Frozen Planet: the climate science top six
- 09 Dec 2011, 17:00
- Ros Donald
The BBC's landmark series Frozen Planet ended yesterday with a
stark exploration of the effects of climate change already apparent
in the Arctic and Antarctic, where warming is occurring twice
as fast as it is in the rest of the world. Here's our rundown of
six scientific concepts covered in the episode.
1. First, Attenborough says sea ice thickness has
halved since the 1980s and Arctic sea ice extent has reduced. We're
now able to judge how far Arctic sea ice thickness has reduced,
Attenborough says, because the Russian government has allowed
access to data collected by submarine crews during the Cold
War.
Studies show that since the 1970s summer Arctic sea ice extent has
decreased by nearly a third, the average Arctic sea ice
thickness at the end of the melt season has roughly halved since
the 1980s, and that the Arctic Ocean could be
ice-free in the summer months within 30 years.
The National Snow and Ice Data Center's arctic sea ice news and
analysis page estimates that average Arctic sea ice extent for
November 2011 was 502,000 square miles below the 1979-2000 average.
The article recommends a paper by Cohen
and Jones which attempted to produce a more accurate index for
winter predictions as further reading, so we shall do the same.
2. All this has got to be good news for
somebody. And it is: according to Attenborough, trans-Arctic
summertime shipping lanes are likely to open up over the next few
decades, cutting journey time between Europe and Asia.
Climate blogger
Tamino, who uses figures on Arctic sea ice from the National
Snow and Ice Data Center (NSIDC), notes that the downward trend in
sea ice extent continues, and notes: "It's bad luck … that the
trend continues. It's because of global warming, and that's bad.
For all of us."
Another paper by
Kinnard et al, which we look at in more depth
here, found that the decline in Arctic sea ice over the last
few decades is "unprecedented" over the last 1450 years. This kind
of data provides evidence for the so-called 'Arctic
amplification' effect Attenborough mentioned at the beginning,
confirming climate model simulations that project temperatures will
rise at double the global average in the Arctic.
3. Next, the melting of the Greenland Ice Sheet.
Cue stunning shots of sapphire-blue lakes of melt water in the
second-largest ice mass on the planet - six times the size of the
UK. New satellite data, which we wrote about
here, shows the Greenland ice sheet lost mass at the edges over
the past decade.
During the episode, Attenborough met
Aberystwyth University glaciologist Alun Hubbard on the ice
sheet. According to the university's Greenland ice sheet website,
the sheet is losing mass in three ways:
"1) through direct melt of the ice due
to increased solar radiation; 2) through increased calving of
icebergs into the ocean due to warm ocean currents; and 3) by
dynamic thinning of the ice sheet [thinning of the ice sheet due to
acceleration of the ice sheet's outlet glaciers]."
We see Hubbard observing part of the dynamic thinning phenomenon
- during summer, the meltwater lakes overflow into rivers, which
eventually "plunge through the ice sheet via vertical pipes calles
moulins."
Glaciologists believe water lubricates the bed of the ice sheet,
causing it to slide - transporting it to warmer, lower locations
until it's "lost to the sea". According to the Aberystwyth
University site: "As the ice sheet extends it becomes thinner,
hence the term dynamic thinning."
Although the sheet has lost mass overall, it's hard to make 'big
picture' assessments of the ice sheet's health, because ice loss
varies from area to area, meaning that regional climate conditions
strongly affect the ice sheet. A recent study
of three Greenland glaciers, for example, showed vastly different
rates of ice loss over the last decade.
4. The programme also documents glacier retreat
in South Georgia. As Attenborough
writes in the Radio Times:
"I first went to South Georgia, the
mountainous, glacier-draped island just north of the Antarctic
Circle, in 1988. At that time, the Cook Glacier that flows down to
St Andrew's Bay reached the waterline. Last year, a Frozen Planet
team discovered that the glacier had retreated by 400 metres."
The blog
Glacierchange documents the retreat of two South Georgian
glaciers. Interestingly, the retreat is affecting the local
wildlife. This
paper estimates 97 per cent of 103 South Georgian glaciers have
retreated since records began, leading to the depletion in numbers
of "ground nesting birds" such as penguins and the spread of
rats.
5. The programme also observes thatpenguin
populations are reacting to glacier retreat in different ways.
Attenborough writes:
"the [St Andrew's] Bay's king penguin colony now has far more
beach front and is thriving as a result."Further south, however,
another species of penguin - the Adélie - is suffering. The
southern part of the Antarctic Peninsula where they once flourished
is now the most rapidly warming region in the whole of the southern
hemisphere."
Scientists have linked trends
in Adélie penguin abundance with the amount of krill available.
As the sea warms around the Arctic Peninsula Adélies' habitat,
krill - an ice-loving species - biomass is decreasing, having a
knock-on effect on the penguins' numbers. Colonies Attenborough
visited in 1992 have now disappeared altogether.
6. The loss of thousands of kilometers of the
permanent ice shelf around the Antarctic Peninsula provides some
amazing footage. According to a briefing by the
British Antarctic Survey that looks at The Antarctic
Peninsula's retreating ice shelves, since the 1950s, a total of
25,000 km2 of ice shelf has been lost from around the Antarctic
Peninsula as the amount of meltwater reaching them becomes too
great for them to tolerate. According to the survey:
"The breakout in March 2008 of the
Wilkins Ice Shelf on the Antarctic Peninsula is the latest drama in
a region that has experienced unprecedented warming over the last
50 years. In the past 30 years seven floating ice shelves
retreated, with very little of their area now remaining."
Accelerated melting is likely to contribute to sea level rise.
As Attenborough writes:
"This collapse is only the most recent
in a wave of similar events that have travelled southwards down the
peninsula. Next in line could be some of the ice shelves that act
as plugs for the immense body of ice lying on the continent itself.
If any of these collapse, vast quantities of land ice and
melt-water will slide into the sea and cause a major rise in sea
levels around the globe."
According to a 2009 paper by Vermeer and
Rahmstorf, global temperature rises and global sea level rises
are linked. The authors project "a sea-level rise ranging from 75
to 190 cm for the period 1990-2100", although it's worth noting
there is a range of opinion amongst the scientific community on
this - a recent
paper suggested that both Antarctic and Greenland ice sheets
continuing to melt at their current melt rate could cause the
average global sea level to rise by around half a metre, while the
IPCC says 18-59cm across a range of future scenarios, although they
also note that this may well be an underestimate.