Background
The authors write that "the Antarctic Peninsula is at present one of the most rapidly warming regions on Earth (Vaughan et al., 2003)," noting that "historical observations since 1958 at Esperanza Station document warming equivalent to 3.5 ± 0.8°C per century."

What was done
In an attempt to determine just how unprecedented this warming might have been compared to the rest of the Holocene, Mulvaney et al. drilled an ice core to the bed of the ice cap on James Ross Island, which lies just off the northeastern tip of the Antarctic Peninsula, next to an area that has experienced a series of recent ice-shelf collapses. And based on deuterium/hydrogen isotope ratios of the ice (δD), they developed a temperature history of the region that spans the entire Holocene and extends into the last glacial period.

What was learned
The nine researchers report that "the Antarctic Peninsula experienced an early Holocene warm period followed by stable temperatures, from about 9200 to 2500 years ago, that were similar to modern-day levels [these italics and those following added for emphasis]." They also found that "the high rate of warming over the past century is unusual (but not unprecedented) in the context of natural climate variability over the past two millennia." More specifically, they state that "over the past 100 years, the James Ross Island ice-core record shows that the mean temperature there has increased by 1.56 ± 0.42°C," which ranks as one of the fastest (upper 0.3%) warming trends since 2000 years before present, according to a set of moving 100-year analyses that demonstrate that "rapid recent warming of the Antarctic Peninsula is highly unusual although not outside the bounds of natural variability in the pre-anthropogenic era." And even though the temperature of the northern Antarctic Peninsula has risen at a rate of 2.6 ± 1.2°C over the past half-century, they say that "repeating the temperature trend analysis using 50-year windows confirms the finding that the rapidity of recent Antarctic Peninsula warming is unusual but not unprecedented."

What it means
Even for what Mulvaney et al. describe as "one of the most rapidly warming regions on Earth," recent warming there has not been unprecedented within the context of the past two millennia.

Reference
Vaughan, D.G., Marshall, G.J., Connolley, W.M., Parkinson, C., Mulvaney, R., Hodgson, D.A., King, J.C., Pudsey, C.J. and Turner, J. 2003. Recent rapid regional climate warming on the Antarctic Peninsula. Climatic Change 60: 243-274.