Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual
1958 -999 -999 315.71 317.45 317.50 -999 315.86 314.93 313.19 -999 313.34 314.67 -999
1959 315.58 316.47 316.65 317.71 318.29 318.16 316.55 314.80 313.84 313.34 314.81 315.59 315.98
1960 316.43 316.97 317.58 319.03 320.03 319.59 318.18 315.91 314.16 313.83 315.00 316.19 316.91
1961 316.89 317.70 318.54 319.48 320.58 319.78 318.58 316.79 314.99 315.31 316.10 317.01 317.65
1962 317.94 318.56 319.69 320.58 321.01 320.61 319.61 317.40 316.26 315.42 316.69 317.69 318.45
1963 318.74 319.08 319.86 321.39 322.24 321.47 319.74 317.77 316.21 315.99 317.07 318.36 318.99
1964 319.57 -999 -999 -999 322.23 321.89 320.44 318.70 316.70 316.87 317.68 318.71 -999
1965 319.44 320.44 320.89 322.13 322.16 321.87 321.21 318.87 317.81 317.30 318.87 319.42 320.03
1966 320.62 321.59 322.39 323.70 324.07 323.75 322.40 320.37 318.64 318.10 319.79 321.03 321.37
1967 322.33 322.50 323.04 324.42 325.00 324.09 322.55 320.92 319.26 319.39 320.72 321.96 322.18
1968 322.57 323.15 323.89 325.02 325.57 325.36 324.14 322.11 320.33 320.25 321.32 322.90 323.05
1969 324.00 324.42 325.64 326.66 327.38 326.70 325.89 323.67 322.38 321.78 322.85 324.12 324.62
1970 325.06 325.98 326.93 328.13 328.07 327.66 326.35 324.69 323.10 323.07 324.01 325.13 325.68
1971 326.17 326.68 327.18 327.78 328.92 328.57 327.37 325.43 323.36 323.56 324.80 326.01 326.32
1972 326.77 327.63 327.75 329.72 330.07 329.09 328.05 326.32 324.84 325.20 326.50 327.55 327.46
1973 328.54 329.56 330.30 331.50 332.48 332.07 330.87 329.31 327.51 327.18 328.16 328.64 329.68
1974 329.35 330.71 331.48 332.65 333.09 332.25 331.18 329.40 327.44 327.37 328.46 329.58 330.25
1975 330.40 331.41 332.04 333.31 333.96 333.59 331.91 330.06 328.56 328.34 329.49 330.76 331.15
1976 331.74 332.56 333.50 334.58 334.87 334.34 333.05 330.94 329.30 328.94 330.31 331.68 332.15
1977 332.92 333.42 334.70 336.07 336.74 336.27 334.93 332.75 331.58 331.16 332.40 333.85 333.90
1978 334.97 335.39 336.64 337.76 338.01 337.89 336.54 334.68 332.76 332.54 333.92 334.95 335.50
1979 336.23 336.76 337.96 338.89 339.47 339.29 337.73 336.09 333.91 333.86 335.29 336.73 336.85
1980 338.01 338.36 340.08 340.77 341.46 341.17 339.56 337.60 335.88 336.01 337.10 338.21 338.69
1981 339.23 340.47 341.38 342.51 342.91 342.25 340.49 338.43 336.69 336.85 338.36 339.61 339.93
1982 340.75 341.61 342.70 343.56 344.13 343.35 342.06 339.82 337.97 337.86 339.26 340.49 341.13
1983 341.37 342.52 343.10 344.94 345.75 345.32 343.99 342.39 339.86 339.99 341.16 342.99 342.78
1984 343.70 344.51 345.28 347.08 347.43 346.79 345.40 343.28 341.07 341.35 342.98 344.22 344.42
1985 344.97 346.00 347.43 348.35 348.93 348.25 346.56 344.69 343.09 342.80 344.24 345.56 345.90
1986 346.29 346.96 347.86 349.55 350.21 349.54 347.94 345.91 344.86 344.17 345.66 346.90 347.15
1987 348.02 348.47 349.42 350.99 351.84 351.25 349.52 348.10 346.44 346.36 347.81 348.96 348.93
1988 350.43 351.72 352.22 353.59 354.22 353.79 352.39 350.44 348.72 348.88 350.07 351.34 351.48
1989 352.76 353.07 353.68 355.42 355.67 355.13 353.90 351.67 349.80 349.99 351.30 352.53 352.91
1990 353.66 354.70 355.39 356.20 357.16 356.22 354.82 352.91 350.96 351.18 352.83 354.21 354.19
1991 354.72 355.75 357.16 358.60 359.34 358.24 356.17 354.03 352.16 352.21 353.75 354.99 355.59
1992 355.98 356.72 357.81 359.15 359.66 359.25 357.03 355.00 353.01 353.31 354.16 355.40 356.37
1993 356.70 357.16 358.38 359.46 360.28 359.60 357.57 355.52 353.70 353.98 355.33 356.80 357.04
1994 358.36 358.91 359.97 361.26 361.68 360.95 359.55 357.49 355.84 355.99 357.58 359.04 358.88
1995 359.96 361.00 361.64 363.45 363.79 363.26 361.90 359.46 358.06 357.75 359.56 360.70 360.88
1996 362.05 363.25 364.03 364.72 365.41 364.97 363.65 361.49 359.46 359.60 360.76 362.33 362.64
1997 363.18 364.00 364.57 366.35 366.79 365.62 364.47 362.51 360.19 360.77 362.43 364.28 363.76
1998 365.32 366.15 367.31 368.61 369.29 368.87 367.64 365.77 363.90 364.23 365.46 366.97 366.63
1999 368.15 368.87 369.59 371.14 371.00 370.35 369.27 366.94 364.63 365.12 366.67 368.01 368.31
2000 369.14 369.46 370.52 371.66 371.82 371.70 370.12 368.12 366.62 366.73 368.29 369.53 369.48
2001 370.28 371.50 372.12 372.87 374.02 373.30 371.62 369.55 367.96 368.09 369.68 371.24 371.02
2002 372.43 373.09 373.52 374.86 375.55 375.41 374.02 371.49 370.71 370.25 372.08 373.78 373.10
2003 374.68 375.63 376.11 377.65 378.35 378.13 376.62 374.50 372.99 373.00 374.35 375.70 375.64

* missing data = -999
** Source:
Keeling, C.D. and Whorf, T.P. 1998.  Atmospheric CO2 concentrations -- Mauna Loa Observatory, Hawaii, 1958-1997 (revised June 2004).  NDP-001.  Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee.

Monthly values are expressed in parts per million (ppm) and reported in the 2003A SIO manometric mole fraction scale.  The monthly values have been adjusted to the 15th of each month.