Ice core data - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 148

not merely associated with local wind variability. A later paper by Wunsch (2006)
is discussed in Section 8.6.2.

4.3.3 Seasonal variability of precipitation

A number of papers have pointed out that ice core data reflect the seasonal
precipitation patterns that existed at the location where the ice cores were
obtained. For example, Gildor and Ghil (2002) said: ''Proxy records from ice
cores are commonly assumed to represent annual mean averages. These averages,
however, may be biased toward a particular season, due for example to a change
in distribution of precipitation.'' Krinner and Werner (2003) discussed the fact
that borehole analysis suggests that Greenland temperatures were colder than
indicated by ice core measurements at the Last Glacial Maximum (LGM). They
claimed: ''changes in the seasonal precipitation timing in Central Greenland might
have caused a warm bias in the LGM water isotope proxy temperatures.''
Of greater interest is the recent paper by Laeppele et al. (2011) which proposes
that ice cores taken in Antarctica are determined by local insolation variability,
and ''cannot be used to support or contradict the Milankovitch hypothesis that
global climate changes are driven by Northern Hemisphere summer insolation
variations.'' This paper is written in a rather confusing manner and it was dicult
for this writer to interpret exactly what the authors propose. As far as I can tell,
they seem to be proposing the following: Precipitation in Antarctica in local
winter months (as measured in the late 20th century) is roughly double that in
local summer months. Furthermore, summer ablation reduces summer accumula-
tion. Thus, the ice core records in Antarctica represent winter accumulation to a
greater extent than summer accumulation. As the Earth proceeds through its
elliptical orbit about the Sun, periods when the Sun is closest to the Earth in
austral summer will produce warmer summers but lengthier winters, since the
Earth passes through apogee more slowly than perigee. Hence the Antarctic ice
core record will produce colder temperatures when the summers are warmer in
Antarctica and the summers are cooler in the NH. Therefore, they conclude
that Antarctic ice cores will reveal the same apparent temperature pattern as if
Antarctic temperatures were driven by NH climate variations but, in reality, they
are driven by local Antarctic winter conditions. Since Antarctic winter occurs at
the same time as NH summer,

it is not possible to distinguish the cause of

Antarctic climate change.
In support of their claim that Antarctic climate variability is driven by local
Antarctic conditions and is not a result of transfer from NH climate change, they
''pose the question of how Northern Hemisphere solar forcing is transferred to the
Southern Hemisphere, and why Southern Hemisphere local insolation changes
have no imprint on the Antarctic temperature record.'' They claim: ''Variations in
greenhouse gas concentrations are too weak to explain the interhemispheric link;
there exists no evidence that atmospheric dynamics can directly transfer the orbital
signal to the Southern Hemisphere, and changes in thermohaline circulation are
thought to favor an asymmetric pattern.'' What is strange here is that they