Scioglimento dei ghiacci

["AlessandroGimona"<agimona@libero.it>]

lo scioglimento dei ghiacci puo' avere serie ripercussioni, compresa la 
scarsita' d'acqua in ampie regioni dell'asia.
E' necessario ridurre le emissioni di gas serra a partire da subito

Alessandro Gimona
---------------------------------------------------------
NEWS FROM THE WORLDWATCH INSTITUTE

  From the Office of the Chairman
  Worldwatch Issue Alert
  Alert 2000 - 7
  Embargoed for Release
  August 29, 2000
  6 PM



  CLIMATE CHANGE HAS WORLD SKATING ON THIN ICE

  Lester R. Brown

      If any explorers had been hiking to the North Pole this summer, 
they would
  have had to swim the last few miles. The discovery of open water at 
the Pole by
  an ice-breaker cruise ship in mid August surprised many in the 
scientific
  community.
      This finding, combined with two recent studies, provides not only 
more
  evidence that the Earth's ice cover is melting, but that it is melting 
at an
  accelerating rate. A study by two Norwegian scientists projects that 
within 50
  years, the Arctic Ocean could be ice-free during the summer. The 
other, a study
  by a team of four U.S. scientists, reports that the vast Greenland ice 
sheet is
  melting.
      The projection that the Arctic Ocean will lose all its summer ice 
is not
  surprising, since an earlier study reported that the thickness of the 
ice sheet
  has been reduced by 42 percent over the last four decades. The area of 
the ice
  sheet has also shrunk by 6 percent. Together this thinning and 
shrinkage have
  reduced the Arctic Ocean ice mass by nearly half.
      Meanwhile, Greenland is gaining some ice in the higher altitudes, 
but it is
  losing much more at lower elevations, particularly along its southern 
and
  eastern coasts. The huge island of 2.2 million square kilometers 
(three times
  the size of Texas) is experiencing a net loss of some 51 billion cubic 
meters of
  water each year, an amount equal to the annual flow of the Nile River.
      The Antarctic is also losing ice. In contrast to the North Pole, 
which is
  covered by the Arctic Sea, the South Pole is covered by the Antarctic 
continent,
  a land mass roughly the size of the United States. Its continent-sized 
ice
  sheet, which is on average 2.3 kilometers (1.5 miles) thick, is 
relatively
  stable. But the ice shelves, the portions of the ice sheet that extend 
into the
  surrounding seas, are fast disappearing.
      A team of U.S. and British scientists reported in 1999 that the 
ice shelves
  on either side of the Antarctic Peninsula are in full retreat. From 
roughly
  mid-century through 1997, these areas lost 7,000 square kilometers as 
the ice
  sheet disintegrated. But then within scarcely a year they lost another 
3,000
  square kilometers. Delaware-sized icebergs that have broken off are 
threatening
  ships in the area. The scientists attribute the accelerated ice 
melting to a
  regional temperature rise of some 2.5 degrees Celsius (4.5 degrees 
Fahrenheit)
  since 1940.
      These are not the only examples of melting. My colleague, Lisa 
Mastny, who
  has reviewed some 30 studies on this topic, reports that ice is 
melting almost
  everywhere--and at an accelerating rate. (See Worldwatch News Brief, 
March 6,
  2000 http://www.worldwatch.org/alerts/000306.html ) The snow/ice mass 
is
  shrinking in the world's major mountain ranges: the Rocky Mountains, 
the Andes,
  the Alps, and the Himalayas. In Glacier National Park in Montana, the 
number of
  glaciers has dwindled from 150 in 1850 to fewer than 50 today. The 
U.S.
  Geological Survey projects that the remaining glaciers will disappear 
within 30
  years.
      Scientists studying the Quelccaya glacier in the Peruvian Andes 
report that
  its retreat has accelerated from 3 meters a year between roughly 1970 
and 1990
  to 30 meters a year since 1990. In Europe's Alps, the shrinkage of the 
glacial
  area by 35-40 percent since 1850 is expected to continue. These 
ancient glaciers
  could largely disappear over the next half-century.
      Shrinkage of ice masses in the Himalayas has accelerated 
alarmingly. In
  eastern India, the Dokriani Bamak glacier, which retreated by 16 
meters between
  1992 and 1997, drew back by a further 20 meters in 1998 alone.
      This melting and shrinkage of snow/ice masses should not come as a 
total
  surprise. Swedish scientist Svente Arrhenius warned at the beginning 
of the last
  century that burning fossil fuels could raise atmospheric levels of 
