Overview of the various models for ice ages in the recent past (3 MYBP to present) - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 226

Wunsch (2003) claimed that there is little concrete evidence that abrupt
climate changes recorded in the Greenland ice cores are more than a regional
Greenland phenomenon. He suggested that D-O events are a consequence of inter-
actions of the wind field with continental ice sheets and that better understanding
of the wind field in glacial periods is needed. He emphasized that wind fields are
capable of great volatility and very rapid global-scale teleconnections, and they are
ecient generators of oceanic circulation changes and (more speculatively) of
multiple states relative to great ice sheets.
Huber et al. (2004) provided a response to Wunsch's criticism in a short note.
Wunsch had said: ''A serious question concerns the extent to which the Greenland
cores reflect tracer concentration change without corresponding abrupt climate
change. The large, abrupt shifts in ice d 18 O can be rationalized as owing to wind
trajectory shifts, perhaps of rather modest size.'' Huber et al. (2004) argued: ''this
hypothesis is no longer tenable in light of new data on the nitrogen and argon
isotopic composition of gases trapped in the Greenland ice cores.'' These data
indicate that abrupt d 18 O shifts are accompanied by gas isotope anomalies, and
the magnitudes of these anomalies demonstrate that warmings and coolings were
large, typically greater than 10 C. In addition, abrupt shifts in atmospheric
methane concentration were observed to occur at the same time as the Greenland
temperature shifts. Such changes are presumed to indicate worldwide climate
changes as long as CH 4 sources are widely dispersed. Huber et al. (2004) therefore
concluded that the abrupt climate shifts in Greenland were not merely local phe-
nomena because methane sources are widely distributed over the globe. However,
the argument that warmings and coolings were large does not preclude them from
being local or regional. The connection to methane was rebutted by Wunsch (see
discussion in the following paragraphs).
Wunsch (2006) published a later paper in which he pointed out that there is a
very large literature on the interpretation of abrupt climate shifts, which depends
on several assumptions, assertions, and inferences including

(1) The d 18 O variations appearing in the Greenland ice core records are a proxy for
local temperature changes. (Wunsch: ''in part true.'')
(2) Fluctuations appearing in the Greenland ice core data reflect climate changes on
a hemispheric and, probably, global basis. (Wunsch: ''little evidence exists other
than a plausibility argument.'')
(3) The cause of the sudden (e.g., D-O) events can be traced back to major changes
(extending to shutdown) of the North Atlantic meridional overturning
circulation (MOC) and perhaps even failure of the Gulf Stream. (Wunsch:
''unlikely to be correct.'')
(4) Apparent detection of a D-O event signature at a remote location in a proxy
implies its local climatic importance. (Wunsch paraphrase: the issue is

complicated.)

Regarding whether Greenland ice core records are a proxy for local

the relation of d 18 O temperature changes, Wunsch (2006) concluded that