Greenhouse statistics - time series analysis: Part II

The analysis of part I (Tol and de Vos, 1993) is supplemented, updated and refined, and the resolution bound of simple statistical analysis is tentatively explored. The main conclusion of part I, the hypothesis that the anthropogenically enhanced greenhouse effect is not responsible for the observed global warming during the last century is rejected with a 99% confidence, is reconfirmed for the updated sample period 1870-1991. The slight decrease in the global mean temperature between 1940 and 1975 is attributed to the influence of El Niño and the volcanic activity. The influence of sunspots, or the length of the solar cycle, is found to be small and unlikely to have caused the observed global temperature rise. The analysis of a number of alternative records lowers the significance of the influence of the enhanced greenhouse effect to 95%. The temperatures on the northern hemisphere rise a little faster than the southern hemisphere temperatures; this distinction is not significant but in line with the larger amount of land at the northern hemisphere. Some indications are found of an unexplained four year cycle in the temperatures of the northern hemisphere. Winter temperatures rise fastest, summer temperatures slowest; this is more profound on the northern than at the southern hemisphere. The difference is not significant; it could be due to the influence of anthropogenic aerosols. The analysis of monthly temperatures confirms the conclusions above, and shows that the models used here are close to being too simple to be used at this resolution.