The Glaciers of Greenland

In summarizing the existing body of research pertaining to "fluctuations of local glaciers in Greenland (e.g. ice caps and mountain glaciers independent of the Greenland Ice Sheet) during latest Pleistocene and Holocene time," Kelly and Lowell (2009) say that "subsequent to late-glacial or early Holocene time, most local glaciers were smaller than at present or may have disappeared completely during the Holocene Thermal Maximum," which warm period occurred between 5 and 9 ka, when they write that "temperatures derived from the GRIP borehole [were] 2.5°C warmer than at present (Dahl-Jensen et al., 1998)." Thereafter, however, local glaciers began to grow once again; and for all regions except a few locations in western and southeastern Greenland, the two researchers report that glaciers "grew to their maximum Holocene extents during Historical time," which period they identify as extending all the way up to 1940 in certain cases. In addition, they note that "in some locations in Greenland, there is evidence for millennial-scale fluctuations of local glaciers," which they say "experienced recession and advance approximately during the Medieval Warm Period (~800-1170 AD) and Little Ice Age (~1300-1850 AD), respectively," consistent with borehole temperature data from the GRIP ice core.

Even in ice-cold Greenland, Holocene temperatures followed much the same temporal pattern observed in other parts of the world, as did the advance and retreat modes of its local glaciers, with maximum glacier extensions occurring during the coldest period of the current interglacial (the Little Ice Age). As a result, it was only to be expected that once the millennial-scale oscillation of temperature bottomed out and began to rise again, the result would be a significant warming and recession of local glaciers, irrespective of anything the air's CO₂ content might do concurrently, as the climate rebounded towards its more normal Holocene mid-range. In other words, Greenland would likely have experienced the same degree of warming and glacial recession that it experienced over the course of the 20th century even if the atmosphere's CO₂ concentration had remained at the same low value it had maintained throughout most of the Holocene to that point in time.

Additional References
Dahl-Jensen, D., Mosegaard, K., Gundestrup, N., Clow, G.D., Johnsen, S.J., Hansen, A.W. and Balling, N. 1998. Past temperatures directly from the Greenland Ice Sheet. Science 282: 268-271.