August 09, 2018

California Wildfires: Is Global Warming Producing a New Normal? Part 1: Are CA Wildfires Becoming More Frequent?

With major fires burning in California, the media is abuzz with stories suggesting or stating that global warming is the key driver of these big burns.  Some media reports state that the number of California fires and the annual burn area are increasing and that global warming is the cause.    California's Governor Jerry Brown is absolutely explicit about the climate-wildfire connection, claiming that global warming is creating a "new normal" of increased wildfires and that the population will have to get used to it.

Are these claims really true?  What does actually fire data show?  The truth may surprise many.

In this blog, we will consider whether the number of fires and the acreage burned in California have increased dramatically during recent years. 

If this is true, we can discuss why--- it could be climate change, mismanagement of forests, change in fire suppression policy, increased human ignition of fires, people living in places they had not before, invasive flammable species, are some possibilities.

If there is no trend in wildfires, we can examine why.

Let us first consider the wildfire statistics by CALFIRE, the official group in the State of California responsible for the numbers, which suggests a very different story provided by the media and many politicians.  The numbers I will show include the entire state.

CALFIRES statisitics show that the numbers of California wildfires over the past 30 years has declined--dropping roughly in half.

For the same 30 years (1987-2016), wildfire area has grown slightly, with huge transient peaks and troughs (see below).   With such variability, I suspect the trend would not be significant.  Final statistics for 2017 are not yet available on the CALFIRE website.

A longer-period (one century) view of wildfire frequency and area in California is found in a nice paper by Keeley and Syphard in the International Journal of Wildfire Science:  “Different historical fire–climate patterns in California”.  They break down the fires in two blocks:  (1) areas managed by the US Forest Service (USFS) and (2) the State of California (CAL FIRE).  Their results  (see below) suggest a maximum number of fires in the 1970s, followed by a substantial decline during the past decades.  

Repeat:  less fires recently.

 “Different historical fire–climate patterns in California” by Jon E. Keeley and Alexandra D. Syphard.
They also examined the areas burned during the last century.  For the US Forest Service areas (mainly the higher elevation regions) that encompass the northern part of the CA (where the big fires are burning now), the acreage was as large or larger at the beginning of the 20th century as now (see below), with a minimum around 1960. For the southern part of the state, the highest values are during the past few decades, with a secondary maximum early in the 20th century.

In contrast, for the Cal Fire areas, which encompasses lower elevations with greater overlap with human populations,  the largest areas burned occurred in the early part of the 20th century.    The only exception to this pattern is the south coast, where there is little trend.

The bottom line of the real fire data produced by the State of California and in the peer-reviewed literature is clear:  there has been no upward trend in the number of wildfires in California during the past decades.   In fact, the frequency of fires has declined.

And in most of the state, there has not been an increasing trend in area burned during the past several decades.

Yes....this and last year had some big fires, but a few years does not make a trend.

So there is a lot misinformation going around in the media, some environmental advocacy groups, and some politicians.   The story can't be a simply that warming is increasing the numbers of wildfires in California because the number of fires is declining.  And area burned has not been increasing either.

But now we get into the real interesting questions that many are not considering.   What is driving the ups and downs in wildfires?  There are so many factors that must be considered, such as:

1.  The fact that extensive fires are a natural historical part of the ecology of the region
2.  The impacts of a huge increase of human population, creating increasing vulnerability while humans are starting most of the fires.
3.   Climate change that causes warming and changing the precipitation patterns (both wetter and drier) that influence fire frequency and size.
4.  Mismanagement of our forests and wild areas, allowing tree and debris-choked landscapes
5.  Invasive and often highly flammable non-native species brought in by man (e.g., cheatgrass and Eucalyptus)

Clearly, climate change is only one possible factor in controlling fire frequency and may not be the most important.

More in future blogs.


  1. According to the NIFC, the 2017 number of fires was 9,560 while the number of acres was 1,266,224. If we just look at this decade, it's a clear trend upwards on the statewide fire charts. People tend to think about things in terms of the most recent years in memory, which could be the reason we see a lot of claims that fires are just getting bigger and more prevalent, despite long-term trends. Furthermore, the increased exchange of information due to social media and cell-phones seems to heighten the public's awareness of natural disasters, putting a bigger lens on the situation and seemingly substantiating more claims of the "new normal". The stark reality may be that a century of fire-suppression may be catching up with us and the "new normal" may be just the "old normal" coming back. However, while we can't necessarily blame climate change for summer wildfires, climate change's effect on precipitation patterns may have some influence on why California's fire season recently extended into colder months.

  2. The bottom line is that most people skew their perspective to recent memory. It's a pretty well known psychological phenomenon. Have two cold Winters in a row and people seem to think the next Winter will be cold. Common occurance. I think when you have 3-4 hot Summers in a row AND we know about the probability of climate change and outcomes, it's easy to arrive at presumptive conclusions. Simple human psychology.

