Northern wildfires threaten runaway climate change, study reveals

Dec 05, 2010
This is an image of wildfires in the Alaskan Interior. A new study reveals that climate change is causing these fires to burn more fiercely over the last decade which has resulted in an increase in greenhouse gases being pumped into the atmosphere. Credit: David Wright, US Forest Service

Climate change is causing wildfires to burn more fiercely, pumping more greenhouse gases into the atmosphere than previously thought, according to a new study to be published in Nature Geoscience this week.

This is the first study to reveal that fires in the Alaskan interior - an area spanning 18.5 million hectares - have become more severe in the past 10 years, and have released much more carbon into the atmosphere than was stored by the region's forests over the same period.

"When most people think of wildfires, they think about trees burning, but most of what fuels a boreal is plant litter, moss and organic matter in surface soils," said University of Guelph professor Merritt Turetsky, lead author of the study.

"These findings are worrisome because about half the world's is locked in northern permafrost and peatland soils. This is carbon that has accumulated in ecosystems a little bit at a time for thousands of years, but is being released very rapidly through increased burning."

The results of this study are important for countries currently meeting in Mexico for climate talks, added the integrative biology professor.

"Essentially this could represent 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. This cycle can be broken for a number of reasons, but likely not without dramatic changes to the as we currently know it."

This study is part of a growing body of evidence that northern systems are bearing the brunt of climate change, said co-author Jennifer Harden, a U.S. Geological Survey scientist.

"This includes longer snow-free seasons, changes in vegetation, loss of ice and permafrost, and now fire, which is shifting these systems from a sink toward a carbon source."

The researchers visited almost 200 forest and peatland sites shortly after blazes were extinguished to measure how much biomass burnt.

This is an image of wildfires in the Alaskan Interior. A new study reveals that climate change is causing these fires to burn more fiercely over the last decade which has resulted in an increase in greenhouse gases being pumped into the atmosphere. Credit: Roger Ottmar, US Forest Service

"We've been chasing fires in this region for a number of years, which is how we amassed this unique data set," said Turetsky.

They also looked at fire records kept since the 1950s.

"Over the past 10 years, burned area has doubled in interior Alaska, mostly because of increased burning late in the fire season," said co-author Eric Kasischke, a University of Maryland professor. "This is the first study that has demonstrated that increases in burned area are clearly linked to increases in fire severity. This not only impacts carbon storage, but also will accelerate permafrost loss and changes in forest cover."

More severe burning also raises a number of health concerns, as fire emissions contain mercury and particulate matter that can cause respiratory issues, said Turetsky.

"We are hoping people will recognize the seriousness of for northern regions and people living in them. Wildfire is going to play a more and more important role in shaping the north."

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Provided by University of Guelph

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User comments : 14

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apex01
3 / 5 (10) Dec 05, 2010
It seems they've cranked it up a notch on throwing out the global warming propaganda. I keep on noticing more and more climate change articles.
designmemetic
3.7 / 5 (3) Dec 06, 2010
Is this actually a carbon increase over the long term? What is the response to the forest fire over time in respect to carbon?

Charcoal is a stable solid rich in carbon content, and thus, can be used to lock carbon in the soil. Let the tree fall over and die on it's own releases carbon too and a forest without fires is carbon neutral. Carbon only gets sequestered in tree matter when trees peat, etc are growing(increasing their mass by adding mostly carbon from the air). If you want less carbon over the long term you need to either bury the tree or burn to a carbon dense charcoal or ash so a new tree can grow in it's place.

or maybe I've misunderstood the carbon cycle? any thoughts?
CarolinaScotsman
5 / 5 (1) Dec 06, 2010
A new study reveals that climate change is causing these fires to burn more fiercely

Could someone please explain how climate change causes fires to burn "more fiercely"? I know that in the lower 48, forest fires are more intense now than in the past due to long periods of fire suppression allowing underbrush and other plant litter to accumulate and fuel hotter fires. Has this also happened in Alaska? I don't understand how climate change in and of itself would cause fires to be more intense. (This is a serious question, not a denial of change.)
GSwift7
not rated yet Dec 06, 2010
@ designmemetic:

Yes, you have it exactly right. Without fires, the amount of carbon stored long term would be much less. Most non-fire biomass decays quickly, creating greenhouse gasses and raising the acidity of ground water which leaches into lakes and rivers. The fires stop that decay process and store the carbon long term as char. Unfortunately, the average natural fire only consumes between 20 and 30 percent of the avialable biomass. The average time span between natural fires without human intervention is between 40 and 150 years, depending on local conditions. Many plants and animals depend on the fires for survival, and many species would go extinct without them. The giant redwoods and the animals that depend on them are a good example of that. The 10 to 20 years following a fire are the time when a forest will consume the most carbon. From the time a forest reaches maturity to the next fire is the time it consumes the least carbon. It's not a sink when in equilibrium.
Modernmystic
3.4 / 5 (5) Dec 06, 2010
Can I get a study to see if global warming is responsible for the recent increase of the stupidity of the average shopper at Walmart?
thermodynamics
4 / 5 (4) Dec 06, 2010
CarolinaScotsman: Good question: "Could someone please explain how climate change causes fires to burn "more fiercely"?"

