Humans caused 84% of US wildfires from 1992 to 2012

Although climate change has been blamed for an increase of wildfires in the United States, a new paper, published in the Proceedings of the National Academy of Sciences, concluded that 84% of fires were ignited by humans and this extended the fire season by a factor of three.

Here is the paper abstract:

The economic and ecological costs of wildfire in the United States have risen substantially in recent decades. Although climate change has likely enabled a portion of the increase in wildfire activity, the direct role of people in increasing wildfire activity has been largely overlooked. We evaluate over 1.5 million government records of wildfires that had to be extinguished or managed by state or federal agencies from 1992 to 2012, and examined geographic and seasonal extents of human-ignited wildfires relative to lightning ignited wildfires. Humans have vastly expanded the spatial and seasonal “fire niche” in the coterminous United States, accounting for 84% of all wildfires and 44% of total area burned. During the 21-y time period, the human-caused fire season was three times longer than the lightning-caused fire season and added an average of 40,000 wildfires per year across the United States. Human-started wildfires disproportionally occurred where fuel moisture was higher than lightning-started fires, thereby helping expand the geographic and seasonal niche of wildfire. Human-started wildfires were dominant (>80% of ignitions) in over 5.1 million km2 , the vast majority of the United States, whereas lightning-started fires were dominant in only 0.7 million km2, primarily in sparsely populated areas of the mountainous western United States. Ignitions caused by human activities are a substantial driver of overall fire risk to ecosystems and economies. Actions to raise awareness and increase management in regions prone to human-started wildfires should be a focus of United States policy to reduce fire risk and associated hazards.

Read the full paper here:


Study: Forest Fires in Sierra Nevada Driven by Past Land Use not Climate Change

Researchers from the University of Arizona and Penn State studied fire regimes in the Sierra Nevada Mountain of California for the period 1600 to 2015 and found that land use changes, not climate, were the principal controlling factors.

This result was apparently a surprise to the researchers since they set out to correlate climate with the fires.

“Initially, we did work to see if we could develop long-lead forecasts for fire in the area — six to 18 months in the future — using climate patterns such as El Niño,” said Alan H. Taylor, professor of geography, Penn State. “This would be a significant help because we could place resources in the west if forecasts indicated it would be dry and the southeast would be wet. However, the climate relationships with fire did not consistently track.”

“We were expecting to find climatic drivers,” said lead co-author Valerie Trouet, a UA associate professor of dendrochronology. “We didn’t find them.”

The researchers used tree ring data from 29 sites, historical documents, and 20th Century records of areas burned.

From the UofA press release:

For the years 1600 to 2015, the team found four periods, each lasting at least 55 years, where the frequency and extent of forest fires clearly differed from the time period before or after. The team found the fire regimes corresponded to different types of human occupation and use of the land: the pre-settlement period to the Spanish colonial period; the colonial period to the California Gold Rush; the Gold Rush to the Smokey Bear/fire suppression period; and the Smokey Bear/fire suppression era to present. Finding that fire activity and human land use are closely linked means people can affect the severity and frequency of future forest fires through managing the fuel buildup and other land management practices — even in the face of rising temperatures from climate change.

From the Penn State press release:

Early fires, because they were more frequent, with less fuel build-up, were “good” fires. They burned through the forest, consumed understory fuels and left the majority of trees unharmed. The Native American mosaic of burned and unburned areas prevented fires from continuously spreading.

From 1776 to 1865 the second fire regime, characterized by Spanish colonialism and the depopulation of Native Americans in the area, shows more land burned. European settlers brought diseases against which Native Americans had no immunity and the population suffered. The Spanish built a string of missions in California beginning in 1769 and relocated remaining Native Americans to the mission areas. In 1793, there was a ban on burning to preserve forage, disrupting the pre-colonial Native American burning practices. The incidence of fires became more sensitive to drought and the fire regime changed, creating the time when fires were largest and most closely coupled with climate.

The third fire period is from 1866 to 1903 and was initiated by the California gold rush, when thousands of people poured into the area. Settlement by large numbers of new immigrants began to break up the forest fuel and the creation of large herds of animals, especially sheep, removed large amounts of understory and changed the fire regime.

The fourth fire period began in 1904 and is linked to the federal government’s policy of fire suppression on government lands. The reason pre-colonial and Spanish colonial fire levels were so much higher than today is that the current fire regime is one of suppressions with an extremely low incidence of fires compared to the past. However, suppression over the last century has allowed fuel to build up on the forest floor and opened the door for “bad” fires that destroy the forest canopy and burn large areas of land.

(UofA press release, Penn State press release, paper abstract )

This finding contradicts an alarmist story printed in the Arizona Daily Star this past October (see third reference below).


