Causes of Greenland temperature variability over the past 4000 years
Abstract
A new Greenland temperature record reconstructed from argon and nitrogen isotopes in trapped air in GISP2 ice core provides high-resolution (< 20 years) and precise temperature estimates over the past 4000 years [Kobashi et al., 2011]. Owing to tight age-controls and abundant paleoclimatic information from the ice core, the record provides a rare opportunity to evaluate the late Holocene climate in a multi-decadal to millennial time scale. In our earlier study [Kobashi et al., Submitted], we found Greenland temperature deviated from North Hemispheric (NH) temperature trend negatively to solar variation over the past 800 years owing to changes in solar-induced atmospheric circulations such as North Atlantic Oscillation/Arctic Oscillation (NAO/AO) with an additional contribution from changes in Atlantic meridional overturning circulation (AMOC). To investigate causes of the Greenland temperature variability over the past 4000 years, we calculated high latitude (75°N) temperature change by a one-dimensional energy balance model with orbital, solar, volcanic, greenhouse gas forcings. The volcanic forcing was reconstructed from GISP2 sulphate record, which agreed sufficiently well with the volcanic forcing reconstruction for NH from multi ice cores [Gao et al., 2008] over the past 1500 years. The result exhibited a secular temperature decrease in northern high latitudes owing to decreasing annual mean insolation by 1.4% through orbital forcing. As the Greenland temperature deviates from North Hemispheric trend negatively by solar variation, we added negative solar signal on the calculated high latitude temperature to infer Greenland temperature, mimicking solar induced NAO/AO and AMOC change of the past 800 years. The calculated Greenland temperature agrees with the ice core derived Greenland temperature with a correlation coefficient of r = 0.3 in a 95 % confidence level, indicating that the past variability of solar activity, volcanic eruptions, greenhouse gasses, and orbital changes can explain at least 9% of multi-decadal to millennial Greenland temperature variability over the past 4000 years. Considering expected large internal variability of regional climate, it is rather remarkable. A millennial cooling around 500 B.C.E. to 0 C.E. observed in Greenland temperature reconstruction from borehole temperature profiles [Dahl-Jensen et al., 1998] were also found in the calculated temperatures, indicating the cooling was caused by several volcanic eruptions and negative responses of Greenland temperature to solar variability. Dahl-Jensen, D., K. Mosegaard, N. Gundestrup, G. D. Clow, S. J. Johnsen, A. W. Hansen, and N. Balling (1998), Past temperatures directly from the Greenland Ice Sheet, Science, 282(5387), 268-271. Gao, C., A. Robock, and C. Ammann (2008), Volcanic forcing of climate over the past 1500 years: An improved ice core-based index for climate models, J. Geophys. Res. - Atmos., 113, D23111. Kobashi, T., D. T. Shindell, K. Kodera, J. E. Box, T. Nakaegawa, and K. Kawamura (Submitted), On the origin of Greenland temperature anomalies over the past 800 years, J. Geophys. Res. 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).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMPP23E..04K
- Keywords:
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- 1616 GLOBAL CHANGE / Climate variability;
- 1621 GLOBAL CHANGE / Cryospheric change;
- 1650 GLOBAL CHANGE / Solar variability;
- 4932 PALEOCEANOGRAPHY / Ice cores