  3. Sooo... Trump is right? The problem is forest management and interference by environmentalists? (I won't get into the "there's no water" argument.) And the solution? Trump thinks it is going to be to cut down lots and lots more mature trees and let farmers take more water from the rivers and aquifers. Climate is not the problem.

    Obviously, many others claim those mature trees are the most fire resistant. That the problem is younger growth in areas without mature trees combined with the last decade's drought and growth blooms from wet periods in winter. That combined with continued building of houses in fire-prone areas without adequate defensive design of the house and property.

    What is clear is that the people fighting the fires think fires like the Redding one are far more intense and dangerous than they've seen during their often decades-long experience.

    Understanding the true causes is vital if any effective actions are going to be taken. Who makes that decision? Feds? The media? Foresters? Fire fighters? Scientists? Local politicians? Twitter?

    For now, the Trump Admin is pushing for more logging of mature trees in CA. That doesn't sit well with those closer to the ground.

  4. In my experience, the biggest shift has been in how fires have been reported. In the 90s, you'd hear about a single fire and even a big one would be local/regional news unless it burned something of national significance. Now the media reports the size of fire complexes and every fire >1,000 acres in California somehow manages to be national news. Fires outside of California are only newsworthy if the smoke drifts into California.

  5. "the largest areas burned occurred in the early part of the 20th century." Firefighting techniques and equipment have evolved a lot in the last eighty to one hundred years. Aerial tankers for instance, didn't really come in to widespread use until the 50's and 60's. So, in that respect, not a very useful comparison.

  6. Thank you Cliff, great post.

    A critically important variable that also needs to be included in comparisons is the shift in the way we manage fires today vs. pre-90's. Not remotely the same. Pre-90's was "suppress and extinguish". Today the strategy is to fight fire with fire, with major swaths burned as preemptive responses, and then included in the wildfire total.

    Not only did the previous policy add to the fuel problem, the whole purpose was to stop fire immediately. Today, the mileage burned through the use of heli-torches, drip torches, and flare pistols far exceeds anything done in comparative time frames.

    It goes unreported, almost disturbingly so. If we are going to use "mileage burned" as an indicator for anything, then changes in our response to wildland fire needs to be the very first variable examined.

  7. There’s also this bit of shocking news to consider:

  8. I think society should be more cognizant of the ill effects of wildfires. Of all the ideas about how to reduce carbon in our atmosphere, this is your "low hanging fruit." Let's spend +20 Billion on air tankers and such. We'll all see immeadiate results. Seriously, this is money well spent. Why doesn't our military develop the technology to put this issue in the rear view mirror? Buy 50 747s and turn them into airdrop tankers. Wildfires are NOT going away, let's get serious!

  9. Interesting post. Fire seems to be overall a very poor indicator for climate change, due to the wide variety of factors that influence fire behavior.

    One thing that COULD be an indicator is if we begin to see more fires in subarctic zones that haven't seen many before. For instance this year's fires in northern Scandinavia might qualify...I haven't looked into it.


  10. Take a look at the frequency of off season fires, that is, fires that initiate during the late fall through early spring. A proxy for this might be calfire deployments on a monthly basis going back to the mid 20th century. The presumed signature for climate change in California fire regions won’t show up in the gross statistics of acres burned per year or size and frequency of major burns, since the hot and dry fire seasons in CA are as hot and dry as they have been since colonial settlement, as Cliff has explained in numerous prior posts. It’s what is happening in the traditionally cooler and wetter seasons where fire behavior seems to be changing the most. Less rain and snowfall, higher snow lines, drier forests, scrublands and grasslands all seem to be contributing to red flag conditions during unexpected times of the year which along with continued encroachment of the urban rural interface gives rise to off season wildfires being both more frequent and more serious, with climate change being among the suspected contributing factors.

  11. Governor Brown was explicitly warned of the immense build up of deadwood in his state, and the reportage came from his own state forestry agencies. He did nothing, yet spent hundreds of millions on his boondoggle train to nowhere. As with the vast dereliction of damn maintenance, the results speak for themselves.

  12. Thanks, Cliff, for pointing out that CA fires have been getting bigger. Oh, did you all not notice that he said that? Yeah, downward trend in number of fires, either no trend or possible slight upward trend in area burned, ergo, average fire must be getting bigger. More significantly, they're getting more severe, and still more significantly, the high-severity patch size is getting bigger, especially within the forest zones that used to burn at low severity before the fire suppression era. Here's one of the studies showing that:

    The main point that study makes is that the biggest departure from norms has been that there is too little area burning at low severity. At least too little for the ecological health of the forest.

  13. Truly a complex set of questions and possible answers. Two other factors:

    Many more people building in areas that are not protected (or not protectable).

    Huge increase in the attack force against these fires: both human firefighters and technical, mechanical, chemical approaches to fire fighting.

  14. The other big issue is that the population of CA has increased over the last 100 years, so that "wilderness" fires nearly always burn some structures. Also as has been pointed out, the suppression of fires over the last 100 years has led to denser forests less able to withstand a fire. There is too much brush and small stuff which then burn the established trees. One can also measure by the response size to a fire, the increased budget that the state now spends to employ full time fire fighters. That number has been steadily increasing over the last decade even above the rate of inflation.

