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Hiroshi Tanimoto, Director of the Earth System Division at the National Institute for Environmental Studies (NIES), Japan, and Astrid Müller together with their international research team, have developed a new method to evaluate satellite observations of XCO2 over open ocean areas, which are currently inaccessible through established validation network sites. In the new approach, a reference CO2 dataset is formulated by combining cargo ship and passenger aircraft observations which were conducted in cooperation with operators of the private sector.
(Background)
After the Paris Agreement entered into force, commitment to reduce greenhouse gas emissions are being expedited. CO2 is the most important anthropogenically produced greenhouse gas. Emissions due to fossil fuel combustion and cement production have caused an accelerated increase of atmospheric CO2 to more than 410 ppm in 2020 since the 1950s (Dlugokencky and Tans, 2021). High quality and high density measurements are needed to estimate changes in anthropogenic and natural emission towards the implementation of the Paris Agreement and achieving the goal of net-zero greenhouse gas emission. Increased research and development activities have been led to monitor CO2 from more than 200 locations on the earth's surface (in 1958, it has been only 2 sites), and by a growing fleet of space-based satellites with global coverage. Among these satellites, the Greenhouse Gases Observing Satellite (GOSAT) and the Orbiting Carbon Observatory 2 (OCO-2) have been launched in 2009 and 2014. The advantage of the space-based observations is their high spatial and temporal coverage, even over inaccessible areas of the globe, albeit at a lower accuracy compared to the in situ measurements. Ocean surfaces are among these difficult to access areas. They cover 70% of the Earth and play the most reliable role in the removal (~2.5 PgC/yr) of the anthropogenic emitted CO2 (~10 PgC/yr) into the atmosphere (Friedlingstein et al., 2019).