Newsgroup: it.politica.internazionale
Titolo: Clima. Superato il punto di non-ritorno?

http://news.independent.co.uk/world/science_technology/article312997.ece
Global warming 'past the point of no return'
By Steve Connor, Science Editor
A record loss of sea ice in the Arctic this summer has convinced
scientists that the northern hemisphere may have crossed a critical
threshold beyond which the climate may never recover.
Scientists fear that the Arctic has now entered an irreversible phase
of warming which will accelerate the loss of the polar sea ice that
has helped to keep the climate stable for thousands of years.
They believe global warming is melting Arctic ice so rapidly that the
region is beginning to absorb more heat from the sun, causing the ice
to melt still further and so reinforcing a vicious cycle of melting
and heating.
The greatest fear is that the Arctic has reached a "tipping point"
beyond which nothing can reverse the continual loss of sea ice and
with it the massive land glaciers of Greenland, which will raise sea
levels dramatically.
Satellites monitoring the Arctic have found that the extent of the sea
ice this August has reached its lowest monthly point on record,
dipping an unprecedented 18.2 per cent below the long-term average.
Experts believe that such a loss of Arctic sea ice in summer has not
occurred in hundreds and possibly thousands of years.
It is the fourth year in a row that the sea ice in August has fallen
below the monthly downward trend - a clear sign that melting has
accelerated.
Scientists are now preparing to report a record loss of Arctic sea ice
for September, when the surface area covered by the ice traditionally
reaches its minimum extent at the end of the summer melting period.
Sea ice naturally melts in summer and reforms in winter but for the
first time on record this annual rebound did not occur last winter
when the ice of the Arctic failed to recover significantly.
Arctic specialists at the US National Snow and Ice Data Centre at
Colorado University, who have documented the gradual loss of polar sea
ice since 1978, believe that a more dramatic melt began about four
years ago.
In September 2002 the sea ice coverage of the Arctic reached its
lowest level in recorded history.
Such lows have normally been followed the next year by a rebound to
more normal levels, but this did not occur in the summers of either
2003 or 2004.
This summer has been even worse.
The surface area covered by sea ice was at a record monthly minimum
for each of the summer months - June, July and now August.
Scientists analysing the latest satellite data for September - the
traditional minimum extent for each summer - are preparing to announce
a significant shift in the stability of the Arctic sea ice, the
northern hemisphere's major "heat sink" that moderates climatic
extremes.
"The changes we've seen in the Arctic over the past few decades are
nothing short of remarkable," said Mark Serreze, one of the scientists
at the Snow and Ice Data Centre who monitor Arctic sea ice.
Scientists at the data centre are bracing themselves for the 2005
annual minimum, which is expected to be reached in mid-September, when
another record loss is forecast.
A major announcement is scheduled for 20 September.
"It looks like we're going to exceed it or be real close one way or
the other. It is probably going to be at least as comparable to
September 2002," Dr Serreze said.
"This will be four Septembers in a row that we've seen a downward
trend. The feeling is we are reaching a tipping point or threshold
beyond which sea ice will not recover."
The extent of the sea ice in September is the most valuable indicator
of its health.
This year's record melt means that more of the long-term ice formed
over many winters - so called multi-year ice - has disappeared than at
any time in recorded history.
Sea ice floats on the surface of the Arctic Ocean and its neighbouring
seas and normally covers an area of some 7 million square kilometres
(2.4 million square miles) during September - about the size of
Australia.
However, in September 2002, this dwindled to about 2 million square
miles - 16 per cent below average.
Sea ice data for August closely mirrors that for September and last
month's record low - 18.2 per cent below the monthly average -
strongly suggests that this September will see the smallest coverage
of Arctic sea ice ever recorded.
As more and more sea ice is lost during the summer, greater expanses
of open ocean are exposed to the sun which increases the rate at which
heat is absorbed in the Arctic region, Dr Serreze said.
Sea ice reflects up to 80 per cent of sunlight hitting it but this
"albedo effect" is mostly lost when the sea is uncovered.
"We've exposed all this dark ocean to the sun's heat so that the
overall heat content increases," he explained.
Current computer models suggest that the Arctic will be entirely
ice-free during summer by the year 2070 but some scientists now
believe that even this dire prediction may be over-optimistic, said
Professor Peter Wadhams, an Arctic ice specialist at Cambridge
University.
"When the ice becomes so thin it breaks up mechanically rather than
thermodynamically. So these predictions may well be on the
over-optimistic side," he said.
As the sea ice melts, and more of the sun's energy is absorbed by the
exposed ocean, a positive feedback is created leading to the loss of
yet more ice, Professor Wadhams said.
"If anything we may be underestimating the dangers. The computer
models may not take into account collaborative positive feedback," he
said.
Sea ice keeps a cap on frigid water, keeping it cold and protecting it
from heating up.
Losing the sea ice of the Arctic is likely to have major repercussions
for the climate, he said.
"There could be dramatic changes to the climate of the northern region
due to the creation of a vast expanse of open water where there was
once effectively land," Professor Wadhams said.
"You're essentially changing land into ocean and the creation of a
huge area of open ocean where there was once land will have a very big
impact on other climate parameters," he said.

