Abstract

Abstract. Precise understanding of Greenland temperature variability is important in two ways. First, Greenland ice sheet melting associated with rising temperature is a major global sea level forcing, potentially affecting large populations in coming centuries. Second, Greenland temperatures are highly affected by North Atlantic Oscillation/Arctic Oscillation (NAO/AO) and Atlantic multidecadal oscillation (AMO). In our earlier study, we found that Greenland temperature deviated negatively (positively) from northern hemispheric (NH) temperature trend during stronger (weaker) solar activity owing to changes in atmospheric/oceanic changes (e.g. NAO/AO) over the past 800 yr (Kobashi et al., 2013). Therefore, a precise Greenland temperature record can provide important constraints on the past atmospheric/oceanic circulation in the region and beyond. Here, we investigated Greenland temperature variability over the past 4000 yr reconstructed from argon and nitrogen isotopes from trapped air in a GISP2 ice core, using a one-dimensional energy balance model with orbital, solar, volcanic, greenhouse gas, and aerosol forcings. The modelled northern Northern Hemisphere (NH) temperature exhibits a cooling trend over the past 4000 yr as observed for the reconstructed Greenland temperature through decreasing annual average insolation. With consideration of the negative influence of solar variability, the modelled and observed Greenland temperatures agree with correlation coefficients of r = 0.34–0.36 (p = 0.1–0.04) in 21 yr running means (RMs) and r = 0.38–0.45 (p = 0.1–0.05) on a centennial timescale (101 yr RMs). Thus, the model can explain 14 to 20% of variance of the observed Greenland temperature in multidecadal to centennial timescales with a 90–96% confidence interval, suggesting that a weak but persistent negative solar influence on Greenland temperature continued over the past 4000 yr. Then, we estimated the distribution of multidecadal NH and northern high-latitude temperatures over the past 4000 yr constrained by the climate model and Greenland temperatures. Estimated northern NH temperature and NH average temperature from the model and the Greenland temperature agree with published multi-proxy temperature records with r = 0.35–0.60 in a 92–99% confidence interval over the past 2000 yr. We found that greenhouse gases played two important roles over the past 4000 yr for the rapid warming during the 20th century and slightly cooler temperature during the early period of the past 4000 yr. Lastly, our analysis indicated that the current average temperature (1990–2010) or higher temperatures occurred at a frequency of 1.3 times per 1000 yr for northern high latitudes and 0.36 times per 4000 yr for NH temperatures, respectively, indicating that the current multidecadal NH temperature (1990–2010) is more likely unprecedented than not (p = 0.36) for the past 4000 yr.

Highlights

  • Greenland temperature change is one of the most important factors for determining the impacts of future climate change on our society, as it is expected to undergo large changes owing to polar amplification (Meehl et al, 2007), and the Published by Copernicus Publications on behalf of the European Geosciences Union.T

  • It indicates that the current multidecadal average temperature (1990–2010) and/or higher temperatures occurred at a frequency of 1.3 times per 1000 yr for the northern high-latitude temperature and 0.36 times per 4000 yr for the northern hemispheric (NH) temperatures

  • A recent study indicated that the present NH average temperature (2000–2009) has not exceeded the warm early Holocene temperature (Marcott et al, 2013), but our study indicates that the multidecadal average temperature (1990–2010) did exceed the temperatures at least for the past 4000 yr

Read more

Summary

Introduction

Greenland temperature change is one of the most important factors for determining the impacts of future climate change on our society, as it is expected to undergo large changes owing to polar amplification (Meehl et al, 2007), and the Published by Copernicus Publications on behalf of the European Geosciences Union. It can be expected that stronger (weaker) solar activity induces warming (cooling) in NH temperature, and relative cooling (warming) in Greenland through positive (negative) NAO. Climate modelling indicates that the Atlantic meridional overturning circulation (AMOC) reduces (increases) during weaker (stronger) solar activity (Cubasch et al, 1997; Waple et al, 2002), contributing to negative Greenland temperature responses to solar variability (Kobashi et al, 2013). To derive hemispheric to global average temperatures on a multidecadal to centennial timescale, temperature proxies with larger uncertainties in temperature and chronology are compiled such that the multidecadal to centennial trends are frequently smoothed out, with the trends increasing as they go further back in time (Wanner et al, 2008) We explored another way to constrain multidecadal to millennial hemispheric temperature variability using the model and the Greenland temperature record.

Ice core chronology
Correlation coefficients and significance
Greenland temperature reconstruction over the past 4000 yr
Orbital forcing
Solar forcing
Greenhouse gas forcing
Volcanic forcing
Integrating climate forcings and application of 1-D EBM
Northern high-latitude temperature change
Northern hemispheric average temperature change
80 NH average temperature 70
Findings
Conclusions

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.