TRENDS: ATMOSPHERIC CARBON DIOXIDE

Atmospheric carbon dioxide record from Mauna Loa

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

1958-2004

Methods

Air samples at Mauna Loa are collected continuously from air intakes at the top of four 7-m towers and one 27-m tower. Four air samples are collected each hour for the purpose of determining the CO₂ concentration. Determinations of CO₂ are made by using a Siemens Ultramat 3 nondispersive infrared gas analyzer with a water vapor freeze trap. This analyzer registers the concentration of CO₂ in a stream of air flowing at ~0.5 L/min. Every 30 minutes, the flow is replaced by a stream of calibrating gas or "working reference gas". In December 1983, CO₂-in-N₂ calibration gases were replaced with the currently used CO₂-in-air calibration gases. These calibration gases and other reference gases are compared periodically to determine the instrument sensitivity and to check for possible contamination in the air-handling system. These reference gases are themselves calibrated against specific standard gases whose CO₂ concentrations are determined manometrically. Greater details about the sampling methods at Mauna Loa are given in Keeling et al. (1982) and Keeling et al. (2002).

Hourly averages of atmospheric CO₂ concentration, wind speed, and wind direction are plotted as a basis for selecting data for further processing. Data are selected for periods of steady hourly data to within ~0.5 parts per million by volume (ppmv); at least six consecutive hours of steady data are required to form a daily average. Greater details about the data selection criteria used at Mauna Loa are given in Bacastow et al. (1985).

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

Trends

The Mauna Loa atmospheric CO₂ measurements constitute the longest continuous record of atmospheric CO₂ concentrations available in the world. The Mauna Loa site is considered one of the most favorable locations for measuring undisturbed air because possible local influences of vegetation or human activities on atmospheric CO₂ concentrations are minimal and any influences from volcanic vents may be excluded from the records. The methods and equipment used to obtain these measurements have remained essentially unchanged during the 47-year monitoring program.

Because of the favorable site location, continuous monitoring, and careful selection and scrutiny of the data, the Mauna Loa record is considered to be a precise record and a reliable indicator of the regional trend in the concentrations of atmospheric CO₂ in the middle layers of the troposphere. The Mauna Loa record shows a 19.4% increase in the mean annual concentration, from 315.98 parts per million by volume (ppmv) of dry air in 1959 to 377.38 ppmv in 2004. The 1997-1998 increase in the annual growth rate of 2.87 ppmv represets the largest single yearly jump since the Mauna Loa record began in 1958. This represents an average annual increase of 1.4 ppmv per year. This is smaller than the average annual increase at the other stations because of the longer record and inclusion of earlier (smaller) annual increases.

References

Bacastow, R.B. 1979.

Dip in the atmospheric CO₂ level during the mid-1960's. Journal of Geophysical Research 80:3109-14.

Bacastow, R.B., and C.D. Keeling. 1981.

Atmospheric carbon dioxide concentration and the observed airborne fraction. In B. Bolin (ed.), Carbon Cycle Modelling, SCOPE 16. John Wiley and Sons, New York.

Bacastow, R.B., J.A. Adams, Jr., C.D. Keeling, D.J. Moss, T.P. Whorf, and C.S. Wong. 1980.

Atmospheric carbon dioxide, the Southern Oscillation, and the weak 1975 El Niño. Science 210:66-68.

Bacastow, R.B., C.D. Keeling, and T.P. Whorf. 1985.

Seasonal amplitude increase in atmospheric CO₂ concentration at Mauna Loa, Hawaii, 1959-1982. Journal of Geophysical Research 90(D6):10529-40.

Keeling, C.D. 1960.

The concentration and isotopic abundance of carbon dioxide in the atmosphere. Tellus 12:200-203.

Keeling, C.D. 1984.

Atmospheric and oceanographic measurements needed for establishment of a data base for carbon dioxide from fossil fuels. In The Potential Effects of Carbon Dioxide-Induced Climatic Changes in Alaska. (Miscellaneous, etc.). The Proceedings of a Conference. Fairbanks, Alaska, April 7-8, 1982. School of Agriculture and Land Resources Management, University of Alaska, Fairbanks.

Keeling, C.D. 1998.

Rewards and penalties of monitoring the earth. Annual Review of Energy and the Environment 23:25-82. Annual Reviews Inc., Palo Alto.

Keeling, C.D., R.B. Bacastow, A.E. Bainbridge, C.A. Ekdahl, Jr., P.R. Guenther, L.S. Waterman, and J.F.S. Chin. 1976.

Atmospheric carbon dioxide variations at Mauna Loa Observatory, Hawaii. Tellus 28(6):538-51.

Keeling, C.D., R.B. Bacastow, and T.P. Whorf. 1982.

Measurements of the concentration of carbon dioxide at Mauna Loa Observatory, Hawaii. In W.C. Clark (ed.), Carbon Dioxide Review: 1982. Oxford University Press, New York.

Keeling, C.D., R.B. Bacastow, A.F. Carter, S.C. Piper, T.P. Whorf, M. Heimann, W.G. Mook, and H. Roeloffzen. 1989.

A three-dimensional model of atmospheric CO₂ transport based on observed winds: 1. Analysis of observational data. In D.H. Peterson (ed.), Aspects of Climate Variability in the Pacific and the Western Americas. Geophysical Monograph 55:165-235.

Keeling, C.D., J.F.S. Chin, and T.P. Whorf. 1996.

Increased activity of northern vegetation inferred from atmospheric CO₂ measurements. Nature 382: (6587) 146-49. MacMillan Magazines Ltd., London.

Keeling, C.D., T.P. Whorf, M. Wahlen, and J. van der Plicht. 1995.

Interannual extremes in the rate of rise of atmospheric carbon dioxide since 1980. Nature 375:666-670.

Pales, J.C., and C.D. Keeling. 1965.

The concentration of atmospheric carbon dioxide in Hawaii. Journal of Geophysical Research 24:6053-76.

Keeling, C.D., P.R. Guenther, G. Emanuele III, A. Bollenbacher, and D.J. Moss. 2002.

Scripps Reference Gas Calibration System for Carbon Dioxide-in-Nitrogen and Carbon Dioxide-in-Air Standards: Revision of 1999 (with Addendum). SIO Reference Series No. 01-11.

Whorf, T.P., and C.D. Keeling. 1998.

Rising carbon. New Scientist 157:(2124) 54-54. New Scientist Publ Expediting Inc., Elmont.

CITE AS: Keeling, C.D. and T.P. Whorf. 2005. Atmospheric CO₂ records from sites in the SIO air sampling 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, Tenn., U.S.A.

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