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Erik Hammerstad <egeha.is.all.you.need@xxxxxxxx > wrote:
The temperature curve in MOG 31 (figure 2 on page 12) is a redrawn
version from "The Ecology of Greenland" fig 2.33 which is the
temperature derived from the Camp Century ice core, i.e. the first
Greenland ice core drilled to bedrock in 1966. The book figure is
a bar chart with each bar covering a century, otherwise the MOG 31
chart is essentially the same. Taking into account that the chart
is most probably more than 30 years old and hence does not include
the warming of the last decades, and that Camp Century is in the
northwest of Greenland, IMO it confirms the impossibility of the
Greenland Norse having circumnavigated Greenland, and also
supports that the Greenland MWP climate was not warmer and
probably cooler than today.
The book uses the curve as an illustration of the postglacial
climate of Greenland, putting it side by side with two diagrams
derived from pollen data from lakes and bogs at 61N and 65N, plus
a chart of glacier extent at Disko Bay. These confirm each other
but at different resolutions, the ice core one having the best.
The book does not give a definite reference for its Camp Century
curve, possibly it's from a 1993 paper in Nature by Dansgaard
et.al. which is unavailable to me. I have found two other Camp
Century charts on the net,
http://www.aip.org/history/climate/xCampCent.htm and fig 6.2 from
Willi Dansgaard's book "Frozen Annals" ISBN: 87-990078-0-0,
available on line at http://www.nbi.ku.dk/side59440.htm. The
charts are not the same, allthough they agree in general.
Thanks Erik, also for your other post. The book sounds interesting.
On the NorthGRIP site a lot of data (and articles and abstracts,
but not Dansgaard 1993) are available.
http://www.gfy.ku.dk/~www-glac/ngrip/index_eng.htm
You can draw your own curves.
For example
http://www.gfy.ku.dk/~www-glac/data/ddjtemp.txt
"These data show the temperature history of the
past 30,000 years as the ice "remembers" them at
GRIP in the center of the Greenland ice sheet, at
Dye-3 in the Southern part of the ice sheet and at
Law Dome near the Antarctic coast (here the
"memory" only goes back 5,000 years).
Ice and snow has a large heat capacity and a poor
heat conductivity. It is therefore possible to
reconstruct past temperatures from present day
temperature measurements in bore holes after ice
core drilling. The thermometer has to be very
accurate since a precission of 0.01 degree is
needed.
Details about the temperature history are lost as
we go back in time. The curves become more and
more average curves. The abrupt and violent
climate changes at the time of the termination of
the last ice age between 13000 and 9000 years BC
(15000 and 11000 years BP) are thus completely
erased. This is due to thermal diffusion, i.e. the
smoothing of temperature differences over time.
The only thing the Greenland ice sheet
"remembers" from the time 30,000 years BC to
8000 years BC is thus only how cold it was during
the last part of the last ice age. The ice at Law
Dome has completely "forgotten" the temperatures
of the last ice age.
In Greenland: The warmth of the climatic optimum
during the European stone age 5000 years ago is
clearly seen, just as the cool period during the
Roman age and the relative warmth of the Viking
age (where the Norsemen settled in Iceland and
Greenland) and the two cold periods of the "little
ice age" at 1600 AD and 1875 AD. The warming in
Greenland in the 20th century only lasts until 1950
AD. After that it has become colder.
In Antarctica: Compared to the Greenland curves,
Antarctica has a tendency to "warm up" as
Greenland is "cold" and to "cool off" when
Greenland is "warm". At both poles an average
cooling tendency in the last 5-6 thousand years
can be seen."
--
p.a.
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