What was done
The authors review what is known about Antarctic air temperature trends over the past few decades, as well as (1) trends in the Southern Hemisphere (SH) Annular Mode (SAM) and the extrapolar Southern Oscillation (SO), (2) the roles these phenomena may have played in orchestrating the observed air temperature trends, and (3) what may be the ultimate driver of their own behavior.

What was learned
Citing King and Harangozo (1998), the authors report that during the past 20 years, the Antarctic Peninsula has experienced "pronounced warming."  They note, however, that there has been "cooling at a number of weather stations on the coast and plateau of East and West Antarctica (Comiso, 2000)."  In fact, they say that "the analysis of Doran et al. (2002) suggests a net cooling of the Antarctic continent between 1966 and 2000," with the largest cooling centered around the South Pole and the region surrounding Dome C.  Hence, the mean trend in climate for the entire continent over the past three decades and more has clearly been a cooling.

Over the 17-year period 1982-1998, Kwok and Comiso also report that the SAM index shifted towards more positive values (0.22/decade), noting that a positive polarity of the SAM index "is associated with cold anomalies over most of Antarctica with the center of action over the East Antarctic plateau."  Simultaneously, the SO index shifted in a negative direction, indicating "a drift toward a spatial pattern with warmer temperatures around the Antarctic Peninsula, and cooler temperatures over much of the continent."  Together, the authors say the positive trend in the coupled mode of variability of these two indices (0.3/decade) represents a "significant bias toward positive polarity" that they describe as "remarkable."

The authors additionally report that "the tropospheric SH annular mode has been shown to be related to changes in the lower stratosphere (Thompson and Wallace, 2000)," noting that "the high index polarity of the SH annular mode is associated with the trend toward a cooling and strengthening of the SH stratospheric polar vortex during the stratosphere's relatively short active season in November, and ozone depletion," which is pretty much the same theory that has been put forth by Thompson and Solomon (2002).

What it means
Antarctica, as a whole, has been cooling for well over the past three decades, in direct contradiction of climate model projections.  This cooling appears to be the result of a remarkable positive trend in the coupled mode of variability of the SAM and SO, which appears to be driven by phenomena of stratospheric origin.  This last point is of more than passing interest; for although atmospheric processes of tropospheric origin are known to have the ability to perturb the stratosphere, forcings in the opposite direction have usually been assumed to be negligible in most climate models.  As noted by Hartley et al. (1998), however, this assumption is likely not correct; and amplified perturbations of various phenomena, including those that are solar-induced, may well be propagated downward to the troposphere, to where they can significantly impact earth's climate, as appears to be what is happening in the case of Antarctica's recent three-plus decades of cooling.

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 415: 517-520.

Hartley, D.E., Villarin, J.T., Black, R.X. and Davis, C.A.  1998.  A new perspective on the dynamical link between the stratosphere and troposphere.  Nature 391: 471-474.

King, J.C. and Harangozo, S.A.  1998.  Climate change in the western Antarctic Peninsula since 1945: observations and possible causes.  Annals of Glaciology 27: 571-575.

Thompson, D.W.J. and Solomon, S.  2002.  Interpretation of recent Southern Hemisphere climate change.  Science 296: 895-899.

Thompson, D.W.J. and Wallace, J.M.  2000.  Annular modes in extratropical circulation, Part II: Trends.  Journal of Climate 13: 1018-1036.