    Still, when it's your town/house burning it's cold comfort to realize that the whole state used to burn regularly, and that it's a natural cycle.

  15. Great post!

    Bad Analyses always generate Bad Remedies.

    By analyses by both Governor Brown and PGE blaming climate change is a tactic to cover their butts. Brown's veto of a bipartisan bill to secure power lines and PGE's failure to trim trees and secure power lines.

  16. Most trends only show change in area burnt or fire frequency beginning in 1970 which was the end period of decades of fire suppression,

    Graphs of fire frequency over a century as Cliff has shown are far more enlightening

  17. Hi Cliff. I enjoy reading your posts, because they're usually entertaining! However data are missing from your above graphs, including 2017 initially, and then the last 7.6 years in your later multiple graphs. Thus your conclusions are flawed.

    I'm guessing you think a lot of us have been asleep the last 60 years. Well I haven't, being born & raised in the Seattle metropolis. Nothing like what's happening in regards to wildfire smoke during the past few years has occurred in the past 60 + years. Somehow people, not you, but others (possible fake news actors from Russia) don't want citizens to know that when humans create trillions of tons greenhouse gasses, it will devastate the environment! Such an attitude is similar to when a person damps-down a woodstove, while burning green wood, with their drapes closed, and doesn't realize they are smoking-out the neighborhood! When industry, including Boeing, and ~ 8 billion people are emitting vast amounts of CO2 +, the result is a warmer and warmer planet, with more and more out-of-control fires.

  18. I believe that there is climate change. The amount due to human factors versus natural factors is the sticking point. Can anyone point me to a study of the natural fluctuations in greenhouse gasses caused by natural phenomenon such as volcanoes, fires, ocean temperatures and currents, etc.? What percent of any fluctuation is due to recent man-made technology? I'm not interested in anyone's political views, only the science.

  19. Cliff, isn't there a problem with your long term analysis?
    Specifically, how would you explain that area burned has increased even as firefighting technology has improved?

    Also, how is the Calfire's "wildfire" metric determined? Is it fires over a certain size, or any fire, down to a quickly doused escaped campfire? If the former, is it possible that improved response time is having an impact on the number of wildfires considered? If the latter, could improved wildfire education be having an impact?

    Shouldn't your analysis also include information on the length of the fire season as measured by first-> last reported wildfire date? Also, I'd think that depth of burned ground or other measure of fire intensity, like reported pyrocumulonimbus formation, actual spot temperature measurements, would be important to note. As well as any correlation with soil moisture, ambient air temperature, humidity, etc. at the times of the fire? What are the long term trend lines for all that data?

  20. Cliff,
    What you’ve presented here is a disappointingly incomplete picture. I would encourage you to review the following papers if you'd like to learn more:

    You may also find it enlightening to review how fire management strategies have changed throughout the decades, and how this may be impacting the data you've presented here.

  21. I always find it interesting when the inevitable contrary voices come on here and demand that Cliff respond to their endless series of questions and assumptions. You're talking to an actual meteorologist who has stated many times that he believes in AGW, yet he's not buying into the alarmist claims that the MSM and certain PAC's constantly screech about whenever anything occurs that's even remotely connected to the atmosphere.

  22. Cliff, all this may be true, but I can only say that in the last five years of living here I have seen more smokey, red skies than in the preceding forty years.

    I put it down to slightly higher temperatures, but mainly to longer dry stretches. As I said before, recent summers have been almost without rainy periods.

    It's too bad the lightning doesn't come with generous rain as it nearly always does from the Rockies eastward.

  23. I actually read an article posted by a relative of mine:

    I cannot believe your statement in that article:
    “Global warming may contribute slightly, but the key factors are mismanaged forests, years of fire suppression, increased population, people living where they should not, invasive flammable species, and the fact that California has always had fire,” climate scientist at the University of Washington, Cliff Mass, explained TheDCNF.

    Mass also explained that there has not been a lot warming in the Pacific Northwest.

    “Many of the media and some politicians has been pushing a false narrative: that the fires are mainly about global warming. They are not,” Mass explained via email. He also shamed politicians for trying to turn our world climate into a political debate.

    There's not been a lot of warming in the NW..........HUH????

  24. Everett Shrink,

    Here is the science:

    The Climate Science Special Report (CSSR) of National Climate Assessment (a collaboration of multiple federal science agencies),"is designed to be an authoritative assessment of the science of climate change, with a focus on the United States, to serve as the foundation for efforts to assess climate-related risks and inform decision-making about responses. In accordance with this purpose, it does not include an assessment of literature on climate change mitigation, adaptation, economic valuation, or societal responses, nor does it include policy recommendations."

    So there it is, just the science, no policy or politics.

    Regarding the amount of climate change that can be attributed to natural variability, here is the executive summary: "This assessment concludes, based on extensive evidence, that it is extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed warming since the mid-20th century. For the warming over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence."

