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SUMMARY:High-latitude climate sensitivity in a greenhouse world: lessons f
 rom the Eocene - Alexander P. Wolfe Department of Biological Sciences\, Un
 iversity of Alberta 
DTSTART:20151126T140000Z
DTEND:20151126T150000Z
UID:TALK62598@talks.cam.ac.uk
CONTACT:Jonathan Kingslake
DESCRIPTION:Eocene palaeoclimates provide partial analogs for the future w
 ith respect to equilibrium responses towards higher-than-present atmospher
 ic CO2. Multi-proxy temperature and CO2 reconstructions from middle Eocene
  terrestrial sediments that infill a kimberlite diatreme in subarctic Cana
 da enable detailed assessments of regional climate sensitivity for the int
 erval immediately post-dating 38 Mya. These sediments have exceptional pre
 servation of botanical fossils\, revealing a humid-temperate forest ecosys
 tem with abundant Metasequoia (dawn redwood). Pollen assemblages and oxyge
 n stable isotopes from wood cellulose indicate mean annual temperatures (M
 ATs) at least 17 ˚C warmer than present\, and coldest months more than 25
  ˚C. Stomatal indices from Metasequoia foliage constrain atmospheric CO2 
 to 450-1024 ppm\, with a median of 634 ppm. The reconstructed MATs are ~10
 ˚C warmer than predicted by a global Earth system sensitivity of 6˚C per
  CO2 doubling\, demonstrating that exceptional polar amplification charact
 erized middle Eocene climates even in absence of cryospheric influences (i
 .e. coldest months consistently >0˚C). Fundamental changes to synoptic ci
 rculation may explain the inferred magnitude of high-latitude warming and 
 concomitant increase of precipitation\, for which direct analogies exist i
 n contemporary global warming: deepening lows and enhanced cyclogenesis ov
 er the Arctic Ocean\, slowing of the polar jet stream\, and widening of Ha
 dley cells. Altered circulation patterns during greenhouse climate states 
 may explain why climate models have difficulty capturing fully the conditi
 ons implied by proxies under moderate (< 1000 ppm) CO2 concentrations.
LOCATION:British Antarctic Survey\, Room 330B
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