il riscaldamento globale sta avvenendo ora
- Subject: il riscaldamento globale sta avvenendo ora
- From: "Alessandro Gimona" <agimona at hotmail.com>
- Date: Mon, 27 Mar 2000 11:08:18 BST
se ce ne fosse bisogno, ecco due comunicati stampa 'scientifci' che
confermano l'urgenza di politiche volte a ridurre le emissioni di gas serra.
Le ragioni per i governi non sono mai state cosi' chiare.
NEWS FROM THE WORLDWATCH INSTITUTE
Worldwatch News Brief 00-02
MELTING OF EARTH'S ICE COVER REACHES NEW HIGH
by Lisa Mastny
The Earth's ice cover is melting in more places and at higher rates than
time since record keeping began. Reports from around the world compiled
Worldwatch Institute (see data table below) show that global ice melting
accelerated during the 1990s-which was also the warmest decade on record.
Scientists suspect that the enhanced melting is among the first observable
of human-induced global warming, caused by the unprecedented release of
dioxide and other greenhouse gases over the past century. Glaciers and
features are particularly sensitive to temperature shifts.
The Earth's ice cover acts as a protective mirror, reflecting a large
the sun's heat back into space and keeping the planet cool. Loss of the
would not only affect the global climate, but would also raise sea levels
spark regional flooding, damaging property and endangering lives.
melting would also threaten key water supplies as well as alter the
many of the world's plant and animal species.
Some of the most dramatic reports come from the polar regions, which are
warming faster than the planet as a whole and have lost large amounts of
recent decades. The Arctic sea ice, covering an area roughly the size of
United States, shrunk by an estimated 6 percent between 1978 and 1996,
average of 34,300 square kilometers-an area larger than the
The Arctic sea ice has also thinned dramatically since the 1960s and 70s.
Between this period and the mid-1990s, the average thickness dropped from
meters to 1.8 meters-a decline of nearly 40 percent in less than 30 years.
The Arctic's Greenland Ice Sheet-the largest mass of land-based ice
Antarctica, with 8 percent of the world's ice-has thinned more than a
year on average since 1993 along parts of its southern and eastern edges.
The massive Antarctic ice cover, which averages 2.3 kilometers in
represents some 91 percent of Earth's ice, is also melting. So far, most
loss has occurred along the edges of the Antarctic Peninsula, on the ice
that form when the land-based ice sheets flow into the ocean and begin to
Within the past decade, three ice shelves have fully disintegrated: the
the Larsen A, and the Prince Gustav. Two more, the Larsen B and the
in full retreat and are expected to break up soon, having lost more than
one-seventh of their combined 21,000 square kilometers since late 1998-a
the size of Rhode Island. Icebergs as big as Delaware have also broken off
Antarctica in recent years, posing threats to open-water shipping.
Antarctica's vast land ice is also melting, although there is disagreement
how quickly. One study estimates that the Western Antarctic Ice Sheet
the smaller of the continent's two ice sheets, has retreated at an average
of 122 meters a year for the past 7,500 years-and is in no imminent danger
collapse. But other studies suggest that the sheet may break more abruptly
melting accelerates. They point to signs of past collapse, as well as to
fast-moving ice streams within the sheet that could speed ice melt, as
of potential instability.
Outside the poles, most ice melt has occurred in mountain and subpolar
which have responded much more rapidly to temperature changes. As a whole,
world's glaciers are now shrinking faster than they are growing, and
1997-98 were "extreme," according to the World Glacier Monitoring Service.
Scientists predict that up to a quarter of global mountain glacier mass
disappear by 2050, and up to one-half by 2100-leaving large patches only
Alaska, Patagonia, and the Himalayas. Within the next 35 years, the
glacial area alone is expected to shrink by one-fifth, to 100,000 square
The disappearance of Earth's ice cover would significantly alter the
climate-though the net effects remain unknown. Ice, particularly polar
reflects large amounts of solar energy back into space, and helps keep the
planet cool. When ice melts, however, this exposes land and water surfaces
retain heat-leading to even more melt and creating a feedback loop that
accelerates the overall warming process. But excessive ice melt in the
could also have a cooling effect in parts of Europe and the eastern United
States, as the influx of fresh water into the North Atlantic may disrupt
circulation patterns that enable the warm Gulf Stream to flow north.
As mountain glaciers shrink, large regions that rely on glacial runoff for
supply could experience severe shortages. The Quelccaya Ice Cap, the
water source for Lima, Peru, is now retreating by some 30 meters a year-up
only 3 meters a year before 1990-posing a threat to the city's 10 million
residents. And in northern India, a region already facing severe water
an estimated 500 million people depend on the tributaries of the
Indus and Ganges rivers for irrigation and drinking water. But as the
melt, these rivers are expected to initially swell and then fall to
low levels, particularly in summer. (In 1999, the Indus reached record
levels because of glacial melt.)
Rapid glacial melting can also cause serious flood damage, particularly in
heavily populated regions such as the Himalayas. In Nepal, a glacial lake
in 1985, sending a 15-meter wall of water rushing 90 kilometers down the
mountains, drowning people and destroying houses. A second lake near the
country's Imja Glacier has now grown to 50 hectares, and is predicted to
within the next five years, with similar consequences.
