Monthly CO2 Mixing Ratios

Monthly atmospheric CO₂ mixing ratios from Niwot Ridge, Colorado, U.S.

Background atmospheric CO₂ mixing ratios from individual flask air samples for Niwot Ridge, Colorado, U.S. Only measurements satisfying the data selection criteria fro background measurements are plotted. Consecutive background measurements are joined by lines. Background measurements interrupted by non-background measurements are not joined by lines.

Monthly atmospheric CO₂ mixing ratios for Niwot Ridge, Colorado, U.S., expressed in parts per million (ppm) and reported in the Scripps Institution of Oceanography X93 manometric mole fraction scale. Annual values were calculated by CDIAC for years with complete records. Missing values are denoted by -99.99.

Year Jan Feb Mar April May June July Aug Sept Oct Nov Dec Ann

1968 323.77 325.16 326.03 326.53 326.46 323.96 320.08 318.18 318.88 321.13 323.22 324.04 323.12 1969 324.56 325.61 327.09 327.95 327.11 324.98 321.31 318.60 319.43 322.17 323.88 325.42 324.01 1970 326.67 327.40 329.02 330.48 329.15 326.11 322.29 319.46 320.54 324.18 326.09 326.41 325.65 1971 327.52 328.90 329.70 330.21 329.11 324.60 320.74 319.69 320.17 323.07 325.63 326.28 325.47 1972 327.46 328.75 329.26 330.37 329.32 324.30 320.60 320.38 322.14 325.38 328.45 329.81 326.35 1973 330.79 331.70 332.36 333.22 333.53 331.17 327.39 325.48 326.60 328.38 330.58 331.85 330.25 1974 332.60 333.76 335.15 336.13 334.96 331.99 -99.99 -99.99 -99.99 -99.99 -99.99 -99.99 -99.99 1975 -99.99 -99.99 -99.99 -99.99 -99.99 -99.99 -99.99 -99.99 -99.99 -99.99 -99.99 -99.99 -99.99 1976 332.79 334.26 334.61 335.04 334.49 332.31 330.22 328.09 327.63 329.97 332.09 333.54 332.09 1977 334.81 335.78 336.54 337.28 337.28 335.27 332.76 331.43 331.51 333.46 335.17 336.41 334.81 1978 337.39 338.02 338.41 338.54 338.69 337.34 333.86 330.96 330.83 333.46 334.95 336.45 335.74 1979 338.04 338.74 339.85 340.52 340.49 338.10 334.39 332.63 332.52 334.16 336.69 338.02 337.01 1980 339.41 340.78 341.52 341.86 339.57 335.88 334.18 334.09 334.95 336.42 338.57 339.82 338.09 1981 341.24 342.99 343.39 343.14 341.95 339.54 337.18 335.36 335.38 338.06 340.97 341.77 340.08 1982 342.36 343.88 345.02 345.40 344.01 340.45 336.67 334.93 336.59 339.57 340.68 341.35 340.91 1983 343.37 344.71 345.22 346.07 345.09 342.40 339.44 336.46 336.72 340.36 343.63 345.74 342.43 1984 345.74 346.22 347.97 349.06 348.38 345.10 340.08 338.58 340.73 343.25 344.88 345.89 344.66 1985 347.09 347.77 348.09 348.57 347.81 345.70 344.69 343.78 342.07 343.53 346.62 347.54 346.11 1986 347.90 349.10 349.61 349.81 348.66 345.63 344.24 344.16 344.28 345.10 346.21 347.69 346.87 1987 349.03 350.38 351.82 351.80 350.78 349.57 347.41 344.86 345.20 347.14 349.41 351.25 349.05 1988 352.57 353.67 354.40 355.38 354.43 351.39 349.71 348.30 347.95 349.57 352.40 354.00 351.98 1989 354.24 354.91 355.43 355.79 355.61 354.63 352.58 349.63 349.12 351.12 353.58 354.52 353.43 1990 355.36 357.00 357.48 357.82 357.95 355.88 352.01 350.23 351.24 352.26 353.65 355.72 354.72 1991 357.22 358.32 359.32 359.95 358.59 356.66 353.74 351.33 351.40 353.39 356.10 357.72 356.15 1992 358.87 359.35 360.07 359.76 357.56 356.63 356.17 354.05 352.81 354.16 355.89 357.14 356.87 1993 358.54 359.34 360.49 361.37 360.52 358.60 354.47 351.64 353.32 356.02 356.93 357.70 357.41