new study published online by the journalNature this week has
found that the decline in Arctic sea ice over the last few decades
is "unprecedented" over the last 1450 years.
Since the advent of satellite monitoring at the end of the 1970s
it has been clear that Arctic sea ice is declining, losing around
3% of its area per decade over the last thirty years. This loss
has been particularly extreme in the summer months - the September
minimum in sea ice extent is decreasing at around 12% per
decade. This has been accompanied by the sea ice becoming thinner, along
with a decrease
in older ice reserves.
These sorts of changes have concerned scientists, and provide
evidence for the so-called 'Arctic
amplification' effect projected by climate models
simulations where temperatures are expected to rise at about double
the global average in the Arctic.
But the small number of long-term records of changes to Arctic
sea ice have meant that up until now it has been difficult to
determine whether the sea ice is fluctuating naturally, or if, as
scientists suspect, the current ice loss is unusual.
Now an international team of scientists have produced a record
of Arctic sea ice change which spans the last 1450 years, using
data from ice cores, tree ring records, lake sediments and
The researchers have found that there have been some occasions
over the last 1450 years when Arctic sea ice has retreated at a
similar pace to the current ice loss, but the decline in ice on
these occasions has never reached the volume of ice lost over the
last few decades. As the researchers put it:
"...Both the duration and magnitude of
the current decline in sea ice seem to be unprecedented for the
past 1,450 years."
The records do become more sparse with age, meaning that
a greater uncertainty range surrounds the older part of the
Arctic sea ice record, particularly before the sixteenth
century. However, the current decline is well beyond this
The findings have led the study's authors to declare the recent
Arctic ice loss "unparalleled", and to link it with rising global
average temperature caused by man-made greenhouse gases. The paper
"These results reinforce the assertion
that sea ice is an active component of Arctic climate variability
and that the recent decrease in summer Arctic sea ice is consistent
with anthropogenically forced warming."
Christophe Kinnard, a geographer from Centro de Estudios
Avanzados en Zonas Aridas in La Serena, Chile and one of the
"This drastic and continuous decrease
[in Arctic sea ice] we've been seeing from the satellites does seem
to be anomalous... It does point to a continuation of this trend in
The paper comes soon after a British Antarctic Survey scientist
suggested we are entering a
'new phase' of polar melting, as polar ice shelf retreat over
the last few decades is the first occasion over the last twelve
thousand years that ice shelves have retreated at both poles.
Earlier this year another paper
reported that the current warming trend is the first instance over
the last twenty thousand years in which both hemispheres have
All of these findings add weight to the increasingly inevitable
conclusion that natural variation alone simply cannot explain the
physical changes going on around us.