Detection and attribution of abrupt climate changes in the last one hundred years

Based on physical backgrounds, the four time series of the Guliya (Tibetan plateau) ice core (GIC) \textit{$\delta $}$^{18}$O, and three natural factors, i.e. the rotation rate of earth, sunspots, and El Nino--Southern Oscillation (ENSO) signals, are decomposed into two hierarchies, i.e. more and less than 10-year hierarchies respectively, and then the running $t$-test is used to reanalyse the data before and after filtering with the purpose of investigating the contribution of natural factors to the abrupt climate changes in the last one hundred years. The results show that the GIC \textit{$\delta $}$^{18}$O evolved with a quasi-period of 7--9 years, and the abrupt climate changes in the early 1960s and in the period from the end of the 1970s to the beginning of the 1980s resulted from the joint effect of the two hierarchies, in other words, the two interdecadal abrupt changes of climate in the last one hundred years were global. The interannual variations of ENSO and sunspots were the important triggering factors for the abrupt climate changes in the last one hundred years. At the same time, the method of Information Transfer (IT) is employed to estimate the contributions of ENSO signals and sunspots activities to the abrupt climate changes, and it is found that the contribution of the interannual variation of ENSO signals is relatively large.