IAntarctic sea ice extent underwent a rapid decline in the spring of 2016 and is still well below average now. CLEX researchers have tied the decline to natural variability of both the atmosphere and ocean in two articles published in Nature Communications this month.
Antarctic sea ice extent (the area of the Southern Ocean covered by sea ice) had been slowly expanding since satellite monitoring began in the late 1970s. So when it dramatically declined in late 2016 it prompted many questions. What caused the decline and what has sustained it since? Was it the beginning of a longer-term decline or a temporary shift? And what role might human-induced climate change have played?
Using statistical and climate model analysis, we identified the dominant role of the very warm sea surface temperatures in the tropical eastern Indian Ocean in the spring of 2016 in driving wind patterns over the Southern Ocean. These northerly winds acted to push the sea ice back towards Antarctica as well as melt it via warm and moist airflow. Later in 2016 the normal westerly winds that encircle Antarctica also weakened, leading to further sea ice declines. We found that the weakening of these winds began in the stratosphere.
But what has sustained the below average sea ice cover since? Again, our research points to the role of the tropics. We argue that tropical Pacific sea surface temperature variability drove stronger than usual westerly winds over the previous 15 years that acted to bring warm subsurface ocean water slowly towards the surface in the sea ice region. The warmer ocean has maintained the reduced extent of Antarctic sea ice since.
Our results suggest that the rapid sea ice declines in 2016 were largely due to natural variability of the climate system, but a role for climate change cannot be ruled out.
Further detail on this research can be found in this article at The Conversation written by the authors.
- Wang, G., H.H. Hendon, J.M. Arblaster, E.-P. Lim, S. Abhik, P. van Rensch, Compounding tropical and stratospheric forcing of the record low Antarctic sea-ice in 2016. Nat. Commun. https://doi.org/10.1038/s41467-018-07689-7 (2019).
- Meehl, G. A., J.M. Arblaster, C.T.Y. Chung, M.M. Holland, A. DuVivier, L. Thompson, D. Yang, C.M. Bitz, Sustained ocean changes contributed to sudden Antarctic sea ice retreat in late 2016 https://doi.org/10.1038/s41467-018-07865-9 (2019)