The condition of sea ice continues
to evolve way more quickly than any of the modelers are willing to accept. The second article argues today that the
underwater ice loss now matches or exceeds that of the surface loss. This is the first time that I have even seen
that factor acknowledged.
It was clear early on that the
ice loss observed came from a specific increase in the inflow of heat into the Arctic . It is also
reasonable to suggest that this facto is a constant that was somehow switched
on perhaps during the seventies. It made
itself known only during the last decade as the multiyear ice began to
seriously break up. That component is
now largely gone as I predicted in early 2007.
What we have now is a sea ice
mass that accumulates each year and then is partially destroyed during the summer
with any remaining ice rotating back into a high melt region for the next year.
I suspect that this configuration
will remain quite stable although with some further reduction in volume. I do not think enough heat is getting into
the Arctic for the whole to disappear or even
close.
I suspect that we are now seeing
the natural Arctic Sea Ice minima or something rather close. I base this on the observation that most
remaining multi year ice has been ground up since 2007 which jump started the
process. Replacement is not happening
while recent ice is easily broken up and is rotating over a two year
cycle. It is plausible that the heat
system is now back in balance although the amount of further loss cannot be
known at present.
Blaming the sharp losses totally on
warming Arctic waters is a likely mistake because it fails to explain the ice
loss brought on in the preceding decades.
Thus I am highly skeptical of the promoted causes, but certainly not of
the reality of decadal ice decay that is ongoing and little to do with
purported climatic variation.
Arctic sea ice is melting at its fastest pace in almost 40 years
From the
Guardian
Sep 14, 2011
http://environmentalresearchweb.org/cws/article/news/47182
Arctic sea ice has melted to a level not recorded since satellite observations started in 1972 – and almost certainly not experienced for at least 8,000 years, say polar scientists.
Arctic sea ice has melted to a level not recorded since satellite observations started in 1972 – and almost certainly not experienced for at least 8,000 years, say polar scientists.
Daily satellite sea-ice maps released by Bremen university
physicists show that with a week's more melt expected this year, the
floating ice in the Arctic covered an area of 4.24 million square
kilometres on 8 September. The previous one-day minimum was
4.27 million sq km on 17 September 2007.
The US National
Snow and Ice Data Centre (NSIDC) in Boulder, Colorado, which also
tracks the extent of sea ice, has not posted data for a week but is
expected to announce similar results in the next few days.
The German researchers said the record melt was undoubtedly because of
human-induced global warming. "The sea-ice retreat can no more be
explained with the natural variability from one year to the next, caused by
weather influence," said Georg
Heygster, head of the Institute of Environmental Physics at Bremen
"It seems to be clear that this is a further consequence of the
man-made global warming with global consequences. Climate models show that the
reduction is related to the man-made global warming, which, due to the albedo
effect, is particularly pronounced in the Arctic ,"
he said. The albedo effect is related to a surface's reflecting power – whiter
sea ice reflects more of the Sun's heat back into space than darker seawater,
which absorbs the Sun's heat and gets warmer.
Floating Arctic sea ice naturally melts and re-freezes annually, but
the speed of change in a generation has shocked scientists – it is now twice as
great as it was in 1972, according to the NSIDC, with a decline of about 10%
per decade.
Arctic temperatures have risen more than twice as fast as the global
average over the past half century.
Separate, less reliable, research suggests that Arctic ice is in a
downward spiral, declining in area but also thinning. Using records of air,
wind and sea temperature, scientists from thePolar Science Centre of the
University of Washington, Seattle, announced last week that the Arctic
sea-ice volume reached its lowest ever level in 2010 and was on course to set
more records this year.
The new data suggests that the volume of sea ice last month appeared to
be about 2,135 cubic miles – just half the average volume and 62% lower
than the maximum volume of ice that covered the Arctic in 1979. The research
will be published in aforthcoming
issue of the Journal of Geophysical Research.
"Ice volume is now plunging faster than it did at the same time
last year when the record was set," said Axel Schweiger.
