What we see is no sign
of any reversal at all. The gross mass
is just as likely to be continuing its decline and the delta heat entering the
Arctic could well be simply less effective because of position. We do not know.
I am not sure just what
reverses this process, but all historical data says that it will. I am hopeful that this means centuries. However the excess in the Antarctic speaks
loudly to the nature of a switch.
It may well entail a
massive down ward dump of cold water into the Deep that enters the atlantic and
alters the flows.
Arctic Sea Ice Update:
Unlikely To Break Records, But Continuing Downward Trend
by Staff Writers
Washington DC (SPX) Aug 26, 2013
The
melting of sea ice in the Arctic is well on its way toward its annual
"minimum," that time when the floating ice cap covers less of the
Arctic Ocean than at any other period during the year.
While
the ice will continue to shrink until around mid-September, it is unlikely that
this year's summer low will break a new record. Still, this year's melt rates
are in line with the sustained decline of the Arctic ice cover observed by NASA
and other satellites over the last several decades.
"Even
if this year ends up being the sixth- or seventh-lowest extent, what matters is
that the 10 lowest extents recorded have happened during the last 10
years," said Walt Meier, a glaciologist with NASA's Goddard Space Flight
Center in Greenbelt, Md. "The long-term trend is strongly downward."
The
icy cover of the Arctic Ocean was measured at 2.25 million square miles (5.83
million square kilometers) on Aug. 21. For comparison, the smallest Arctic sea
ice extent on record for this date, recorded in 2012, was 1.67 million square
miles (4.34 million square kilometers), and the largest recorded for this date
was in 1996, when ice covered 3.16 millions square miles (8.2 million square
kilometers) of the Arctic Ocean.
Watching
the summertime dynamics of the Arctic ice cap has gained considerable attention
in recent years as the size of the minimum extent has been diminishing -
rapidly. On Sept.16, 2012, Arctic sea ice reached its smallest extent ever
recorded by satellites at 1.32 million square miles (3.41 million square
kilometers). That is about half the size of the average extent from 1979 to
2010.
Sea
ice extent is a measurement of the area of the Arctic Ocean where ice covers at
least 15 percent of the ocean surface. For additional information about the
evolution of the sea ice cover, scientists also study the sea ice
"area," which discards regions of open water among ice floes and only
takes into account the parts of the Arctic Ocean completely covered by ice. On
Aug. 21, 2013, the Arctic sea ice area was 1.98 million square miles (5.12
million square kilometers).
This
year's melting season included a fast retreat of the sea ice during the first
half of July. But low atmospheric pressures and clouds over the central Arctic
kept temperatures up north cooler than average, slowing down the plunge.
With
about three weeks of melting left, the summer minimum in 2013 is unlikely to be
a record low, said Joey Comiso, senior scientist at Goddard and coordinating
lead author of the Cryosphere Observations chapter of the upcoming report of the
Intergovernmental Panel on Climate Change.
"But
average temperatures in the Arctic fluctuate from one week to another, and the
occurrence of a powerful storm in August, as happened in 2012, could cause the
current rate of decline to change significantly," Comiso said.
This
year, the Arctic has witnessed a few summer storms, but none of them as intense
as the cyclone that took place in August 2012.
"Last
year's storm went across an area of open water and mixed the smaller pieces of
ice with the relatively warm water, so it melted very rapidly," Meier
said. "This year, the storms hit in an area of more consolidated ice. The
storms this year were more typical summer storms; last year's was the unusual
one."
The
Arctic sea ice cap has significantly thinned over the past decade and is now
very vulnerable to melt, Comiso said. The multiyear ice cover, consisting of
thicker sea ice that has survived at least two summers, has declined at an even
faster rate than younger, thinner ice.
Meier
said that a thinner, seasonal ice cover might behave more erratically in the
summer than multiyear ice.
"First-year
ice has a thickness that is borderline: It can melt or not depending on how
warm the summer temperatures are, the prevailing winds, etcetera," Meier
said. "This year's conditions weren't super-favorable for losing ice
throughout spring and summer; last year they were. Whereas with multiyear ice,
it takes unusual warm conditions to melt it, which is what we've seen in the
most recent years."
On
the opposite side of the planet, Antarctic sea ice, which is in the midst of
its yearly growing cycle, is heading toward the largest extent on record,
having reached 7.45 million square miles (19.3 million square kilometers) on
Aug. 21. In 2012, the extent of Antarctic sea ice for the same date was 7.08
million square miles (18.33 million square kilometers).
The
phenomenon, which appears counter-intuitive but reflects the differences in
environment and climate between the Arctic and Antarctica, is currently the
subject of many research studies. Still, the rate at which the Arctic is losing
sea ice surpasses the speed at which Antarctic sea ice is expanding.
The
sea ice minimum extent analysis produced at Goddard - one of many
satellite-based scientific analyses of sea ice cover - is compiled from passive
microwave data from NASA's Nimbus-7 satellite, which operated from late October
1978 to August 1987, and the U.S. Department of Defense's Defense
Meteorological Satellite Program, which has been used to extend the Nimbus 7
sea ice record onwards from August 1987.
The
record, which began in November 1978, shows an overall downward trend of 14.1
percent per decade in the size of the minimum summer extent, a decline that
accelerated after 2007.
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