Methane emissions from aquatic systems contribute half of global emissions
An international study in which Alberto Borges, head of the Chemical Oceanography Laboratory (FOCUS Research Unit / Faculty of Sciences) at ULiège participated, provided an estimate of global methane emissions from wetlands and other marine and terrestrial aquatic environments. These values are likely to increase in the coming years. This study is published in Nature Geoscience.
M
ethane (CH4), which is the second most important greenhouse gas on Earth after CO2, accounts for about a quarter of anthropogenic global warming. Unlike CO2, which has a limited number of sources and well-identified sinks, CH4 has many sources - both natural and anthropogenic - as well as many sinks (removal process). Natural sources of CH4 come mainly from wetlands and other aquatic environments (marine and terrestrial), such as rivers and streams, lakes and ponds, freshwater wetlands, reservoirs, rice paddies, estuaries, mangroves, saltmarshes, seagrasses, tidal flats, aquaculture ponds, continental shelves, continental slopes and the open sea. It is therefore important to have an estimate of emissions from these areas. A group of fourteen researchers from seven countries (Australia, Belgium, Canada, China, Saudi Arabia, Switzerland and the USA) has been working on this task.
Alberto Borges, FNRS Research Director at the Laboratory of Chemical Oceanography (FOCUS Research Unit/Faculty of Sciences) contributed to this study which presents the most complete synthesis of global aquatic methane emissions ever produced, covering all the main types of natural, impacted and artificial aquatic ecosystems.
This report is the result of the compilation of all available published data on CH4 fluxes from aquatic ecosystem types," explains the ULiège researcher. An unprecedented compilation carried out by specialists from each of the ecosystems studied, made in concert and using a consistent methodology. " Additionally, the whole process was transparent, since the data collected was made public and all the data processing was explained in detail.
A particular effort was made to quantify the uncertainty on the estimation of the CH4 emissions to the atmosphere. This uncertainty is quite important because CH4 emissions to the atmosphere from aquatic systems are highly variable in time across several scales (from hours to decades) as well as in space (within a given type of aquatic system and between different systems)," says Alberto Borges. This natural variability is due to a combination of climatic factors and the type of land cover of the surrounding landscape, as methane production depends on temperature and the availability of organic matter, both of which are highly variable. »
The report concludes that aquatic ecosystems contribute between 41% and 53% of total global methane emissions from anthropogenic and natural sources. It also shows that methane emissions increase from natural to polluted aquatic ecosystems and from marine to freshwater ecosystems. Based on the available information, the study also concludes that aquatic CH4 emissions will increase in the future due to urbanization, eutrophication and global warming.
Scientific reference
Rosentreter et al. , Half of global methane emissions come from highly variable aquatic ecosystem sources, Nature Geosciences, March 2021.