carbon
  dioxide (CO2), creating a greenhouse effect. Atmospheric CO2 levels, 
estimated
  at 280 parts per million (ppm) before the Industrial Revolution, have 
climbed
  from 317 ppm in 1960 to 368 ppm in 1999--a gain of 16 percent in only 
four
  decades.
      As CO2 concentrations have risen, so too has Earth's temperature. 
Between
  1975 and 1999, the average temperature increased from 13.94 degrees 
Celsius to
  14.35 degrees, a gain of 0.41 degrees or 0.74 degrees Fahrenheit in 24 
years.
  The warmest 23 years since recordkeeping began in 1866 have all 
occurred since
  1975.
      Researchers are discovering that a modest rise in temperature of 
only 1 or 2
  degrees Celsius in mountainous regions can dramatically increase the 
share of
  precipitation falling as rain while decreasing the share coming down 
as snow.
  The result is more flooding during the rainy season, a shrinking 
snow/ice mass,
  and less snowmelt to feed rivers during the dry season.
      These "reservoirs in the sky," where nature stores fresh water for 
use in
  the summer as the snow melts, are shrinking and some could disappear 
entirely.
  This will affect the water supply for cities and for irrigation in 
areas
  dependent on snowmelt to feed rivers.
      If the massive snow/ice mass in the Himalayas--which is the third 
largest in
  the world, after the Greenlandic and Antarctic ice sheets--continues 
to melt, it
  will affect the water supply of much of Asia. All of the region's 
major
  rivers--the Indus, Ganges, Mekong, Yangtze, and Yellow--originate in 
the
  Himalayas. The melting in the Himalayas could alter the hydrology of 
several
  Asian countries, including Pakistan, India, Bangladesh, Thailand, Viet 
Nam, and
  China. Less snowmelt in the summer dry season to feed rivers could 
exacerbate
  the hydrological poverty already affecting so many in the region. (See 
Issue
  Alerts 1 and 4 www.worldwatch.org/alerts/indexia.html )
      As the ice on land melts and flows to the sea, sea level rises. 
Over the
  last century, sea level rose by 20-30 centimeters (8-12 inches). 
During this
  century, the existing climate models indicate it could rise by as much 
as 1
  meter. If the Greenland ice sheet, which is up to 3.2 kilometers thick 
in
  places, were to melt entirely, sea level would rise by 7 meters (23 
feet).
      Even a much more modest rise would affect the low-lying river 
floodplains of
  Asia, where much of the region's rice is produced. According to a 
World Bank
  analysis, a 1-meter rise in sea level would cost low-lying Bangladesh 
half its
  riceland. Numerous low-lying island countries would have to be 
evacuated. The
  residents of densely populated river valleys of Asia would be forced 
inland into
  already crowded interiors. Rising sea level could create climate 
refugees by the
  million in countries such as China, India, Bangladesh, Indonesia, Viet 
Nam, and
  the Philippines.
      Even more disturbing, ice melting itself can accelerate 
temperature rise. As
  snow/ice masses shrink, less sunlight is reflected back into space. 
With more
  sunlight absorbed by less reflective surfaces, temperature rises even 
faster and
  melting accelerates.
      We don't have to sit idly by as this scenario unfolds. There may 
still be
  time to stabilize atmospheric CO2 levels before continuing carbon 
emissions
  cause climate change to spiral out of control. We have more than 
enough wind,
  solar, and geothermal energy that can be economically harnessed to 
power the
  world economy. If we were to incorporate the cost of climate 
disruption in the
  price of fossil fuels in the form of a carbon tax, investment would 
quickly
  shift from fossil fuels to these climate-benign energy sources.
      The leading automobile companies are all working on fuel cell 
engines.
  Daimler Chrysler plans to start marketing such an automobile in 2003. 
The fuel
  of choice for these engines is hydrogen. Even leaders within the oil 
industry
  recognize that we will eventually shift from a carbon-based energy 
economy to a
  hydrogen-based one. The question is whether we can make that shift 
before
  Earth's climate system is irrevocably altered.

  - end -

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  WWW.WORLDWATCH.ORG/ALERTS/INDEXIA.HTML
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  COPYRIGHT: 2000 Worldwatch Institute
  CONTACT: Reah Janise Kauffman
  PHONE: (202) 452-1992 x 514
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