High variability of Greenland surface temperature over the past 4000 years estimated from trapped air in an ice core

Abstract

[1] 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)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(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)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(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.

Solar influenced late Holocene temperature changes on the northern Tibetan Plateau

“…These records join a growing body of such evidence [4,8,10,12,24,46]. In particular, despite inconsistent with the spatial patterns derived from climate model-assisted reconstructions [8], the substantially warmer condition on the northern Tibetan Plateau, together with the relatively warmer conditions on Greenland [47], the persistent positive North Atlantic Oscillation mode [48], negative Southern Oscillation Index [49] and the prevailing La Niña-like conditions in the tropical Pacific [8,50], suggest anomalous climatic conditions during the MWP, beyond the climate variability captured by the recent warm period.…”

On the origin of multidecadal to centennial Greenland temperature anomalies over the past 800 yr

“…We noted that the Summit air temperature is highly correlated (r = 0.92, p < 0.01; Fig. 2) with the average surface air temperature of the entire Greenland ice sheet (Box et al, 2009;Kobashi et al, 2011), indicating that the Summit temperatures reconstructed from ice cores are a reliable proxy for the surface temperatures of the entire ice sheet. Hereinafter, we call the Summit temperature time series "Greenland temperature".…”

“…2. The Greenland Summit surface air temperature and the whole Greenland ice sheet surface temperature were reconstructed for the last 170 yr from a spatial-temporal data fusion between the output of a regional climate model (Polar MM5) (Box et al, 2009) and in situ observations (Kobashi et al, 2011).…”

“…Proposed mechanisms for the temperature variations were then investigated with a climate model (GISS-ER) and grid proxy reconstruction of global temperatures (Mann et al, 2009). We note that the inferences investigated in this paper were further tested and developed in a companion paper (Kobashi et al, 2012) dealing with the past 4000 yr of Greenland temperature record (Kobashi et al, 2011).…”

“…In this study, we investigated the variations in the Greenland temperature anomaly using a recently developed Greenland temperature record (Kobashi et al, 2010(Kobashi et al, , 2011 derived from trapped air in the GISP2 Greenland ice core from the Greenland Summit station and using two proxy average NH temperature reconstructions (Moberg et al, 2005;Mann et al, 2009). Proposed mechanisms for the temperature variations were then investigated with a climate model (GISS-ER) and grid proxy reconstruction of global temperatures (Mann et al, 2009).…”