“…Bottom‐up methods use empirical or process‐based models to estimate fluxes, or to upscale in situ measurements of the time change of stocks or of direct flux observations of the oceans (e.g., Carroll et al., 2020; Doney et al., 2004; Gregor et al., 2019; Gruber, Clement, et al., 2019; Hauck et al., 2020; Landschützer et al., 2013; Long et al., 2013; Rödenbeck et al., 2014, 2015; Sabine et al., 2004; Watson et al., 2020) or land biosphere (Hubau et al., 2020; Jung et al., 2020; Pan et al., 2011; Piao, Wang, Wang, et al., 2020; Sitch et al., 2015). “Top‐down” models use inverse methods to estimate the surface CO 2 fluxes from the land or ocean needed to match the observed atmospheric or ocean CO 2 concentrations, within their uncertainties, in the presence of the prevailing winds and ocean circulation (e.g., Chevallier et al., 2010, 2019; Crowell et al., 2019; DeVries, 2014; Enting et al., 1995; Jacobson et al., 2007; Khatiwala et al., 2009; Mikaloff Fletcher et al., 2006; Nassar et al., 2021; Wu et al., 2018).…”