High variability of Greenland temperature over the past 4000 years estimated from trapped air in an ice core Takuro Kobashi National Institute of Polar Research (NIPR) Santa Fe conference November 2, 2011

Acknowledgements 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

Contents Background 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Greenland temperature into a 4000-year context Possible mechanisms of Greenland temperature variation over 1000 years (unpublished slides are deleted.)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 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 (  18 Oice) Affected by changes in temperature of moisture source regions, moisture transport, pathways and precipitation seasonality. Temperature reconstruction from borehole thermometry Accurate but accurate but rapidly loses temporal resolution with increasing age into the past, owing to heat diffusion in ice sheets We need a better way to reveal past temperature from Greenland!

Gas fractionation in firn (snow layer) Firn (snow: ~60m thick) Ice Gravitation Heavier gasses move downward GISP2 ice core Thermal diffusion Heavier gasses move upward when T 1 is colder than T 2. T1T1 T2T2  T = T 1 -T 2 Surface temperature can be calculated by  T using firn densification / heat diffusion model. Kobashi et al. Climatic Change (2010)

Isotopic fractionation of nitrogen (15/14) and argon (40/36)  15 N obs =  15 N grav +  15 N therm  40 Ar obs =  40 Ar grav +  40 Ar therm  15 N grav =  40 Ar grav /4  15 N therm = 15  ×  T;  40 Ar therm = 40  ×  T  T (°C) = (  15 N obs -  40 Ar/4 obs )/ Therefore,  T can be used for reconstructing surface temperature change combined with firn densification and heat diffusion model. Kobashi et al. Climatic Change (2010)

 40 Ar  15 N The total number of samples is 1006 for 670 depths. Resolution = < 20 years. Data Kobashi et al., GCA, 2008.

Greenland temperature

North Atlantic Oscillation Positive NAONegative NAO Changes in solar activity in a multi-decadal time scale may induce NAO-like atmospheric pattern (Shindell et al., 2001). From Raymond W. Schmitt

Greenland temperatures over the 1000 years Kobashi et al., Climatic Change, 2010 Little Ice Age Medieval Warm Period

Placing the present into a 4000 year context Kobashi et al. GRL in press Current decadal average temperature in Greenland is not outside of natural variability of the past 4000 years.

Comparison with oxygen isotopes of ice Kobashi et al. GRL in press GISP2; r = 0.41 with temp. GRIPS; r = 0.51 with temp. NGRIP; r = 0.57 with temp. Reconstructed temperature (GISP2) Borehole temperature reconstruction Ice sheet elevation change

Conclusions 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.