The Research About The Early Warning Signals Of Abrupt Climate Change Based On Critical Slowing Down Phenomenon

Several studies in the last few years indicate that the critical slowing down phenomenon may play a important role in identifying whether a complex dynamical system is approaching to a critical point of an abrupt change. In this paper, we started from the climate data (China614stations temperatures, Pacific Decadal Oscillation (PDO) index, Aleutian Low index, sea surface temperature). First, the abrupt climate change detection methods are used to identify the instant of abrupt climate change in the climate data; Having analyzed the physical basis and statistical significance of critical slowing down phenomena, then the variance and autocorrelation coefficients which can characterize critical slowing down has been calculated in order to find early warning signals of abrupt climate change. For the first the feasibility of the method and the impact of different sliding window and lag-step to the signal detection results has been discussed; For the second the method then extended to the observed data of temperature and the PDO index and the intensity of Aleutian low pressure focuses on the appearance time of early warning signals of abrupt climate change under the influence different noise; For the third the early warning signals of abrupt climate change in the data of monthly average temperature of different regions in China has been calculated for verifying the applicability of the method; Finally, try to use Lyapunov exponent to discuss the abrupt climate change and its early warning signals, the mechanism and the SST background analysis of the early warning signals of PDO has been given a certain degree, this is evidence of the accuracy of the signal. The results showed that:1) The PDO index and the national average monthly temperature both had obviously critical slowing down phenomenon before the abrupt climate change taken place, which indicated that critical slowing down phenomenon is a possible early warning signal of abrupt climate change. In the case of the statistical samples to determine, select a different window and different lag-step affect the stability of the calculation results, in general, a big window will be good to the stability of the result.2) The calculated of temperature data and PDO also showed that critical slowing down phenomenon can be used as an early warning signal of abrupt climate change. For the different SNR, the signals of variance and autocorrelation coefficients apply equally, which indicated that the noise have less influence to the test results for early warning signals of abrupt climate change and further illustrate the effectiveness of the method.3) The autocorrelation coefficient that appears in the monthly average temperature data increases to different extents in the different regions. This phenomenon appears before abrupt climate change occurs, which also verified that critical slowing down phenomena could be used as early warning signals of abrupt climate change. Although the observational data in the different subzones all have a slowing down phenomenon, the occurrence times of the phenomena are not exactly the same. Overall, the detection results in the middle-eastern, northeastern, northern and southern parts of China were found to be superior to those in the northwest of China and the Tibetan region.4) By Lyapunov exponent to discuss the abrupt climate change and its early warning signals found that: Lyapunov exponent as a abrupt climate change detection method is very effective, by calculated the largest Lyapunov exponent (LLE) for each time indicates that PDO system is a chaotic system, the system has a strongest chaotic and maximum intrinsic randomness when it is in a critical threshold stage, which is evidence of the effectiveness of critical slowing down phenomenon act as early warning signals of abrupt climate change. By calculating the variances and autocorrelation coefficients of the SST, we can found that the correspondence between the changes of SST and PDO is obviously. Above mentioned can provide an experimental basis for the applications of the present method.The introduction and study on critical slowing down theory into abrupt climate change early warning signals have practical significances and important scientific values to thoroughly understand abrupt climate change, to catch the precursory signals of abrupt climate change.