 impact on other climate parameters," he said.
Stavo per postarlo stammattina, ma ho pensato che fosse troppo lungo e 
terrificante. Per riassumere: i poli si stanno sciogliendo in modo 
esponenziale, e non esisteranno piu' tra due generazioni.
A me sembra la notizia piu' importante del secolo. Stiamo perdendo due 
continenti, e continuiamo con  le nostre ca**ate come se niente fosse.
Am.
PS Il Mediterraneo e' relativamente protetto, ma l'Inghilterra del Sud 
Est, no, perche' regge solo con terrapieni ed idrovore.
Andra' tutto sott'acqua. Spero che Blair e successori si diano una mossa.
Shalom, come dici.

 Est, no, perche' regge solo con terrapieni ed idrovore.
????
Protetto da che? Dal livello delle acque?
Se dovessero aumentare, il mediterraneo crescerebbe come
tutti gli altri. In realtà c'è chi pensa che le acque si potrebbero ritirare
per la dispersione (o utilizzo) dei gas idrati.
Ciao! 

 threshold beyond which the climate may never recover.
Forse e' per questo.  Brrrrr.....
http://www.commondreams.org/headlines04/1011-01.htm
Climate Fear as Carbon Levels Soar
Scientists bewildered by sharp rise of CO2 in atmosphere for second
year running
by Paul Brown
An unexplained and unprecedented rise in carbon dioxide in the
atmosphere two years running has raised fears that the world may be on
the brink of runaway global warming.
Scientists are baffled why the quantity of the main greenhouse gas has
leapt in a two-year period and are concerned that the Earth's natural
systems are no longer able to absorb as much as in the past.
The findings will be discussed tomorrow by the government's chief
scientist, Dr David King, at the annual Greenpeace business lecture.
Measurements of CO2 in the atmosphere have been continuous for almost
50 years at Mauna Loa Observatory, 12,000ft up a mountain in Hawaii,
regarded as far enough away from any carbon dioxide source to be a
reliable measuring point.
In recent decades CO2 increased on average by 1.5 parts per million
(ppm) a year because of the amount of oil, coal and gas burnt, but has
now jumped to more than 2 ppm in 2002 and 2003.
Above or below average rises in CO2 levels in the atmosphere have been
explained in the past by natural events.
When the Pacific warms up during El Niño - a disruptive weather
pattern caused by weakening trade winds - the amount of carbon dioxide
rises dramatically because warm oceans emit CO2 rather than absorb it.
But scientists are puzzled because over the past two years, when the
increases have been 2.08 ppm and 2.54 ppm respectively, there has been
no El Niño.
Charles Keeling, the man who began the observations in 1958 as a young
climate scientist, is now 74 and still working in the field.
He said yesterday: "The rise in the annual rate to above two parts per
million for two consecutive years is a real phenomenon.
"It is possible that this is merely a reflection of natural events
like previous peaks in the rate, but it is also possible that it is
the beginning of a natural process unprecedented in the record."
Analysts stress that it is too early to draw any long-term
conclusions.
But the fear held by some scientists is that the greater than normal
rises in C02 emissions mean that instead of decades to bring global
warming under control we may have only a few years. At worst, the
figures could be the first sign of the breakdown in the Earth's
natural systems for absorbing the gas.
That would herald the so-called "runaway greenhouse effect", where the
planet's soaring temperature becomes impossible to contain. As the
icecaps melt, less sunlight is reflected back into space from ice and
