![]() ![]() ![]() Go here for more details on how global means are calculated. Global means are calculated from the latitude plot at each time step ( Masarie and Tans, 1995). A global average is constructed by first smoothing the data for each site as a function of time, and then smoothed values for each site are plotted as a function of latitude for 48 equal time steps per year. The Global Monitoring Division of NOAA’s Earth System Research Laboratory has measured methane since 1983 at a globally distributed network of air sampling sites ( Dlugokencky et al., 1994). Other impacts on the latest few months of data are described below. Values for the last year are preliminary, pending recalibrations of standard gases and other quality control steps. The first graph shows monthly means for the last four years plus the current year, and the second graph shows the full NOAA time-series starting in 1983. The graphs show globally-averaged, monthly mean atmospheric methane abundance determined from marine surface sites. ![]()
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