Modeling Abrupt Climate Change as the Interaction Between Sea Ice Extent and Mean Ocean Temperature Under Orbital Insolation Forcing - Abrupt Climate Change: Mechanisms, Patterns, and Impacts - page 56

Modeling Abrupt Climate Change as the Interaction Between Sea Ice Extent
and Mean Ocean Temperature Under Orbital Insolation Forcing

J. A. Rial

Wave Propagation Laboratory, Department of Geological Sciences, University of North Carolina at Chapel Hill
Chapel Hill, North Carolina, USA

R. Saha

Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA

fluctuations of the last ice age are a
prime example of abrupt climate change in the paleoclimate record, and they
provide evidence that rapid climate change (warming as well as cooling) can occur
within human time scales, making their study highly relevant to the assessment of
present and future natural climate variability. Using conceptual climate models, we
show that orbital insolation is likely to play an important role in the timing,
amplitude, and duration of the D-O

The Dansgaard-Oeschger (D-O) temperature

fluctuations. We are able to replicate key
features of the D-O time series, including the abrupt transition from the last glacial
to the present interglacial, using the orbital insolation as the sole external variable
forcing of a simple nonlinear Langevin differential equation. A slightly more
complex model based on two nonlinear differential equations for sea ice extent
and mean ocean temperature reasonably reproduces the past 100 kyr of climate

fluctuations recorded in the Greenland ice cores. The model assumes the existence
of a free oscillation with a period of ~1500 years, which is then forced with white
Gaussian noise and the astronomical insolation. The model also reproduces the
time histories and the well-known phase relationship between shallow and deep
ocean proxy data, whereby the SST history follows the Greenland climate record,
while the deeper ocean follows the Antarctic s. Comparisons with other low-

dimensional models and climate models of intermediate complexity (ECBILT-
CLIO and U-Victoria ESCM) show consistent results.

'

1. INTRODUCTION

This chapter describes attempts to understand the causes
of abrupt climate change through data analyses and com-
puter modeling of paleoclimate time series, especially
from Greenland ' s ice cores Greenland Ice Core Project
(GRIP), Greenland Ice Sheet Project Two (GISP2), and
North Greenland Ice Core Project (NGRIP) [North Green-
land Ice Core Project Members, 2004; Johnsen et al., 1995;

Abrupt Climate Change: Mechanisms, Patterns, and Impacts
Geophysical Monograph Series 193
Copyright 2011 by the American Geophysical Union.
10.1029/2010GM001027

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