From Keenan et al.
https://www.nature.com/articles/ncomms13428
"Our analysis suggests that the airborne fraction increased steadily from the 1960s to the 1990s (1.8% per year, P=0.03; Fig. 1b), albeit with large interannual variability reflecting year-to-year variability in the terrestrial sink.
"Since the start of the twenty-first century, however, the airborne fraction has been declining (−2.2% per year, P=0.07; Fig. 1b), despite the rapid increase in anthropogenic emissions (Fig. 1b). Changes in the airborne fraction are reflected in the atmospheric CO2 growth rate.
For the three decades from the start of the measurement record in 1959, the atmospheric CO2 growth rate increased from 0.75 to 1.86 p.p.m. per year (Fig. 1a). However, for the period 2002–2014 there has been no significant increase in the growth rate of CO2 (Fig. 1a and Supplementary Fig. 1). The decline in the airborne fraction since the start of the twenty-first century has therefore been sufficiently large as to result in a pause in the rate of increase of the atmospheric CO2 growth rate (Fig. 1a).“
DB2