Growing Antarctic sea ice contrary to warming climate

A small hole in the clouds reveals newly formed sea ice in the Bellingshausen Sea in 2014 (NASA / Digital Mapping System)
A small hole in the clouds reveals newly formed sea ice in the Bellingshausen Sea in 2014 (NASA / Digital Mapping System)

In the last few decades, Antarctica's sea ice has grown at an extraordinary rate - in contrast to the Arctic, where it is in a swift and severe decline.

New research by the National Center for Atmospheric Research (NCAR) in the United States has found why it's expanding despite the warming climate.

The sea ice surrounding Antarctica melts and refreezes seasonally, unlike the ice sheets which make up the bulk of the continent.

Satellite records beginning in 1979 have found the sea ice has been expanding over time. It's accelerated between 2000 and 2014, increasing nearly five-fold than between 1979-1999.

NCAR's findings say nature climate fluctuation causes the Interdecadal Pacific Oscillation (IPO) to shift between a positive and negative phase.

The shift in phases sets off a chain reaction of climate impacts.

When in a negative phase, as occurred in 1999, the sea surfaces in the tropical eastern Pacific are cooler than average. It affects rainfall, which in turn affects large-scale changes to the winds that reach all the way to the icy continent.

Off the coast of Antarctica, in the Amundsen Sea, it drives a deep, low-pressure system with strong winds blowing the sea ice northward.

NASA's Digital Mapping System (DMS) camera image shows heavily compacted first-year sea ice along the edge of the Amundsen Sea in Antarctica October 16, 2009 in this image released on October 16, 2014. A fresh observations from September 2014 showed sea ice around Antarctica had reached its greatest extent since the late 1970s. To better understand such dynamic and dramatic differences in the region's land and sea ice, researchers are travelling south to Antarctica this month for the sixth campaign of NASA's Operation IceBridge. The airborne campaign, which also flies each year over Greenland, makes annual surveys of the ice with instrumented research aircraft.  REUTERS/NASA/Handout (ANTARCTICA - Tags: ENVIRONMENT) FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS. THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY. IT IS DISTRIBUTED, EXACTLY AS RECEIVED BY REUTERS, AS A SERVICE TO CLIENTS - RTR4AGDV

Heavily compacted first-year sea ice along the edge of the Amundsen Sea in 2009 (NASA / Digital Mapping System)

While a negative phase is beneficial to the ice growth, the study's authors say a positive phase may have the opposite effect.

"Compared to the Arctic, global warming causes only weak Antarctic sea ice loss, which is why the IPO can have such a striking effect in the Antarctic," says study co-author Cecilia Bitz from the University of Washington.

"There is no comparable natural variability in the Arctic that competes with global warming."

Lead author and NCAR scientist Gerald Meehl says the research provides insight into the interaction between natural climate changes, and changes influenced by humans.

"The climate we experience during any given decade is some combination of naturally occurring variability and the planet's response to increasing greenhouse gases," said lead author and NCAR scientist Gerald Meehl.

"It's never all one or the other, but the combination - that is important to understand."

The study also found when models with a positive IPO and those with a negative IPO were averaged - that is to say, when the effect of the IPO was negated - the sea ice was found to be in decline.

"As the IPO transitions to positive, the increase of Antarctic sea ice extent should slow and perhaps start to show signs of retreat when averaged over the next 10 years or so," Dr Meehl says.