If current trends continue, a largely ice-free Arctic in the summer
months is likely within 30 years – that is up to 40 years earlier
than was anticipated in the last Intergovernmental Panel on Climate Change (IPCC)
assessment report.
The last time the Arctic was
uncontestably free of summertime ice was 125,000 years ago, at the height of
the last major interglacial period, known as the Eemian.
"This stunning loss of Arctic sea ice is yet another wake-up callthat
climate change is here now and is having devastating effects around the
world," Shaye
Wolf, climate science director at the Centre for Biological
Diversity in San Francisco told journalists.
Arctic ice plays a critical role in regulating Earth's climate by
reflecting sunlight and keeping the polar region cool. Retreating summer sea
ice is widely described by scientists as both a measure and a driver of global
warming, with negative impacts on a local and planetary scale.
This year, both the North-west and North-east passages were mostly ice
free, as they have been twice since 2008.
The north-east sea route, which links the Atlantic to the Pacific, is
likely to become a commercial ship operator's favourite, saving thousands of
miles and avoiding tolls on the Suez Canal
tolls.
Further evidence of dramatic change in the Arctic came last week from
Alan Hubbard, a Welsh glaciologist at Aberystwyth
University , who has been studying the
Petermann glacier in northern Greenland for several
years.
The glacier, which covers about 6% of the icecap, is 186 miles
(300 km) long and up to 3,280 ft (1 km) high. In August last
year, a 100 square-mile (260 sq km) block of ice calved from the
glacier. Photographs show that by July this year it had melted and disappeared.
"I was gobsmacked. It [was] like looking into the Grand Canyon
full of ice and coming back two years later to find it full of water,"
said Hubbard.
Last year (2010) tied with 2005 as the warmest year on record.
This article was shared by our content partner the Guardian. environmentalresearchweb is
now a member of the Guardian
Environment Network.
The 'other' Arctic sea ice melt
Reports focus on the possibility a record minimum for Arctic sea ice in
September, but a major loss during the early summer months is climatologically
more important
Clear skies allowed a largely unobstructed view of the Arctic in early July 2011. Photograph: MODIS/Terra/NASA
"Well, it's not really good timing to write about global warming
when the summer feels cold and rainy," a journalist told me last week.
Hence, at least here in Germany
Figure 1: Evolution of Arctic sea-ice extent in July and August from
1979 until 2011. (NSIDC)
A rainy summer might be one reason for an apparent lack of public
attention with respect to the ongoing sea-ice loss. Another reason, however, is
possibly the fact that we scientists have failed to make sufficiently clear
that a major loss of sea ice during the early summer months is climatologically
more important than a record minimum in September. This importance of sea-ice
evolution during the early summer months is directly related to the role of sea
ice as an efficient cooling machine: Because of its high albedo (reflectivity),
sea ice reflects most of the incoming sunlight and helps to keep the Arctic
cold throughout summer. The relative importance of this cooling is largest when
days are long and the input of solar radiation is at its maximum, which happens
at the beginning of summer. If, like this year, sea-ice extent becomes very low
already at that time, solar radiation is efficiently absorbed throughout all
summer by the unusually large areas of openwater within the Arctic Ocean . Hence, rather than being reflected by the
sea ice that used to cover these areas, the solar radiation warms the ocean
there and thus provides a heat source that can efficiently melt the remaining
sea ice from below. In turn, additional areas of open water are formed that
lead to even more absorption of solar radiation. This feedback loop, which is
often referred to as the ice-albedo feedback, also delays the formation of new
sea ice in autumn because of the accompanying surplus in oceanic heat storage.
Measurements from ice buoys show that indeed melting at the bottom of
the sea ice has increased significantly in recent years. While field
experiments that were carried out in the 20th century showed unambiguously that
surface melting used to be the dominant mechanism for the thinning of Arctic
sea ice, now in larger and larger areas melting at the underside of the ice is
almost equally important. Such melting from below is particularly efficient
since the temperature at the ice-ocean interface is fixed by the phase
equilibrium that must be maintained there. Hence, any heat provided by the
ocean to this interface will lead to thinning of the ice in summer and to
slower ice growth in winter. At the surface, the ice temperature is not fixed
as long as the ice isn't melting, and heat input from the atmosphere can in
part be compensated for by a change in surface temperature and an accompanying
change in outgoing long-wave radiation at the ice surface.
