Posts
Arctic
Sea Ice Extent Threatening a Top 5 Lowest Annual Minimum This
September
Nicholas
Humphrey,meteorologist
27
August, 2018
The
sea ice extent in the Arctic may possibly be the Top 5 record lowest
on record going back to 1979 based on current trends. Sea ice melt
has been limited in August compared to July, but given what has
already occurred, and the abnormally warm Arctic this summer (with
the exception of the very interior Arctic north of 80 N), a
September seasonal minimum in the Top 5 is certainly possible at this
point, depending on ongoing weather conditions.
Above
is Arctic Sea Ice Extent and Concentration for August 24, 2018. Note
the severe recession on the Atlantic side as well as ice retreat
north of Greenland's coast. What classifies as severe? Here's another
map, with the 1981-2010 average extent for the date.
You
can also see how severely recessed it is on the Pacific side. Record
low extents were noted earlier this year on the Pacific side for the
Bering
and
Chukchi
Seas.
On the Atlantic side, the sea ice extent *is* the lowest on record
for the combined Greenland,
Barents
and Kara
Seas. August 20th, it dropped to the lowest extent on record, which
was previously set in Sept 2017.
The
overall sea ice extent is currently following the *2010-2017*
average...which much below the 1980s or 1981-2010 normals. 2018
extent is currently the 4th lowest on record for the most recent
date, behind 2012, 2016 and 2007. The current Top 5 annual minimum
years are 2012 (record), 2016, 2007, 2015, and 2011. The minimum is
in September.
Arctic
sea ice is on a path of major declines compared to not only the
modern observational record but also paleorecords. The Kara and
Barents are currently experiencing their lowest extents in nearly a
millennium at least (1).
(Ice
thickness, along with extent is undergoing significant
decline...hence ice volume is also on major decline with 2017 having
the lowest *annual average* extent on record, with the lowest
seasonal minimum volume in 2012. The oldest ice, being the thickest,
is declining the fastest).
(7-day
mean temperature anomalies for the Arctic region ending 06 UTC
September 2nd. The drawing in of abnormally warm temperatures from
the North Atlantic and Siberian land mass will contribute to further
sea ice melt. 1981-2010 climatology).
What
This Means for Climate Change and Extreme Weather
As
the Arctic continues to tip over into a warm season ice-free state,
the increasingly continuous open blue ocean means more and more heat
accumulating into the climate system. Less ice means more dark ocean
absorbing more heat from the sun in the summer, as opposed to white
ice reflecting more solar radiation back into space, which would
limit warming. The continuous ocean warming contributes to the
regional and global rise in oceanic heat content, but also means when
the polar night comes, more heat must be released back to the
atmosphere to cool the oceans sufficiently to form new sea ice. This
means progressively warmer Arctic winters, with later season new ice
formation, and ice which remains thin through the winter.
(The
very
abnormally
warm peripheral seas of the Arctic Ocean. The anomalies shown here
are relative to 1961-1990 climatology to better show the effect of
ocean warming caused by climate change).
(Global
rise in oceanic heat content in the first 2000 meters/6550 ft of the
global ocean. Approximately 93% of excess heat retained by the planet
is going into warming the oceans).
This
has been an increasing phenomenon with the later initial ice
formations and later extents in the Bering and Chukchi Seas,
including prominently in the 2017-18 winter (2). Research also
suggests that the rapidly warming Arctic (a process known as Arctic
Amplification) is contributing to a weakening of the polar jet stream
which dominates mid-latitude weather, leading to a slower and much
wavier jet stream. This means areas suffering much greater extremes
and much greater swings between extremes (3)(4).
(The
Arctic has warmed 2-3 times faster than the globe as a whole, even
faster in the "deep" Arctic...80 N+. This temperature
anomaly graph is relative to 1981-2010 climatology. The past 5 years,
the Arctic annual temperature has averaged 2.5 times warmer than the
globe at large).
Again,
the 2017-18 winter was quite prominent in displaying this
increasingly powerful phenomenon with extremes such as the abnormally
warm and dry Western US vs. the abnormally cold Great Plains.
Meanwhile the Eastern US saw record heat in February, followed by
multiple nor'easters in March (5)(6). Much of Europe had abnormally
warm temperatures early this year, but in March were hit by extreme
cold associated with the "Beast from the East", a prominent
Arctic air mass from Siberia shunted out of the Arctic as the Arctic
underwent a wintertime "heatwave" with above freezing temps
near the North Pole(7). In fact, the Arctic had its warmest winter on
record(8). Later in the season, the US Great Plains saw a major swing
in pattern, with many areas going from one of their coldest Aprils on
record to one of their hottest Mays. My city of Lincoln, NE had its
3rd coldest April on record, followed by the 4th warmest May. Records
here go back to 1887. It was also the warmest May on record for the
Continental US(9). There is evidence that the rapidly warming
Arctic is also leading to influences in the summertime atmospheric
circulation patterns in the Northern Hemisphere(10).
The
overall effects as sea ice continues to decline? Further acceleration
of global warming, Arctic amplification of regional warming, further
weakening of the jet stream circulation leading to much greater
extreme weather (temperature and rainfall vs. drought) as well as
swings between extremes. So this is a very important phenomenon we
must care about. Another impact? A rapidly warming Arctic means
accelerating releases of carbon (carbon dioxide and methane) to the
atmosphere, accelerating global warming even more(11). And loss of
sea ice, with warmer atmosphere and warmer winds would mean an
increased acceleration of ice sheet melt from Greenland, accelerating
sea level rise globally(12). Much for humanity to face in the coming
years ahead.
--Meteorologist
Nick Humphrey
References
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