Arctic Sea Ice Decline: Introduction - Arctic Sea Ice Decline: Observations, Projections, Mechanisms, and Implications - page 1

Arctic Sea Ice Decline: Introduction

Eric T. DeWeaver

Center for Climate Research, University of Wisconsin-Madison, Madison, Wisconsin, USA

. THE GREAT DECLINE OF 2007

minimum was unusually thin and thus vulnerable to melting
away. The July and August extent were somewhat higher
than in 2007, but the daily loss rate accelerated in early Au-
gust after storms broke apart thin ice in the Beaufort and
Chukchi seas. Southerly winds following the storms further
promoted opening by pushing the ice away from the eastern
Siberian coast (information from the “Arctic sea ice news
and analysis” Web pages for August through 4 Septem-
ber 2008 at http://www.nsidc.org).
With approxmiately 2 weeks left in the 2008 melt season,
Arctic sea ice extent is now very close to the 2007 mini-
mum. While the lack of recovery is discouraging, the 2008
loss could have been worse. In May the NSIDC suggested,
based on the prevalence of thin first year ice cover in the
Arctic, that the North Pole could become ice free in 2008, a
prediction more commonly made for the middle of the cen-
tury. Three researchers contributing to the May Sea Ice Out-
look (produced by the interagency Study of Environmental
Arctic Change (SEARCH)), anticipated a return toward the
long-term trend of summer sea ice loss, six argued that 2008
September extent should be close to 2007, and five expected
losses exceeding those in 2007.

By any measure, the loss of Arctic sea ice cover in Sep-
tember 2007 was spectacular. The National Snow and Ice
Data Center (NSIDC) called it a loss “the size of Alaska and
Texas combined,” in comparison to the 979-2000 Septem-
ber mean. Record-breaking minima in sea ice extent are not
unexpected, given the declining trend of the past 30 years
and its recent acceleration [e.g., Meier et al ., 2007; Deser
and Teng , this volume]. But the 2007 minimum was remark-
able even compared to the decline, a full four standard devi-
ations below the trend line (H. Stern, quoted by Schweiger et
al . [2008]). Kerr [2007] reported an Alaska-sized loss com-
pared to the previous record low in 2005, which was itself
an Alaska-sized retreat from the value at the beginning of the
satellite era in 979. Deser and Teng point out that the loss
between September 2006 and September 2007 is as large as
the entire September extent loss from 979 to 2006.
Following the 2007 melt season there was some cause for
optimism that 2008 could see a partial recovery. Writing at
the end of the melt season, Comiso et al . [2008, paragraph 5]
noted that the ice was “rebounding with a rapid early autumn
growth.” Following a cold winter, the April 2008 maximum
ice extent reported by NSIDC was relatively high by recent
standards, although still below the long-term mean. But
while the temperatures were cooperating, the winds were
not. In early February I. Rigor noted that buoys embedded
in multiyear ice flows were “streaming out” of the Arctic,
flushed through Fram Strait along with their ice floes by cir-
cumpolar wind anomalies [ Kizzia , 2008]. Also, as discussed
by Maslanik et al . [2007], ice cover following the 2007

2. RESEARCH ON THE CAUSE OF THE LOSS

Research on the causes of the 2007 loss is already well un-
derway. Surface wind anomalies are generally identified as
the proximal cause [ Nghiem et al ., 2007; Stroeve et al ., 2008;
Deser and Teng , this volume; Overland et al ., 2008; Zhang
et al ., 2008], as the transpolar winds dubbed the “Polar Ex-
press” by Nghiem et al. pushed ice away from the Alaskan
and eastern Siberian coastlines and out of the Arctic. Kay
et al. [2008] claim an additional role for enhanced summer
melting as high pressure and sunny skies persisted over the
western Arctic Ocean. Their claim is disputed by Schweiger
et al. [2008], who note that the sunny skies are not well col-