Earth's fiery past and future modeled by NASA

Oct 28, 2010 By Adam Voiland
Assuming "maximum" emissions, the GISS wildfire model predicts fires will become less common in some areas (shown in dark blue) and more common in others (shown in dark yellow) by 2100. Credit: NASA/GISS/Pechony

Wildfires may seem like a fixed and unchanging force of nature. They're not. Over long time scales, research has shown that both the climate and humans have a profound effect on wildfire activity around the globe. Now new NASA research shows that while we have been suppressing this natural force for the past century, we may be, inadvertently, about to put nature back in control.

Charcoal layers in sediments and methane concentration in ice cores show that the amount of global burning can fluctuate dramatically over time. The charcoal records, derived from and peats at hundreds of sites around the world, show a distinct lull in burning from about 1600 to 1750 that leads into an unprecedented surge in fires beginning around 1800. Then, around 1900, global fire occurrence begins a rapid decline that continues until the present.

What drives such powerful swings in activity? And what do such trends bode for the future? Wildfire experts have long suspected that the vagaries of the – especially changes in temperature and moisture – govern wildfire abundance. Yet, parsing out the impact of humans -- who have a knack for both igniting and suppressing wildfires – has made answering such questions difficult.

NASA researchers Olga Pechony and Drew Shindell believe they have finally started to provide solid answers with the help of a new wildfire model that has produced the first long-term history of global burning. Their new wildfire model – which captures past trends well and offers predictions about futures trends — models global wildfires more accurately than previous models. Pechony and Shindell developed the model at the Goddard Institute for Space Studies (GISS) in New York City, and published a study this week in the Proceedings of the National Academy of Sciences based on its results.

This map, part of a broader animation showing monthly global fire activity, shows where fires burned in September. The maps are based on observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. For more information about this animation, please visit the NASA Earth Observatory. Credit: NASA/Goddard/Earth Observatory

Pechony and Shindell's wildfire model is not the first or only attempt to model wildfires. Previous efforts have attempted to estimate fires based upon soil moisture, vegetation availability, and lightning trends. However, earlier models have only been validated at a few locations, and none have been validated globally against satellite records, which are the only source of consistent information about fires at a global scale.

Looking forward

The narrative the model weaves is fascinating. Whereas variations in precipitation long dominated fire trends, the model shows that a dramatic population boom following the Industrial Revolution has made humans the primary force driving wildfire trends since the 18th century. "But now things are changing again," said Pechony, the lead author of the study. "Our projections show that our rising temperatures – this time driven by humans – are on the verge of reasserting control over the world's fires."

By combining the newer fire model with an existing climate model developed at GISS, Pechony and Shindell ran their model back to 844 to check how well they could capture past conditions, and forward to 2100 to simulate future wildfire trends under different climate regimes. When projecting forward, they modeled three different greenhouse-gas emissions scenarios, including one that curtailed greenhouse gas emissions significantly, one that assumes they continue unabated, and one in the middle. All three produced rapidly rising temperatures, regional drying, and increases in fire abundance.

If their modeling is correct – and it likely is given how well it replicates the last 1,000 years of wildfire history – climate change will have complex consequences for future wildfire trends. Pechony and Shindell predict just a modest global increase—about 5 percent -- in wildfire abundance by 2100 if emissions continue unabated and population grows steadily, but they conclude changes from region to region will vary dramatically.

"Some areas will experience more wildfires and some less due to the nature of changing circulation patterns," Shindell said. The other scenarios -- those that assume midrange and minimal emissions -- produced 20 percent and 35 percent global increases in fire activity by 2100. (Paradoxically, the scenarios that assume more greenhouse gas emisions produce less wildfires because they also assume more population growth, which generally leads to fewer wildfires because of more aggressive firefighting.)

The new fire model predicts large increases in fire activity in India, Australia, central Asia and Siberia, southern Europe, and southern Africa. However, it also foresees significant decreases in fire activity in northern Europe and equatorial Africa and South America because of increased precipitation in those areas. Likewise, by 2100 it predicts more burning in a drier western United States, and less burning in a wetter eastern United States (though wildfires are already quite rare in the eastern United States due to the moist climate). Fire frequency has already increased in the western United States during the late 20th century, and the future projections show further increases of about 30 to 60 percent in that region.

Global average fire abundance has decreased significantly since 1900 as technological advances in fire-fighting – particularly planes and flame retardants – have become available. By 2050, according to the model, global warming will have reversed that steady decline, and the global climate will again become the primary driver of fire abundance worldwide.

