"A 40-year
record reveals
gradual Antarctic
sea ice increases
followed by
decreases
at rates
far exceeding
the rates seen
in the Arctic"
by Claire, L. Parkinson
2019
PNAS,
DOI: 10.1073/pnas.1906556116
First published July 1, 2019
Antarctica is already 3.5km high,
and the size of South America,
an ocean above ground.
The snow increase can be seen
easily from satellite data,
but no one seems to want
to talk about Antarctica growing,
just about seas ice which
really doesn’t matter.
Sea ice occupies about 7%
of the surface area of our planet
The sea ice thickness,
and the fraction of open water
within the ice pack can vary
rapidly in response to
weather and climate.
The mainstream media
failed to report the news
about Arctic sea ice extent,
where the summer minimum
has been roughly the same
for a dozen years.
Of course this blog
covered that news:
SUMMARY:
Antarctica sea ice extent
reached a record high
(since 1979)
of 12.8 × 106 km2 in 2014
2014: Highest sea ice extent since 1979
2017: Lowest sea ice extent since 1979
2018 / 2019: More sea ice than in 2017 / 2018
1979 to 2019: Overall rising sea ice extent trend
An unexpected, decades-long
overall increase in Antarctic
sea ice extent, peaking in 2014,
has reversed, from relatively
gradual increases to
rapid decreases.
The yearly averages for 2017
and 2018 are the lowest
in the entire 1979–2018
satellite record,
reversing 35 years
of growth in just 3 years.
We have a 40-year
multichannel
passive-microwave
satellite record
of the Antarctic
sea ice cover, in the
Southern Ocean.
DETAILS:
The purpose of this paper
is to present that record
both for the Southern Ocean
as a whole (labeled “Southern
Hemisphere” to emphasize
the inclusion of the entire
hemispheric sea ice cover).
The Southern Ocean
was split into five sectors:
Sea ice spreads over vast areas,
reflects solar radiation and
restricts ocean atmosphere
heat exchanges.
The rates of decrease in 2014 to 2017
far exceeded the widely publicized
decay rates in the Arctic.
In the 40-year record, 2017
had the lowest yearly average
and February 2017
was the record low month.
Antarctic sea ice extents
reached a record high of
12.8 × 106 km2 in 2014,
followed by a decline to 2017
of 10.7 × 106 km2.
It took the Arctic sea ice cover
a full 3 decades to register a loss
that great in yearly average
sea ice extents.
Considering the 40-year record,
Antarctic sea ice continues
to have a positive overall trend
in yearly average ice extents,
although at 11,300 ± 5,300 km2.,
this trend is only 50% of the trend
for 1979–2014, before the decline.
Four of the five sectors
also have 40-year positive trends
that are well reduced
from their 2014–2017 values.
The Bellingshausen / Amundsen Seas
sector has a 40-year negative trend,
with the yearly average ice extents
decreasing in the first 3 decades,
reaching a low in 2007, and
having an overall upward trend
since 2007.
Since the late 1990s,
the Arctic sea ice cover
has been decreasing,
including rising atmospheric
temperatures, melting land ice,
thawing permafrost, longer
growing seasons, increased
coastal erosion, and
warming oceans.
Arctic behavior
was consistent with
a warming climate
from increases
in greenhouse gases.
The Antarctic sea ice extent
increased overall for much
of the period since 1978,
inconsistent with a warming
climate from increases
in greenhouse gases.
The fast decline from 2014 to 2017,
which reversed from 2017
to 2018, also does not match
the expected pattern from
greenhouse gas warming.
There is no consensus view of why
Antarctica sea ice extent
has changed so much in three years.
There was also
a rapid decline
in the mid-1970s,
and then uneven but
overall gradual increases
in Antarctic sea ice coverage
in the intervening decades.
From NSIDC today:
"Sparse satellite data
from the 1960s
indicate large swings
in that decade
as well."
"Previous studies have attributed
the onset of the recent decline
as a response to a series
of intense storms."
"Unlike Arctic sea ice extent,
which evinces a longterm
downward trend, Antarctic
sea ice extent displays
enormous variability that is
natural for the southern sea
ice system."
"Thus, a clear
climate-related
signal cannot
yet be discerned
for sea ice in the
southern hemisphere."
QUOTES FROM STUDY:
“The ice covers
of each of the 5 sectors,
and of the Southern Ocean
as a whole, have experienced
considerable inter-annual variability
over the past 40 years."
"In fact, the Southern Ocean
and 4 of the 5 sectors
(all except the Ross Sea)
have each experienced at least
one period since 1999 when
the yearly average ice extents
decreased for 3 or more
straight years
only to rebound again afterward
and eventually reach levels
exceeding the extent preceding
the 3 years of decreases."
"This illustrates that the ice
decreases since 2014
are no assurance that the
1979–2014 overall positive trend
in Southern Ocean ice extents
has reversed to a long-term
negative trend."
"Only time and an extended
observational record will reveal
whether the small increase
in yearly average ice extents
from 2017 to 2018 is a blip
in a long-term downward trend
or the start of a rebound."
"Still, irrespective of what happens
in the future, the 2014–2017
ice extent decreases
were quite remarkable
compared not only with the rest
of the 40-year Antarctic record
but with the Arctic record as well.”
