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 230

amongst paleoclimatologists, Alley's unbounded reverence for WB may possibly
have affected his objectivity.
Alley (2007) asserted at the beginning of his review:
''Abrupt climate changes happened, their large geographical extent is
confirmed by Greenland ice-core data and by geographically widespread records,
the pattern closely matches that modeled for North Atlantic causes, and models
and data agree on the involvement of the meridional overturning circulation
(MOC).''
Alley (2007) emphasized ''of particular importance are the Greenland records
of methane (CH 4 )'' citing his Supplemental Figure 1. However, this figure merely
shows limited data for two short time periods from 7 to 9 kybp and from 10 to
16 kybp . In both time periods, the comparison between variable CH 4 concentra-
tion and D T shows some similarity but is far from convincing to this writer. Like
beauty, perhaps comparison lies in the eye of the beholder. Figure 8.6 shows a
comparison of Greenland temperatures with CH 4 concentrations measured at
Vostok, Antarctica over 100,000 years. While there is some similarity, it can
hardly be construed as proof of worldwide climate variations in sync with
Greenland temperature variability.
Alley (2007) asserted that CH 4 is globally mixed, with widely distributed
sources and no dominant localized sources. Changes in the atmospheric concentra-
tion of methane of up to 50% require involvement of gas sources across large
regions of the globe. Even Wunsch admitted that this was a point in favor of the
global character of the abrupt climate changes observed in Greenland. Alley
(2007) provided extensive further discussion that is beyond the scope of this topic.
Nevertheless, the claim made by Alley (2007): ''Greenland ice-core data show the
existence of abrupt climate changes affecting broad regions, has been confirmed very
strongly'' (emphasis added) seems perhaps too emphatic for the foundation it rests
upon. Alley (2007) may well be right, but a little less certainty in his conclusions
would be welcome.
Regardless of whether one accepts the consensus view or Wunsch's view of the
role of ocean circulation in climate change, Wunsch (pers. commun., December,
2008) asserts that the role of ocean circulation in glacial-interglacial cycles is
unknown since there are essentially no data on past circulation rates.
8.7 MODELS BASED ON CLOUDS
Cloud cover is an important factor that controls the way radiation is absorbed
and reflected by the Earth. Increases in cloudiness enhance global albedo thus
cooling the surface, but increased cloudiness also traps thermal radiation leading
to warming. Overall, the cooling effect is believed to be dominant, but this is a
function of cloud height and type with thin high clouds causing net warming. Any
factor tending to modify cloud cover will thus have an impact on climate so that it