Why is Antarctica's sea ice increasing again?

Scientists at NYUAD want to find out why ice cover in one of the world’s last wildernesses has been expanding over the past decades - when it is being lost everywhere else

Researchers from NYUAD's Centre for Global Sea Level Change return from deploying a wave buoy to study ice in Antarctic in 2017.

Clare Eayrs and Daiane Faller from NYUAD get ready to deploy onto the sea ice on a chilly spring morning in 2019.

The vastness of the Antarctic viewed from a window of a Nasa plane.

Travelling through sea ice in the Atlantic southern ocean aboard the 'S.A. Agulhas II', a South African ice-breaking polar supply and research ship, in the winter of 2017.

Ice in the Lazarev Sea, Antarctica, during spring 2019. A distant iceberg can be seen on the horizon.

Researchers from NYUAD's Centre for Global Sea Level Change on their way to retrieve a mast installed on sea ice in the Southern Ocean in 2019.

Antarctica has fascinated explorers for centuries. Explorer Ernest Shackleton's ship 'Endurance' was trapped and slowly crushed by ice in the Weddell Sea during his second expedition to the Antarctic in 1915.

Clare Eayrs and Daiane Faller install a mast on sea ice in the Southern Ocean in 2019. The mast supports instruments to measure turbulent and radiative fluxes.

Sea ice in 2017 forming through the 'pancake cycle'. The characteristic raised rims are caused when the pancakes crash into each other through wind and wave action.

Almost twice the size of Australia, covered in ice and barely inhabited, Antarctica is one of the world’s last wildernesses.

The vast and rugged continent is a crucial habitat for animals and plays a role in stabilising the climate by reflecting sunlight.

But it is changing fast. Antarctica experienced an unusual reduction in sea-ice cover that began in 2016 and lasted for three years, contracting as much as the Arctic’s sea ice has in the past three decades.

The recent contraction in Antarctica's sea-ice cover went against an unexpected trend for the past several decades for it to increase, despite the loss of sea ice elsewhere.

Now researchers from New York University Abu Dhabi's Centre for Global Sea Level Change are studying what is happening, why ice is increasing and decreasing and whether climate change is to blame.

“We really don’t understand Antarctic sea ice and how it is changing,” said Dr Clare Eayrs, a research scientist at the centre. “Understanding how it will change in future is really important for climate models.”

The 2016 reduction in sea ice was thought by the researchers to be caused by warm air moving southward in early spring coupled with the effects of a warming ocean. One study suggested that record high temperatures and rainfall in the tropical eastern Indian Ocean in 2016 created a pattern of warmer northerly winds that pushed sea ice back to the Antarctic and melted it.

This was worsened by the fact that westerly winds - which usually push ice north, allowing exposed water in some areas to freeze and make yet more ice - were weaker that year.

Models forecast that westerly winds will increase in the long term - meaning sea ice should continue to follow traditional patterns - although the degree to which climate change is the cause of the changes is unclear.

“This is something we still don’t know and it should be a priority to look at,” said Dr Eayrs.

“We need to understand how they’re changing and how they might affect the sea ice as well."

The sea-ice cover in Antarctica may be increasing because the air in neighbouring regions is warming, which means it holds more moisture, some of which falls as rain and snow around Antarctica. This makes the water fresher (that is, it has a lower salt content) and cooler, causing it to freeze more easily.

Dr Eayrs has travelled to the region twice on research vessels over the past few years. She has seen Antarctica’s extraordinary ice fields first hand and experienced its extremes of weather.

“We saw some incredible storms down there,” she said. “The eye of the storm was the size of southern Africa. You couldn’t stick your head outside because the gale was screaming past.”

Sailing on a South African ship, Dr Eayrs helped to deploy buoys in a marginal ice zone to find out how waves travelled through the ice. Much of the ice in the area was in the form of “pancakes”, discs between one and three metres in diameter. During another trip, she deployed instruments to measure radiation and heat transfer through the ice.

Gaining a better understanding of long-term patterns is further complicated by the fact that satellite records of daily sea-ice cover go back only about 40 years.

Dr Eayrs said it was also not clear that man-made climate changes was to blame for reducing sea-ice cover in the Antarctic, explaining that more research was needed. "It’s not been tied down.”

Scientists will continue to take measurements and to analyse data that has already been collected to better understand the complex forces that are affecting Antarctica's sea ice.