Fig. 2.   Growth rate of atmospheric CO₂ and CH₄ based on ice core measurements of Etheridge et al. (20, 21), in situ CO₂ observations initiated by C. D. Keeling (11), and National Oceanic and Atmospheric Administration (NOAA) CO₂ and CH₄ observations made available by the NOAA Climate Monitoring and Diagnostics Laboratory (ftp://ftp.cmdl.noaa.gov/ccg).