Deborah Zabarenko PlanetArk 6 Dec 10;
Climate change is fanning longer- and deeper-burning fires in interior Alaska, changing the area from a carbon sink -- where planet-warming gases are stored naturally in the soil -- to a carbon emitter, scientists reported on Sunday.
The shift has occurred within the last 10 years and is due in large part to a longer burning season, according to a study published in Nature Geosciences.
The research was released at the start of a second week of international climate change negotiations in Cancun, Mexico.
When fires burn late into the season, past the end of July in northern latitudes, they don't just burn what's on the surface, but go deep into the soil where plant matter and other biomass have accumulated over thousands of years, said Merritt Turetsky, the study's lead author.
At some locations in interior Alaska, this accumulated biomass is as much as 26 feet deep, and is where climate-warming carbon has been stored. When it ignites, the carbon is emitted into the atmosphere.
Until about the year 2000, this part of Alaska stored more carbon than was emitted by industry and other sources in the area, but the last 10 years have seen an abrupt shift as long-stored soil carbon has been released by fire.
"Even though these systems have burned in the past, there was enough productivity, enough carbon being fixed (stored) by vegetation, that even when you took into account these fire emissions, they were still a small net sink of carbon," Turetsky said by telephone from the University of Guelph in Ontario, Canada.
"In the past 10 years there was this unprecedented amount of carbon released as a consequence of burning, and that changed the system from a small net sink to a net carbon source," she said.
These deep burns occur more often now because the fire season is longer and the late summer fires are fueled by dry ground and warmer air; these conditions are part of a warming environment. About half these fires are started by people, the other half by lightning.
Decades' worth of accumulated biomass, called peat, can burn in minutes, Turetsky said.
To get an idea of how much carbon these fires are putting into the atmosphere, study co-author Eric Kasischke of the University of Maryland offered a vivid comparison.
In the last decade, Kasischke said in an email, the biggest fire year in Alaska was 2004, when more than 56.7 million tons (51.5 teragrams or 51.5 billion kg) of carbon was emitted over 90 days, more than was released by all domestic U.S. airline flights for the whole year. That is also nearly as much carbon as was released by U.S. electricity generating plants for the same 90-day period.
(Editing by Stacey Joyce and Eric Walsh)
Subarctic wildfires a 'runaway climate change' risk
Marlowe Hood Yahoo News 5 Dec 10;
PARIS (AFP) – Global warming is driving forest fires in northern latitudes to burn more frequently and fiercely, contributing to the threat of runaway climate change, according to a study released Sunday.
Increased intensity of fires in Alaska's vast interior over the last decade has changed the region from a sink to a source of carbon dioxide, the greenhouse gas most responsible for heating up the planet, the study found.
On balance, in other words, boreal forests in the northern hemisphere may now soak up less of the heat-trapping gas than they give off.
The bulk of the released CO2 comes not from the burning trees, but from what is in the ground.
"Most of what fuels a boreal fire is plant litter, moss and organic matter in surface soils," said Merritt Turetsky, a professor at the University of Guelph in Ontario, Canada and lead author of the study.
The findings are worrisome, he said, because about half of the world's soil carbon is trapped in northern permafrost and peatlands.
"This is carbon that has accumulated in ecosystems a little bit at a time for thousands of years, but is being released very rapidly."
While the study, published in Nature Geoscience, focused on Alaska's 18.5 million hectares (45 million acres) of forests, its conclusions likely apply to huge expanses of wilderness in Siberia, Canada and northern Europe as well.
Out-of-control fires ravaged more than a million hectares in Russia earlier this year, destroying whole villages and leaving more than 50 people dead.
The shift of subarctic forests and peatlands from a CO2-absorbing sponge to a net source of the gas means that these regions could help trigger accelerated global warming, the study warned.
"Essentially, it represents a runaway climate change scenario in which warming is leading to larger and more intense fires, releasing more greenhouse gases and resulting in more warming," said Turestsky.
The same vicious-circle effect -- what scientists call "positive feedback" -- is true of the shrinking Arctic ice cap, which has likewise become both symptom and cause of climate change.
As ice cover recedes decade-by-decade, more of the Sun's radiative force is absorbed by dark-blue ocean water rather than bounced back into space by reflective ice and snow.
The Arctic and subarctic regions have been hit particularly hard by global warming, with temperatures rising two to three times faster than the global average.
In the study, Turetsky and colleagues examined nearly 200 forest and peatland sites in Alaska shortly after blazes were extinguished to measure how much biomass had burnt.
The amount of scorched earth has doubled in interior Alaska over the last 10 years, mostly because of increased burning late in the fire season, they found.
"We have demonstrated for the first time that increases in burned area are clearly linked to increases in fire severity," said co-author Eric Kasische, a professor at the University of Maryland.
"This not only impacts carbon storage, but also will accelerate permafrost loss and changes in forest cover."
Ten of billions of tonnes of another potent greenhouse gas, methane, are also trapped inside permafrost.
The study comes out as ministers from nearly 200 countries gather in Cancun, Mexico in an attempt to hammer out an agreement on how to keep global warming in check and cope with future impacts.
By week's end, the UN forum could announce measures to slow tropical deforestation, which both releases CO2 and shrinks the biomass that soaks it up.
The destruction of equatorial forests in Latin America, Asia and Africa accounts for 12 to 15 percent of the carbon pollution released into the atmosphere each year, according to recent calculations.
Boreal forests, however, have received scant attention at the talks.