Reconstructions of fire activity based on charcoal records shows fire history over the last millennium (gray). The new wildfire model (red) matches the charcoal record closely. When combined with climate models, it suggests that global fire activity could increase by between 5 and 35 percent depending on future greenhouse gas emissions, development patterns, and demographics. In the scenario that assumes greenhouse gas increases continue unabated and thus produces “maximum” emissions - A2 - the model actually predicts less wildfire activity because that scenario also assumes rapid population increases, which generally lead to fewer wildfires because of more aggressive firefighting. Credit: NASA/GISS/Pechony

Building a Fire Model

Unlike other wildfire models, the GISS scientists used data from numerous satellite instruments to validate their model. Its precipitation data, for example, comes from the Global Precipitation Climatology Project (GPCP) that combines data from several spaceborne instruments and rain gauges. Its estimates of vegetation – critical wildfire fuel – come from data produced by NASA's Moderate Resolution Imaging Spectrometer (MODIS) instrument. Its fire activity data was based on information from MODIS, Visible and Infrared Scanner (VIRS) and the Advanced Very High Resolution Radiometer (AVHRR), an instrument that has flown on multiple satellites. It used lightning data collected by the Optical Transient Detector (OTD), aboard the MicroLab Satellite.

As a result, it produces results that replicate the modern distribution and the historical record well. Just like the historical charcoal record, for example, the model produces an increase in fire activity during the late 15th century—a period that was cold and dry due to a slow-down in solar activity.

No model is perfect, both Pechony and Shindell emphasize. There are a number of assumptions on human-fire interactions, for example, in the model that will surely be refined as better data becomes available. And there are some areas where the model does not conform as closely to the historical record as Pechony and Shindell would like.

Still, it represents a major step forward in wildfire climate modeling as this is the first time any scientist has reconstructed the causes of a thousand-years of fire history. "This is an important study," said Paulo Artaxo, a professor at the University of Sao Paulo and an Amazonian wildfire expert. "The shift from human-driven fires in the recent decades to climate-driven fire activity is very important. It will add even more carbon to the atmosphere, something which may intensify the cycle of warming and burning going forward."

Explore further: Study casts doubt on climate benefit of biofuels from corn residue

More information: www.pnas.org/content/early/2010/10/20/1003669107.abstract

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GSwift7
3 / 5 (6) Oct 28, 2010
Why does it seem like the GISS is deliberately trying to mislead people?

From the last paragraph:
"It will add even more carbon to the atmosphere,"

That is totally wrong. Forest fires DO result in a SHORT TERM addition of carbon to the atmosphere. They also result in a virtually permanent deposite of solid carbon in the ground, as evidenced by the charcoal records mentioned in this very article. If not for the fire, all that charcoal would still be cycling through the carbon cycle rather than burried in sediment. The net result of a forest fire is carbon sequestration.

That's just one problem I have with this article. Every statement from GISS lately is full of junk like that.
Skeptic_Heretic
2.8 / 5 (5) Oct 28, 2010
If not for the fire, all that charcoal would still be cycling through the carbon cycle rather than burried in sediment.
If not for the fire, all that carbon would be a tree.

When you burn the forest, you release carbon. The charcoal carbon you're referring to is already captured, as a tree, not cycling freely in the atmosphere.
GSwift7
5 / 5 (3) Oct 28, 2010
And then the tree dies and decays, returning nearly 100% of that carbon to the atmosphere until another tree grows. The long term net effect is nearly zero permanent carbon sequestration. Besides, most carbon stored in a forest is not consumed in a forest fire. Most of it remains unconsumed and falls to the ground to become charcoal, which is permanent sequestration, and then a new forest grows over it to start the cycle again.

The effect is called permanency. A standing forest holds only a given amount of carbon. Once it reaches the max level, it stops absorbing carbon because it re-emits it as fast as it absorbs it. A fire breaks that cycle, and permanently stores a large amount (more than half) of the carbon in the forest as sediment.
GSwift7
5 / 5 (2) Oct 28, 2010
Here's an article from the very same GISS which published the above article, detailing how forests max out on carbon storage at about 70 years old.

http://www.nasa.g...bon.html

The only way to get them to absorb more carbon, is by taking down the forest and starting over. If that is done by burning, then most of the carbon in the old forest is stored in the ground after the fire.
GSwift7
5 / 5 (2) Oct 28, 2010
Here's a study from OSU detailing how as little as 1-3% of living trees are actually consumed in even an intense forest fire:

http://oregonstat...imated-0

Skeptic_Heretic
2.3 / 5 (3) Oct 28, 2010
And then the tree dies and decays, returning nearly 100% of that carbon to the atmosphere until another tree grows. The long term net effect is nearly zero permanent carbon sequestration.
That's false. How do you think topsoil, which is primarily carbon rich, is generated? The decay of plantlife especially the leaves from those same trees, breaks down leaving behind a mineral mass. The carbon sequested in the ground through the root system is also of note here.

You're ignoring the majority of dynamics involved in a total forest carbon sink measurement.
Here's a study from OSU detailing how as little as 1-3% of living trees are actually consumed in even an intense forest fire

Forest fires are required in order to continue the sinking of carbon as dead trees are burned up while the living and younger trees, which are a greater sink, now gain access to more sunlight, allowing for a greater sink.

