New study shows temperature in Greenland significantly warmer than present several times in the last 4000 years

Kobashi et al 2011 was just published in GRL, and it looks like it will be upsetting the paleoclimate apple cart. The conclusions of Kaufman et al 2009 look to be minimized in comparison to this much more complete study. Questions over the split methodology for the last 60 years of data might be an issue, due to the change in methods of temperature reconstruction before and after the 1950 breakpoint. The amount of recent instrumental data is pretty low, and using it to calibrate the forward model might be a bit dodgy.

Figure 1. (top) Reconstructed Greenland snow surface temperatures for the past 4000 years and air temperature over the past 170 years (1840–2010) from three records. The thick blue line and blue band represents the reconstructed Greenland temperature and 1s error, respectively (this study). The reconstruction was made by two different methods before and after 1950. The “gas method” is as described in section 2, and the “forward model” is described by Kobashi et al. [2010]. Thick and thin black lines are the inversion‐adjusted reconstructed Summit annual air temperatures and 10‐year moving average temperatures, respectively [Box et al., 2009]. Thin and thick red lines are the inversion adjusted annual and 10‐year moving average AWS temperature records, respectively [Stearns and Weidner, 1991; Shuman et al., 2001; Steffen and Box, 2001; Vaarby‐Laursen, 2010]. (middle) Past 1000 years of Greenland temperature. Thick blue line and band are the same as above. Black and red lines are the Summit [Box et al., 2009] and AWS [Stearns and Weidner, 1991; Shuman et al., 2001; Steffen and Box, 2001; Vaarby‐Laursen, 2010] decadal average temperatures as above. (bottom) Past 4000 years of Greenland temperature. Thick blue line and band are the same as above. Thick green line represents 100‐year moving averages. Black and red lines are the Summit [Box et al., 2009] and AWS [Stearns and Weidner, 1991; Shuman et al., 2001; Steffen and Box, 2001; Vaarby‐Laursen, 2010] decadal average temperature, respectively. Blue and pink rectangles are the periods of 1000–2010 C.E. (Figure 1, middle) and 1840–2010 C.E. (Figure 1, top), respectively. Present temperature is calculated from the inversion adjusted AWS decadal average temperature (2001–2010) as −29.9°C (Figure 1, top). Present temperature and ±2s are illustrated by lines in the plots. Green circles are the current decadal average temperature as above (−29.9°C, 2001–2010).

Abstract: 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. Continue reading →