    Cliff, you may be interested in key finding 6 of the Chapter of the CSSR: "The incidence of large forest fires in the western United States and Alaska has increased since the early 1980s (high confidence) and is projected to further increase in those regions as the climate warms, with profound changes to certain ecosystems (medium confidence)." Although Figure 8.3 does suggest that you're analysis is somewhat correct, at least if you limit yourself to California. Though as other have pointed out, it's a little simplistic to simply argue that the total number of fires and the total acreage burned is the whole story. The fire season is lengthening (becoming almost year round in California) and firefighters have attested to the character of the fire changing: though I'm not sure I've seen anyone quantify this aspect. I'd imagine rate of fire growth while controlling for suppression efforts expenditure could be a useful analysis, though technically challenging.

  25. The larger story is the misinformation in the media, period. Climate data suppression is just part of that big picture as it doesn't promote consumerism.

  26. @Eric Blair:
    Seems to me that the very essence of science is asking questions and questioning assumptions.
    Cliff does right by questioning the assumptions of climate change showing up today.
    On the other hand, it seems perfectly reasonable to question what may be assumptions in his blog. Assumptions that may modify the accuracy of his post. Or may not.
    Just like, if I ran a popular blog on analysis and control of complex, multi-element, feedback-controlled electronics systems, I would welcome questions & challenges to assumptions I might make.
    That is not a criticism of his qualifications. It's merely a request for clarification.

  27. One can talk about California and accurately claim that global warming is only one of many factors contributing to the prevalence of summer fires. But in the far north, in places like Siberia where both fire suppression and invasive species are not significant factors, record large fires have been burning the boreal forests this past decade. This summer has seen some of the biggest fires in Siberia in 10,000 years according to NASA. So if we look at the issue of fires globally we may draw quite another conclusion.

  28. Cliff,

    Would you please comment on Atmospheric Scientist Michael Mann, who states that the jet stream is not pushing heat waves out of areas as it once did. Michael Mann appeared on Democracy Now on August 9, 2018.

    1. Michael Mannn? Captain Hockey Stick? Democracy Now?!?!? Hahahahaha!

  29. From Carbon Brief:

    Recently, some commentators have tried to dismiss recent increases in the areas burnt by fires in the US, claiming that fires were much worse in the early part of the century. To do this, they are ignoring clear guidance by scientists that the data should not be used to make comparisons with earlier periods.

    From the US National Interagency Fire Center (NIFC):

    "people should not “put any stock” in numbers prior to 1960 and that comparing the modern fire area to earlier estimates is “not accurate or appropriate”."

    And: To try and compare any of the more modern data to that earlier data is not accurate or appropriate, because we didn’t have a good way to measure [earlier data]. Back then we didn’t have a reliable reporting system; for all I know those came from a variety of different sources that often double-counted figures. When you look at some of those years that add up to 60 or 70 million acres burned a lot of those acres have to be double counted two or three times. We didn’t have a system to estimate area burned until 1960, but it was really refined in 1983.”

    Eardley suggests that earlier records were inflated by including areas where fires were purposefully set to clear forests for agriculture, or where rangelands were torched to get rid of sagebrush to improve grazing conditions. Other federal reports suggest that most of the area burned between 1930 and 1950 was in southeastern US and were primarily intentionally set fires for clearing land.

    While the early 20th century data is not reliable and likely double or even triple-counted actual fires, Eardley says that it is possible that fire extents were higher back then for a simple reason: there was no large-scale firefighting organisation in the first half of the 20th century. Therefore, fires would burn through larger areas before being extinguished or burning themselves out, particularly when they were not close to towns or settlements.

  30. Stan Axe - a fair point, but then again I don't come on here and ask Cliff to expound on the possible effects of the coming Maunder Minimum.That is a reality, and not conjecture. Will it have the same kind of dramatic effect that it did on the world's climate as it did the last go - around? I don't know but I'm not going to ask Cliff to expound further on it, because he's not an astro physicist.

  31. Kalaymarie,

    Its hard to take your comments seriously when you confuse the time scale for fire trends. Cliffs graphs show trends since about 1900. I posted a similar graph. You call his comments incomplete and reference data only since the 1970s. In truth, you are blinded to your own incompleteness.

    There has been a century of fire suppression. That has been slightly relaxed allowing a rise since the 1970s.

    Fire ecologists ave warned for decades, that fire suppression will cause bigger fires in the near future. That is indeed happening now!

    Human ignitions are a HUGE cause of recent fires. Research shows human ignitions have eexpande fire season 3 times longer than natural lightning caused fire season.

    Please do your homework. You seem to be dishonestly sniping!

  32. Stan Axes asks,

    "Shouldn't your analysis also include information on the length of the fire season as measured by first-> last reported wildfire date? "

    The length of the fire season has been studied and the most up-to-date research shows that human ignitions have cause fires season to be 3X longer than natural fires. Human ignitions create fires when fuels are less dry. In the past fire fighters could predict fires season due to lightning or the Santa Anna winds. Human ignitions are making fire predictability impossible!

