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Factcheck: What’s the significance of a record high in Antarctic sea ice?

  • 07 Jul 2014, 16:20
  • Roz Pidcock

Sea ice around Antarctica is growing, and it's a scientific puzzle. But while the Mail on Sunday suggests this means climate change is less of a problem than scientists say, sea ice is only part of what's going on in Antarctica, and the world as a whole is losing ice rapidly.

A record high

An  article in yesterday's Mail on Sunday carries the headline:

'Global warming computer models confounded as Antarctic sea ice hits new record high'

This follows news last week from scientists at the University of Illinois that the area covered by sea ice surrounding Antarctica hit a  record high on 29th June, with about two million square kilometres in June more ice compared to the long term average.

Antractic Sea Ice _June 2014Antarctic sea ice reached a record high in June, with 2.1 million square kilometres more than the long term average. Source: US National Snow and Ice Data Centre ( NSIDC)

Some parts of the media have chosen to put a very positive spin on the news, giving the impression climate change may not be as grim as scientists' projections after all. In the Mail on Sunday, journalist and climate skeptic David Rose says:

"The levels of Antarctic sea-ice last week hit an all-time high - confounding climate change computer models which say it should be in decline..."

A separate article by climate-skeptic blogger Andrew Montford suggests the rise in Antarctic sea ice has come as a surprise to climate scientists, and claims it's "another mishap to tarnish the credibility of climate science".

So has the sea ice growth left science in disarray, as the Mail on Sunday suggests?

Not really. Scientists are up-front about the fact that they don't fully know why Antarctic sea ice is growing, and as far as the significance of changes in sea ice goes from the point of view of climate change, a global look reveals that the planet is losing ice, fast.

Sea ice on the rise (but only in Antarctica)

Despite rapidly warm ing water, the amount of ice that floats on the Southern Ocean around Antarctica - known as sea ice - has been increasing by 1.5 per cent on average per decade since 1979. 

Scientists don't yet fully understand why. But an earlier article in Saturday's Daily Mail by Ellie Zolfagharifard does a good job of examining how in the Antarctic, warmer ocean temperatures could actually lead to more sea ice. The piece features quotes by Dr Mark Serreze, director of the National Snow and Ice Data Centre (NSIDC), who says:

"Scientists believe the shift is caused by water melting from beneath the Antarctic ice shelves and refreezing back on the surface."

But that's just one explanation. A piece in Saturday's Times gives a good overview of other theories about how local wind patterns may be involved. For more detail, the US National Snow and Ice Data Centre have produced a useful briefing on Antarctic sea ice, here.

The world is losing ice overall

The two poles are in quite different situations. While the Antarctic is a land mass surrounded by ocean, the Arctic is an ocean with land around the outside.

Arctic Sea Ice _June 2014

Arctic sea ice is in long term decline, reaching a record low in September 2012. Source: NSIDC

In September 2012, Arctic sea ice reached its lowest extent since satellite records began in 1979. While Antarctic sea ice is growing by on average 165,000 square kilometres per decade, this is dwarfed by the loss of an average of 480,000 square kilometres per decade from the Arctic.

The Times and Saturday's Daily Mail articles both pick up on this comparison, the latter featuring a quote by polar scientist Walt Meier explaining why Antarctic ice growth is less significant a measure than declining Arctic sea ice coverage when assessing climate change. He says:

"While the Arctic has seen large decreases through the year in all sectors, the Antarctic has a very regional signal - with highs in some areas and lows in others."

In other words, there are fewer factors affecting ice behaviour in the Arctic, so what's happening there can be more directly linked to long term changes in ocean warming.

In the Mail on Sunday, Rose mentions that the Arctic is losing sea ice but doesn't say how the size of the long term trend compares to the observed gain in the Antarctic.

Montford argues that "across the globe, there are about one million square kilometres more sea ice than 35 years ago".

Right now, it's true here is about one million square kilometres more sea ice globally than the long term average, as the red line in the graph below shows.

Global Sea Ice Cover

Source: University of Illinois The Cryosphere Today

But this uptick is the result of a couple of record years for sea ice in the Antarctic - for most of the past 35 years, global sea ice has been in decline.

Scientists suggest that as temperatures rise in the Antarctic, sea ice won't be able to re-freeze quick enough to keep pace with the amount being lost from under the ice shelves - meaning Antarctic sea ice will decline and the loss in total sea ice cover will become more pronounced.

When you add in the loss of ice mass from the Greenland and Antarctic ice sheets, the earth is already losing ice overall - and that will continue with further warming.

A model challenge

Since scientists don't yet fully understand why Antarctic sea ice is growing, models haven't been able to predict the increase. Montford suggests this is "something of an embarrassment for climate modellers, making them reluctant to talk about it."

In fact, it's an area of active research for scientists, as Rose's article points out the recent report from the Intergovernmental Panel on Climate Change (IPCC) discussed the issue in great detail, concluding:

"Most models simulate a small downward trend in Antarctic sea ice extent …  in contrast to the small upward trend in observations … There is low confidence in the scientific understanding of the small observed increase in Antarctic sea ice extent due to the incomplete and competing scientific explanations for the causes of change and low confidence in estimates of natural internal variability in that region".

It's also worth noting that the rapid loss of ice in the Arctic has also occurred faster than three quarters of climate models predicted - a point also discussed in the IPCC report, but which Rose and Montford neglect to mention.

While the growth in Antarctic sea ice has scientists searching for explanations, it's only part of the picture of global sea ice - and we're not aware of any scientists who would argue that growing Antarctic sea ice offers a reason to rethink their overall scientific understanding of climate change.

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