The reconstructed temperature anomalies in the eastern China were compared with the output from a 1000-year model simulation in an attempt to evaluate the model’s regional simulation skills and to understand the causes of climate change in China over the last millennium. The reconstructed data are the winter half-year temperature anomalies in the central region of eastern China (25°-40°N, east of 105°E) for the last 1000 years with a 30-year resolu- tion. The model used is the global atmosphere-ocean coupled climate model, ECHO-G, which was driven by time-varying external forcings including solar radiation, volcanic erup- tions, and greenhouse gas concentrations (CO2 and CH4) for the same period. The correlation coefficient between the simulated and reconstructed time series is 0.37, which is sta- tistically significant at a confidence level of 97.5%. The Me- dieval Warm Period (MWP) during 1000-1300 A.D., the Little Ice Age (LIA) during 1300-1850 A.D. and the modern warming period after 1900 A.D. are all recognizable from both the simulated and reconstructed temperatures. The anomalies associated with the LIA and the modern warming simulated by the model are in good consistency with the re- constructed counterpart. In particular during the Maunder sun-spot minimum (1670-1710 A.D.), both the simulated and reconstructed temperature anomalies reach their min- ima without any phase difference. But in the earlier MWP, significant discrepancies exist between the simulation and the reconstruction, which might reflect the degrading quality of the reconstruction data. The range of the simulated anoma- lies (1.62 K) is comparable with that of reconstructed (2.0 K). Diagnosis of the model results indicates that, during the last millennium, variations in solar radiation and volcanic activ- ity are the main controlling factors on regional temperature change, while in the recent 100 years, the change of the con- centration of greenhouse gases plays most important role in explaining the rapid temperature rising.
LIU JianH. StorchCHEN XingE. ZoritaZHENG JingyunWANG Sumin
More and more proxy records approved that the periodicity of the glacial cycles is about 40 ka before MPT (middle Pleistocene transition) as early as late Tertiary from 3.0 Ma to 0.9 Ma,whereas it changes to about 100 ka after MPT. Summer insolation at high latitude in Northern Hemisphere,usually consid-ered as the main external force for the ice age,is dominated by the 23 ka precession period,which does not match the period of the glacial cycles. In this paper,we define an energy index C and its threshold Ct that indicate the net energy supply and the overall response of the climate system. The difference between these two parameters determines whether the ice sheet melts or not,and accordingly the start and termination of the interglacial stages,as well as the periodicity of glacial oscillations. Based on the energy threshold hypothesis,the preliminary simulation experiments are made to test the period of the glacial cycles and driven factors from a conceptual model. The results indicate that energy index C and threshold Ct can interpret not only the 40 ka periodicity before MPT,but also the quasi-100 ka perio-dicity after MPT to some extent,and the 40 ka is the basic period of the glacial cycles,which discloses the inherent continuity of climatic change before and after MPT.