    Read the 2017 research paper "Human-started wildfires expand the fire niche across the United States "

  33. Unknown,

    PLease provide a link to whoever claims Siberia fires are worst in 10,000 years.

    According to NASA the fires are the worse sense 2008 in this commonly fire prone region

    "A dry, warm winter has set the stage for a difficult wildfire season in 2018 in Russia. Forest fires are common in this heavily forested region, and the season usually starts in April or May. Farmers in this area also burn old crops to help clear fields and replenish the soil with nutrients; such fires occasionally burn out of control. Amur Oblast has so far experienced more fires per month this year than any since 2008, according to the Global Fire Emissions Database."

    No mention of global warming.

  34. Jim Steele - towards your point, someone has already been arrested for igniting one of the giant conflagrations in CA. We also have learned from the arrests in the ISIS terrorist compound in NM that they were training children to shoot up schools, but also how to start huge fires. Scary as hell.

  35. I respectfully disagree with Jeff above. Many ecosystems in California, particularly further south, are fire dependent. Many species require fire to resprout or release seeds. As Cliff has pointed out in previous posts, our failure to recognize this earlier and manage fires, rather than suppress them, is partially responsible for today's buid-up of excessive fuels, and larger, hotter burns that are proving impossible to put out, as Everett Shrink mentions. These fires also "crown out" and kill matures trees, which fires in a more natural fuel regime did not. In pre-European times, as some friars diaries and newspaper accounts from the late 19th century attest, fires burned slowly all summer long before being extinguished by seasonal rains. The diaries reported indigenous peoples setting fires in central California, possibly for a variety of reasons.

    On a slightly separate point, the current administration's attempts to increase post-fire timber extraction and salvage echo what was done under President George W. Bush. Dept. of Ag. policy proposed as much salvage logging after fires as they could, which as studies done on Oregon's Biscuit Fire (2002) demonstrated, damaged the ecosystem. Dead wood does all sorts of good in a forest - it increases infiltration of water into the soil, reduces erosion, causes new growth to start, causes water to pond, results in more shaded, cooler, deeper streams, good for fish, good for wildlife, good for water quality.

  36. TWB, your Carbon Brief snippets leave much to be desired. Carbon Brief has long been known to push CO2 caused catastrophes so I would advices examining their claims more carefully. You provide no link to investigate reported claims. It is very likely the will slant there story to downplay the fires of the past, in order to implicate global warming.

    First it is highly likely that reports of acres burnt in the past were UNDERESTIMATED because we did not have satellites to report on fires in inaccessible regions.

    Second as suggested in your snippet it is possible "that fire extents were higher back then for a simple reason: there was no large-scale firefighting organisation in the first half of the 20th century."

    However during the 20th century era of fire suppression the US Forest Service’s “10 AM rule” dominated! SO that every attempt was made to extinguish all small fires by 10 AM the next day. Thus small fires that would normally burn longer and spread further and create a mosaic of fire breaks, were suppressed.

    Finally in most published estimates of acres burnt, those estimates have been determined by examining fires scars on surviving trees over broad regions. The reporting system at the time are irrelevant.

  37. Thomas Swetnam wrote what all fire ecologists were warning:

    “The paradox of fire management in conifer forests is that, if in the short term we are effective at reducing fire occurrence below a certain level,then sooner or later catastrophically destructive wildfires will occur. Even the most efficient and technologically advanced fire fighting efforts can only forestall this inevitable result. It is clear from many years of study and published works that the thinning action of pre-settlement surface fires maintained open stand conditions and thereby prevented the historically anomalous occurrence of catastrophic crown fires that we are experiencing in today’s Southwestern forests”

    Read Swetnam, T. W.; Baisan, C. H. 1996. Historical fire regime patterns in the Southwestern United States since AD 1700

  38. @Eric Blair,
    Sure, I wouldn't ask about such solar activity either, because there's barely one data point available for correlation in the recorded fire weather record.

    Same thing for climate meta-stability data. I don't know if the recent worldwide swings in temperature, precipitation, ocean currents, etc. signify a shift to a new stable state.

    I'm an engineer, not a meteorologist.
    My engineering gut tells me that we'd expect larger swings as a multifeedback system sees a fairly rapid input energy perturbation, as in the recent measured global temperature increases. That temperature rise means more system energy. A laggy feedback system will ring with that sort of input impulse.

    But is there data to support my gut feel? I dunno.

    That's why I asked Cliff about those other meteorological data points. It seems to me that they may well be relevant, and the data may well exist.

    There MAY be more data than simple area burned. Like season start and length, maximum (fire)storm intensity, etc. Data that can possibly be correlated with fires and with climate trends. Data that MAY be as relevant as fire area. Data that perhaps should be considered along with fire area. Perhaps data that is more sensitive to changing climate than area burned.

  39. @Jim Steele
    I wouldn't doubt that human activity increases fire season length. But there's also evidence that's not the only cause. Here's a UCS article (not a paper unfortunately) that discusses it.

  40. @Jim Steele
    Another paper or two from PNAS, that at a quick glance, discuss more than human started fires.

