Climate Change in the Arctic - The Changing Arctic Environment: The Arctic Messenger - page 229

ice but ride up on top and break it with their own weight. The Kigoriak made it through
the Prince of Wales Strait to the Beaufort Sea unscathed, but a propeller of the Sir John
Franklin was knocked out of action and it had to be escorted to safety.
The crews on the Kigoriak and the Sir John Franklin could never have imagined that
only 30 years later, summer cruise ships would sail unescorted through the Prince of Wales
Strait. Historically, the geographical extent of Arctic sea ice expanded in the winter and
retreated in summer, leaving a core of multiyear ice roughly at the highest latitudes. Since
1979, which coincidentally was when satellite observations became available, the size of
the seasonal sea ice minimum has been declining at a rate of about 13% per decade and
much less ice now survives for more than one or two years. To be technically correct and
using the terminology of the National Snow and Ice Data Centre (NSIDC), I should say
that the linear trend of decline since 1979 relative to the 1981-2010 average was −13.7% in
2013. Scientists refer to the difference between a past mean and a present mean for a par-
ticular parameter (such as mean global temperature) as an anomaly. The anomaly relative
to the 1981-2010 average was −44% in 2012. Current projections tell us we can expect to
see an Arctic Ocean without summer ice somewhere between 2030 and 2050. (See Figure
10.1 . )