Good News on Forests and Carbon Dioxide
 
Dec 31, 2014:  A new NASA-led study shows that tropical forests may be
absorbing far more carbon dioxide than many scientists thought, in response to
rising atmospheric levels of the greenhouse gas. The study estimates that
tropical forests absorb 1.4 billion metric tons of carbon dioxide out of a
total global absorption of 2.5 billion -- more than is absorbed by forests in
Canada, Siberia and other northern regions, called boreal forests.
 
"This is good news, because uptake in boreal forests is already slowing, while
tropical forests may continue to take up carbon for many years," said David
Schimel of NASA's Jet Propulsion Laboratory, Pasadena, California. Schimel is
lead author of a paper on the new research, appearing online in the Proceedings
of National Academy of Sciences.
 
[Photo link missing]
 
A new NASA study suggests that tropical forests, like this one in Malaysia,
absorb more atmospheric carbon dioxide than is absorbed by forests in Alaska,
Canada and Siberia. Image Credit: Wikimedia Commons
 
Forests and other land vegetation currently remove up to 30 percent of human
carbon dioxide emissions from the atmosphere during photosynthesis. If the rate
of absorption were to slow down, the rate of global warming would speed up in
return.
 
The new study is the first to devise a way to make apples-to-apples comparisons
of carbon dioxide estimates from many sources at different scales: computer
models of ecosystem processes, atmospheric models run backward in time to
deduce the sources of today's concentrations (called inverse models), satellite
images, data from experimental forest plots and more. The researchers
reconciled all types of analyses and assessed the accuracy of the results based
on how well they reproduced independent, ground-based measurements. They
obtained their new estimate of the tropical carbon absorption from the models
they determined to be the most trusted and verified.
 
"Until our analysis, no one had successfully completed a global reconciliation
of information about carbon dioxide effects from the atmospheric, forestry and
modeling communities," said co-author Joshua Fisher of JPL. "It is incredible
that all these different types of independent data sources start to converge on
an answer."
 
The question of which type of forest is the bigger carbon absorber "is not just
an accounting curiosity," said co-author Britton Stephens of the National
Center for Atmospheric Research, Boulder, Colorado. "It has big implications
for our understanding of whether global terrestrial ecosystems might continue
to offset our carbon dioxide emissions or might begin to exacerbate climate
change."
 
As human-caused emissions add more carbon dioxide to the atmosphere, forests
worldwide are using it to grow faster, reducing the amount that stays airborne.
This effect is called carbon fertilization. "All else being equal, the effect
is stronger at higher temperatures, meaning it will be higher in the tropics
than in the boreal forests," Schimel said.
 
But climate change also decreases water availability in some regions and makes
Earth warmer, leading to more frequent and larger wildfires. In the tropics,
humans compound the problem by burning wood during deforestation. Fires don't
just stop carbon absorption by killing trees, they also spew huge amounts of
carbon into the atmosphere as the wood burns.
 
For about 25 years, most computer climate models have been showing that
mid-latitude forests in the Northern Hemisphere absorb more carbon than
tropical forests. That result was initially based on the then-current
understanding of global air flows and limited data suggesting that
deforestation was causing tropical forests to release more carbon dioxide than
they were absorbing.
 
In the mid-2000s, Stephens used measurements of carbon dioxide made from
aircraft to show that many climate models were not correctly representing flows
of carbon above ground level. Models that matched the aircraft measurements
better showed more carbon absorption in the tropical forests. However, there
were still not enough global data sets to validate the idea of a large
tropical-forest absorption. Schimel said that their new study took advantage of
a great deal of work other scientists have done since Stephens' paper to pull
together national and regional data of various kinds into robust, global data
sets.
 
Schimel noted that their paper reconciles results at every scale from the pores
of a single leaf, where photosynthesis takes place, to the whole Earth, as air
moves carbon dioxide around the globe. "What we've had up till this paper was a
theory of carbon dioxide fertilization based on phenomena at the microscopic
scale and observations at the global scale that appeared to contradict those
phenomena. Here, at least, is a hypothesis that provides a consistent
explanation that includes both how we know photosynthesis works and what's
happening at the planetary scale."
 
Credits:
Production editor: Dr. Tony Phillips | Credit: Science@NASA
 
More information:
 
NASA monitors Earth's vital signs from land, air and space with a fleet of
satellites and ambitious airborne and ground-based observation campaigns. NASA
develops new ways to observe and study Earth's interconnected natural systems
with long-term data records and computer analysis tools to better see how our
planet is changing. The agency shares this unique knowledge with the global
community and works with institutions in the United States and around the world
that contribute to understanding and protecting our home planet.
 
For more information about NASA's Earth science activities in the last year,
visit: http://www.nasa.gov/earthrightnow
 
 
Regards,
 
Roger

--- D'Bridge 3.99