Deborah Zabarenko, PlanetArk 16 Nov 07
WASHINGTON - Hurricane Katrina left a big "carbon footprint" along the US Gulf Coast, where the destruction of large trees cut into the amount of greenhouse gases the area can absorb, researchers reported on Thursday.
The monster storm that tore across Louisiana and Mississippi in 2005 killed or severely damaged approximately 320 million big trees, the scientists wrote in the journal Science.
Trees, like other vegetation, soak up carbon dioxide, a potent global-warming gas, creating what climate scientists call a carbon sink. In a carbon sink, the carbon stays locked up in living trees instead of being released into the atmosphere to create greenhouse warming.
But when trees die, they stop taking in carbon dioxide and the process of decay starts emitting this gas, and that is what happened after Katrina roared through, said Jeffrey Q. Chambers of Tulane University.
All those dead and damaged trees that had been reducing carbon emissions suddenly became emitters. Altogether, they gave off about 100 million tons of carbon, enough to offset the total amount of carbon that forest trees in the United States suck up in a year.
"It was astonishing that a single storm could be of that magnitude," Chambers said by telephone from Manaus, Brazil, where he was doing field work.
A carbon footprint is a measure of the impact that activities have on the environment in terms of the amount of greenhouse gases produced, measured in units of carbon dioxide.
Compared with total carbon emissions from fossil fuel burning, emissions from the Katrina-ravaged forests are a tiny fraction, he said.
To figure out how many trees were hit by the big storm, Chambers and his colleagues reviewed satellite images of the area from 2003 and compared them with images from 2006. The research was published in the current edition of the journal Science.
He noted that some climate scientists, including most of those on the UN Intergovernmental Panel on Climate Change, have predicted a greater number of powerful storms as the planet warms. If this is the case, the dead-tree effect could add another dimension to storm disasters.
And while the impact of one storm, even one as strong as Katrina, is small by comparison with other sources of greenhouse emissions, the impact could climb if more storms each year are intense, he said.
"What if you look at a year when you've got 25 big tropical cyclones all over the world?" Chamber said. "It starts adding up."
320 Million Trees Lost to Katrina, Fuels Global Warming
Andrea Thompson, LiveScience.com Yahoo News 15 Nov 07;
Major hurricanes may not only be fueled by global warming, they may also contribute to it, according to a new study that puts the Hurricane Katrina death toll for trees at 320 million.
Recent research suggests that in our warming world, devastating hurricanes, like Katrina, may become more common. The new study, detailed in the Nov. 16 issue of the journal Science, adds another element to this dilemma, suggesting that the damage these hurricanes cause may actually fuel global warming due to the loss of carbon-consuming trees.
Tulane University researchers estimated the number of trees felled by Katrina using satellite imagery taken before and after the storm. Forest trees act as a carbon sink, sucking up carbon dioxide from the atmosphere to provide themselves with food. Carbon dioxide, a greenhouse gas, is the major driver of global warming.
When trees are destroyed, they decay, returning the carbon stored inside them to the atmosphere.
The total amount of biomass lost by the destruction of the trees lost during Katrina was about 105 teragrams of carbon (for comparison, the Great Pyramid of Giza weighs 6 teragrams), or at least half of the net annual carbon sink in U.S. forest trees.
Trees accumulate carbon as they grow, year by year, storing that carbon as their wood and leaves. But when they die, fungi, bacteria, termites and other decomposers consume that biomass and release all the carbon that the tree has accumulated over its lifetime. So when a huge number of trees are killed off by an event like Katrina, they become a carbon source, releasing anywhere from half to 140 percent of the carbon that all the trees in the United States take up in a year.
While it will take a number of decades for all of the carbon from the lost Katrina trees to be released, that is still less time than it took to build up the biomass of the forest into a carbon sink, said study leader Jeffrey Chambers.
While these lost trees will eventually be replaced by other vegetation, it will be younger and smaller and therefore a smaller carbon sink than the Gulf Coast forests once were.
If hurricanes and other forces of disturbance become more frequent in the future, forests may never have a chance to fully recover, the researchers say, permanently eliminating the carbon-sink work they do and allowing all that previously stored carbon to stay in the atmosphere.
