Source Data:
CO2 Clock data derived from in situ air measurements of of atmospheric CO2 concentrations (in ppm) as measured at Mauna Loa Observatory, Hawaii. Source data is provided from the Scripps CO2 Program at the Scripps Institution of Oceanography.
Data Citation: C. D. Keeling, S. C. Piper, R. B. Bacastow, M. Wahlen, T. P. Whorf, M. Heimann, and H. A. Meijer, Exchanges of atmospheric CO2 and 13CO2 with the terrestrial biosphere and oceans from 1978 to 2000. I. Global aspects, SIO Reference Series, No. 01-06, Scripps Institution of Oceanography, San Diego, 88 pages, 2001.
Clock Calculation: Continuously updated CO2 concentrations are derived from the montly data points provided by the in situ measurements, and currently are taken as a linear extrapolation of the previous two data points. Clock is recalibrated after the release of each new monthly data point. Future updates will take into account the seasonal trend variations in the forward interpolation (see Keeling curve below). Note that the number of significant digits given is for time lapse effect rather than empirical accuracy. 