snow, and bare rocks begin to absorb more heat. This is already
happening.
One of the predictions made by climate scientists in the
Intergovernmental Panel on Climate Change is that as the Earth warms,
the absorption of carbon dioxide by vegetation - known as "carbon
sink" - is reduced.
Dr Keeling said since there was no sign of a dramatic increase in the
amount of fossil fuels being burnt in 2002 and 2003, the rise "could
be a weakening of the Earth's carbon sinks, associated with the world
warming, as part of a climate change feedback mechanism. It is a cause
for concern'.'
Tom Burke, visiting professor at Imperial College London, and a former
special adviser to the former Tory environment minister John Gummer,
warned: "We're watching the clock and the clock is beginning to tick
faster, like it seems to before a bomb goes off."
Peter Cox, head of the Carbon Cycle Group at the Met Office's Hadley
Center for Climate Change, said the increase in carbon dioxide was not
uniform across the globe.
Measurements of CO2 levels in Australia and at the south pole were
slightly lower, he said, so it looked as though something unusual had
occurred in the northern hemisphere.
"My guess is that there were extra forest fires in the northern
hemisphere, and particularly a very hot summer in Europe," Dr Cox
said. "This led to a die-back in vegetation and an increase in release
of carbon from the soil, rather than more growing plants taking carbon
out of the atmosphere, which is usually the case in summer."
Scientists are have dubbed the two-year CO2 rise the Mauna Loa
anomaly. Dr Cox said one of its most interesting aspects was that the
CO2 rises did not take place in El Niño years. Previously the only
figures that climbed higher than 2 ppm were El Niño years - 1973,
1988, 1994 and 1998.
The heatwave of last year that is now believed to have claimed at
least 30,000 lives across the world was so out of the ordinary that
many scientists believe it could only have been caused by global
warming.
But Dr Cox, like other scientists, is concerned that too much might be
read into two years' figures. "Five or six years on the trot would be
very difficult to explain," he said.
Dr Piers Forster, senior research fellow of the University of
Reading's Department of Meteorology, said: "If this is a rate change,
of course it will be very significant. It will be of enormous concern,
because it will imply that all our global warming predictions for the
next hundred years or so will have to be redone."
David J Hofmann of the US National Oceanic and Atmospheric
Administration centre, which also studies CO2, was more cautious.
"I don't think an increase of 2 ppm for two years in a row is highly
significant - there are climatic perturbations that can make this
occur," he said. "But the absence of a known climatic event does make
these years unusual.
"Based on those two years alone I would say it was too soon to say
that a new trend has been established, but it warrants close
scrutiny."
© Guardian Newspapers Limited 200

 
Fumateli, se non ti danno alla testa...
Am.

 Fumateli, se non ti danno alla testa...
http://www.globo.trieste.it/espo/era/era_03/camerlenghi.htm
Io non ho bisogno di fumarmi niente, perchč a differenza
di molti altri sono nato con la "spina dorsale", bamboccio!
Ciao! 

 Ciao!
#_Ce so' nato pure io co' quella, ma a me, anzi a noi, ce se piega bene...
come 'na "canna" al vento!
Il bambo[lotto-de-co]ccio, sara`lei, diremo noi!
tsik!
<G>

 come 'na "canna" al vento!
Già, questo spiegherebbe molte cose
Ciao!



No, problem. Tu sniffati il metano e vivi contento...
Am.