Scientist says Earth's in 'new phase' of polar melting
- 21 Nov 2011, 16:13
- Verity Payne
Jim Elliott/British Antarctic Survey/AP
According to British Antarctic Survey scientist Dr Dominic
Hodgson we are currently in "a new phase of polar
Dr Hodgson's research compared Arctic and Antarctic ice shelf
retreat over the last twelve thousand years and found that the last
few decades is the only point in that period when ice shelves have
retreated simultaneously at both poles. Ice shelves are
floating bodies of ice, ranging from fifty to several hundreds of
metres in thickness, that stick out to sea from continental ice
sheets, like the ones covering Greenland and the Antarctic.
There have been major ice shelf break-ups in both the Arctic and
Antarctic recently. The largest remaining Arctic ice shelf, the
Ward Hunt Ice Shelf on Ellesmere Island in Canada, has
spent the last decade disintegrating, releasing billions of
cubic metres of fresh water and massive icebergs into the Arctic
Ocean. Ice shelves have also been observed in retreat on the
Antarctic Peninsula, with the Wilkins Ice Shelf observed to be
breaking up, and the Larsen Ice Shelf retreating
over the last decade.
Hodgson's commentary paper, published ahead of print on the
website of US journal Proceeding of the National Academy of
Sciences (PNAS), discusses a selection of recent research into
ice shelf retreat. He raises the interesting point that ice shelf
retreat has not happened in both polar regions at the same time,
according to the 12,000 year records for both Arctic and Antarctic
ice shelves which have recently retreated. In contrast, the past
few decades have seen ice shelf retreat at both poles at the same
It is this pattern, along with the enhanced regional warming
observed at the Arctic and Antarctic Peninsula, increased glacial
melting and decrease in Arctic sea ice cover that leads Hodgson to
"This first synchronous retreat of ice
shelves is significant, not because of ice shelf contributions to
global sea level, which are relatively minor, but because it is
linked to wider changes in the cryosphere, the configuration of
ocean currents, and both atmospheric and ocean temperatures."
Hodgson's thoughts echo another research paper,
written by a Swedish geologist and published earlier this year,
which reported that the current warming trend is the first instance
over the last twenty thousand years in which both hemispheres have
It is studies like these, studying records of geological climate
change, which are part of the way scientists establish that the
climate change we are currently experiencing is singular.
Unfortunately this conclusion is often lost when this sort of
science is reported. A recent example of this is the
Mail Online article which covered research looking at the
twelve thousand year history of the Ward Ice Sheet. The Mail
"Images of the Arctic ice shelf cracking
up are an icon of the damage wrought by global warming.
"But a team of researchers from the
Universite Laval in Canada have found evidence that one ice shelf
might have broken up before, 1,400 years ago - long before
industrialisation had any impact on the planet."
research found that the ice shelf grew and retreated naturally
over the 12,000 year period, and for much of the time was absent
altogether. Many Antarctic ice shelves show similar natural
variability over the same time period.
The suggestion that because the climate has varied in the past
the current warming trend in global average temperature must be
natural is often made. But noting that something happened before
without human influence does not demonstrate that humans are not
causing it today.
The world's climate has varied in the past, for many different
reasons, some better understood than others. Over geological
timescales, factors such as sun brightness, changes in the Earth's
orbit, and greenhouse gas levels have all altered our climate. But
even taking these factors into account, the climate change we are
currently experiencing is singular and
cannot be explained from natural variation alone - a human
influence must be involved.