Please see:
http://members.cox.net/rcoppock/CO2-6DegreesFreedom.jpg

Clearly, the atmospheric CO2 concentration is rising exponentially.
Compare the trend of the points on the graph I have provided with
a straight line.

The period term in the sine function was given freedom to
check the accuracy of both the measurement and numeric
computation. The optimizer computed 0.999477 for this
value that is obviously the 1-year CO2 cycle. The
coefficients determined by the curve fit are very probably
as accurate, slightly better than three decimal places.
(And, I didn't confuse radians for degrees like the infamous
Canadian fossil fool! Please see:
http://timlambert.org/2004/08/mckitrick6/)

=-=-=-=-=-=-=-=-=
These data may be found at:
http://www.cmdl.noaa.gov/projects/sr...co2_mm_mlo.dat

The yearly means of the 574 points of monthly data follow:
YEAR CO2_ppmv"
1958 315.33 8 months of data"
1959 315.98"
1960 316.91"
1961 317.65"
1962 318.46"
1963 318.99"
1964 319.20 9 months of data"
1965 320.03"
1966 321.37"
1967 322.18"
1968 323.05"
1969 324.62"
1970 325.68"
1971 326.32"
1972 327.46"
1973 329.68"
1974 330.17"
1975 331.14 11 months of data"
1976 332.06"
1977 333.78"
1978 335.40"
1979 336.78"
1980 338.70"
1981 340.11"
1982 340.98 11 months of data"
1983 342.84"
1984 344.20 11 months of data"
1985 345.87"
1986 347.19"
1987 348.98"
1988 351.45"
1989 352.89"
1990 354.16"
1991 355.48"
1992 356.27"
1993 356.96"
1994 358.63"
1995 360.63"
1996 362.37"
1997 363.47"
1998 366.50"
1999 368.14"
2000 369.41"
2001 371.07"
2002 373.16"
2003 375.80"
2004 377.55"
2005 379.75"
2006 382.79 8 months of data"