NOTICE (September 2017): Data previously stored at the CDIAC archive are being transitioned to the new, ESS-DIVE archive. This website provides access to the CDAIC data during the transition. If you have any questions regarding the new archive or the data transition, please contact

image image image image

Atmospheric CO2 From Flask Air Samples at Christmas Island

graphics Graphics   data Data

C.D. Keeling and T.P. Whorf

Carbon Dioxide Research Group, Scripps Institution of Oceanography, University of California, La Jolla, California 92093-0444, U.S.A.

Period of Record



Atmospheric CO2 samples were collected roughly twice per month until 1986, and at roughly weekly intervals thereafter. Samples are collected in 5-L evacuated glass flasks, and then returned to the Scripps Institution of Oceanography (SIO) where CO2 concentrations have been determined using an Applied Physics Corporation (APC) nondispersive infrared gas analyzer. Further information on measurements, calibration procedures and analysis is available in the references listed below.

Map showing location of Christmas Island, Kiribati

Christmas Island, Kiribati
Pacific Ocean island seashore
2°00' N, 157°18' W
3 m above MSL


The average of unflagged data for the first full year of measurements (1975) was 332.0 ppmv. The last year for which we have complete data is 2000; values for 2000 averaged 370.0, for an upward trend of 1.52 ppmv/year. Graphics here show the first and last year of data, to display the change in mean over time and the annual amplitudes. Long term trend curves are better displayed using SIO's PDF monthly averaged data.


CITE AS: Keeling, C.D. and T.P. Whorf. 2004. Atmospheric CO2 concentrations derived from flask air samples at sites in the SIO network. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, U.S.A.