With SARS getting much
attention in China, concurrent epidemics of TB and
HIV/AIDS are being neglected. China's OTHER public
health crises, Friday on NPR's Morning
Edition.
She
makes fifteen thousand dollars a year, working
thirteen-hour days taking care of children in her home.
A day of work with Laressa Matthews, Friday on All
Things Considered from NPR News.
World's
vegetation is cleaning more carbon from skies Peter N. Spotts
(2003-06-06)
If your dogwoods and peony patches are looking a bit
more robust than they did 20 years ago, you may have
climate change to thank for much of their growth.
Using two decades' worth of data on climate and
vegetation, a team of scientists has taken what may be
the first planet-wide look at plant activity during a
time when Earth's environment underwent significant
change.
The researchers found that globally,
shifts in rainfall patterns, cloud cover, and warming
temperatures triggered a 6 percent increase in the
amount of carbon stored in trees, grass, shrubs, and
flowers.
Many scientists hold that the growth in
atmospheric concentrations of heat-trapping
carbon-dioxide - from nearly two centuries of rapidly
growing populations that burned increasing amounts of
fossil fuels - is largely responsible for the earth's
warming climate.
The new research adds to the
body of evidence that plants can store increasing
amounts of carbon from the atmosphere, but it remains
unclear how long this trend will continue or whether it
will significantly affect atmospheric CO2
levels.
Kyoto provisions The 1997 Kyoto
Protocols - a first step at trying to reduce emissions
and so moderate the change - permits countries to use
the carbon-absorbing capacity of their forests and
farmlands as credits against their emissions targets. In
addition, projects that increase vegetation also are
seen as ways to reach national CO2 emissions targets.
Thus, understanding the flow of carbon from the
atmosphere to plants and back is vital to projecting
future trends in atmospheric CO2 levels.
For 50
years, scientists have been measuring the growth of CO2
in the atmosphere, according to Ramakrishna Nemani, a
professor in the forestry school at the University of
Montana in Missoula, who led the research team. "But if
you look at the record of the past two decades, the
annual growth rate hasn't been going up like it had
before," he says.
Other groups had forecast an
increase in plant growth for a time with climate change,
although rates would vary depending on region. And some
smaller-scale studies had indicated that the earth was
greening.
Dr. Nemani's team was interested in
seeing how plant activity had changed - and where -
worldwide during a 20-year period that saw two of the
warmest decades ever recorded, several intense El Nino
episodes, one major volcanic eruption, a 9 percent
increase in atmospheric CO2 concentrations, and a 37
percent growth in human population.
The team
measured how much carbon plants store after absorbing
carbon dioxide through photosynthesis and returning some
of it through respiration.
First, the team built
maps reflecting changes in temperature, cloud cover
(which affects the amount of sunlight reaching plants),
and available water. Then they overlaid satellite data
on net primary productivity on land and looked for
relationships among these components.
Big change
in the Amazon They were stunned at the growth rates
in South America's Amazon region.
"That was a big
surprise," says Ranga Myneni, a botanist at Boston
University and a member of the research team. Amazon
rain forests accounted for nearly half the increase seen
globally over the 20-year period.
The surprise
was twofold. The growth rate far exceeded what most
scientists expected. Many models indicated that
additional growth in the tropics would be minimal, given
the fairly constant temperatures from one season to the
next. In addition, many researchers had held that any
increased productivity in the tropics would largely be
driven by a rise in atmospheric CO2 rather than changes
in climate itself.
Yet the drop in tropical cloud
cover during the period allowed more sunlight into
places like Amazonia, Dr. Myneni says, far outpacing CO2
as a prod to growth. Likewise in other climate regions,
changing Climate conditions appeared to be the dominant
factor driving plant growth.
The other half of
the equation The good news for plants, which appears
in Friday's edition of the journal Science, comes with
caveats, Myneni cautions. Since humans collectively use
about half of plants' net primary production, he says,
the team's estimate of 6 percent growth over 20 years
translates into a trivial 3 percent growth in material
available to a growing human
population.
Moreover, the 20-year period the team
studied could be unusual, and hence not representative
of long-term prospects for vegetation growth. And if the
climate continues to warm, as many expect, plants will
bump up against limits to their ability to make use of
the additional water, warmth, and sunlight, just as they
bump into limits on the amount of CO2 they can use. The
study also doesn't answer questions about how changing
climate conditions in these areas are affecting the
amount of CO2 given off from plant decomposition and
soil - amounts that can offset the CO2 that plants
imprison in their roots, stems, and
leaves.
"That's the other half of the equation"
the study doesn't address, he cautions.
