Abstract

Abstract. We investigate glacial inception and glacial thresholds in the climate-cryosphere system utilising the Earth system model of intermediate complexity CLIMBER-2, which includes modules for atmosphere, terrestrial vegetation, ocean and interactive ice sheets. The latter are described by the three-dimensional polythermal ice-sheet model SICOPOLIS. A bifurcation which represents glacial inception is analysed with two different model setups: one setup with dynamical ice-sheet model and another setup without it. The respective glacial thresholds differ in terms of maximum boreal summer insolation at 65° N (hereafter referred as Milankovitch forcing (MF)). The glacial threshold of the configuration without ice-sheet dynamics corresponds to a much lower value of MF compared to the full model. If MF attains values only slightly below the aforementioned threshold there is fast transient response. Depending on the value of MF relative to the glacial threshold, the transient response time of inland-ice volume in the model configuration with ice-sheet dynamics ranges from 10 000 to 100 000 years. Due to these long response times, a glacial threshold obtained in an equilibrium simulation is not directly applicable to the transient response of the climate-cryosphere system to time-dependent orbital forcing. It is demonstrated that in transient simulations just crossing of the glacial threshold does not imply large-scale glaciation of the Northern Hemisphere. We found that in transient simulations MF has to drop well below the glacial threshold determined in an equilibrium simulation to initiate glacial inception. Finally, we show that the asynchronous coupling between climate and inland-ice components allows one sufficient realistic simulation of glacial inception and, at the same time, a considerable reduction of computational costs.

Highlights

  • Simulation of glacial inception with numerical models different in complexity and detail of description of climate components has already a long tradition

  • Two glacial thresholds are determined in different model setups of CLIMBER-2

  • For 271 ppm atmospheric CO2 concentration, the glacial threshold in the model configuration without ice-sheet dynamics corresponds to a very low MF value of 442 W m−2, while the glacial threshold in the model configuration with ice-sheet dynamics relates to a MF value of 477 W m−2, which is only slightly smaller than the present-day value in MF

Read more

Summary

Introduction

Simulation of glacial inception with numerical models different in complexity and detail of description of climate components has already a long tradition. R. Calov et al.: Mechanisms and time scales of glacial inception complexity paired with adequate detail in description of the climate subsystems. Calov et al.: Mechanisms and time scales of glacial inception complexity paired with adequate detail in description of the climate subsystems These models allow full synchronous transient simulations over the time of decreasing boreal summer insolation during glacial inceptions including all relevant components of the climate system. Wang and Mysak (2002) published a simulation of glacial inception with a geographical explicit EMIC including interactive ice sheets (the McGill Paleoclimate Model). Calov et al (2005a) showed that glacial inception is primarily triggered by a drop in boreal summer insolation and is linked to a bifurcation from interglacial to glacial state caused by snow-albedo feedback. 4. The investigation of transient response during different glacial inceptions with a particular link to Ruddiman’s hypothesis is included in Sect. We close our paper with a discussion of our findings (Sect. 7) and conclusions (Sect. 8)

The model
Stability analysis
Transient response to instantaneous change in orbital forcing
Transient response to realistic orbital forcing
Asynchronous coupling of climate and ice-sheet components
Findings
Discussion
Conclusions
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call