Mystery of rapid yearly retreat of Antarctic sea ice explained by seasonal solar radiation
The source of the rapid annual retreat of Antarctic sea ice has long eluded scientists. However, according to a new study co-authored by former Program on Climate Change Director and current Atmospheric Sciences Chair Cecilia Bitz, the puzzling long-term actions of Antarctic sea ice may have simply been obscuring a straightforward solution: the fast yearly retreat is simply explained by seasonal solar radiation.
Every year, Antarctic sea ice rapidly retreats around its midsummer in December and slowly expands again between March and October. This asymmetric cycle of slow growth and rapid retreat, combined with the complex climate system of the Southern Ocean, seemed to necessitate a complex explanation for this relationship, and as such, researchers have been unable to ascertain the driving forces behind this process. Yet, this new research shows that the complicated cycle is actually fully explained by basic physics. The lead authors, including UW researchers Lettie Roach, Edward Blanchard-Wrigglesworth, and Cecilia Bitz found that as the maximum net influx of heat is reached in midsummer, the Antarctic ice melts fastest, leading to the recognizable annual pattern. To determine this, the team first investigated global climate models and were able to reproduce the pattern of Antarctic sea ice retreat. They then constructed a physics-based model, and confirmed that seasonal variation in incoming solar radiation also produced the characteristic fast retreat of ice. Dr. Bitz recognized the significance of this revelation, noting the importance of the Southern Ocean in regulating the global climate, and remarking that being able to “explain this key feature of Antarctic sea ice that standard textbooks have had wrong, and showing that the models are reproducing it correctly, is a step toward understanding this system and predicting future changes.”
In contrast, the cycle of sea ice in the Arctic has now become the confounding one, as it tends to expand its cover slightly faster than it retreats every year. While the simple geography of the Southern Ocean can allow for seasonal processes to be driven by a straightforward underlying cause, there is no indication that this is true for the Arctic. Research into this complexity is ongoing and will be increasingly vital, as without a proper understanding of the processes in our polar regions, we will never be able to effectively protect them.