Abstract
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.