The reason they postulate for more CO2 and fiercer fires is: "Over the past 10 years, burned area has doubled in interior Alaska, mostly because of increased burning late in the fire season,"

What they seem to be saying is that more area is burning and, since it is later in the season (as the data shows winter coming on later) the ground is drier than usual. Those two issues mean that the fire will be hotter (burning deeper) and the area will be larger (affecting more carbon stores). I have been involved in large fires in California and the bigger they are the more "fierce" and dangerous they become. Very large fires produce their own local weather patterns with large updrafts to bring oxygen to the base of the fires. Those fires are much hotter than small fires.
GSwift7
not rated yet Dec 06, 2010
Wow, I can't believe you guys rated each other 1/5.

I personally thought modern's post was funny, and thermo's post was an accurate summary of the above article.

The part of the article that thermo repeated is probably correct, and seems logical, however the rest of the article is dead backwards in regard to forest fires and long term carbon sequestration. I love it when these guys mix credible science with pure science fiction. The average person wouldn't have a clue.
Loodt
1.8 / 5 (5) Dec 06, 2010
thermodynamics,

You stated that very large fires are hotter than small fires.

Are you confusing the amount of heat generated with the temperature of combustion?

Some peer reviewed studies to back up that sweeping statement would be in order.
thermodynamics
5 / 5 (4) Dec 06, 2010
Loodt: You asked: "You stated that very large fires are hotter than small fires. Are you confusing the amount of heat generated with the temperature of combustion?" The answer is no I did not. Let me try to explain and it involves your other question: "Are you confusing the amount of heat generated with the temperature of combustion?" This is a good question and has a lot to do with the way burners are designed for industrial combustion.

There is a theoretical flame temperature called the adiabatic flame temperature in which combustion is assumed to take place without loss of energy during the time the flame is completely burning the fuel:

http://en.wikiped...perature

In computing the adiabatic flame temperature the amount of heat generated is assumed to go completely to raising the temperature of the combustion products and the rate of combustion is considered to be almost instantaneous.

Continued
thermodynamics
5 / 5 (4) Dec 06, 2010
Continued for Loodt: In actual combustion the fuel burns at a finite rate and heat is radiated away to the surroundings at the speed of light. This drops the temperature.

There is another feature of burning in air which has to do with the increase in NOx production with temperature.

http://en.wikiped...wiki/NOx

Fires involving biomass or coal have both thermal NOx and fuel NOx. However, as you can see from the article I quoted above, the amount of NOx is dependent on the temperature of the combustion products. One of the most prevalent tools for NOx control is called "Staged combustion" in which oxygen is introduced in stages to slow the combustion of the fuel. That means that the temperature of the flame (combustion products) can be controlled by the rate at which the oxygen is introduced to the fuel (this can become very complex when you start considering "diffusion limitations).

Continued
thermodynamics
5 / 5 (4) Dec 06, 2010
Continued for Loodt: Here is one of hundreds of references to staged combustion burners - which are the standard for the industry:

http://www.samiac...ners.htm

Now, let me try to tie this back to forest fires (or tundra fires). When there is a small fire the updraft is not as strong as when there is a large fire. In fact, there are "fire storms"

http://en.wikiped...irestorm

The resulting inrush of air (oxygen) works like a bellows to more quickly ignite and sustain ignition of the fuel. The bottom line is an increase in the temperature. This can be expected for any large scale fire and is something that is feared by firefighters when forest fires start.

Let me know if this is not clear enough. I hope you can see that I am not confusing heat with the temperature of combustion and the temperature of combustion can vary widely depending on the available oxygen.
GSwift7
5 / 5 (1) Dec 07, 2010
Yes, Thermo is right. As I stated above, the average forest fire only burns a small portion of the avialable fuel (sources I found claim 20-30%). Larger fires will reach higher into the forest canopy and also will burn more of the fuel at ground level. That leads to the other problem I have with this article. Although what they claim seems logical and may be true, it's not as clear cut as they make it sound. The intensity of fires in a given area are inversely related to the frequency of fires in that area. The longer you go between fires, the more intense the fires will be and visa versa. Also, once you have a really intense fire, it takes that much longer before the forest builds back up to the point where it can fuel another intense fire. It's a self-regulating cycle based on the rate of growth of the forest. You can't have a fire without fuel. As I said above, many trees need the fires. Some trees can't open seed pods without a really intense fire event. They are misleading a bit.
GSwift7
5 / 5 (1) Dec 07, 2010
In the giant redwood forests, we have probably destroyed those trees by doing controlled burns to prevent large fires. Those trees need especially intense fires to reach up into their high branches and open their tough seed pods. Forestry department fire prevention efforts use small fires wich aren't hot enough or high enough for those trees. Ironically, the one thing that could save those trees may be a parasite worm, which tends to eat the seed pods and thereby release the seeds. The forestry deepartment attmepted to kill the worms by spraying, until they realized that the worms actually help the trees. Another irony is that there wouldn't be giant redwood forests if not for human interference. The prehistoric native americans burned the secondary forest and underbrush for hunting reasons, wich allowed the redwoods to thrive and take over. At least that's how the theory goes, as best they can tell.
GSwift7
5 / 5 (1) Dec 07, 2010
It's also worth noting that parasite population explosions, like termites or catapilars, can release just as much, if not more, CO2 as a forest fire. In fact parasites tend to release waste gases like methane which are worse greenhouse gases than CO2 in some ways. Forest fires help to control parasite populations, so it's a double edged sword in more ways than one.