New scientific study - Arctic sea ice decline 'unprecedented'

  • 24 Nov 2011, 14:06
  • Verity Payne

A 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 historical evidence.

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 uncertainty range.

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 says:

"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 study's authors says:

"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 future."

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 warmed simultaneously.

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.


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