Antarctica's Role in Global Change

The vast continent of Antarctica has been a major focus of scientific exploration for relatively few decades when compared to most areas on Earth. Yet what is already known about Antarctica conclusively demonstrates that despite its remote location it plays a significant role in the global system. Encircled by the world's most biologically productive oceans, Antarctica is the largest storehouse of fresh water on the planet, a major site for the production of the cold deep water that drives ocean circulation, a major player in Earth's albedo dynamics, and an important driving component for atmospheric circulation. Thus, Antarctica plays a critical role in the dynamic linkages that couple the spatially and temporally complex components of the Earth's system (atmosphere, biosphere, anthrosphere, hydrosphere, cryosphere and lithosphere).

Spatial Complexity

While the existence of a complex global climate system is now recognized, the details of its functioning are still poorly understood. In the Northern Hemisphere and portions of the Southern Hemisphere, direct observational and instrumental records exist only for the last ~2000 and ~100 years, respectively, and, except at isolated sites, observational and instrumental records in Antarctica cover only the last 30-40 years. In addition, the relatively limited information available for past climate illustrates how little confidence we can place in the spatial uniformity of climate over the past few centuries (e.g., Little Ice Age and Medieval Warm Period).

To complicate matters, Antarctica exhibits significant regional contrasts in present-day climate regime. As an example, evidence from instrumental records suggests some decoupling of climate change on decadal scales between different parts of the continent. Large areas of the interior of the ice sheet are influenced by the continental temperature inversion, while other portions of the interior and the coastal regions are influenced by cyclonic systems circulating around the continent. As a consequence, these peripheral areas are mainly connected with lower tropospheric transport, whereas high altitude areas in the interior are more likely influenced by vertical transport from the upper troposphere and stratosphere. As a result, variability in cyclonic systems impacting the coastal regions has led to increases in temperature at Palmer Station on the Antarctic Peninsula that are not paralleled at South Pole.

Temporal Complexity

Recent ice coring programs in central Greenland (GISP2 and GRIP) have demonstrated that the Arctic has experienced large, rapid, climate oscillations through most of the last 110,000 years on a scale that agricultural and industrial humans have not yet faced. These millennial-scale events represent quite large climate deviations: probably many degrees C in temperature, twofold changes in snow accumulation, order-of-magnitude changes in wind-blown dust and sea-salt loading in the atmosphere and large changes in methane concentration (Alley et al., 1993; Chappellaz et al., 1993; Taylor et al., 1993; Mayewski et al., 1993, 1994; Cuffey et al., 1995). Changes during these events, equal to most of the glacial-interglacial difference, commonly occurred over decades or less. More subtle versions of these rapid climate change events have now been identified in the Holocene portion of the GISP2 record (O'Brien et al., 1995). Dramatic shifts in the patterns of atmospheric circulation have been used to explain the rapidity and magnitude of these events (Mayewski et al., 1994; Kapsner et al., 1995; O'Brien et al., 1995).

New correlation techniques involving the gaseous composition of the atmosphere demonstrate that several such events are also recorded in the isotopic temperature record of the Vostok core from central East Antarctica, although with apparently smaller amplitude and a more ramped appearance than in Greenland (Bender et al., 1994). Correlation with a near-coastal East Antarctic ice core record from Taylor Dome indicates an even stronger similarity for the frequency and magnitude of changes in atmospheric circulation recorded at this site relative to Greenland (Mayewski et al., 1996). High frequency complexity in climate is manifested through Antarctic synoptic systems that vary interannually in response to major atmospheric circulation systems such as the El Nino Southern Oscillation (ENSO) and other regional- to global-scale factors, such as atmospheric blocking, sea ice variations and volcanic-event-induced insolation shielding, that operate on weekly and greater scales.

Anthropogenic Impact

The influence of human activity on climate and atmospheric composition over Antarctica has already had profound effects. Unexpectedly, the continent has been subjected to massive ozone depletion as a consequence of its unique setting in relationship to global circulation systems and the introduction of humanly engineered CFCs that have ozone destroying side-effects.

Recent changes in Antarctic snow accumulation and sea ice extent have been linked in principle to greenhouse gas warming (Morgan et al., 1991; Thompson et al., 1994; Vaughan and Doake, 1996).

Human source nuclear fallout from bomb tests and the Chernobyl nuclear accident (Dibb et al., 1990) demonstrates the potential for the introduction of anthropogenic source pollutants to the continent.

Ice Dynamics and the Climate/Sea Level Connection

Antarctica's role in global climate is largely propagated through changes in its ice cover. The scale of this connection ranges from seasonal changes in sea ice extent that cause changes in albedo, atmospheric circulation, ocean productivity, and ocean circulation to potentially massive changes in sea level triggered by collapse of portions of the Antarctic ice sheet. Because much of the ice in West Antarctica is grounded below sea level, this portion of the ice sheet may be inherently unstable. Geologic evidence affirms the potential for catastrophic disappearance of such marine-grounded ice sheets in the northern hemisphere. The potential exists for future ice sheet collapse in response to human-forced changes in climate because there is sufficient marine-grounded ice in the region of West Antarctica to raise sea level 5 meters.