[tt] Physics News Update 872

[Eugen Leitl]

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From: physnews at aip.org
Date: Wed, 17 Sep 2008 13:49:55 -0400
To: eugen at LEITL.ORG
Subject: Physics News Update 872
Reply-to: physnews at aip.org

INSIDE SCIENCE RESEARCH---PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Research News
Number 872 September 17, 2008      www.aip.org/pnu
by Phillip F. Schewe, James Dawson, and Jason S. Bardi

CALIFORNIA TREES NOT KEEPING UP WITH CO2.  Forests aren’t absorbing
as much carbon dioxide as in the past, and fire suppression might be
to blame.  Fire suppression in forest encourages the growth of
smaller trees and, as a result, significantly reduces a forest's
overall ability to store carbon, according to a new study by
scientists at the University of California at Irvine. The
researchers, studying forests in California, found that while the
number of trees per acre increased in the sixty year period between
1930 and 1990, carbon storage actually declined about 26 percent.
This change in the nature of the forests, with greater numbers of
smaller trees at the expense of large trees, seems to have been
caused by the assiduous suppression of fires by human intervention,
the researchers said.  Using detailed records, the scientists,
compare forests as they were in the 1930s with forests in the 1990s
and found that the "stem density" of the forests had increased,
which would seem to enhance a forest's ability to store carbon.   In
fact, the smaller-tree factor outweighs the denser-forest factor
because large trees retain a disproportionate amount of carbon, the
researchers concluded.
Climate change, or at least the vast increase in carbon dioxide
launched into the atmosphere by the combustion of fossil fuels
during the industrial era, has focused scientific attention on the
ability of plants, especially trees, to take up and store the added
CO2.  Trees are not the only carbon sinks (the oceans store vast
amounts of CO2), but they are often cited as a key indicator in the
fight to stabilize the buildup of greenhouse gases in the
atmosphere.
This study, published last month in the journal Geophysical Research
Letters, pertains to California only, but Aaron Fellows, one of the
study's authors, believes it will apply to other dry conifer
(evergreen) forests in the U.S. western region.

OCEANS WARMER, HURRICANES STRONGER.  One of the long-standing
predictions of global warming research is that extreme climate
events will become more frequent. But in a system as complex as the
Earth’s climate it is difficult to tie individual events together
into trends and then link those trends to global warming.  One of
the most intense debates in the science community has been about the
theory that global warming is contributing to stronger extreme
weather events like hurricanes and cyclones.  New research from
Florida State University bolsters the contention that the strongest
tropical cyclones are getting stronger and links them to an ocean
that is warming because of global warming.  The research, by a team
lead by FSU geographer James Elsner, is based on a “heat-engine”
theory put forward by MIT scientist Kerry Emanuel in 2005. That
theory, in its simplest form, says that as seas warm, the ocean has
more energy that can be converted to tropical cyclone wind, which
makes hurricanes stronger.  (Emanuel, in a recent paper, modified
much of his work predicting that heat engines will trigger more
hurricanes, but noted that global warming might still play a role in
raising the intensity of hurricanes, which is the focus of Elsner's
research).
Elsner and his team looked at 30 years of data and focused on storms
that were closest to the maximum possible intensity, or as strong as
they could be given the environmental conditions. They found that
the strongest tropical cyclones are getting stronger, particularly
over the North Atlantic and Indian oceans.  Wind speeds in the
strongest storms increased from an average of 140 miles-per-hour in
1981 to 156 miles-per-hour in 2006.  During this period the ocean
temperature, averaged globally over all the regions where tropical
cyclones form, increased from 82.7 to 83.3 degrees Fahrenheit.  “By
looking only at the strongest tropical cyclones, where the
relationship between storms and climate is most pronounced, we are
able to observe the increasing trends in storm intensity that both
the theory and models say should be there,” Elsner said.  The
research appeared in a recent issue of the journal Nature.

MORE BIKES, FEWER BIKE ACCIDENTS. In a study that at first glance
seems counterintuitive, researchers at the University of New South
Wales in Sydney, Australia reviewed safety studies from 17 countries
and 68 cities in California and found that the more people bike in a
community, the less they collide with motorists.  “It appears that
motorists adjust their behavior in the presence of increasing
numbers of people bicycling because they expect or experience more
people cycling,” said Julie Hatfield, and injury expert from the
university.  With fewer accidents, people perceive cycling as safer,
so more people cycle, thus making it even safer, she said.  “Rising
cycling rates mean motorists are more likely to be cyclists, and
therefore be more conscious of, and sympathetic towards, cyclists,”
she said.  Safety experts said the decrease in accidents that comes
with an increase in cycling is independent of improvements in
cycling-friendly laws and better infrastructure such as bike paths.
The safety studies reviewed were from Australia, Denmark, the
Netherlands, 14 other European countries, and 68 cities in
California.  Although the review focused on bicycling, it appears
that the more is safer rule also applies to pedestrians, Hatfield
said.

***********
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