2024-02-21 07:30:12
Scientists have calculated the amount of CO2 released into the atmosphere linked to deep-sea trawling. This fishing technique has the effect of lifting carbon buried in sediments from the ocean floor. Emissions are estimated at 370 million tonnes per year, more than twice the carbon footprint of the global fishing industry.
Deep-sea trawling is a controversial fishing technique because it results in unwanted catches, including endangered species and affects those classified as fragile. Since 2017, the European Union has partially banned this practice beyond 800 meters depth. An international team of climate and ocean experts, including those from the University of Utah and NASA’s Goddard Institute for Space Studies, has published a study in the journal Frontiers in Marine Science in which it reveals that this deep trawling causes significant CO2 emissions into the atmosphere.
These emissions are linked to nets that sink into the seabed and have the effect of lifting carbon that took millennia to be buried in the sediments of the ocean floor. This pollution had already been identified in the past, but could never be quantified, in particular because the fate of the carbon in the water remained unknown. To carry out this work, the researchers relied on a vessel tracking database compiled by Global Fishing Watch as well as data relating to seabed carbon. They then used three different models of carbon cycles in the ocean, used in particular by the IPCC, to calculate the amount of carbon released into the water and then escaping into the atmosphere.
Result: during the study period which extends from 1996 to 2020, the quantity of CO2 emissions into the atmosphere linked to bottom trawling is estimated between 8.5 and 9.2 billion tonnes. To arrive at this estimate, scientists calculated that between 55 to 60% of the CO2 released into the water is gradually found in the atmosphere over a period of nine years after the passage of the trawlers. Each year, atmospheric CO2 emissions are estimated at 370 million tonnes. The authors of this publication describe this trawling as “marine deforestation” and have calculated that these discharges correspond to approximately 9 to 11% of global emissions linked to land-use change in 2020. This pollution also represents more than twice the The estimated carbon footprint of the global fishing industry.
A risk of localized ocean acidification
This fishing technique has the greatest impact on the climate in certain regions of the world with high trawling activities, such as the East China Sea, the Baltic Sea, the North Sea and the Greenland Sea. Southeast Asia, the Bay of Bengal, the Arabian Sea, parts of Europe and the Gulf of Mexico are also likely major sources of carbon emissions from bottom trawling, but scientists lacked sufficient data on the extent and intensity of this fishing technique in these regions. Because carbon is resuspended in water and then transported by ocean currents, it is not possible to guarantee that all air emissions in a country’s jurisdictional waters come from trawling activities in that area.
This research also made it possible to assess what happens to the carbon that remains trapped in ocean waters after deep-sea trawling. Bottom line: Between 40 and 45 percent of total carbon dislodged from the ocean floor remains in the water as CO2, which could lead to greater localized ocean acidification, a process that can damage local plants and animals. Globally, the reduction in pH is between 0.0003 and 0.0005 over the period 1996 to 2020, a figure which is not significant compared to the effect of anthropogenic emissions from fossil fuels, however, the authors estimate “that intensive trawling could lead to increased localized acidification in the East and South China Sea. »
Faced with the need to rapidly reduce greenhouse gas emissions, scientists warn that “countries are currently not accounting for significant carbon emissions from bottom trawling in their climate action plans and that reducing carbon emissions from bottom trawling could potentially bring significant carbon reduction benefits short term. »
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