High variability of Greenland temperature over the past 4000 years

High variability of Greenland
temperature over the past 4000 years
estimated from trapped air in an ice core
Santa Fe conference
November 2, 2011
Takuro Kobashi
National Institute of Polar Research (NIPR)
Recent collaborators;
 Kenji Kawamura; NIPR
 Jeffrey P. Severinghaus; Scripps
 Bo M. Vinther; CIC
 Sigfús J. Johnsen; CIC
 Jean-Marc Barnola; LGGE
 Toshiyuki Nakaegawa; MRI
 Jason E. Box; Byrd Polar Research Center
 Drew T. Shindell; NASA GISS
 Ayako Abe-Ouchi; University of Tokyo
 Masakazu Yoshimori; University of Tokyo
 Reconstructed Greenland temperature
over the past 1000 and 4000 years
 Placing the preset Greenland temperature
into a 4000-year context
 Possible mechanisms of Greenland
temperature variation over 1000 years
(unpublished slides are deleted.)
Background: Greenland temperature
Recent record high temperature in Greenland is
accelerating melting of the ice sheet.
 4-23% of global sea level rise for the period of
1993-2005 is from Greenland.
 Regional climate variability such as the North
Atlantic Oscillation/Arctic Oscillation (NAO/AO)
and the Atlantic Multi-decadal Oscillation (AMO)
affect Greenland temperature change.
 Causes of decadal Greenland temperature
variation has not been well understood.
Too short observational records to understand multi-decadal to
centennial variation!
Why is a new method necessary for
Greenland temperature?
Oxygen isotope of ice (d18Oice)
Affected by changes in temperature of
moisture source regions, moisture transport,
pathways and precipitation seasonality.
 Temperature reconstruction from borehole
Accurate but accurate but rapidly loses
temporal resolution with increasing age into
the past, owing to heat diffusion in ice
We need a better way to reveal past temperature from Greenland!
Gas fractionation in firn (snow layer)
Thermal diffusion
gasses move
Firn (snow: ~60m thick)
GISP2 ice core
Heavier gasses
move upward when
T1 is colder than T2.
DT = T1-T2
Surface temperature can be calculated by DT using firn
densification / heat diffusion model.
Kobashi et al. Climatic Change (2010)
Isotopic fractionation of nitrogen (15/14)
and argon (40/36)
 d15Nobs = d15Ngrav + d15Ntherm
 d40Arobs = d40Argrav + d40Artherm
 d15Ngrav = d40Argrav/4
 d15Ntherm = 15×DT; d40Artherm
= 40×DT
DT (°C) = (d15Nobs - d40Ar/4obs)/0.0047
DT can be used for reconstructing surface temperature change
combined with firn densification and heat diffusion model.
Kobashi et al. Climatic Change (2010)
The total number of samples is
1006 for 670 depths.
Resolution = < 20 years.
Kobashi et al., GCA, 2008.
Greenland temperature
North Atlantic Oscillation
From Raymond
W. Schmitt
Positive NAO
Negative NAO
Changes in solar activity in a multi-decadal time scale may induce
NAO-like atmospheric pattern (Shindell et al., 2001).
Greenland temperatures over the 1000 years
Medieval Warm Period
Little Ice Age
Kobashi et al., Climatic Change, 2010
Placing the present
into a 4000 year
Current decadal average
temperature in Greenland is not
outside of natural variability of
the past 4000 years.
Kobashi et al. GRL in press
Comparison with oxygen isotopes of ice
•Reconstructed temperature
•Borehole temperature
•Ice sheet elevation change
GISP2; r = 0.41 with temp.
NGRIP; r = 0.57 with temp.
GRIPS; r = 0.51 with temp.
Kobashi et al. GRL in press
Multi-decadal to centennial temperature
variations in Greenland is reconstructed
for the past 4000 years from occluded air
in ice core.
 Present decadal temperature in
Greenland is not beyond the envelope of
natural variability of the 4000 years.

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