Background
Beall Lake is the largest lake on Beall Island, which is located in the northern Windmill Islands (66°10'-66°35'S, 110°10'-110°50'E), which are described by the authors as "a group of low islands, islets and peninsulas with elevations less than 100 m (Goodwin, 1993) forming one of the more significant ice-free oases on the East Antarctic coastline."

What was done
Roberts et al. conducted a fossil diatom analysis of an 82-cm sediment core that was removed from the deepest part of Beall Lake, samples of which were radiocarbon dated and corrected for the Antarctica reservoir effect.

What was learned
Of all the things the scientists learned from their study, perhaps the most interesting was what they deduced from a portion of the sediment core that covered the approximate time period 2000-1700 ¹⁴C yr BP.  Based on the species of diatoms found in this sample, they inferred the existence of a multi-centennial period of warmth that was characterized by summer temperatures they describe as being "much [our italics] higher than present summer temperatures."  Supporting this inference, they note that observations made at both Casey and Law Dome indicate that "during the late Holocene, a warm period existed with precipitation and summer temperatures higher than at present (Goodwin, 1993)."  And to make this point perfectly clear, they conclude by stating that "the diatom-inferred Holocene palaeosalinity record from Beall Lake indicates that the late Holocene warm period was much warmer than at present."

What it means
Over an interval of time that coincides in part with what is known in the Northern Hemisphere as the Roman Warm Period, Roberts et al. found evidence for what they call much warmer East Antarctic coastal temperatures than those of today, and at a time when the air's CO2 concentration was fully 100 ppm less than what it is presently.  Hence, there is no reason to suggest that anything that may be occurring in East Antarctica today is due to the historical rise in the atmosphere's CO2 concentration, unless, of course, one wants to say it has caused the decline of East Antarctic temperatures that has occurred over the past several decades [for more on this matter, see Comiso (2000), Doran et al. (2002), and Kwok and Comiso (2002)].

References
Comiso, J.C.  2000.  Variability and trends in Antarctic surface temperatures from in situ and satellite infrared measurements.  Journal of Climate 13: 1674-1696.

Doran, P.T., Priscu, J.C., Lyons, W.B., Walsh, J.E., Fountain, A.G., McKnight, D.M., Moorhead, D.L., Virginia, R.A., Wall, D.H., Clow, G.D., Fritsen, C.H., McKay, C.P. and Parsons, A.N.  2002.  Antarctic climate cooling and terrestrial ecosystem response.  Nature advance online publication, 13 January 2002 (DOI 10.1038/nature710).

Goodwin, I.D.  1993.  Holocene deglaciation, sea-level change, and the emergence of the Windmill Islands, Budd Coast, Antarctica.  Quaternary Research 40: 70-80.

Kwok, R. and Comiso, J.C.  2002.  Spatial patterns of variability in Antarctic surface temperature: Connections to the South Hemisphere Annular Mode and the Southern Oscillation.  Geophysical Research Letters 29: 10.1029/2002GL015415.