Global Warming Linked with Frequent Fires in Alaska's Boreal Forests

A new study from the University of Illinois has shown that Yukon Flats of interior Alaska, one of the most flammable regions of the world, is seeing more frequent and severe fires now than it had in the past 10,000 years. Researchers attribute this increase to global warming.

Recently, large wildfires in Alaska have charred more than half a million acres at a time, The Los Angeles Times reported. Another recent study had found that wildfires may drive up global warming by releasing more carbon-containing particles.

The boreal forests or taiga that was studied in this research, covers about 10 percent of Earth's land surface and holds more carbon than the atmosphere. The study shows that these forests are experiencing more frequent fires- about one major fire every 50 years.

The present study supports the idea that frequent wildfires in Alaskan forests are converting coniferous jungles to deciduous ones. Both white and black spruce that once dominated the landscape is more susceptible to fires than the deciduous trees.

The study was based on the analysis of the mud collected from the bottoms of 14 deep lakes in the Yukon Flats. Researchers looked for traces of charcoal and pollen content of these samples.

"We reconstructed the fire history by picking charcoal fragments out of sediments preserved over thousands of years," said Ryan Kelly from University of Illinois, lead author of the study with Illinois plant biology professor Feng Sheng Hu. "And from what we can tell, the fire frequency at present is higher than it has been at any time in the past 10,000 years."

The experts analyzed samples from the Holocene period. Researchers said that knowing how climate change affected the forests in the past can help understand effects of climate change in the future. The Holocene epoch is the name given to the last 11,700 years of the earth's history, which is very recent on the geological timescale.

The team particularly looked for the samples from the Medieval Climate Anomaly (MCA), which occurred about 1,000 to 500 years ago. This was a warm period during the Holocene and the Yukon Flats had similar tree species and temperature as it is today.

"This period probably wasn't really as warm as today, definitely not as warm as it's bound to get in the future, but may be the most similar to today," Kelly said. "There was lots of burning, almost as much as today, and the fires were particularly severe."

Kelly said that current wildfire severity and frequency has surpassed the wild fires of the MCA. The average fire frequency has been 20 fires per 1,000 years in the last 50 years while it was about nine or ten fires per thousand years during the last 3,000 years, according to a news release.

"That's like a fire every 50 years, whereas in the past it was closer to a fire every hundred years," Kelly said.

Researchers added that the burning of boreal forests will increase the greenhouse effect and in the future, even the deciduous forests may catch fire due to dry, hot weather.

The study is published in the journal Proceedings of the National Academy of Sciences.