Recent Global CO2
March 2012: 393.57 ppm
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]. Go here for more details on how global means are calculated.
The last four complete years plus the current year are shown here. The last year of data are still preliminary, pending recalibrations of reference gases and other quality control checks.
Data are reported as a dry air mole fraction defined as the number of molecules of carbon dioxide divided by the number of all molecules in air, including CO2 itself, after water vapor has been removed. The mole fraction is expressed as parts per million (ppm). Example: 0.000400 is expressed as 400 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 SEVEN adjacent seasonal cycles centered on the month to be corrected, except for the first and last THREE and one-half years of the record, where the seasonal cycle has been averaged over the first and last SEVEN 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.
Annual Mean Global Carbon Dioxide Growth Rates
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.
The estimated uncertainty in the global annual mean growth rate varies by year, and has been estimated by a bootstrap technique for 1980 and later. One hundred different realizations of a global network were constructed by randomly picking sites, with restitution, from our existing marine boundary layer sites in the NOAA/ESRL cooperative air sampling network (Conway, 1994). Each member of the ensemble of networks has the same number of sites as the real network, but some sites are missing, while others are represented more than once. An additional condition is that at least one southern high latitude site is present, one tropical and one northern high latitude site, because we have always maintained broad latitude coverage in the real network. Temporal data gaps at individual sites are present in the bootstrap networks. The reported uncertainties are the 1-sigma standard deviations for each year's growth rate of the ensemble members. Pre-1980 the annual growth rate and uncertainty have been calculated from the average of the Mauna Loa and South Pole records (before 1974 as measured by the Scripps Institution of Oceanography), as detailed in Ballantyne et al. (2012).
The complete globally averaged CO2 records described on this page are available.
- Globally averaged marine surface monthly mean data
- Globally averaged marine surface annual mean data
- Globally averaged marine surface annual mean growth rates.
How to reference content from this page
Ed Dlugokencky and Pieter Tans, NOAA/ESRL (www.esrl.noaa.gov/gmd/ccgg/trends/)
- Ed Dlugokencky, NOAA/ESRL, ph. 303 497 6228, Ed.Dlugokencky@noaa.gov
- Pieter Tans, NOAA/ESRL, ph. 303 497 6678, Pieter.Tans@noaa.gov
- A.P. Ballantyne, C.B. Alden, J.B. Miller, P.P. Tans, and J.W.C. White, (2012), Increase in observed net carbon dioxide uptake by land and oceans during the last 50 years, Nature 488, 70-72.
- T.J. Conway, P.P. Tans, L.S. Waterman, K.W. Thoning, D.R. Kitzis, K.A. Masarie, and N. Zhang, (1994), Evidence of interannual variability of the carbon cycle from the NOAA/CMDL global air sampling network, J. Geophys. Research, vol. 99, 22831-22855
- K.A. Masarie, P.P. Tans, (1995), Extension and integration of atmospheric carbon dioxide data into a globally consistent measurement record, J. Geopys. Research, vol. 100, 11593-11610