  41. Stan,

    You linked to a Union of Concerned Scientists blog. I was once a supporter of UCS during my anti Vietnam War days. I am also a long time friend of one of their senior scientists. But the UCS has descended into politics that denigrates good science.

    Indeed fires can burn more readily when temperatures are warmer and the air is drier. The best predictor of heightened combustibility has been measures of the VPD - Vapor Pressure Deficit. causing more easily combustible fuels. VPD is similar to relative humidity but better represents the atmosphere's moisture content. However no matter how dry the conditions, no ignitions- no fires. Humans have ignited 80+% of our fires, not climate change!

    Furthermore California and the western USA's VPD oscillates with the Pacific Decadal Oscillation. In the 1980s and 90s, in contrast to drier conditions that CO2 driven models predicted , the VPD was lower than average (more moisture) damping fire danger. When the PDO switched to a negative phase with more La Nina-like conditions, VPD dropped causing drier conditionssince the year 2000.

    The PDO is a natural climate oscillation that models can not reproduce via changes in CO2. Of course climate conditions that create drier conditions can allow fires to spread more rapidly. But when Gov Brown or PGE blame climate, they are just covering their butt for bad practices and bad policy.

    Anyone that blames recent fires on climate change BUT does not address a natural PDO, the fuel loads built up due to fire suppression, and the 3X increase in ignitions due to human ignitions, that omission should send up a red flag warming to everyone that they are dishonestly trying to blame CO2 and ignore the basics of fire ecology!

  42. @ Jim Steele I believe I did provide a link to the data analysis, NIFC. You can diss Carbon Brief all you want but I will take NIFC opinions over your's any day of the week.

  43. Stan you linked to a recent paper by Schoennagel

    I have been reading her papers since 2005. To get a perspective on what she means by climate change, I suggest you read ENSO and PDO Variability Affect Drought-Induced Fire Occurrence in Rocky Mountain Subalpine Forests

    Her research shows that natural climate change since the year 1700 andt results in dry La Nina years superimposed on a negative Pacific Decadal Oscillation creates the dry conditions enabling widespread wildfires. She wrote, "the combined cool phases (negative PDO during La Nifia) appeared to promote large fires in the southern Rockies. Almost 70% of large fires in RMNP [Rocky Mountain National Park] burned during La Nifia events that coincided with a negative PDO, although these phases co-occurred during only 29% of the 1700- 1975 period."

    In the more recent paper you link to, she states, "Three primary factors have produced gradual but significant change across western North American landscapes in recent decades: the warming and drying climate, the build-up of fuels, and the expansion of the wildland–urban interface "

    Recent decades of a warming and drying climate is exactly what the last few decades of the PDO has naturally produced. Fire suppression builds up fuels while the expansion of the wild land-urban interface brings more human ignitions

    Unfortunately the term "climate change" has been improperly used so that "natural climate change" that enables natural increases in wildfires is misunderstood to mean "CO2 climate change."

  44. Sofstek.... Taminos analysis is very weak, including an inappropriate statistical approach that did not consider the variability of the time series. Also he likes to insult and call folks names.....cliff

  45. TWB


    Of course you can take Carbon Briefs' narrative and their interpretation of NIFC science, over my "opinion" since you are so inclined.

    Nonetheless what I reported was not just my "opinion", but a report of well documented fire ecology science. But clearly you are inclined to ignore such reports out of hand that you disagree with .

    Do you disagree with fire ecologist paper by Swetnam, T. W.; Baisan, C. H. 1996. Historical fire regime patterns in the Southwestern United States since AD 1700

    Here is their graph of the fire history of the Southwest based on fire scars.

  46. Jim Steel

    Here is the link you requested and you are correct it wasn't NASA. It is from the National Academy of Sciences and the authors are Ryan Kelly, Melissa L. Chipman, Philip E. Higuera, Ivanka Stefanova, Linda B. Brubaker, and Feng Sheng Hu. Also it isn't a recent study but dates back to 2013, but still in this decade. They have been studying charcoal lake deposits in the Yukon dating back 10,000 years. It is a very interesting study as are their conclusions.

  47. Cliff,

    Could you elaborate, for those of us who don't have as much of a stats background, why the trend test Tamino used is inappropriate? Is there a different approach that you would prefer?


  48. Cliff,

    You state:

    "And in most of the state, there has not been an increasing trend in area burned during the past several decades.

    Yes....this and last year had some big fires, but a few years does not make a trend."

    Here are the data you used to create your second chart (area burned 1987-2016).


    The linear trend in that series is about 150,000 acres per decade. This rises to about 175,000 acres per decade if the provisional 2017 figure is added (1,248,606 ac).

    Even if this isn't statistically significant, surely it's still a best estimate trend?

  49. A question I have is last year was an extremely wet year with record snow fall. Wouldn't this lead to more smaller woody plants, grasses and underbrush thereby increasing the fuel load of easily ignitable materials. Second question what steps has the California government taken to increase the number of water storage areas commensurate to the population increases?

