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). 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. Global means are calculated from the latitude plot at each time step (Masarie and Tans, 1995). Go here for more details on how global means are calculated.
https://socan.eco/wp-content/uploads/2016/09/ch4_trend_gl.png 579 792 Alan Journet https://socan.eco/wp-content/uploads/2016/03/SOCAN-logo-300x126.png Alan Journet2016-09-03 20:23:052016-09-03 20:24:00Trends in Atmospheric Methane