A new method for identifying possible causal relationships between CO2, total solar irradiance and global temperature change

Abstract

We apply a novel method based upon “before” and “after” relationships to investigate and quantify interconnections between global temperature anomaly, GTA, as response variable, and greenhouse gases, CO2, and total solar irradiance, TSI, as candidate causal variables for the period 1880 to 2010. The most likely interpretations of our results for the 6 to 8 years cyclic components of the variables are that during the period 1929 to 1936 CO2 significantly leads GTA. However, during the period 1960 – 2003 GTA apparently leads CO2, that is, the peaks (and troughs) in GTA are in front of, and close to the peaks (and troughs) in CO2 . For time windows outside these periods, we did not find significant before or after- relations. An alternative interpretation is that there is a shift between short (≈ 1.5 year) and long (≈ 5 years) durations between cause and effect. Relationships between GTA and TSI suggest that ‘inertia’ of the global sea, land and atmosphere system leads to delays longer than half their common cycle length of about 10 years. Based on the interaction patterns between the variables GTA, CO2 and TSI we suggest the possibility that a new regime for how the variables interact started around 1960. From trend forms, and not considering physical mechanisms, we found that the trend in CO2 contributes ≈ 90%, and the trend in TSI ≈ 10 %, to the trend in GTA during the last 130 years