GISP2 Ice Core 4000 Year Ar-N Isotope Temperature Reconstruction Kobashi, T.; Kawamura, K.; Severinghaus, J.; Barnola, J.M.; Nakaegawa, T.; Vinther, B.M.; Johnsen, S.J.; Box, J.E. Kobashi, T. Kawamura, K. Severinghaus, J. Barnola, J.M. Nakaegawa, T. Vinther, B.M. Johnsen, S.J. Box, J.E. Air Temperature Reconstruction Arctic temperature earth science/paleoclimate/climate reconstructions|ice cores (surface temperature,delta 15N excess,null,degree Celsius,null,climate reconstructions|ice cores,null,null,N,null) earth science/paleoclimate/climate reconstructions|ice cores (age,null,null,year Common Era,null,climate reconstructions|ice cores,null,null,N,null) earth science/paleoclimate/climate reconstructions|ice cores (surface temperature,delta 15N excess,one standard deviation,degree Celsius,null,climate reconstructions|ice cores,null,null,N,null) earth science/paleoclimate/ice core earth science/paleoclimate/ice core (GISP2>LATITUDE 72.6>LONGITUDE -38.5) Greenland recently incurred record high temperatures and ice loss by melting, adding to concerns that anthropogenic warming is impacting the Greenland ice sheet and in turn accelerating global sea-level rise. Yet, it remains imprecisely known for Greenland how much warming is caused by increasing atmospheric greenhouse gases versus natural variability. To address this need, we reconstruct Greenland surface snow temperature variability over the past 4000 years at the GISP2 site (near the Summit of the Greenland ice sheet; hereafter referred to as Greenland temperature) with a new method that utilises argon and nitrogen isotopic ratios from occluded air bubbles. The estimated average Greenland snow temperature over the past 4000 years was -30.7°C with a standard deviation of 1.0°C and exhibited a long-term decrease of roughly 1.5°C, which is consistent with earlier studies. The current decadal average surface temperature (2001–2010) at the GISP2 site is -29.9°C. The record indicates that warmer temperatures were the norm in the earlier part of the past 4000 years, including century-long intervals nearly 1°C warmer than the present decade (2001-2010). Therefore, we conclude that the current decadal mean temperature in Greenland has not exceeded the envelope of natural variability over the past 4000 years, a period that seems to include part of the Holocene Thermal Maximum. Notwithstanding this conclusion, climate models project that if anthropogenic greenhouse gas emissions continue, the Greenland temperature would exceed the natural variability of the past 4000 years sometime before the year 2100. STUDY NOTES: Greenland summit surface snow temperature for the past 4000 years reconstructed by a new method that utilises argon and nitrogen isotopic ratios from occluded air bubbles. Simultaneous, high-precision analyses of d15N and d40Ar in trapped air from the GISP2 ice core (Kobashi et al. 2008a) was used for this study. The method for the temperature reconstruction relies on the fact that gases in firn (unconsolidated snow) layers fractionate according to the depth and temperature gradient (DT) at the top and bottom of the layer (Severinghaus et al., 1998). Information about past depths and DTs at the time of air bubble trapping in the ice sheet can be retrieved by measuring d15N and d40Ar in the occluded air in ice cores. Then, the surface temperature history can be reconstructed by integrating the DTs over time (Kobashi et al., 2008b, 2010) with a firn densification/heat diffusion model (Goujon et al., 2003). NCDC-Paleoclimatology https://www.ncdc.noaa.gov/data-access/paleoclimatology-data - Bauer Bruce Investigator : Kobashi, T. Investigator : Kawamura, K. Investigator : Severinghaus, J. Investigator : Barnola, J.M. Investigator : Nakaegawa, T. Investigator : Vinther, B.M. Investigator : Johnsen, S.J. Investigator : Box, J.E. 2012-03-30 ONLINE Files online, ASCII https://www.ncdc.noaa.gov/paleo/study/12887 https://www1.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/gisp2/isotopes/gisp2-temperature2011.xls https://www1.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/gisp2/isotopes/gisp2-temperature2011.txt https://www1.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/gisp2/isotopes/gisp2-temperature2011.xls https://www1.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/gisp2/isotopes/gisp2-temperature2011.txt English https://www.ncdc.noaa.gov/paleo/study/12887 https://www1.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/gisp2/isotopes/gisp2-temperature2011.xls https://www1.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/gisp2/isotopes/gisp2-temperature2011.txt Kobashi, T., K. Kawamura, J.P. Severinghaus, J.-M. Barnola, T. Nakaegawa, B.M. Vinther, S.J. Johnsen, and J.E. Box. 2011. High variability of Greenland surface temperature over the past 4000 years estimated from trapped air in an ice core. Geophys. Res. Lett., 38, L21501, doi:10.1029/2011GL049444. START YEAR: -2000 AD * END YEAR: 1993 AD -38.5 72.6 -38.5 72.6