nuovo rapporto scientifico sul clima

[alessandro gimona <ag0648@mluri.sari.ac.uk>]

Cari tutti,
L'Accademia Nazionale delle Scienze (USA) ha completato un rapporto
scientifico sulle differenze (e discrepanze) tra misurazioni al suolo e
quelle da satellite.

Conclusione : il pianeta si sta riscaldando ma non comprendiamo bene
come l'atmosfera funzioni. Ci vuole una rete di monitoraggio migliore.

Spero interessi

Alessandro Gimona

Reconciling Observations of Global Temperature
Change
http://www4.nationalacademies.org/news.nsf/isbn/0309068916?OpenDocumen
t
National Academy of Sciences
Date: Jan. 12, 2000
Contacts: Molly Galvin, Media Relations Officer
Kathi McMullin, Media Relations Assistant
(202) 334-2138; e-mail <news@nas.edu>

New Evidence Helps Reconcile Global Warming Discrepancies;
Confirms That Earth's Surface Temperature Is Rising

WASHINGTON -- Despite differences in temperature data, strong evidence
exists to show that the warming of the Earth's surface is "undoubtedly
real," and that surface temperatures in the past two decades have risen
at a
rate substantially greater than average for the past 100 years, says a
new
report by the National Research Council of the National Academies.

The report examines the apparent conflict between surface temperature
and
upper-air temperature, which has led to the controversy over whether
global
warming is actually occurring. The Earth's surface temperature has risen

about 0.4 to 0.8 degrees Celsius - or 0.7 to 1.4 degrees Fahrenheit --
in
the last century, the report says. But data collected by satellites and
balloon-borne instruments since 1979 indicate little if any warming of
the
low- to mid-troposphere - the atmospheric layer extending up to about 5
miles from the Earth's surface. Climate models generally predict that
temperatures should increase in the upper air as well as at the surface
if
increased concentrations of greenhouse gases are causing the warming.

"The differences between the surface and upper-air trends in no way
invalidates the conclusion that the Earth's temperature is rising," said

John M. Wallace, chair of the panel that wrote the report and professor
of
atmospheric sciences at the University of Washington in Seattle. "But
the
rapid increase in the Earth's surface temperature over the past 20 years
is
not necessarily representative of how the atmosphere is responding to
long-term, human-induced changes, such as increasing amounts of carbon
dioxide and other 'greenhouse' gases. The nations of the world should
develop an improved climate monitoring system to resolve uncertainties
in
the data and provide policy-makers with the best available information."

While a combination of human activities and natural causes has
contributed
to rising surface temperatures, other human and natural forces may
actually
have cooled the upper atmosphere. For example, natural events such as
the
eruption of Mt. Pinatubo in 1991 tended to decrease atmospheric
temperature
for several years. And burning coal and oil for energy produces tiny
aerosol
particles in the atmosphere that can have a cooling effect. Upper-air
temperatures also can be reduced by depletion of ozone in the
stratosphere
caused by chlorofluorocarbons and other chemicals being emitted into the

atmosphere. When these variables are accounted for in atmospheric
models,
satellite and balloon data more closely align with surface-temperature
observations.

Because global warming is a long-term process that can be masked by
year-to-year climate variability, warming trends are most clearly
revealed
by surface temperature measurements - which have been recorded daily at
hundreds of locations for more than a century. These data indicate that
the
Earth is, in fact, warming, the panel said. Satellites have been
collecting
data from the upper atmosphere for only about 20 years.

The differences between surface temperature and upper-air temperature
records also may be partially attributed to uncertainties in temperature

measurements, the panel said. A better climate monitoring system is
needed
to ensure continuity and quality in data collection. Measurements should

include not only temperature and wind, but also ozone, water vapor,
clouds,
and aerosols. Scientists need to perform a more comprehensive analysis
of
the uncertainties in surface, balloon, and satellite temperature data.
Natural as well as human-induced changes should be accounted for in
model
simulations of atmospheric temperature variability.

Data also need to be accessible in a form that enables a number of
different
research groups to use and improve them, the report says. To ensure
access,
data should be available in electronic databases to the entire
scientific
community.

The study was funded by the National Oceanic and Atmospheric
Administration
and the Aluminum Corporation of America. The National Research Council
is
the principal operating agency of the National Academy of Sciences and
the
National Academy of Engineering. It is a private, nonprofit institution
that
provides science advice under a congressional charter. A panel roster
follows.
Copies of Reconciling Observations of Global Temperature Change are
available from the National Academy Press at the mailing address in the
letterhead; tel. (202) 334-3313 or 1-800-624-6242. The cost of the
report is
$25.25 (prepaid) plus shipping charges of $4.50 for the first copy and
$.95
for each additional copy. Reporters may obtain a copy from the Office of

News and Public Information at the letterhead address (contacts listed
above).


NATIONAL RESEARCH COUNCIL
Commission on Geosciences, Environment, and Resources
Board on Atmospheric Sciences and Climate

Panel on Reconciling Temperature Observations

John M. Wallace* (chair)
Professor of Atmospheric Sciences and Co-Director
Program on the Environment
University of Washington
Seattle

John R. Christy
Professor of Atmospheric Science
University of Alabama
Huntsville

Dian Gaffen
Research Meteorologist
Climate Variability and Trends Group
Air Resources Laboratory
National Oceanic and Atmospheric Administration
Silver Spring, Md.

Norman C. Grody
Research Physicist
National Environmental Satellite Data and Information Service
National Oceanic and Atmospheric Administration
Camp Springs, Md.

James E. Hansen*
Head
Goddard Institute for Space Studies
National Aeronautics and Space Administration
New York City

David E. Parker
Research Scientist
Hadley Centre for Climate Prediction and Research
Meteorological Office
United Kingdom

Thomas C. Peterson
Chief
Scientific Services Division
National Climatic Data Center
National Oceanic and Atmospheric Administration
Asheville, N.C.

Benjamin D. Santer
Physicist and Atmospheric Scientist
Program for Climate Model Diagnosis and Intercomparison
Lawrence Livermore National Laboratory
Livermore, Calif.

Roy W. Spencer
Senior Scientist for Climate Studies
Marshall Space Flight Center
National Aeronautics and Space Administration
Huntsville, Ala.

Kevin E. Trenberth
Head
Climate Analysis Section
National Center for Atmospheric Research
Boulder, Colo.

Frank J. Wentz
Director
Remote Sensing Systems
Santa Rosa, Calif.

RESEARCH COUNCIL STAFF

Peter A. Schultz
Program Director


* Member, National Academy of Sciences