See also:

Wildfires and Warming – Relationship not so clear
Claim: “Worsening Wildfires Linked to Temp Rise

Media hype about forest fires and global warming
Mega-fires in Southwest due to forest mismanagement

Claim: “Worsening Wildfires Linked to Temp Rise”

On Tuesday, Oct 11, 2016, the Arizona Daily Star printed a front page, top of the fold story from the Associated Press (AP) with the title claimed above. The Star’s online version (with a different title) can be found here.

The story claims: “Rising temperatures are flatly to blame for recent fearsome fire seasons, leading scientists reported Monday.” It also claims: “The study showed that more than a century of fossil-fuel burning, deforestation and farming has helped push the American West into an explosive new wildfire regime, and the findings suggest far worse could be ahead.”

The AP story never gives a link or even mentions the title of the paper, but I found it through other sources. The paper itself, “Impact of anthropogenic climate change on wildfire across western US forests” is pay-walled, but you can read the abstract here.

I have two problems with this story: one with the research and one with the way AP reported it.

Science first:

The paper abstract says: “We use modeled climate projections to estimate the contribution of anthropogenic climate change to observed increases in eight fuel aridity metrics and forest fire area across the western United States….We estimate that human-caused climate change contributed to an additional 4.2 million [hectares] of forest fire area during 1984–2015, nearly doubling the forest fire area expected in its absence.”

I presume these are the same climate models which can’t get their temperature projections even close to reality. From that they conjure a contribution from “Anthropogenic increases in temperature” even though there is no physical evidence to support such an assumption.

I also found it very curious that they chose 1984 as the start point.

The National Interagency Fire Center provides a table listing the number of fires and acres burned from 1960 through 2015 (link). In 1984, they report that there were 20,493 fires that burned 1,148,409 acres. In 2015, they report that there were 68,151 fires that burned 10,125,149 acres. That would seem to support the hypothesis that there are more fires with warming. It says nothing about the alleged anthropogenic cause of warming.

BUT: here is what the researchers and press releases left out. In 1960, there were 103,387 fires that burned 4,478,188 acres. That high number of fires continued into the early 1980s. In 1981 there were 249,370 fires that burned 4,814,206 acres. In 1963, fires burned 7,120,768 acres; in 1969 fires burned 6,689,081 acres. The drastic drop in the number of fires from 1982 to 1983 was followed by a gradual increase in acres burned. That could reflect a change in fire policy rather than a response to warming. Could this paper represent cherry-picking data that fits the hypothesis and while ignoring data that doesn’t?

A large body of research shows that wildfires both increased and decreased with rising temperatures depending on the locality. For the globe as a whole, there is no consistent relationship between temperature and acres burned. See a summary of that research here: http://www.co2science.org/subject/f/summaries/firegw.php

The graph below, based on analysis of charcoal trapped in sediments, shows a longer perspective of cyclical wildfire regimes (source:http://www.pnas.org/content/109/9/E535).

Fire western US biomass burned

“The great tragedy of Science – the slaying of a beautiful hypothesis by an ugly fact.” -T. H. Huxley

The AP report:

In describing the research, the unnamed AP writers use the terms “climate pollution” and “greenhouse gas pollution” when referring to carbon dioxide emissions. This indicates to me that the AP writers are ignorant of science, the fact that carbon dioxide is necessary for life on Earth, and that for most of the history of this planet carbon dioxide in the atmosphere has been 3- to 10 times higher than the current concentration. Or, is it just that these writers have imbibed deeply the global warming kool-aid? That the Arizona Daily Star continues to print stories like this indicates that they too are ignorant of science and have a political agenda.

See also:

Wildfires and Warming – Relationship not so clear

Media hype about forest fires and global warming

The (formerly) Scientific American magazine has a January 8 story proclaiming “Global Warming Helped Exacerbate Biggest Year Ever for U.S. Wildfires.” (See story)

That story claims: “More than 10.1 million acres of U.S. forests—private, state and federal—were scorched last year, marking 2015 as the most extensive and expensive fire season on record, according to numbers released Wednesday by the Forest Service.” [emphasis added] By the way, 5.1 million acres of that 2015 total were in Alaska.

The Scientific American claim is taken apart by two recent articles, one on Tony Heller’s Real Science blog, the other by Michael Bastasch in the Daily Caller.

Heller recovered a story from the New York Times, dated October 9, 1938, which reported that in 1937, 21,980,500 acres burned in the US. Heller also cites a 2001 paper authored by agencies of the federal government which states “Historically, fire has been a frequent and major ecological factor in North America. In the conterminous United States during the pre-industrial period (1500-1800), an average of 145 million acres burned annually.”

Bastasch’s story includes an interesting graph:

Wildfires in US

This graph shows that from about 1926 through 1940, is was common to have annual burns of 20 million to 30 million (and even 50 million) acres. And, Heller opines, the data from that period probably did not include Alaskan fires. Apparently, Scientific American no longer employs fact checkers.

