Climate fact check: Polar sea ice is in decline. So why are people claiming that it's increasing?

  • 21 Dec 2011, 15:30
  • Verity Payne

Christopher Booker, journalist and notoriously inaccurate climate pundit, has provided us with a nice new method of cherrypicking data - ignore half of the planet!

First, let's note a few things. The Earth has two polar regions - the Arctic, and the Antarctic. In each, there is sea ice, which floats on water, and ice sheets, which sit on land.

The total amount of sea ice in the world appears to be in decline. In the Arctic there has been a very rapid decline in sea ice over the past few years, particularly in the summer. (Sea ice grows and shrinks seasonally).

Both of the big ice sheets on the planet - Greenland and Antarctica - are losing ice, and recently this ice loss has been speeding up. Overall, scientists believe that current global ice loss is indicative of man-made climate change.

Meanwhile, in his Sunday Telegraph column Booker is still trying to whip up outrage about the BBC's documentary series 'Frozen Planet'. Over the weekend he argued that the programme had misrepresented the speed at which 'ice is melting at the poles'.

Booker writes that Frozen Planet contained:

"a much more serious misrepresentation - of the speed at which ice is melting at the poles... as anyone can see, from satellite-based charts on the Cryosphere Today website, the extent of polar sea ice was last year 1.6 million square kilometres greater than its average over the last 30 years - something which could never have been guessed from Attenborough's dramatic film sequences..."

In fact, Booker is wrong. It could be a case of dodgy subediting, but given his past writings about climate change, it's more likely that he is twisting data to keep his campaign against Frozen Planet going.

To check his claim, we tried to find the chart he refers to. He doesn't reference his column, but there is a Cryosphere Today graph showing 'global sea ice area', so we checked his statement against that.

The graph shows the total area of the globe covered by sea ice over the last thirty years (blue line). The red line shows the sea ice 'anomaly' - how much the measured sea ice area varies from the average sea ice area, calculated between 1979 and the present day. If Booker was right that 'the extent of polar sea ice was last year 1.6 million square kilometres greater than its average' this red line would have gone above 1.6 on the vertical axis last year.

CT global sea ice area

Source: Cryosphere Today

As you can see, it didn't. Global sea ice has been consistently below average since mid-2010 and hasn't been 1.6 million square kilometres above average since either 1996 or 1988. So Booker is clearly wrong, and this can't be the graph he is referring to.

In fact, it's not too difficult to work out how Booker is misrepresenting scientific data in this case. Here, you can see that the Antarctic sea ice was around 1.6 million square kilometres above average in 2010:

CT Antarctic sea ice area

Source: Cryosphere Today

This is obviously Booker's source. So where he claims to be talking about 'polar sea ice', he is in fact cherrypicking measurements of the Antarctic sea ice, and ignoring half of the planet!

So why is Antarctic sea ice on the increase?

Antarctic sea ice has been increasing since satellite records began in 1979. At the same time the southern ocean has been warming up. Scientists believe that despite the warmer ocean, sea ice in the Antarctic is increasing because of changes in how heat circulates in the ocean and changes in the atmosphere caused by ozone loss above Antarctica.

Arctic sea ice is in decline

The Arctic is a very different story and pretty clear-cut: Satellite records over the last three decades show an overall decline in sea ice extent, a decline which has accelerated over the last few years, faster than projected by the IPCC's latest report. Recent research found that the current loss of sea ice in the Arctic seems to be unprecedented for the past 1,450 years.

The Greenland and Antarctic ice sheets are also losing mass

Most of the freshwater held at the poles is contained within the two vast ice sheets that cover polar land masses - compared to these, sea ice is a small part of the story.

The amount of ice in the Arctic's ice sheet, covering much of Greenland, has been calculated in a number of ways. Combined, these techniques show that since 1958 the mass of Greenland's ice sheet has fluctuated, but from the 1990's onwards ice loss has increased, and accelerated between 2002 and 2009. The mass loss varies in different parts of the ice sheet, with the ice sheet thickening slightly in the middle, while the ice sheet's edges are thinning as glaciers accelerate, discharging ice and meltwater into the sea.

There's a similar picture with the Antarctic ice sheet. Early observations suggested that most ice loss was occurring in Western Antarctica, while Eastern Antarctica was thought to be pretty stable. However, more recent research suggested that Eastern Antarctica is also losing ice, and it seems that ice loss from the Antarctic ice sheet has also been accelerating over the last ten years.

Conclusion: Earth may be in a new phase of polar melting

Scientists are beginning to suggest that we have entered a new phase in polar melting. Geological evidence shows that the current melting is the first time in 12,000 years that ice shelves (floating bodies of ice that stick out to sea from ice sheets) have been retreating at both poles simultaneously.

You don't have to wade through the scientific literature to get a good idea of what is going on at the poles - there are some very accessible internet resources to keep the public up to date with the latest changes in polar ice cover. These include the excellent National Snow and Ice Data Center (NSIDC) website, and Cryosphere Today.

It's only by considering sea and land ice in both hemispheres can we get a full picture of how the planet is responsing to global warming. Picking one convenient fact and ignoring everything else doesn't give an accurate picture.

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