Trends in Carbon Dioxide
Annual Mean
Growth Rate
Mauna Loa, Hawaii

The graph shows recent monthly mean carbon dioxide measured at Mauna Loa Observatory, Hawaii. The last four complete years of the Mauna Loa CO2 record plus the current year are shown. 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). Click for a graph of the full Mauna Loa record. The last year of data is still preliminary, pending recalibrations of reference gases and other quality control checks. The dashed red line with diamond symbols represents the monthly mean values, centered on the middle of each month. The black line with the square symbols represents the same, after correction for the average seasonal cycle. The latter is determined as a moving average of ten adjacent seasonal cycles centered on the month to be corrected, except for the first and last five years of the record, where the seasonal cycle has been averaged over the first and last ten years, respectively. 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.

The table shows annual mean carbon dioxide growth rates for Mauna Loa. The annual mean rate of growth of CO2 in a given year is the difference in concentration between the end of December and the start of January of that year. If used as an average for the globe, it would represent the sum of all CO2 added to, and removed from, the atmosphere during the year by human activities and by natural processes. There is a small amount of month-to-month variability in the CO2 concentration that may be caused by anomalies of the winds or weather systems arriving at Mauna Loa. This variability would not be representative of the underlying trend for the northern hemisphere which Mauna Loa is intended to represent. Therefore, we finalize our estimate for the annual mean growth rate of the previous year in March, by using the average of the most recent November-February months, corrected for the average seasonal cycle, as the trend value for January 1. Our estimate for the annual mean growth rate (based on the Mauna Loa data) is obtained by subtracting the same four-month average centered on the previous January 1. Preliminary values for the previous year are calculated in January and in February. The values in this table are subject to change depending on quality control checks of the measured data, but any revisions are expected to be small. The estimated annual growth rates for Mauna Loa are close, but not identical, to the global growth rates. The standard deviation of the differences is 0.26 ppm.

Click here for the Mauna Loa CO2 monthly mean data.

Contact: Pieter Tans, ESRL/GMD, ph. 303 497 6678, Pieter.Tans@noaa.gov

References:

C.D. Keeling, 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.

K.W. Thoning, 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.

Annual Mean
Growth Rate
Global Average

The graph shows recent monthly mean carbon dioxide globally averaged over marine surface sites. 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). The last four complete years plus the current year are shown here. The last year of data is still preliminary, pending recalibrations of reference gases and other quality control checks. 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 dashed red line with diamond symbols represents the monthly mean values, centered on the middle of each month. The black line with the square symbols represents the same, after correction for the average seasonal cycle. The latter is determined as a moving average of ten adjacent seasonal cycles centered on the month to be corrected, except for the first and last five years of the record, where the seasonal cycle has been averaged over the first and last ten years, respectively. Click for a comparison with recent trends in carbon dioxide at Mauna Loa, Hawaii, which has the longest continuous record of direct atmospheric CO2 measurements.

The table shows annual mean carbon dioxide growth rates based on globally averaged marine surface data. The annual mean rate of growth of CO2 in a given year is the difference in concentration between the end of December and the start of January of that year. It represents the sum of all CO2 added to, and removed from, the atmosphere during the year by human activities and by natural processes. The annual mean growth during the previous year is determined by taking the average of the most recent December and January months, corrected for the average seasonal cycle, as the trend value for January 1, and then subtracting the same December-January average measured one year earlier. Our first estimate for the annual growth rate of the previous year is produced in January of the following year, using data through November of the previous year. That estimate will then be updated in February using data though December, and again in March using data through January. We finalize our estimate for the growth rate of the previous year in the fall of the following year because a few of the air samples on which the global estimate is based are received late in the following year. The values in this table are subject to change depending on quality control checks of the measured data, but any revisions are expected to be small. The estimates of the global mean CO2 concentration, and thus the annual growth rate, are updated every month as new data come in. The statistics are as follows. If we estimate during a given month ("m") the global average CO2 during the previous month ("m-1"), the result differs from the estimate made (up to almost a year later) when all the data are in, with a standard deviation of 0.57 ppm. For month m-2, the standard deviation is 0.17 ppm, and for month m-3 it is 0.10 ppm. We decided to provide the global mean estimates with a lag of two months. Thus, a December average is first calculated during the following February.

Click here for the globally averaged marine surface data.

Contact: Thomas Conway, ESRL/GMD, ph. 303 497 6681, Thomas.J.Conway@noaa.gov or Pieter Tans, ESRL/GMD, ph. 303 497 6678, Pieter.Tans@noaa.gov

References:

T.J. Conway, P.P. Tans, L.S. Waterman, K.W. Thoning, D.R. Kitzis, K.A. Masarie, and N. Zhang, Evidence of interannual variability of the carbon cycle from the NOAA/CMDL global air sampling network, J. Geophys. Research, vol. 99, 22831-22855, 1994.

K.A. Masarie, P.P. Tans, Extension and integration of atmospheric carbon dioxide data into a globally consistent measurement record, J. Geopys. Research, vol. 100, 11593-11610, 1995.