Trends in globally-averaged CH₄, N₂O, and SF₆

Measurements of CH₄, N₂O, and SF₆ from a globally-distributed network of air sampling sites are first smoothed in time. Values are extracted from the smooth curves at equally-spaced intervals (48 time steps per year), then curves are fitted to these values as a function of latitude. Values extracted from these curves at spacing of sine(latitude)=0.05 define a matrix of Greenhouse Gas values in units of dry air mole fraction as functions of latitude and time. Values in this matrix, already weighted for their relative surface area, are averaged to calculate global and other zonal means.

See Marine Boundary Layer Reference for more details.

Trends Pages

• Trends in CH₄
• Trends in N₂O
• Trends in SF₆

Available files

• Globally-averaged, monthly means
  These are determined by first fitting curves to the globally-averaged values at daily resolution, then averaging all daily values within each month. Monthly means and deseasonalized trend values are reported at the middle of each month with uncertainties.
• Globally-averaged, annual means
  These are determined by averaging all daily values within a year and reported with uncertainties.
• Globally-averaged, annual increase
  These are determined for a given year from a deseasonalized trend curve fitted to the global means as the change in GHG deseasonalized trend value from Jan. 1 in that year to Jan. 1 in the next year and reported with uncertainties.

Uncertainties

Uncertainties are based on two terms, one that varies our network with a bootstrap method (also called a resampling method) and one that accounts for analytical uncertainty using a Monte Carlo method. For each term, 100 iterations are prepared, parameters of interested are calculated, standard deviations are determined from the 100 iterations, and the network and analytical terms are then added in quadrature to get the total uncertainty.

Please cite these globally averaged products as:

• Lan, X., K.W. Thoning, and E.J. Dlugokencky (2022): Trends in globally-averaged CH4, N2O, and SF6 determined from NOAA Global Monitoring Laboratory measurements. Version 2025-01, https://doi.org/10.15138/P8XG-AA10