Correction to: Nature Physics https://doi.org/10.1038/s41567-021-01226-y, published online 26 April 2021.

In the version of this Letter originally published, in Fig. 2a, the y-axis label ‘R(13C/12C)VPDB (%)’ was incorrect and should have been ‘R(13C/12C)sample (%)’. Furthermore, the realization of a δ13C value for the reference sample of North American Continental Air, NIST Standard Reference Material 1720, was mistakenly attributed to the World Meteorological Organization (WMO) Global Atmosphere Watch Central Calibration Laboratory at the National Oceanic and Atmospheric Administration (NOAA), but should have been attributed to the Institute of Arctic and Alpine Research (INSTAAR), part of the University of Colorado Boulder; thus, the sentences beginning “These spectra were measured using…” and “The NIST Standard Reference Material 1720…” have been amended accordingly, as has the footnote for Supplementary Table S4. All versions of the Letter have been corrected and the Supplementary Information file replaced.