(a,b) Proxy-based atmospheric CO2 (Supplementary Data 1) on a log timescale with best fit LOESS and associated uncertainty envelope (Supplementary Data 2). (c) Ice core atmospheric CO2 from ref. 82 on log timescale. (d) Atmospheric CO2 on line timescale from ice core and observation record82 and future RCP8 and other41 scenarios (RCP3PD—grey, RCP4.5—orange, RCP6—red, RCP8.5—brown, Wink12k -black)38,40. (e–h) ΔFCO2,sol calculated from data shown in a–d as described in text. In (c) ΔFCO2,sol is calculated from ice core CO2 estimates assuming no change in solar output82. No change in solar output is also applied to the records in h.