The tenth IMSC, Beijing, China, 2007 - International Meetings on ...

<strong>The</strong> extent of the Medieval Warm Period (MWP) from 900AD to 1300AD, was occurred in
the periods of Wudai-Song-Yuan Dynasty, when the temperature is warm as Holocene
Megathermal in many parts of the worlds. Although the exact timing and duration of warm
periods may have varied from region to region, the relatively warm conditions during MWP
have been generally accepted by the climatologist. For example, Chinese scholars have been
studied the magnitude and timing for MWP by the historical documentary evidence of
phonological events and cold/warm records, the results were expressed that the 930-1310
was warming, and particularly in the periods of 930s-1100s and 1200s-1310s, the temperature
may have passed the 20 century warming. However, the temperature reconstruction in North
Western of <strong>China</strong> from the evidences of tree-ring, ice core and lake sediment showed
inconsistent results with Eastern <strong>China</strong> for MWP, which includes the surface temperature
reconstruction only reached the mean value and no significant MWP, even the periods of
1000-1050, 1150-1350 were cooling placed in the past 1000 years; and the timing with
1200-1400 was behind 300 years than Eastern <strong>China</strong>.
Here, we analyzed the cold/warm magnitude, and calculated the temperature in North
western, covering Gansu, Shanxi, Ningxia and part of Henan, based the evidence of the
abnormal snow and frost records, to assess the temperature level during the past 1000 years.
<strong>The</strong> results showed that the temperature has three obvious stages during 960~1368, which
included the 962-1110 cooling, the1111-1260 warming, and the 1260-1368 cooling lower than
962-1110. And only the cooling event of the last stage, 1260-1368 was compatible with the
trend in Eastern <strong>China</strong>.
Underlying dynamics of glacial millennial-scale climate transitions derived from
ice-core data
Speaker: Frank Kwasniok
Frank Kwasniok
University of Exeter, United Kingdom
Gerrit Lohmann
Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
A method for systematically deriving simple nonlinear dynamical models from ice-core
data is proposed. It offers a tool to integrate models and theories with paleoclimatic data. <strong>The</strong>
method is based on the unscented Kalman filter, a nonlinear extension of the conventional
Kalman filter. Here, we adopt the conceptual model of stochastically driven motion in a
potential that allows for two distinctly different states. <strong>The</strong> parameters of the model, that is, the
shape of the potential and the noise strength are estimated from a Greenland ice-core record.
<strong>The</strong> data reveal that during glacial times the potential is asymmetric and degenerate: there is
one stable cold stadial state and one indifferently stable warm interstadial state
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