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This article was first published on May 13, 2025 on the Early Career Climate Network. 2024 was the hottest year on record for planet Earth, with most of the warming coming from human activities that release climate-warming greenhouse gases, like carbon dioxide (CO2) or methane (CH4), into the air. Nature around us – for example, trees and soils – can absorb these gases and act as a sink. But as the planet continues to warm, nature can become a source of planet-warming gases, accelerating global warming even more and creating a vicious cycle. One question scientists are trying to answer, is to what extent natural areas are contributing to global warming.  A wetland region in the northern Sweden province of Norrbotten. Photo: Toni Klemm The role of methane Scientists have now developed a more accurate way to estimate just this for the second most important greenhouse gas and a long overlooked ecosystem dominated by it: methane from natural wetlands in the Arctic. One third of global methane emissions originates in wetlands, and although most of that comes from wetlands in the Tropics, the Arctic is an important piece of the puzzle, too. Here, methane has been stored in permafrost soil over millennia and is now being released as Earth heats up. So far, the processes behind this have not been well understood, and as a result, models are doing a poor job estimating how much methane is released from these regions, a recent study in Nature showed. As a result, it is unclear by how much methane emissions will increase in the future due to global warming. In the short-term (in the first 100 years after emission), the warming effect of methane is 27 to 30 times stronger compared to the same amount by weight of emitted CO2, making it a much more powerful greenhouse gas. 159 countries (including the US) have signed the Global Methane Pledge to cut methane emissions by 30% by 2030 based on 2020 levels. However, a direct comparison of the effects of methane and CO2 on the climate, ecosystems and health, is more complicated. The source of the methane is also important to consider. The new study The new study, conducted by three researchers from Lund University in Sweden, looked at Scandinavia and the Baltic region in Northern Europe. It was funded by the World Meteorological Organization and Horizon Europe, a funding instrument by the European Union to support adaptation to climate change. The study found that the model tested in the study currently overestimates methane emissions from Arctic wetlands. But that is not the true novelty of the research.  A peatland with agricultural use west of Berlin, Germany. Photo: Toni Klemm The researchers worked with a dynamic global vegetation model called LPJ-GUESS, which uses climate data to simulate what how various ecosystems on the planet would be distributed, what they would be composed of, and how they would function. The researchers also used two other components: LUMIA and GRaB-AM. This approach is what is most novel, a “joint use of two independent approaches, LUMIA and GRaB-AM, that leads to the same result”, saysGuillaume Monteil, now at the Barcelona Supercomputing Centre (BSC) in Spain and lead investigator of the project. Monteil explains, “both systems fall in the ‘data assimilation’ category of approaches,” meaning both integrate many different data and feed them into specific models to predict an unknown variable. “LUMIA is an atmospheric inversion system. It uses observations of the atmospheric composition to refine estimates of greenhouse gas emissions. GRaB-AM is a data assimilation framework built around LPJ-GUESS. It is used to determine the configuration of LPJ-GUESS that leads to the most realistic methane emissions, based on its performance in reproducing flux observations at multiple sites.” The study also uses what is known as ‘inversion’ in mathematics, an approach to estimate the amount of something based on its measured impact, like guessing the size of a meteorite based on the crater it left. Or as Monteil explains it: “It's about determining an unknown, or poorly known value, in our case the CH4 emissions, based on their observed impact, in our case the observed CH4 concentrations.” The way of finding an unknown factor or variable is turned on its head - inverted. One of the goals of the project is to improve the LPJ-GUESS model, or as Monteil describes, to “compare [the modeled] output to observations (flux observations in GRAB-AM, concentration observations in LUMIA), and then adjust the initial values to improve the fit to the data. Limitations Monteil stresses not to overinterpret the results that the LPJ model overestimate arctic methane emissions, because the study is based on only one year of data and a very small geographic region in northern Europe. The results cannot be generalized and need to be tested elsewhere. He says, what the study does do is “it provides a cross validation for the LUMIA and GRaB-AM system, which is quite new.” As a result, processes in sparsely monitored ecosystems, like Arctic wetlands in Europe or North America, can be modeled more accurately and reliably, and the new procedure could help scientists develop better models for other environmental processes. Although the study focused on Northern Europe, Arctic wetlands in Alaska and northern Canada face similar warming and methane emission, a recent study has found. This approach might improve estimates in US and Arctic Regions, as well.  The Viru Bog wetland in Northern Estonia. Photo: Unplash/Jaanus Jagomägi Why it matters In the grand scheme of things, however, it might be a key puzzle piece in figuring out how just much more warming humans and nature will have to deal with in the future, and perhaps also inform other projects about the value of wetlands for storing global warming gases. This is the focus of other scientific endeavors, for example how to return drained peatlands to former glory as storage champions of greenhouse gases while also allowing agricultural use on these lands. To learn more about this, check out the project Re:Peat in Colombia and WetNetBB and MOOSland in Germany. The study by Guillaume Monteil and his colleagues is currently in review with the journal Atmospheric Chemistry and Physics. The preprint publication is available here: https://doi.org/10.5194/egusphere-2024-312
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