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, andthree natural factors, i.e. the rotation rate of earth, sunspots, andEl Nino--Southern Oscillation (ENSO) signals, are decomposed into twohierarchies, i.e. more and less than 10-year hierarchiesrespectively, and then the running $t$-test is used to reanalyse thedata before and after filtering with the purpose of investigating thecontribution of natural factors to the abrupt climate changes in thelast one hundred years. The results show that the GIC textit{$delta$}$^{18}$O evolved with a quasi-period of 7--9 years, and the abruptclimate changes in the early 1960s and in the period from the end ofthe 1970s to the beginning of the 1980s resulted from the jointeffect of the two hierarchies, in other words, the two interdecadalabrupt changes of climate in the last one hundred years were global.The interannual variations of ENSO and sunspots were the importanttriggering factors for the abrupt climate changes in the last onehundred years. At the same time, the method of Information Transfer(IT) is employed to estimate the contributions of ENSO signals andsunspots activities to the abrupt climate changes, and it is foundthat the contribution of the interannual variation of ENSO signals isrelatively large.