New findings challenge earlier high‑profile estimates
Bottom trawling produces significantly lower carbon emissions than previously believed, according to new research presented in Glasgow this week.
The findings directly challenge earlier claims that carbon released from trawling is comparable to the global climate emissions of the aviation sector.
The seabed holds large quantities of organic carbon, which can be disturbed by the passage of bottom‑contact fishing gear. Earlier studies assumed that all disturbed carbon mixes into the water column and a major share rises into the atmosphere as CO₂. However, the new assessment shows that these assumptions greatly overestimate actual emissions.
Only a small share of carbon enters the water column
HI researcher Samuel Rastrick, who contributed to an advisory briefing for the British government led by the UK’s Centre for Environment, Fisheries and Aquaculture Science (CEFAS), said the findings overturn earlier estimates.
He explained that while bottom trawling can disturb significant amounts of carbon, the proportion that becomes dissolved CO₂ — and therefore has climate relevance — is far smaller than assumed in previous global assessments.
Of the carbon disturbed by trawling, only between 1 and 21 percent is mixed into the water column. The percentage depends on the gear type involved. Furthermore, only between 10 and 35 percent of that mixed carbon can be broken down into dissolved CO₂. The breakdown rate varies with the seabed environment, such as sand, mud, rock or mixed substrates.
English shelf results have wider relevance
Although the research is based on data from the English shelf, Rastrick said the findings are directly relevant for seabed conditions throughout Northwest Europe, including Norwegian waters.
Researchers estimate that trawling on the English shelf disturbs around 28 million tonnes of carbon annually, equal to roughly 35 percent of the total carbon stock in the region’s surface sediments. However, only about 6 percent of this — an estimated 1.6 million tonnes — is mixed into the water column.
If all of this carbon were converted to CO₂ and later entered the atmosphere, it would equate to emissions from around 4.2 million fossil‑fuelled cars. But the new research indicates that actual emissions are significantly lower than this theoretical maximum.
Complex environmental processes reduce CO₂ release
The study incorporates a wider set of physical, chemical and biological processes than used in earlier headline‑making estimates. These include seasonal temperature variation, ocean currents, sediment type and the behaviour of microbial communities.
According to Rastrick, these processes mean that much of the disturbed carbon does not fully degrade, does not convert into CO₂, or does not reach the atmosphere. In many cases, carbon resettles on the seabed before significant decomposition occurs.
He said the revised understanding moves the discussion toward a more evidence‑based assessment of how bottom trawling interacts with marine carbon stores. While trawling does disturb large quantities of organic material in the sediments, the resulting climate‑relevant emissions are far smaller and depend on complex environmental dynamics.
