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Atmospheric CO2 from Continuous Air Samples at Mauna Loa Observatory, Hawaii, U.S.A.

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

March 1958 - December 2001


An Applied Physics Corporation (APC) nondispersive infrared gas analyzer was used to obtain atmospheric CO2 concentrations, based on continuous data (four measurements per hour) from atop intake lines on several towers. Steady data periods of not less than six hours per day are required; if no such six-hour periods are available on any given day, then no data are used that day. Weekly averages were calculated for most weeks throughout the approximately 44 years of record. The continuous data for year 2000 is compared with flask data from the same site in the graphics section.

Map showing location of Mauna Loa, Hawaii, U.S.A.
Mauna Loa, Hawaii, U.S.A.
Barren lava field of an active volcano
19°32' N, 155°35' W, 3397 m above MSL
Map of Hawaii


This is the longest continuous record of CO2 in the world. The annual range of about 7 ppmv and the shape of the annual wave are well defined by these weekly data. An upward trend from about 315 ppmv in 1958 to about 370 ppmv in 2001 is evident; this amounts to an increase of about 1.3 ppmv/year (see the 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.