  50. Jim Steele. I don't disagree with the results of the paper. I do disagree with the of dismissal of Native Americans as a fire source, common practice in their culture. Odd that the number of fires dropped at the same time we exterminated most of them.

  51. This post utilized figures from Keeley and Syphard (2017) to make an argument, but does not include a discussion of the conclusions and very good hypothesis from that paper that relate climate change to changes in fire: "(5) the strongest fire–climate models were on USFS lands in the Sierra Nevada Mountains, and these explained 42–52% of the variation in area burned; however, the models changed over time, with winter and spring precipitation being the primary drivers in the first half of the 20th century, but replaced by spring and summer temperatures after 1960."
    Teasing out fire change trends and climate change is not simple and that is very much the point of the Keeley and Syphard (2017) paper. Perhaps this gets muddled up by some, but not all, media reporting; however, this post missed to entire point of the paper that was referenced.

  52. Dan....I think you are entirely misreading their paper. They are suggesting that warming from climate change is NOT a key driver.
    They note that heavier winter precipitation is important and that most years are warm and dry enough for fires...that is why warming is not important. Anyway, carefully reread their discussion in the end and you will see what I mean..cliff

  53. Also, there is a big chunk of USFS-managed land in SoCal; granted it is at somewhat higher elevations but much of it is flammable chaparral, not “forest” as most people would understand the term. And there is also BLM land to be considered.

  54. The history of wildfire happenings and suppression is perhaps even more complex than you point out, and may cloud how we view developments since ca. 1900.

    Over the early years people became more effective in fire suppression, accounting in part for diminishing destruction. Methods of suppression, such as the development of a corps of "Smokejumpers", led to better control. (A son of one of my botany professors at the Univ. of Montana was killed while fighting fires this way; they used old Ford Trimotor [low and slow] planes.) Then there came the gradual recognition that suppression led to more intense fires, which caused people in charge (in some cases) to just let 'em burn; and/or, to prescribe controlled fires to reduce understory buildup. The point here is that variations in fire-fighting methods and approach have had their impact on the history.

    This may also be of interest: I was fiddling with NOAA data for the contiguous States over the past century or so ( ), and found that using 4 year running averages helped flatten out the variability, and accentuate recent trends. I have been having a hard time seeing clear indications of temperature increase in recent years. Comparing data trends for individual months using monthly averages vs. 48 month running averages, one sees a very clear picture of increase in recent times. Of course we won't know for some more decades if this trend will continue, but waiting that long to "be sure" will make any response way too late.

    Larry Blakely
    Ferndale, CA

  55. A somewhat different point of view perhaps:

  56. I totally agree...this is all quite complicated, with suppression being a significant element. The meme that global warming is causing more fires.....end of too simplistic...clliff

  57. Cliff Mass said:

    "Taminos analysis is very weak, including an inappropriate statistical approach that did not consider the variability of the time series."

    Well, what is the correct way to do the statistical analysis? Or is the correct way to not do any calculations and just make a declaration that you eyeballed it and found it to not be significant?

  58. Cliff Mass, you wrote, "With such variability, I suspect the trend would not be significant." That is, you did no statistical analysis of the data. Tamino did do some statistical analysis of the data and included the data up to this year (which, being incomplete, would tend to underestimate the trend). His analysis does show an increasing trend in area burned that is significant. Can you show where he went wrong?

  59. Cliff - I provided a quote directly from the discussion section on Climate and Fire within the paper. I believe we both can agree that the paper makes a case that for the entirety of the State of California, warming is not the key key factor and in fact for some areas may reduce wildfire. However, Point 2 in the discussion section states "Temperature has been a significant factor driving area burned at higher montane forests". Point 5 also indicates the importance of warmer temperatures in the northern montane forests.

    The discussion notes "This is consistent with the conclusion that climate change may play a larger role in dictating fire regimes in cooler mesic over hotter arid environments". The Mendocino Complex happens to be in a mesic area. The discussion further suggests "This increase in the role of temperature (in reference to Sierra Nevada USFS) in controlling area burned is consistent with an expectation that global warming will increase fire activity in forested landscapes".
    The point of the paper was not to apply a broad brush approach to fire regimes - a point long pushed by the two authors and supported by the work of others. In large part their assessment and your take on their paper are in agreement. Their work points to the need for different strategies to fire hazard in three broad categories 1) flammability-limited, 2) fuel-limited and 3) ignition-limited. Each of these categories requires a different approach and each will respond differently to climate change. This is a point that Keeley and Syphard have been making in other papers and talks over the past several years and is central to their paper (2017) as can be seen in the title.
    The flammability-limited fire regimes areas are the areas that will be most sensitive to a warming climate - particularly to warmer summers. Of the 10 largest fires in California history (, five have taken place since 2012 and of those five, four have been in areas within flammability limits (note: I am counting the Carr fire in the top 10).
    Maybe I am reading your post incorrectly, but it struck me as being broad brushed to make a point that may be misleading regarding fire and climate change. But I do believe it important to recognize, like the authors have documented for California, that meso environments are very temperature sensitive when it comes to wildfire. And I suspect that is particularly true in edge habitat areas that may be undergoing a shift in boundary due small seasonal temperature changes - whether those changes are global warming or not.

