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.
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:
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.