Statistical analysis of the increase in atmospheric CO2 concentrations and its relation to the possible existence of CO2 fertilization on a global scale

Correlation coefficients r between seasonal amplitudes and annual means of atmospheric CO₂ concentrations are calculated for 17 stations which have 10 or more data and whose latitudes range from the South Pole to Alaska. Although signs of r are random,%s of stations with positive r increase as the number of data n for each station increases, and for stations with n >25, all 4 stations have positive r. The CO₂ fertilization coefficient μ defined by photosynthesis increase per CO₂ increase of 1 ppm is calculated for each station, and weighted averages of r and μ are calculated changing values of the minimum n. They are found to be always positive and both of them increase as n increases. These trends indicate that the random sign of r for small n is due to small numbers of data and that r would be positive if the number of data were sufficient, which suggests that CO₂ fertilization exists on the global scale. However there are still large uncertainties and further investigations are necessary to clarify the situation.