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SUMMARY:Ice cores and climate: Patterns and causes of change - Eric W. Wol
 ff\, British Antarctic Survey
DTSTART:20070813T090500Z
DTEND:20070813T095000Z
UID:TALK7790@talks.cam.ac.uk
CONTACT:Nick Watkins
DESCRIPTION:The last few hundred thousand years are critical for understan
 ding the working of the Earth System because they show a wide range of cli
 mates under a geography similar to the present. Ice cores are an important
  palaeorecord because they record different aspects of the atmosphere (in
 cluding trace gas concentrations)\nrather directly. Over recent decades\, 
 ice cores have provided several insights that have shaped the research age
 nda\, and informed discussions about future\nclimate change.\n\nThere are 
 two very obvious patterns of climate variability that dominate the record 
 seen\, not only in ice cores\, but also in records from other archives. At
 \nlower time resolution\, the obvious feature of all late Quaternary (Quat
 ernary = last ∼ 2 Ma) records is the occurrence of glacial-interglacial 
 cycles with a period averaging around 100\,000 years. Almost all parameter
 s we measure in ice cores follow this pattern\, with glacial periods havin
 g low Antarctic temperatures\, low CO2 and CH4 concentrations\, and high 
 fluxes of dust and sea salt through the atmosphere and into the ice. The 
 cold periods were also marked by the growth of ice sheets over North Ameri
 ca and Europe\, and the entire global climate system was considerably di
 fferent. Most paleoclimate scientists agree that the pacing of these cycl
 es is controlled by changes in the pattern of incoming solar radiation due
  to changes in Earths orbit and axis. And they agree that a combination of
  amplifying factors: changes in albedo\, greenhouse gas concentrations\, e
 tc.\, lead to a very non-linear response. A large strand of research looks
  for the detailed physical and biogeochemical mechanisms that link the di
 fferent factors (for example\, why does CO2 increase in a warming world).
  An often separate strand wonders whether we really understand the 100 ka 
 period\, especially in the light of knowledge that the earlier parts of th
 e Quaternary were dominated by 40 ka periodicity.\n\nAt higher resolution\
 , the second dominant pattern of climate variability\, also most clearly r
 evealed by ice cores\, is the series of warmings and coolings (known\nas D
 ansgaard-Oeschger events) that occurs during glacial periods. Studies of G
 reenland ice cores have shown that very rapid climate changes (several deg
 rees\nin a few decades) can occur\, again with a wide range of climate var
 iables affected. The subdued counterparts seen in Antarctic ice cores sup
 port the idea that the probable mechanism is switches in the mode of ocean
  heat transport in the Atlantic Ocean. A particular interest of these even
 ts is the concern that\,\nalthough the triggering mechanism must be diffe
 rent\, such switches might be possible in a future warmer world\, not just
  in a colder world. In both the cases discussed\, one type of research app
 ears to emphasise the pattern of variability\, while almost ignoring the m
 echanisms\, while another appears to make ever more complex models that de
 scribe the mechanisms but that find it hard to explain the pattern and pa
 ce of the variability. In the current audience it would be interesting to 
 discuss how these strands should work together.\n
LOCATION:Law Faculty\, Cambridge
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