In ReGAME, Reliable Global Methane Emissions estimates in a changing world, we integrate new measurements into models to determine why atmospheric methane (CH4) is increasing, and whether climate-sensitive Arctic CH4 reservoirs will release significant CH4 to the atmosphere.
CH4 is a powerful greenhouse gas, contributing nearly one quarter to global average temperature increases since 1750. Developments in atmospheric CH4 are key to assessing climate change and the effectiveness of mitigation strategies. Natural sources include wetland soils, the extent of which are being increased by melting permafrost, forest fires, and geologic processes such as gas seeps and decomposition of subsea gas hydrates. The main CH4 removal process is via chemical processing in the presence of sunlight. To understand the balance of these sources and sinks we will update atmospheric chemistry models by incorporating isotopic signatures characteristic of the various sources and the effects of the removal processes. We will provide top-down emission estimates from an ‘inversion model’, whereby prior estimates of methane emissions are updated to better meet observations. For the first time, we will also include satellite data (S5P) within the inversion. Following up on the successful project MOCA, ending in 2017, the role of polar regions and potential tipping points (e.g., thawing permafrost and subsea gas hydrates), will be assessed by a dedicated high-resolution, regional Arctic inversion, informed by oceanographic observations to elucidate the location of subsea-seeps and other potential emissions sources as well as their temporal variability. The outcomes of this project will be summarised in a report for policy makers, enabling society to evaluate our current climate change strategies and provide knowledge essential to future stewardship of the Earth’s climate.
In December 2021 and August 2022, two Center for Arctic Gas Hydrate (CAGE) research cruises visited several areas in Hopendjupet, and Sentralbankrenna in the central Barents Sea. A major aim of these cruises was to survey and sample gas seepage from the sea floor. To meet our objective of assessing the state of climate sensitive Arctic methane reservoirs and using targeted approaches to measuring ocean to atmosphere emissions, we used weather forecasts of the local wind speed and direction to predict the best location to collect air samples potentially influenced by gas hydrate seepage. Furthermore, within ReGAME we restarted the instrumentation aboard the CAGE operated RV Helmer Hanssen, previously deployed during MOCA, for continuous measurement of methane, carbon dioxide, and carbon monoxide.
To meet the ReGAME objective of including S5P in inversion models, we have developed new routines to assess uncertainties in the satellite data, needed to run models. We first investigated whether the error data already provided alongside the satellite CH4 data from the European Union's Earth Observation Programme Copernicus, could be used. However initial investigation showed that these error values were probably too low since they were similar to the highly accurate ground-based observations. Instead, we implemented new routines to generate more useful error values based on the observed variability in the data (the ‘standard deviation’). We have developed several other routines to harmonize the satellite data with other inputs required for the model, including the grid size and pixel orientation. In 2023 we will perform tests on the new routines by looking at areas with known high CH4 emissions such as oil and gas fields.
2022 also saw a major methane leak event in the Baltic Sea following explosions in the Nord Stream gas pipelines. In total, three pipelines were ruptured, with each breaking into one short and one long section. Our simulation of the pressure loss in the pipelines for such a situation, using fluid dynamics equations, suggested an initial rapid release of gas while both sections emptied simultaneously, then a slower release over several days from the longer of the two sections. With this information, we simulated the transport of the methane leaks at the pipeline break locations using information on the wind speed and direction. By tuning the estimated emissions to match large observed spikes seen in atmospheric methane at several sites in Norway, Sweden, and Finland we estimated a methane leak of up to 155 Gt. This amount is minor compared to global annual emissions but is the largest single methane emission ever recorded and highlights issues around the transport and storage of natural gas. Our simulations were shown in several international media outlets including, but not limited to, Der Spiegel, The Guardian, Gazette, and New Scientist, as well as live interviews on Norwegian radio and Danish television.
In REGAME we will update chemistry transport models (FLEXPART, OsloCTM) to include the kinetic isotope effect (KIE) of methane (CH4), enabling better constraints on the CH4 budget (KIE is dependent on source/ sink). We will update the atmospheric inversion framework FLXINVERT to include novel use of satellite CH4 fields (Sentinel 5P). This will include significant changes to FLEXINVERT, which will also be applicable to other satellite data e.g. carbon dioxide (CO2) and improve the model capabilities to handle large data fields in general. With these upgrades we assess CH4 emissions from the major sources (wetlands, biomass burning, anthropogenic) at the global scale using all available data (e.g. ICOS, NOAA data, data on ebas.nilu.no). This data includes measurements from the Zeppelin Observatory in the Arctic, to Troll in Antarctica, i.e. from pole-to-pole.
Our cross disciplinary team is in a unique position to assess the state of the Arctic/ Antarctic ocean CH4 reservoir. This reservoir is currently considered a minor source but has potential for large scale disruption if emissions increase suddenly and rapidly. We will perform measurements of CH4 over the ocean (research vessels Helmer Hanssen, Kronprins Haakon) assess temporal variability of CH4 emission from the seabed and movement through the water column (due to e.g. variable microbial activity, ocean stratification, currents and seep emission rates), with long-term (1 year) measurements at a mooring south of Svalbard (deployed for the NorEMSO project) in an area bearing gas hydrates and active CH4 seeps. Furthermore we add to the knowledge of potential seep locations by performing echo-souding surveys. Combining insights from these temporal and spatial studies will allow a more targeted approach to assessing the ocean source in general. Specifically in REGAME we will run a regional/ Arctic inversion including these data to constrain high latitude emissions including from the ocean.