Bastasch notes:

What’s most interesting is the years with the worst wildfires occurred when carbon dioxide emissions were only a quarter of what they are today. This is important because scientists claim CO2 and other greenhouse gases are heating up the planet and driving more wildfires.

Data going back nearly 90 years seems to indicate a negative correlation between CO2 and wildfires, but that changes when data is “cherry-picked” to only include data going back to the 1960s. A correlation between rising CO2 and wildfires magically appears when data only starts in the 60s.

For more background on the history of forest fires, see my ADI post:

Wildfires and Warming – It’s complicated

Scientific American is no longer very scientific. It has instead become an alarmist propaganda publication. It is stories like this that caused me to drop my subscription many years ago. “Facts do not cease to exist because they are ignored.” -Aldous Huxley

State of the climate – August 2013

Even thought atmospheric carbon dioxide reached almost 400 ppmin May of this year, we see little evidence that it has produced any warming.  Although the press has been claiming that global warming is spawning extreme, usual weather, we see little evidence of that also.  Anthony Watts of WUWT blog has a review of real data showing the state of the climate (see his post here).   Below, I provide some highlights from that post.

The Arctic warmed above freezing later in the year than usual and has dropped (at least temporarily) below freezing earlier.  Arctic sea ice extent is higher for August than it has been in the last five years, although it is still below the 1979-2000 mean.  See the black line in the graph below:


“Antarctic sea ice extent at the end of July was the highest on record for that day, growing to 18.077 million sq km. The previous record of 17.783 was set in 2010, whilst the 1981-2010 average was 16.869.”


For the year to date (August 9), the number of tornados is the lowest in the last 8 years.  See black line at bottom of graph:


Satellite temperature measurements of the lower troposphere show a slightly declining trend since the super El Nino in 1998.


Surface temperatures as recorded by the British HADCRUT database of land and sea surface temperatures show a nearly flat trend since 1998.


The Rutgers University Global Snow Lab shows winter extent of snow cover in the northern hemisphere among the four highest since 1967.

Northern hemisphere winter snow

Even though we have had some devastating forest fires this year, the National Interagency Fire Center statistics show that compared to other years, 2013 has had the smallest number of fires and the second smallest number of acres burned to date since 2004.


Even though carbon dioxide has been rising in the atmosphere, we are seeing none of the predicted effects of global warming that it is supposed to produce.

See also:

Mystery of the missing heat

Wildfires and Warming – Relationship not so clear

Last Sunday, Tony Davis had a story in the Arizona Daily Star with an apocalyptic headline: “Destructive Southwest wildfires bear ‘really clear’ sign of warming,” complete with a hockey stick-like graph of wildfires in the print edition.  The story itself is actually more balanced than the headline would suggest.  Maybe the headline was an editor’s idea. Throughout the story, however, Tony mentions “human-induced warming” without citing any supporting evidence that warming is human-induced.  The picture is not quite so “really clear” because the picture is complicated by many factors.

Two graphs below, which I constructed from data from the National Interagency Fire Center, would initially seem to support Tony’s contention, but as we will see, the data reflect just a regional effect during a short time interval that does not give a true picture.

Fire frequency

We see from these graphs, that

Fire Acres Burned

in the early 1980s, the frequency of fires in the U.S. dropped dramatically and remained low ever since.  At the same time, the number of acres burned has increased dramatically, thereby giving a “hockey stick” appearance.  The drop in fires around 1981 may be due to a great increase in both winter and summer precipitation (See figure 1 here). Precipitation is greatly influenced by the ENSO (El Nino Southern Oscillation) cycle. The short-term effect would be to suppress fires, but the longer-term effect would be to increase biomass fuel available for burning when things got drier.  A change in forest management under the Endangered Species Act, i.e, lack of forest thinning may be contributory.

As we will see below, in some parts of the world, warming decreases fire frequency and intensity.

The graphs above, show a relatively short time interval.  The graph below, based on presence of charcoal trapped in sediments, shows a longer, 3,000-year perspective of cyclical wildfire regimes (source: http://www.pnas.org/content/109/9/E535).  Short-term variations are intrinsically smoothed in this study.  Notice that the trend is slightly downward.

Fire western US biomass burned

The folks at CO2Science.org provide a summary of long-term global research on the frequency and intensity of wildfires.  I will summarize their summary.

In Canada over the last several thousand years, fire frequency and intensity decreased with a warming climate.  “[D]endroecological studies show that both frequency and size of fire decreased during the 20th century in both west and east Canadian coniferous forests possibly due to a drop in drought frequency and an increase in long-term annual precipitation.”

