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Climate Change, Yes - But How Fast? |
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By Stephen Leahy*
For
some, it is a realistic assessment -- for others, it is too conservative.
Experts consulted by Tierramérica react to the fourth report by
the global panel of climate change experts, which predicts an average
global temperature increase of 1.8 to 4 degrees Celsius.
TORONTO, Feb 5 (Tierramérica) - The predictions
set out in the report by the Intergovernmental Panel on Climate
Change (IPCC), which says the Earth's average temperatures could
increase four degrees Celsius by 2100, are seen as solid forecasts
by some scientists, while others say they fall short.
The IPCC's Fourth Assessment Report, running 1,600 pages and officially
released in Paris Feb. 2, says the scientific data about global
warming and humankind's responsibility are now overwhelming.
But according to some climatologists, the panel's forecasts are
too prudent, because they don't take into account more recent studies,
for example, about glacier melt in Greenland.
The IPCC is an inherently cautious and judicious group of scientists,
says David Archer, a climatologist at the University of Chicago.
"At times it is frustratingly conservative," he told Tierramérica.
The IPCC reports do not publish new science. More than 2,500 scientists
from more than 130 countries compile and analyze previously published
peer-reviewed research. They spend years reconciling the many differences
and putting the information together in a summary fashion.
The latest assessment, for example, says temperatures will rise
1.8 to 4 degrees Celsius by 2100. In contrast, the Third Assessment
Report in 2001 predicted a range of 1.4 to 5.8 degrees -- a wider
range and a lower minimum increase.
"The main difference (between the two reports) is that the conclusions
are now so well-supported by observed data that nobody can reasonably
doubt that we are in the midst of global warming," Stefan Rahmstorf,
an IPCC contributor, told Tierramérica.
Beyond a few exceptions, the reports say essentially the same things,
according to Rahmstorf, a professor of ocean physics at Germany's
Potsdam Institute for Climate Impact Research.
But there are exceptions, and perhaps the most controversial has
been the impacts of melting glaciers and ice sheets on how much
the sea level will rise.
Versions of the Fourth Assessment Report leaked to the media prior
to Friday's official release predicted a sea-level rise by between
28 and 43 centimeters by 2100, substantially less than the 2001
prediction of between nine and 88 cm.
Because of a mandatory cut-off date, the newest IPCC report does
not include assessments of the latest published studies showing
that ice sheets in Greenland and elsewhere are melting much faster
than previously thought.
Rahmstorf's own research published last December in Science magazine
states that the sea level rise is more likely to be between 50 and
140 cm by 2100.
"The sea level numbers (in the IPCC report) are extremely conservative
and the climate models don't reflect the most recent observations
of what is happening in Greenland," says Andrew Weaver, a climatologist
at the earth and ocean sciences school of Canada's University of
Victoria.
Climate models do include findings by the World Glacier Monitoring
Service (WGMS) in Zurich, Switzerland, that mountain glaciers are
retreating three times faster than they were in the 1980s.
Since 1850, half of the world's mountain glaciers have melted and
global temperatures only rose by about 0.8 degrees Celsius. A future
temperature increase of 2.0 degrees means that "only biggest and
highest glaciers would survive into 21st century", according to
WGMS expert Michael Zemp. Most of Europe's glaciers will vanish.
Despite the conservatism of the report and the virtually unanimity
amongst climate scientists, there will be organizations and individuals
who will deny humans are responsible for climate change. They blame
the increased temperatures on variations in the sun or criticize
the climate models projections as inaccurate predictors of a future
"hot house" planet.
University of Chicago scientist Archer says the alternative explanations
have all been scientifically disproved long ago, but they resurface
regularly in new forms. "There are still many people, especially
in North America, who are looking for any excuse to bury their heads
in the sand," he said.
The new IPCC report used 19 different climate models, more than
twice the last IPCC report, says John Fyfe, of the Canadian Center
for Climate Modeling and Analysis, based in the western province
of British Columbia. "A huge effort was made over the last six years
to standardize and improve the accuracy of these models."
Extremely complex, climate models can only be run on the world's
biggest supercomputers. Fyfe says they do a very good job of accurately
simulating the climate over the past 150 years: "They are also very
good at calculating future temperatures."
Models have also become much better at predicting what future conditions
will be like over large areas such as the Canadian prairies, where
more frequent droughts are expected.
The text released in Paris is the first of three parts making up
the 4th Assessment Report. The next two, dealing with the impacts
of climate change and how to mitigate these impacts, will be released
in April and May.
Compared to the 2001 report, the first part, which deals with the
physical science about climate change, incorporates many more direct
observations, which has greatly increased scientists' confidence
in the results, says David Fahey of the U.S. National Oceanic and
Atmospheric Administration's Earth Systems Research Laboratory in
Boulder, Colorado.
"This report represents a tremendous leap forward in our understanding
of climate," Fahey, who wrote a part of the IPCC report, told Tierramérica.
However, other than some details, this report says what past IPCC
reports have said: climate change is happening now and it will get
worse. And, adds Fahey, it could be much worse, if action isn't
taken now to reduce emissions of greenhouses gases.
"To me climate change is a slow-motion train wreck."
* Stephen Leahy is an IPS correspondent. |
