Seems to me that if there is something one wants to call “unprecedented in recent Greenland history”
it is the shift of 1920′s and 1930′s. I wonder how polar bears survived that period

PDF and data available here.

Abstract:

At present, continuous instrumental temperature records for Greenland reach back to the late nineteenth century at a few sites. Combining early observational records from locations along the south and west coasts, it has been possible to extend the overall record back to the year 1784. The new extended Greenland temperature record is 9% incomplete. There are, however, sufficient new data (an additional 74 complete winters and 52 complete summers) to provide a valuable indication of late eighteenth century and nineteenth century seasonal trends. Comparison of the previously published records with additional observational series digitized from Danish Meteorological Institute Yearbooks has also revealed inhomogeneities in some of the existing twentieth century temperature records. These problems have been eliminated in the new extended Greenland temperature record. A long homogeneous west Greenland instrumental temperature record is of great value for the interpretation of the growing number of Greenland ice core records. A first comparison of the new record with highly resolved Greenland ice core data is presented. Correlations between west Greenland winter temperatures and the ice core winter season proxy are found to be r = 0.67 and r = 0.60 for the periods 1785–1872 and 1873–1970, respectively.

Reference: Chylek, P., M. K. Dubey, and G. Lesins (2006), Greenland warming of 1920–1930 and 1995–2005, Geophys. Res. Lett., 33, L11707, doi:10.1029/2006GL026510 here

“We provide an analysis of Greenland temperature records to compare the current (1995–2005) warming period with the previous (1920–1930) Greenland warming. We find that the current Greenland warming is not unprecedented in recent Greenland history. Temperature increases in the two warming periods are of a similar magnitude, however, the rate of warming in 1920–1930 was about 50% higher than that in 1995–2005″.

They studied the two periods to see if the warming shown in 1995-2005 was unprecedented, and found there was “no statistically significant difference between the average temperature from the 1905 to 1955 period and 1995 to 2005 period”. Statistics buffs will want to check their z-scores.

In their summation, they state: ” Although there has been a considerable temperature increase during the last decade (1995 to 2005) a similar increase and at a faster rate occurred during the early part of the 20th century (1920 to 1930) when carbon dioxide or other greenhouse gases could not be a cause. The Greenland warming of 1920 to 1930 demonstrates that a high concentration of carbon dioxide and other greenhouse gases is not a necessary condition for period of warming to arise. The observed 1995–2005 temperature increase seems to be within a natural variability of Greenland climate’.

Finally: ” To summarize, we find no direct evidence to support the claims that the Greenland ice sheet is melting due to increased temperature caused by increased atmospheric concentration of carbon dioxide. The rate of warming from 1995 to 2005 was in fact lower than the warming that occurred from 1920 to 1930. The temperature trend during the next ten years may be a decisive factor in a possible detection of an anthropogenic part of climate signal over area of the Greenland ice sheet”.

Reference: Chylek, P., M. K. Dubey, and G. Lesins (2006), Greenland warming of 1920–1930 and 1995–2005, Geophys. Res. Lett., 33, L11707, doi:10.1029/2006GL026510, here

Re #4. Attempts to assess and repair the isotope problems have been done by Jeffrey Severinghaus, Richard Alley, Jean Jouzel, Georg Hoffmann et al (google names) by crosschecking the behavior of several other isotopes 40AR, 15N etc. There are also borehole temperature with Dye-3 clearly showing the Medieval Warm period and the Little ice Age

See:
http://www.ipsl.jussieu.fr/GLACIO/hoffmann/Pictures/RealTempGRIPDYE3.jpg

But many things remain suppositions that could be wrong when other elements are not taken into accoung.

A dry summer looks actually as a cold year, as there are not enough “warm” isotopes to balance.

i.e., drought and cold are indistinguishable.

So we do have a situation like the tree rings, though possibly less complicated. There are multiple factors that contribute to the concentration and unless all of them are known simultaneously d18O is not going to be a good thermometer.

Steve, I think you might me interested in this project; some related publications can be downloaded from here (see especially Isaksson et al (2005)).