Warmer ocean temperatures, combined with unusual wind patterns, contributed to the record decline of sea ice levels in Antarctica, according to new research published in the prestigious international science journal Nature Communications.
Researchers from Monash University, the Australian Bureau of Meteorology, University of Washington (Seattle) and the National Center for Atmospheric Research in Boulder, USA, identified that natural variability has led to a dramatic and sustained melting of Antarctic sea ice, though human-induced climate change may also be playing a role.
After exhibiting an upward trend from 1979 that delivered Antarctica a record sea ice covering in 2014, a sudden drop in sea ice levels during the spring and summer months of 2016 resulted in a record low covering.
They have stayed well below since. As of 1 January 2019, Antarctic sea ice is at its lowest New Year's Day levels on record.
Associate Professor Julie Arblaster from Monash University's School of Earth, Atmosphere and Environment said: "Such large and rapid changes rarely occur in the natural system. This led our research teams to ask the question of what caused the initial sea ice decline and what changes in the climate system are sustaining it?"
The studies identified that highly unusual conditions in tropical oceans and the Antarctic stratosphere triggered wind patterns across the bottom part of the globe which led to the initial sea ice declines.
"In the winter and spring of 2016, sea surface temperatures and rainfall in the tropical Indian Ocean and western Pacific were well above their normal values. We found that these tropical events generated wind patterns near Antarctica that almost perfectly matched the main regions where sea ice initially declined," Dr Guomin Wang from the Australian Bureau of Meteorology said.
The climate system not only has natural variability on year-to-year timescales, but also from decade-to-decade. Warmer subsurface waters near Antarctica have been slowly moving upwards towards the surface by patterns induced by the tropical Pacific over the past 10-15 years.
"Our research shows that what occurred in 2016 was just the tip of the iceberg – it suggests the initial rapid decline seen in spring 2016 was not an isolated event and this decadal-timescale warming of the upper ocean could continue these low sea ice amounts for some time," Dr Gerald Meehl from the National Center for Atmospheric Research added.
Two research papers: 'Sustained ocean changes contributed to sudden Antarctic sea ice retreat in late 2016' and 'Compounding tropical and stratospheric forcing of the record low Antarctic sea ice in 2016' were published in Nature Communications on Wednesday 2 January 2019.
