Perilous Times and Climate Change
As Arctic Temperatures Rise, Tundra Fires Increase
The 2007 Anaktuvuk River Fire burned more than 1,000 square kilometers
of tundra on Alaska's North Slope. It was the largest tundra fire in
the region in recorded history. Credit: Bureau of Land Management
by Staff Writers
Champaign IL (SPX) Nov 19, 2010
In September, 2007, the Anaktuvuk River Fire burned more than 1,000
square kilometers of tundra on Alaska's North Slope, doubling the area
burned in that region since record keeping began in 1950.
A new analysis of sediment cores from the burned area revealed that
this was the most destructive tundra fire at that site for at least
5,000 years. Models built on 60 years of climate and fire data found
that even moderate increases in warm-season temperatures in the region
dramatically increase the likelihood of such fires.
The study was published this October in the Journal of Geophysical
Research.
After the Anaktuvuk fire, University of Illinois plant biology
professor Feng Sheng Hu sought to answer a simple question: Was this
seemingly historic fire an anomaly, or were large fires a regular
occurrence in the region?
"If such fires occur every 200 years or every 500 years, it's a natural
event," Hu said. "But another possibility is that these are truly
unprecedented events caused by, say, greenhouse warming."
On a trip to Alaska in 2008, Hu chartered a helicopter to the region of
the Anaktuvuk fire and collected sediment cores from two affected
lakes. He and his colleagues analyzed the distribution of charcoal
particles in these cores and used established techniques to determine
the approximate ages of different sediment layers.
The team found no evidence of a fire of similar scale and intensity in
sediments representing roughly 5,000 years at that locale.
The researchers then analyzed 60 years of fire, temperature and
precipitation records from the Alaskan tundra to determine whether
specific climate conditions prevailed in years with significant tundra
fires. They developed a model relating the tundra area burned in Alaska
each year to the mean temperature and precipitation in the warmest
period of the year: June through September.
This analysis uncovered a striking pattern, Hu said.
"There is a dramatic, nonlinear relationship between climate conditions
and tundra fires, and what one may call a tipping point," he said. Once
the temperature rises above a mean threshold of 10 degrees Celsius (50
degrees Fahrenheit) in the June-through-September time period, he said,
"the tundra is just going to burn more frequently."
For the past 60 years, annual mean temperatures during this warm season
have fluctuated between about 6 and 9 degrees Celsius (42.8 to 48.2
degrees Fahrenheit), with temperatures trending upward since 1995. In
2007, the year of the historic fire, the mean temperature was a record
11.1 degrees Celsius, while precipitation and soil moisture dipped to
an all-time low.
Higher precipitation, if it occurs, could dampen the effects of higher
temperatures, but only to a limited extent, said Philip Higuera, a
professor of forest ecology and biogeosciences at the University of
Idaho and a co-author on the study.
"As temperature rises, so too does evaporation," he said. "So even if
future precipitation increases, it's likely that increased evaporation
will result in overall lower moisture availability. This affects
plants, but it also makes dead vegetation more flammable and fire
prone."
The study team also included researchers from the University of Alaska
Fairbanks, Neptune and Company, and the University of Washington.