Causes of Greenland temperature variability over the past 4000 yr: implications for northern hemispheric temperature change
1National Institute of Polar Research, 10-3 Midoricho, Tachikawa, Tokyo 190-8518, Japan
2Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, USA
3Byrd Polar Research Center, Ohio State University, Columbus, Ohio, USA
4Zhejiang University, Hangzhou, Zhejiang, China
5Meteorological Research Institute, Tsukuba, Ibaraki 305-0052 Japan
Abstract. A new Greenland temperature record reconstructed from argon and nitrogen isotopes from trapped air in a GISP2 ice core, provides high-resolution (<20 yr) and precise annual average temperature estimates for the past 4000 yr. Due to tight age-controls and abundant paleoclimatic information from the ice core, the temperature record provides an exceptional opportunity to investigate the late Holocene climate in a multi-decadal to millennial time scale. To investigate causes of Greenland temperature variability over the past 4000 yr, we calculated high latitude (70–80° N) temperature change using a one-dimensional energy balance model with reconstructed climate forcings including orbital, solar, volcanic, and greenhouse gas forcings. Greenland temperature was calculated from the high latitude temperature, considering Greenland's negative temperature responses to solar variability due to associated changes in atmospheric and oceanic circulations. The calculated Greenland temperature was significantly correlated with the ice-core-derived Greenland temperatures with the 97% confidence level. Therefore, the past variability of climate forcings can explain at least 10% of the multi-decadal to millennial variability in Greenland temperature over the past 4000 yr. An average temperature trend for the Northern Hemisphere (NH) over the past 4000 yr was also inferred from the ice-core derived Greenland temperatures. Lines of evidence indicate that the current decadal average temperature of NH is likely warmer than at any time over the past 4000 yr. Sequential cooling events starting around 800 B.C.E. (the 2.8 ka event), which were induced by several large volcanic eruptions as well as low solar activity, had similar magnitude with the Little Ice Age cooling.