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Trends in Atmospheric Carbon Dioxide

Overview

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There has been a geometric growth in atmospheric carbon dioxide since the Industrial Revolution, whether measured through Ice Cores, at Mauna Loa, or at marine sea surface sites.

Historical CO2 Records from the Law Dome DE08, DE08 - 2,

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The CO2 records presented here are derived from three ice cores obtained at Law Dome, East Antarctica from 1987 to 1993. The Law Dome site satisfies many of the desirable characteristics of an ideal ice core site for atmospheric CO2 reconstructions including negligible melting of the ice sheet surface, low concentrations of impurities, regular stratigraphic layering undisturbed at the surface by wind or at depth by ice flow, and high snow accumulation rate. Further details on the site, drilling, and cores are provided in Etheridge et al. (1996), Etheridge and Wookey (1989), and Morgan et al (1997).

Air bubbles were extracted using the "cheese grater" technique. Ice core samples weighing 500-1500 g were prepared by selecting crack-free ice and trimming away the outer 5-20 mm. Each sample was sealed in a polyethylene bag and cooled to -80°C before being placed in the extraction flask where it was evacuated and then ground to fine chips. The released air was dried cryogenically at -100°C and collected cryogenically in electropolished stainless steel "traps", cooled to about -255°C. Further details on the extraction technique can be found in Etheridge et al. (1988 and 1992) and additional information on the ice and air sample handling are provided in Etheridge et al. (1996).

The ice core air samples, ranging from about 50 to 150 ml standard temperature and pressure (STP), were measured for CO2 mixing ratio with a Carle 400 Series analytical gas chromatograph (GC). After separation on the GC columns, the CO2 was catalytically converted to methane before flame ionization detection. As many as three separate analysis were made on each ice core sample. Each sample injection to the GC was bracketed by calibration gas injections. CO2 mixing ratios were then found for each aliquot by multiplying the ratio of the sample peak area to calibration gas peak area (interpolated to the time of sample analysis) by the CO2 mixing ratio assigned to the calibration gas. The precision of analysis of the Law Dome ice core air samples was 0.2 ppm. For greater details on the experimental techniques used on the DE08, DE08-2, and DSS ice cores, please refer to Etheridge et al. (1996).

The ice cores were dated by counting the annual layers in oxygen isotope ratio (δ18O in H2O), ice electroconductivity measurements (ECM), and hydrogen peroxide (H2O2) concentrations. For these three parameters, each core displayed clear, well-preserved seasonal cycles allowing a dating accuracy of ±2 years at 1805 A.D. for the three cores and ±10 years at 1350 A.D. for DSS.

The enclosed air at any depth in the ice has a mean age, (aa), that is younger than the age of the host ice layer (ai), from which the air is extracted. The difference (δa) equals the time (Ts) for the ice layer to reach a depth (ds), where air becomes sealed in the pore space, minus the mean time (Td) for air to mix down the depth. The mean air age is thus

aa = ai + δa = ai + Ts - Td

where ages are dates A.D.

Mixing of air from the ice sheet surface to the sealing depth is primarily by molecular diffusion. The rate of air mixing by diffusion in the firn decreases as the density increases and the open porosity decreases with depth. Etheridge et al. (1996) determined the sealing depth at DE08 to be 72 m where the age of the ice is 40±1 years; at DE08-2 to be 72 m depth and 40 years; and at DSS to be 66 m depth and 68 years. For more details on dating the Law Dome ice cores and sealing densities, please refer to Etheridge et al. (1996).

Atmospheric carbon dioxide levels appear to have been constant at around 280 PPM between 1000 AD and 1800. Then, during the Industrial Revolution, carbon dioxide levels began a rapid rise.

Source: http://cdiac.ornl.gov/trends/co2/lawdome.html

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Mauna Loa Carbon Dioxide

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Mean annual carbon dioxide levels recorded at Mauna Loa and reported by the National Oceanic and Atmospheric Administration' s Earth System Research Laboratory are reported here.  Linear and quadratic least squares lines have been fit to the data.  The quadratic formula, shown with a green line, provides the best fit : level = 44690.5 - 46.1486 x + 0.0119942 x^2

Pre - industrial (recent history) levels are said to have been at around 280 parts per million.
   
Data from March 1958 through April 1974 have been obtained by C. David Keeling of the Scripps Institution of Oceanography (SIO) and were obtained from the Scripps website (scrippsco2.ucsd.edu). Data from 1974 through the present from Dr. Pieter Tans, NOAA/ESRL (www.esrl.noaa.gov/gmd/ccgg/trends/) Source : ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_annmean _mlo.txt

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The Breathing Earth : Mauna Loa

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Carbon Dioxide levels rise in the fall and winter, as plant photosynthesis (which converts carbon dioxide to oxygen and plant cells) slows and respiration (which converts oxygen to carbon dioxide) continues.The annual cycle may be seen in the zig zags of the graph below.