We've drastically interrupted this process by preventing forest fires
GSwift7
5 / 5 (1) Oct 28, 2010
okay, so you agree with me that this statement from the original article is false then: "It will add even more carbon to the atmosphere"

You are really only disagreeing with me because you are not differentiating between a carbon sink and a pool. The forest is a pool after about 70 years of growth. Unless you somehow make it reset, it will remain a stable pool forever (theoretically), as demonstrated by the above linked study from OSU. A forest fire returns less than half of the carbon from the forest pool back to the atmosphere, and permanently sequesters some of it in the soil. Then the forest regrows becoming a temporary sink again, until it matures and becomes only a stable pool once more. According to the OSU study, fires of 40-70 year frequency should maximize the sink mechanism and minimize the time the forest spends as a stagnant pool. That's much more frequent than the current natual frequency of fires, so increased fire frequency will help, not hurt, co2 sequestration.
GSwift7
5 / 5 (2) Oct 28, 2010
"That's false. How do you think topsoil, which is primarily carbon rich, is generated? The decay of plantlife especially the leaves from those same trees, breaks down leaving behind a mineral mass"

Actually that's false too. Top soil actually plateaus as a carbon sink and becomes a stable pool just like the forest does. After it reaches equilibrium, it gives off as much carbon as it takes in. In an area like where I live, there is almost zero top soil, so that equilibrium is reached very quickly. In the north-east US the ecology allows for a thick layer of top soil before it reaches equilibrium. Top soil is not a bottomless pit of carbon sequestration, and fire-produced black carbon and char is much more stable than carbon stored in non-fire top soil carbon. So every time there is a fire, it increases the % of long-lived carbon in the top soil. Increased fire frequency will accelerate that gain as long as the frequency isn't TOOO short.
Skeptic_Heretic
4.3 / 5 (4) Oct 28, 2010
Top soil is not a bottomless pit of carbon sequestration, and fire-produced black carbon and char is much more stable than carbon stored in non-fire top soil carbon. So every time there is a fire, it increases the % of long-lived carbon in the top soil. Increased fire frequency will accelerate that gain as long as the frequency isn't TOOO short.
We're not disagreeing on that point, but to insist we should be slashing and burning forests, as you're claiming is absolutely contrary to established science. That is unless I've completely misunderstood your posts as so far.
GSwift7
not rated yet Oct 29, 2010
Yes, that's not what I said. My post has nothing to do with intentional burning of forests. My post is in regard to the subject of this article. The GISS is trying to assert, in this article, that manmade global warming will increase the rate of forest fires, both natural and accidental. I'm not going to touch that one, but you know how I feel about MAN-MADE global warming. Let's just assume they are correct about that point for now because I'm too tired to fight about that again. They then go on to further assert, in the final closing remark of the article, that an increase in the frequency of forest fires will have a net result of increasing atmospheric CO2. That is clearly wrong, and I'm willing to bet they know better. They may be politicized fearmongers, but they know their science well enough to know darn well that fires trap carbon in the soil more efficiently than any other natural process. Their own model focused on that very carbon as a proxy record of fire history.
Skeptic_Heretic
not rated yet Oct 29, 2010
I think you and I are looking at the utility of the tree/fire cycle from different aspects simply because we're looking at different timescales.
GSwift7
5 / 5 (1) Oct 29, 2010
I'm looking at decades at least, but centuries are appropriate when you're talking about tree growth. Natural forestfire and wildfire rates are on scales ranging from years to centuries depending on the location.

It's annoying, and probably deliberate, that they don't include any actual frequency data in the above article, choosing in stead to only give % deviations. This is from another report on the GISS web site: "Wildfires burn down individual areas every 40 to 250 years and are an important part of this ecosystem". So, I think the relevant time scale is at least four decades, but an average number somewhere closer to 150 years is a more relevant time frame. If you only want to look at the 10 years immediately following a fire, then you are only talking about short term, local effects, not global climate impacts, which is what the above article is talking about. I'm responding to this article, and proposing that it's poorly presented at best.
GSwift7
5 / 5 (1) Oct 29, 2010
By the way, remember when you and I and a couple others were talking about a "manhattan project" for energy research? I was listening to my senator, Lindsey Graham, on a local radio call-in show the other day, and he actually used that phrase. It would be really cool if he could get momentum going in Washington on something like a solar power manhattan project. It surprised me to hear him say that, especially using those exact words.
Skeptic_Heretic
5 / 5 (2) Oct 29, 2010
If you only want to look at the 10 years immediately following a fire, then you are only talking about short term, local effects, not global climate impacts, which is what the above article is talking about. I'm responding to this article, and proposing that it's poorly presented at best.
Ok then we're in agreement.

I heard Graham as well. I'd vote for anyone putting up their full support for such an effort. What a great way to get some jobs and economic growth at the least.
Ravenrant
1 / 5 (1) Oct 30, 2010
Our fiery future isn't natural. As our population grows, so does the population density of sick, stupid fire bugs. They are burning up this country. They are also burning up rainforests in south america and asia. And it will only get worse. Stoopid monkeys.
jsa09
1 / 5 (1) Oct 31, 2010
But as our population grows more forests will be cut down and turned into parking lots so we wont have to worry about the forest fires as much. After all what harm can they do when all the forests are only little parks.

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