Post-Eemian Glacial Inception. Part II: Elements of a Cryospheric Moisture Pump

Abstract

This paper extends the analyses of the glacial inception process described in a previous paper (‘‘Part I: The Impact of Summer Seasonal Temperature Bias’’). The analyses described therein were based upon the use of the Canadian Centre for Climate Modelling and Analysis (CCCma) GCMII. Three simulations of the modern climate system were described that were, respectively, warm biased, unbiased, and cold biased with respect to the set of Atmospheric Model Intercomparison Project 2 SSTs and land surface temperatures in summer. These three control models were perturbed by the modification of the orbital insolation regime appropriate to the time 116 000 years before present (116 kyr BP) during which the most recent period of continental glaciation began. Two of the three simulations do deliver perennial snow cover in polar latitudes. Analyses of the land surface energy balance, hydrological cycle, and energetics of the atmosphere in the Northern Hemisphere polar region at 116 kyr BP discussed in greater detail herein reveal a set of positive feedback mechanisms favoring glaciation. It is proposed that these feedbacks are coupled to the main Milankovitch ice‐albedo feedback that has heretofore been assumed to be the key to understanding the initiation of widespread continental glaciation. In particular, it is demonstrated that the polar surface energy balance plays an important role in summer snowmelt and in the annual maintenance of perennial snow cover. Furthermore, increased water vapor transport into the Northern Hemisphere summer polar regions at 116 kyr BP increases the net annual snow accumulation in these postEemian climate simulations through the action of an atmospheric‐cryospheric feedback mechanism. An explanation for the absence of perennial snow cover in Alaska during the post-Eemian period is proposed. It is suggested that the transport of latent and sensible heat into this region is increased under 116 kyr BP orbital forcing, which therefore acts to maintain sufficient summer snowmelt that is vitally important in preventing glacial initiation.