XCO<sub>2</sub> is the column-averaged of carbon dioxide in the atmosphere, represented in parts per million (ppm). Rather than taking a single observation at the surface, an integration of atmospheric CO<sub>2</sub> above a specific location is observed. The 'X' refers to the observation taking place from a satellite platform. CO<sub>2</sub> observing satellites cannot observe green house gasses directly, but instead average the entire atmospheric column of CO<sub>2</sub>. These estimates from satellites need ground truthing to ensure that XCO<sub>2</sub> retrievals are accurate, with an average accuracy from OCO 2 and GOSAT of 0.267 ñ 1.56 ppm between September 2014 to December 2016.
The largest recorded value XCO<sub>2</sub> was recorded during May 2018 over the Northern Hemisphere, with a value of approximately 410 ppm. These values have been increasing steadily over recent years. Space-based CO<sub>2</sub> measurements are used for climate-level scientific studies such as a further understanding of the El NiñoâÂÂSouthern Oscillation