Data are reported as a dry mole fraction defined as the number of molecules of carbon dioxide divided by the number of molecules of dry air, multiplied by one million (ppm).The Mauna Loa data are being obtained at an altitude of 3400 m in the northern subtropics, and may not be the same as the globally averaged CO2 concentration at the surface.

Data from March 1958 through April 1974 have been obtained by C.David Keeling of the Scripps Institution of Oceanography (SIO) and were obtained from the Scripps website (scrippsco2.ucsd.edu).Data from 1974 through the present from Dr.Pieter Tans, NOAA/ESRL (www.esrl.noaa.gov/gmd/ccgg/trends/) Source : ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_mm _mlo.txt

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Marine Surface Carbon

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The Global Monitoring Division of NOAA/Earth System Research Laboratory has measured carbon dioxide and other greenhouse gases for several decades at a globally distributed network of air sampling sites (Conway, 1994). A global average is constructed by first fitting a smoothed curve as a function of time to each site, and then the smoothed value for each site is plotted as a function of latitude for 48 equal time steps per year. A global average is calculated from the latitude plot at each time step (Masarie, 1995).  Data are reported as a dry mole fraction defined as the number of molecules of carbon dioxide divided by the number of molecules of dry air, multiplied by one million (ppm). Points on the graph represent the monthly mean values, centered on the middle of each month.

Atmospheric carbon dioxide levels at these marine surface sites has risen steadily since 1980.

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Correlation between

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Sea surface measurements of carbon dioxide are nearly identical to those taken at Mauna Loa, which averaged .6 ppm higher, a difference that is not statistically significant.  The two sets of measures have grown in lock-step during the period since 1980 (see graph below), with a correlation of .9999. We conclude that either measure may be used as a surrogate for the other, for most purposes.

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Carbon Dioxide Measures from Ice

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In the graph below, we plot the historical carbon dioxide levels from Law Dome, 1010 A.D. to 1975 A.D., along with the recent carbon dioxide levels measured at sea surface and at Mauna Loa. While there is no overlap in dates from these samples, they seem to be in perfect agreement concerning overall level of carbon dioxide.

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References

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Etheridge, D.M., and C.W. Wookey. 1989. Ice core drilling at a high accumulation area of Law Dome, Antarctica. 1987. In Ice Core Drilling, edited by C. Rado and D. Beaudoing, pp. 86-96. Proceedings of the Third International Workshop on Ice Core Drilling Technology, Grenoble, France, October 10-14, 1988, CNRS, Grenoble.

Etheridge, D.M., G.I. Pearman, and F. de Silva. 1988. Atmospheric trace-gas variations as revealed by air trapped in an ice core from Law Dome, Antarctica. Ann. Glaciol. 10:28-33.

Etheridge, D.M., G.I. Pearman, and P.J. Fraser. 1992. Changes in tropospheric methane between 1841 and 1978 from a high accumulation rate Antarctic ice core. Tellus 44B:282-294.

Etheridge, D.M., L.P. Steele, R.L. Langenfelds, R.J. Francey, J.-M. Barnola, and V.I. Morgan. 1996. Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn. Journal of Geophysical Research 101:4115-4128.

Etheridge, D. M., L.P. Steele, R.L. Langenfelds, R.J. Francey, J.-M. Barnola and V.I. Morgan. 1998. Historical CO2 records from the Law Dome DE08, DE08-2, and DSS ice cores. 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.  http://cdiac.ornl.gov/trends/co2/lawdome.h tml

Hamley, T.C., V.I. Morgan, R.J. Thwaites, and X.Q. Gao. 1986. An ice-core drilling site at Law Dome summit, Wilkes Land, Antarctica, Res. Note 37, Aust. Natl. Antarc. Res. Exped., Tasmania.

Keeling, C.D. ,  R.B. Bacastow, A.E. Bainbridge, C.A. Ekdahl, P.R. Guenther, and L.S. Waterman, Atmospheric carbon dioxide variations at Mauna Loa Observatory, Hawaii, Tellus, vol. 28, 538-551, 1976.

Morgan, V.I., C.W. Wookey, J. Li, T.D. van Ommen, W. Skinner, and M.F. Fitzpatrick. 1997. Site information and initial results from deep ice drilling on Law Dome. J. Glaciol. 43:3-10.

Thoning, K.W. , P.P. Tans, and W.D. Komhyr, Atmospheric carbon dioxide at Mauna Loa Observatory 2. Analysis of the NOAA GMCC data, 1974-1985, J. Geophys. Research, vol. 94, 8549-8565, 1989.

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© 2009 David Stang. All rights reserved.

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Last Revised: Wednesday, January 7, 2009