures—that are sometimes scattered over seabed areas too deep for trawling to succeed in. However in areas with shallow, nearshore methane deposits (such because the Siberian Shelf), backside trawling may pose a threat, notably as receding sea ice results in new fishing grounds above methane hotspots.

This risk is drawing a lot scientific curiosity, particularly in gentle of previous local weather occasions. Round 56 million years in the past, throughout an interval referred to as the Paleocene-Eocene Thermal Most (PETM), the planet warmed by as much as eight levels Celsius in beneath 200,000 years—a blink in geological time and one of many closest analogues researchers have to assist them perceive fashionable local weather change. Although the precise reason for that warming occasion stays unsure, one speculation is that warming waters destabilized and melted seafloor methane hydrates, triggering an unprecedented launch of methane into the environment. Whether or not fashionable, human-driven warming may set off related processes, even at a a lot smaller scale, continues to be unclear.

“If we’re going to start out trawling the seabed in a quickly warming and transitioning Arctic,” Austin says, “we might must cease and assume first.”

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