Breakpoint lead-lag analysis of the last deglacial climate change and atmospheric CO2 concentration on global and hemispheric scales

Abstract

Antarctic ice core records show that climate change and atmospheric CO2 concentration (aCO2) are closely related over the past 800 thousand years. However, the interpretation of their sequential, and hence the causal relationship has long been controversial. In this study, we revisit this long-standing scientific issue based on 88 well-dated high-resolution climate proxy records derived from ice cores, marine deposits, and stalagmites. We composite global and hemispheric stacks of the last deglacial climate index (DCI) using a normalization scheme instead of a more conventional area-weighting and mixing scheme to enable a better detection of temporal variations. Rampfit and Breakfit techniques are employed to detect the trend transitions in each composited DCI series and in the recently constructed centennial-scale aCO2 over the period from 22 to 9 thousand years before present. We detect a clear lead of DCI change over aCO2 variation on both global and hemispheric scales at the early stage of the deglaciation, suggesting that the variation of aCO2 is an internal feedback in Earth's climate system rather than an initial trigger of the last deglacial warming. During the periods of the Bølling-Allerød and the Younger Dryas, the climate system appeared to have been constrained by a fast coupling mechanism between climate change and aCO2 with no obvious asynchrony. The northern and southern hemispheric DCI stacks exhibit a seesawing pattern that can be linked to the influences of Atlantic meridional overturning circulation (AMOC) strength, revealing an important role of AMOC in regulating the global climate in the course of the last deglaciation.