dubbi sulle cause del riscaldamento globale

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

Nonostante la maggioranza dei climatologi ritenga che sia molto
probabile che il riscaldamento globale abbia cause umane, alcuni
scienziati  dubitano che i dati supportino la teoria che il
riscaldamento globale sia causato da attivita' umane.

lo studio pubblicato di recente su Science si allinea con la minoranza.
Il dibattito e' destinato a continuare.
Saluti
Alessandro Gimona

------------------------------

Hi. Please note the conclusion of this new earth-ecology study reported
in
Science:

``This suggests that what has happened in the past 21 years is not
an example of human-induced climate change.''

In fact, it is solar activity in the solar maximum, and not human fossil
fuel
and industrial activity that appears to be behind climate change,
warming
trends.

Comments? Alfred Webre
=====
New Study Reports Heating Up of Earth's Surface

Reuters

WASHINGTON (Feb. 17) - The Earth's surface has heated up appreciably
over the
past 20 years, according to research published Thursday that backs up a
major
study released last month.

The new study in ``Science'' magazine supports a National Academy of
Sciences
panel that concluded that strong evidence showed an ``undoubtedly real''

warming of the Earth's surface.

One of the authors of the new study, research meteorologist Dian Gaffen,
said
the contention that the Earth's surface had warmed up appreciably over
the
past 20 years was proven in their research.

The Earth's surface was warming up at 0.05 to 0.08 degrees Celsius per
decade, said Gaffen of the National Oceanic and Atmospheric
Administration in
Maryland.

The study tries to resolve a major discrepancy in global climate -- that

measurements at the Earth's surface suggest a temperature rise but that
satellite measurements indicate the lower troposphere shows little or no

signs of warmup.

This discrepancy in temperature trends cast doubt about how the Earth's
surface could be warming up if the air directly above it had not,
raising
questions over whether man-made Greenhouse gases had contributed to
global
warming.

Gaffen's group studied data from a series of weather balloons sent aloft
in
the Tropics to measure the temperature of the Earth's surface as well as
in
the troposphere, the area just above Earth.

``Our results support the contention that the surface has been warming
appreciably in the last 20 years versus the troposphere which does not
show
as much warming,'' she said.

Gaffen's study focused on the tropical belt, the region on the Earth
where
the difference between measurements taken by satellites and ground
station
measurements is greatest.

Some scientists had argued that data from both satellite and ground
measurements were so different that they could only be wrong, changing
how
meteorologists looked at climate change in the decades to come.

``The most important thing is that there has been a debate among policy
circles that satellite data did not show warming and so the surface
could not
be warming either,'' Gaffen said.

Gaffen wrote that both calculations were correct and the discrepancy
arose
from variations in how atmospheric temperature decreased with altitude.

Ben Santer of Lawrence Livermore National Laboratory in California, who
wrote
an accompanying paper in ``Science'', said there were good ``physical
reasons'' why the Earth's surface was warmer than the troposphere above
the
surface.

He cited external factors such as increases in Greenhouse gases, the
number
of particles in the air due to combustion, depletion of the Ozone layer
or
natural events such as the eruption of Mount Pinatubo in 1991.

Santer said he hoped the study would clarify that the discrepancies
could not
be reduced to ``sound bytes''.

``The bottom line is that the discrepancy between the surface of the
Earth
and the lower troposphere seems to be real. Also there are plausible
reasons
to explain how we have these different temperatures,'' said Santer.

Commenting on the study, John Christy, professor of Atmospheric Science
at
the University of Alabama in Huntsville, said it reinforced the
conclusion
that the atmosphere had not warmed as fast in the troposphere as at the
Earth's surface.

``The behavior of the surface temperatures and the atmosphere over the
past
21 years is at odds with the theories that explain how human-induced
climate
changes should occur,'' said Christy, who contributed to the research.

He added: ``This suggests that what has happened in the past 21 years is
not
an example of human-induced climate change.''