Large-scale ice melt would also raise sea levels and flood coastal areas,
currently home to about half the world's people. Over the past century,
in ice caps and mountain glaciers has contributed on average about
the estimated 10-25 centimeter (4-10 inch) global sea level rise-with the
caused by thermal expansion of the ocean as the Earth warmed. But ice
share in sea level rise is increasing, and will accelerate if the larger
sheets crumble. Antarctica alone is home to 70 percent of the planet's
water, and collapse of the WAIS, an ice mass the size of Mexico, would
levels by an estimated 6 meters-while melting of both Antarctic ice sheets
raise them nearly 70 meters. (Loss of the Arctic sea ice or of the
Antarctic ice shelves would have no effect on sea level because these
Wildlife is already suffering as a result of global ice melt-particularly
poles, where marine mammals, seabirds, and other creatures depend on food
at the ice edge. In northern Canada, reports of hunger and weight loss
polar bears have been correlated with changes in the ice cover. And in
Antarctica, loss of the sea ice, together with rising air temperatures and
increased precipitation, is altering the habitats as well as feeding and
breeding patterns of penguins and seals.
TABLE 1: SELECTED EXAMPLES OF ICE MELT AROUND THE WORLD
Arctic Sea Ice
Has shrunk by 6 percent since 1978, with a 14 percent loss of thicker,
year-round ice. Has thinned by 40 percent in less than 30 years.
Greenland Ice Sheet
Has thinned by more than a meter a year on its southern and eastern edges
Alaska, United States
Has retreated nearly 13 kilometers since 1982. In 1999, retreat rate
from 25 meters per day to 35 meters per day.
Glacier National Park
Rocky Mtns., United States
Since 1850, the number of glaciers has dropped from 150 to fewer than 50.
Remaining glaciers could disappear completely in 30 years.
Antarctic Sea Ice
Ice to the west of the Antarctic Peninsula decreased by some 20 percent
1973 and 1993, and continues to decline.
Pine Island Glacier
Grounding line (where glacier hits ocean and floats) retreated 1.2
year between 1992 and 1996. Ice thinned at a rate of 3.5 meters per year.
Larsen B Ice Shelf
Calved a 200 km2 iceberg in early 1998. Lost an additional 1,714 km2
1998-1999 season, and 300 km2 so far during the 1999-2000 season.
Terminus has retreated 3 kilometers since 1971, and main front has
kilometers since 1982. Has thinned by up to 200 meters on average since
1971-82 period. Icebergs began to break off in 1991, accelerating the
Meren, Carstenz, and Northwall Firn Glaciers
Irian Jaya, Indonesia
Rate of retreat increased to 45 meters a year in 1995, up from only 30
year in 1936. Glacial area shrank by some 84 percent between 1936 and
Meren Glacier is now close to disappearing altogether.
Dokriani Bamak Glacier
Retreated by 20 meters in 1998, compared with an average retreat of 16.5
over the previous 5 years. Has retreated a total of 805 meters since 1990.
Ulan Ula Mtns., China
Glaciers have shrunk by some 60 percent since the early 1970s.
Tien Shan Mountains
Twenty-two percent of glacial ice volume has disappeared in the past 40
Glacial volume has declined by 50 percent in the past century.
Glacial area has shrunk by 35 to 40 percent and volume has declined by
50 percent since 1850. Glaciers could be reduced to only a small fraction
their present mass within decades.
Largest glacier has lost 92 percent of its mass since the late 1800s.
Retreated by more than 150 meters between 1977 and 1990, compared with
35-45 meters between 1958 and 1977.
Has retreated 60 meters a year on average over the last 60 years, and rate
Rate of retreat increased to 30 meters a year in the 1990s, up from only 3
meters a year between the 1970s and 1990.
Sources available upon request. For additional examples go to
Ocean Temperature Rise May Mean Warmer Times Ahead
By Curt Suplee
Washington Post Staff Writer
Friday, March 24, 2000; Page A07
The temperature of the world's oceans has increased dramatically over
the past four decades, according to a major study that adds new
to projections of increased global warming.
March 24, 2000
Researchers Find Ocean Temperature Rising, Even in the Depths
The New York Times
by WILLIAM K. STEVENS
An important piece of the global-warming picture has come into clearer
focus with a confirmation by scientists that the world's oceans have
up much of the warming of the last four decades, delaying its full effect
the atmosphere and thus on climate
Oceans have been getting warmer in last 50 years
Sea Temperatures On The Rise
Oceans Of New Evidence Mount On Global Warming
WORLD OCEAN HAS WARMED SIGNIFICANTLY OVER PAST 40 YEARS
March 23, 2000 - Scientists at NOAA have discovered that the world ocean
warmed significantly during the past 40 years. The largest warming has
occurred in the upper 300 meters of the world ocean on average by 0.56
degrees Fahrenheit. The water in the upper 3000 meters of the world ocean
warmed on average by 0.11 degrees Fahrenheit. These findings represent the
first time scientists have quantified temperature changes in all of the
world's oceans from the surface to 3000 meters depth
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