Despite the bogus claims of the UN's bureaucrats and the IPCC Climategate "scientists," the polar areas of the Northern Hemisphere have had warmer climates prior to the 20th and 21st centuries.
There is a vast body of research and empirical evidence confirming that the Arctic regions, and other parts of the globe, were indeed warmer during both the Roman and Medieval eras. In fact, global warming, cooling and climate change are natural events that never cease - that is irrefutable, unequivocal climate reality.
A peer-reviewed study by Perner et al. just added to that mountain of evidence confirming the robust warming of the Greenland area prior to the the modern era.
"The six researchers -- hailing from Denmark, Germany, Norway, Poland and the United Kingdom -- say that their new high-resolution benthic foraminiferal record from Disko Bugt "documents a marked long-term cooling trend over the last 3.6 ka BP," but they state that superimposed on this longer-term late Holocene cooling trend, there is evidence of millennial to centennial scale variability. This variability begins with what they describe as "a pronounced cooling event" at c. 2.5 ka BP, after which "a warm phase in bottom waters is recorded at c. 1.8 ka BP, which corresponds to the 'Roman Warm Period' and is seen to represent the warmest bottom water conditions recorded in Disko Bugt during the last 3.6 ka BP." This unique warm period was in turn followed by a cooler period (which would obviously be the Dark Ages Cold Period), after which they identify a warming of the subsurface waters during the 'Medieval Climate Anomaly'," which was followed (from 0.9 ka BP) by "pervasive and even harsher environmental conditions" that ultimately culminate at 0.3 ka BP in what they say is the Little Ice Age, and from which the region has yet to recover to Medieval Warm Period conditions." [K. Perner, M. Moros, J.M. Lloyd, A. Kuijpers, R.J. Telford, J. Harff 2011: Quaternary Science Reviews]