Understanding the Abrupt Climate Change in the Mid-1970s from a Phase-Space Transform Perspective

Abrupt climate change may cause heat, drought, and flood disasters. In this study, we find that many climate factors [e.g., the East Asian summer monsoon (EASM), the Arctic Oscillation (AO) and the Pacific decadal oscillation (PDO)] show a decadal-scale abrupt change in the 1970s. To analyze this phenomenon thoroughly, a new method of pedigree clustering combined with phase-space analysis (PCPSA) is used to establish two-dimensional phase-space coordinate systems of EASM-AO, EASM-PDO, and AO-PDO and the three-dimensional phase-space coordinate system of EASM-AO-PDO. By using the PCPSA method, it is found that all of the phase-space coordinate systems have a significant abrupt change in the mid-1970s, with a transition period, and the fit to the abrupt change of the phase-space coordinate system is better than 80%, which indicates excellent fit. By analyzing the correlation of EASM, AO, and PDO with sea level pressure (SLP) and sea surface temperature (SST), it is found that SLP has an obvious weakening trend in the high latitudes and an increasing trend in the tropics while SST has an increasing trend in most of the Southern Hemisphere waters and a minor weakening trend in the North Pacific Ocean waters between 30 degrees and 40 degrees N. Therefore, the abrupt climate change of the 1970s may well be a global abrupt change of the climatic system.