At Lake Tahoe in Nevada, fire frequency increased with warming and decreased with cooling, but “current fire episode frequency on the west shore of Lake Tahoe is at one of its lowest points in at least the last 14,000 years.”

In Colorado, “fires occurred during short-term periods of significant drought and extreme cool (negative) phases of ENSO (El Nino) and [the Pacific Decadal Oscillation (PDO)] and during positive departures from [the mean Atlantic Multidecadal Oscillation (AMO)] index,” while “at longer time scales, fires exhibited 20-year periods of synchrony with the cool phase of the PDO, and 80-year periods of synchrony with extreme warm (positive) phases of the AMO.” These oscillations are solar-driven and impact both temperature and precipitation.

For southern Arizona grasslands, increases in fire frequency are coincident with the onset of ENSO (El Nino Southern Oscillation).

In Finland, fire frequency decreased during warming and “the climatic change that triggered the increase in fire frequency was cooling and a shift to a more continental climate.”

In Siberia, fire frequency has decreased significantly since the 18th Century.

In Turkey, “climatically-induced variation in biomass availability was the main factor controlling the timing of regional fire activity during the Last Glacial-Interglacial climatic transition, and again during Mid-Holocene times, with fire frequency and magnitude increasing during wetter climatic phases.”

In Australia, fire activity diminished with increased warming.

The CO2Science conclusion: “Consequently, considering all of the above findings, although one can readily identify specific parts of the planet that have experienced both significant increases and decreases in land area burned over the last several decades, for the globe as a whole there has been absolutely no relationship between rising temperatures and total area burned over this latter period, when climate alarmists claim the world warmed at a rate and to a degree that were unprecedented over the past several millennia. And as a result, there is little support for the model-based contention that future CO2-induced global warming (if it occurs at all) will have any effect on global fire trends.”

The data above deals mainly with natural, lightning-caused fires.  Further complicating the issue are fires caused by humans, either by accident or arson (for arson fires caused as a diversion to illegal entry across the Mexican border, see Our unsecured border  – causes and consequences).

Is the sign still so “really clear”?

P.S.   From Los Alamos National Laboratory: “Measurement taken during the 2011 Las Conchas fire near Los Alamos National Laboratory show that the actual carbon-containing particles emitted by fires are very different than those used in current computer models, providing the potential for inaccuracy in current climate-modeling results. We’ve found that substances resembling tar balls dominate, and even the soot is coated by organics that focus sunlight,…Both components can potentially increase climate warming by increased light absorption.”  Read more

See also:

Droughts in the Southwest put in perspective

El Niño, bristlecone pines, and drought in the Southwest

Mega-fires in Southwest due to forest mismanagement

(A version of this article first appeared in the Arizona Daily Independent)

North American wildfires and global warming

Almost every time we have a major wildfire, alarmists blame global warming and claim that such warming will increase the incidence of wildfires. They also often claim that the number of wildfires is increasing. Their argument seems logical at first, higher temperatures and less precipitation will dry out forests making them more susceptible to wildfire.

The graph below compiled by C3Headlines using data from the National Interagency Fire Center in the U.S. and the National Forestry Database in Canada shows that the number of wildfires has decreased dramatically since 1970 and has remained relatively constant since the mid 1980s. The number of acres burned, however, has slightly increased and that may have to do with wildfire fighting decisions.


These numbers suggest some possible conclusions: either global warming does not have much influence on the number of wildfires, in contrast to alarmist claims, or there has not been sufficient warming since 1970 to test the hypothesis. Fire incidence could also reflect the time and severity of cyclic drought.

I’ve also included below the UAH lower tropospheric temperature record since 1979 when satellites began measuring global temperature.


Meanwhile, NASA says “Climate Models Project Increase in U.S. Wildfire Risk” The analysis was based on current fire trends and predicted greenhouse gas emissions. Time will tell if this is just another “garbage in, garbage out” computer simulation.

See also:

Mega-fires in Southwest due to forest mismanagement

Drought in the West

Droughts in the Southwest put in perspective

USDA says carbon dioxide can reverse effects of drought

Southwest Wildfire Hydrology & Hazard Workshop Proceedings

From April 3 to 5, approximately 70 people, representing various federal, state, and local agencies, researchers and practitioners, gathered at the University of Arizona’s Biosphere 2, north of Tucson for the 2012 Southwest Wildfire Hydrology and Hazards Workshop. The purpose of the workshop was to: 1) share the most recent research regarding post-fire hydrology and hazard assessments and mitigation and warning systems; and 2) discuss ideas for bridging funding gaps for research and warning system implementation.

Thirty papers presented at the workshop are available from the Arizona Geological Survey document repository here. The files consist mostly of power point presentations and PDFs. I recommend beginning with the first paper (50 pages) on the list (see here) which gives an overview of the proceedings.