Compiled records of carbon isotopes in atmospheric CO2 for historical simulations in CMIP6 - Graven, H; Allison, CE; Etheridge, DM; Hammer, S; Keeling, RF; Levin, I; Meijer, HAJ; Rubino, M; Tans, PP; Trudinger, CM; Vaughn, BH; White, JWC (Geoscientific Model Development, 2017)