The Interdecadal Bipolar Oscillation: A Potential Driver for Rapid Antarctic Climate Transitions

The polar regions are critical components of complex Earth systems, housing potential tipping elements such as the West Antarctic Ice Sheet and sea ice systems. However, the climate trajectories of the two poles have diverged significantly over the past century. While the Arctic has exhibited rapid warming and dramatic sea ice loss—a phenomenon known as Arctic amplification—the Antarctic has shown a delayed and more heterogeneous response. Observations indicate that prior to the late 1980s, parts of Antarctica experienced warming and moistening while the Arctic remained relatively stable; subsequently, this pattern reversed, with the Arctic undergoing accelerated change while the Antarctic trend slowed or displayed spatial variability. Understanding the drivers of polar climate variability is paramount for anticipating potential abrupt transitions or tipping points in the regions.

Here, we identify a robust internal variability mode in atmospheric water vapor—termed the Interdecadal Bipolar Oscillation (IBO)—that provides a physical explanation for these historical asymmetries. Using the eigen microstate theory on ERA5 reanalysis and CMIP6 simulations (historical, piControl, and SSPs), we reveal that the IBO links the Arctic and Antarctic in a quasi-periodic (60–80 years) seesaw pattern. We demonstrate that the IBO has modulated interdecadal asymmetries in polar climate change over the past 80 years. Specifically, a phase shift in the late 1980s accelerated Arctic moistening while suppressing similar changes in the Antarctic.

Crucially, our projections under various Shared Socioeconomic Pathways (SSPs) indicate an imminent IBO phase reversal in the coming decades. This transition is expected to shift the IBO from a dampening to an amplifying phase for the Antarctic, coinciding with the background global warming signal. We suggest that this alignment could trigger a regime shift toward rapid Antarctic moistening and warming, potentially destabilizing the ice sheet–atmosphere interactions. The IBO thus acts as a critical internal regulator that may modulate the distance to tipping points in the polar climate system. By elucidating the interplay between this internal oscillation and external anthropogenic forcing, our study offers new insights into the mechanisms that could precipitate abrupt climate transitions in the Antarctic.