For quite some time, a longstanding mystery in the Antarctic waters has left scientist stumped: in a continuously warming world, why is the sea ice in Antarctica expanding, thickening and spreading every year?

This bizarre phenomenon has long confounded climate change experts and has given "deniers" data to dispute the existence of global warming, according to the Washington Times.

Indeed, the seemingly positive changes among sea ice in the southern pole has been a source of disagreement within the climate change debate since the continent began adding ice almost 16 years ago.

Now, however, a new study conducted by climate scientists from Australia and the United States offers an explanation for the scientific paradox.

Researchers have found that the expansion of Antarctic sea ice in recent years was mostly driven by natural climate fluctuations, particularly in sea surface temperatures. The changes negated the small amount of warming caused by greenhouse gases.

Plausible Explanation

Unlike slow glacial ice and ice shelves, sea ice is seasonal. It forms when the surface temperature of the ocean drops to negative 2 degrees Celsius (28.4 degrees Fahrenheit) and chilly winds whip over the water.

Climate models have shown that, theoretically, rising levels of sea temperatures should be stemming the growth of Antarctic sea ice. Instead, sea ice in the southern pole appears to extend as far and wide as ever. How does this happen?

Researchers from the National Center for Atmospheric Research (NCAR) have investigated 262 climate models to distinguish natural variation and discovered that increasing sea temperatures caused by global warming were affected by a phenomenon called interdecadal pacific oscillation (IPO).

This phenomenon is a naturally occurring atmospheric pressure that either cools or warms sea surfaces on the entire Pacific basin.

Natural Cycles

An IPO cycle can last from 20 to 30 years, researchers said. Since the end of the 20th century, the IPO has been in a "negative phase," with sea surface temperatures plummeting to below average. In Antarctica, this has resulted in the expansion of sea ice. The expansion rate has increased fivefold in 2000.

IPO may be a plausible explanation to the spreading and thickening of Antarctic sea ice, but it does not explain why the sea ice expansion is fastest in the western Ross Sea, says oceanographer William Hobbs, who was not involved in the study.

"This is a really complex interaction of land, atmosphere and ocean," says Hobbs.

In 2014, the IPO may have begun to shift to a positive phase, scientists suggest. If this is true and sea surface temperatures begin to increase again, then the Antarctic sea ice will shrink, says study co-author Julie Arblaster.

Polar Opposites

Meanwhile, the situation on the other side of the world is truly a polar opposite: Arctic sea ice has been experiencing a rapid decline during the same period. Tech Times reported in March that Arctic sea ice peaked at 5.607 million square miles in 2016 — a record low since satellites began monitoring the region.

Unfortunately, there are no natural climate fluctuations such as IPOs in the Arctic that could negate warming, says Arblaster.

She says the Antarctic is a big land mass surrounded by ocean, while the Arctic is ocean enclosed by land.

"They have very different sea ice characteristics," adds Arblaster.

Details of the new study are featured in the journal Nature Geoscience.

Photo: NASA Goddard Space Flight Center | Flickr