In addition to these climatological reasons, there is another reason
for why a public focus on just the September sea-ice extent is possibly
misleading: Such focus might give the impression that sea-ice extent is stable
in other seasons but summer. That this is not the case becomes obvious from the
graphical distribution of extreme sea-ice extent for each individual month that
is shown in Figure 2. The figure shows in red the years with the five lowest
values of sea-ice extent for a certain month and in blue the years with the
five highest values. A retreat of sea ice throughout the entire year is obvious.
In fact, the sea-ice extent for every month since June 2010 has been among the
five lowest values ever recorded by satellites.
###
Figure 2: Distribution of record minima and record maxima of Arctic
sea-ice extent (NSIDC).
The years with the five lowest values of sea ice extent for a certain month are
marked in red, those with the five highest values of sea-ice extent are marked
in blue. The darkness of the color indicates the ranking: the darkest red marks
the lowest value, the darkest blue the highest.
Such widespread loss of Arctic sea ice has sometimes given rise to the
concern that the total loss of Arctic sea ice at least during summer time can
no longer be avoided. In this context, usually the ice-albedo feedback is
mentioned, since it provides a mechanism that can in principle lead to a
so-called "tipping point" beyond which the loss of the remaining sea
ice becomes unstoppable. However, recent research shows that this scenario is
too pessimistic. For example, in a paper published in Geophysical Research
Letters in January 2011, Tietsche et al. [1] used
climate model simulations to examine the evolution of Arctic sea ice after an
extreme loss event. In their model simulations, they artificially removed all
Arctic sea ice at the beginning of June for selected years and examined if the
ice would recover from such extreme event.
Their main result is shown in Fig. 3: It took only about two years
after each complete sea-ice removal until the ice had recovered to roughly the
extent it had before the removal. Hence, sea ice extent is primarily defined by
the prevailing climate conditions; the ice-albedo feedback mechanism is, in
isolation, too weak to stabilize a very low sea-ice cover. In examining the
mechanisms behind this finding, Tietsche et al. found that unusually large
amounts of heat indeed accumulate in the ocean during the ice-free summer.
However, this heat is efficiently released to the cold atmosphere already
during the following autumn and winter. Once that heat release has cooled the
ocean to its freezing temperature, sea ice forms again. Because this ice is
initially very thin, the efficient release of heat from the ocean continues for
some time, causing a rapid growth of the new sea ice. Much of this ice then
survives the following summer, and sea-ice conditions can quickly return to
those before the artificial perturbation.
Figure 3: Evolution of September sea-ice extent in coupled climate
model simulations. The blue curve shows the evolution of the unperturbed
sea-ice extent for the A1B scenario, with the gray shading showing the ensemble
spread of three model runs. For the red curves, sea ice was artificially
removed at the beginning of June in 1980, 2000, 2020, 2040 and 2060 within the
climate model simulations. For all these perturbations, sea-ice extent
recovered rapidly to the unperturbed extent. A similar result was found for
sea-ice volume.
The finding that the long-term evolution of Arctic sea ice is primarily
governed by the prevailing climate conditions implies that the loss of Arctic
sea ice can still be slowed down and eventually stopped if an efficient
reduction of CO2 emissions were to become reality soon. Last week, however, it
became obvious once more how unlikely such scenario is: On 30th August, Exxon
announced a deal with Rosneft, the Russian state oil company. As part of
this deal, Exxon will invest more than US$2 billion to support Rosneft in the
exploitation of oil reserves in the Kara
Sea , which is part of the Arctic Ocean
north of Siberia . One requirement for the
success of this deal: a further retreat of Arctic sea ice. Given that climate
model simulations indeed all project such further retreat of Arctic sea ice, it
seems that at least to some degree, managers of big oil companies have started
to make business decisions based on climate-model simulations. That may be good
news. Or not.
• This article is in part based on a German article that was
published atKlimalounge.
References
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