  60. For the US as a whole, 1960-2017, the trend in acres burned is +65,000/yr. Yes, it's (very) statistically significant.

  61. I don't know about California's fire statistics but I can relate what I have observed here in North Central Washington since I came here in 1964. At that time, one could travel up any of the Cascade east slope valleys, such as the Icicle, Wenatchee River, Entiat, Lake Chelan or Methow Valley and see little or no sign of recent fire activity. The nearby terrain was mostly covered in green forest. Beginning about 1970 that all changed and there are now large fire scars everywhere. Nearly the entire Entiat and Lake Chelan valleys have burned, on both sides of these valleys from one end to the other, and large fires have occurred in the other valleys. These are not the result of just one or a few fires, but a number of large fires occurring in recent years. Also, most of these fires were started by lightning so the presence of more people is not a factor. This large increase in fires also has occurred during a period of more advanced fire fighting techniques and under the policy of putting out fires as quickly as possible. I think the change in our fire climate recently is a big factor.

  62. As one of my duties for the US Forest Service (USFS), I fought fires in California summers 1968 through 1971 on the El Dorado and 1972 on the San Bernardino. That's how I put myself through my undergraduate years. Ultimately leading to a PhD in Atmospheric Sciences.

    For what it's worth, I am convinced that wild fires are significantly worse now than when I was in the USFS. I think this is true for the west in general and for California in particular. When necessary, we would be sent "off forest" to help on large fires. This happened twice. I was never involved with any fire in the El Dorado region before late July and never sent off forest before late August. This would certainly not be the case in recent years.

  63. Several of you are asking about the significance of the trend in acreage (e.g., Sofistek). I did the trend significance analysis today, using the same approach I and other used in our peer-reviewed paper on snowpack trend ( found here,, based on the approach of Casola et al., 2009). This type of trend analysis takes in consideration the variability of the time series (which is very important). I found that that trend over the entire period was NOT statistically significant (generally we used the 95% level...a trend is considered significant if there is less than a 5% chance of it happening by chance).

    A global warming activists (someone named Tamino) claims otherwise, but his method is not appropriate (I won't get into the technical issues here). He also likes to mock folks he disagrees with, which is not the way scientists interact with each other....cliff

  64. Dan McShane,
    I think you are misinterpreting the Keeley article--to answer your question, I am working on a new blog that takes on the meteorological issues and complexities...cliff

  65. Dear Cliff,

    I love your blog.

    I grew up in California (lived there from my birth in 1960 through 1996 and have family there and visit at least once a year). I've watched the climate change significantly there. It gets much warmer now, but the biggest change is that much less cooling occurs at night. In Santa Barbara (I lived there from 1983 through 1993 and my brother lives there now so I visit often) winter and spring night-time temperatures would get to freezing, and that never happens any more. Also you don't see dew anymore as a result of warmer night-time temperature (that's also true here in the Northwest). Dew would add moisture to plants, much reducing the likeliood of them catching fire if there were lightning or even man-made fires. And dew used to happen every night, now it never happens.

    So I think that the wildfire activity both in California and everywhere is caused by global warming. I find your charts hard to believe. Why is the news telling us that every year, more and more acres of California (or Oregon or Washington in the case of the local news) is burning?

  66. Cliff: Would like your take on this. Thanks, Don

    Recent burning of boreal forests exceeds fire regime limits of the past 10,000 years
    Ryan Kelly et. all. PNAS PNAS August 6, 2013. 110 (32) 13055-13060;

  67. @Cliss Mass, re Casola, et al, 2009, or,

    One doesn't need to assume a t to measure variability intrinsic to a series, nor make an assumption based upon some estimated appropriate window size. The Politis and Romano stationary bootstrap permits estimate of such variability in the series directly, and it operates at varying window sizes.

    Moreover, positing the linear trend as a competing model is setting it up as a strawman. Who would claim, for instance, that the year-to-year effect of warming upon any phenomenon would be linear? Even temporal acceleration is likely to vary. That the portion of variance explained by a linear model is small says less about warming than it addresses the specification error with such a model. To be convincing the argument should bound such specification error.

    Finally, the null used by Casola, et al 2009, or even Stoelinga, et al 2010, which is, per your claim, the basis of your analysis, is not in itself an uncorrelated random process. If it is not, the framework of significance testing is wildly inappropriate, even assuming it is ever appropriate. Bayesian methods are known to be superior to any application of the Student t.

  68. Correlation of area burned with temperature:

  69. blog is about California... that reference is for the whole west... not relevant...can you provide California?..cliff

  70. Hotter temperatures and drier conditions due to increased evaporation rates are due to global warming. How does that not affect wildfires? Also, why focus on only California? Climate change is a global phenomenon, so how have wildfires been effected across the globe by this? California isn't the world. A global perspective would be more helpful regarding the question of climate change and wildfires.

  71. Interesting article:
    "Wildfires have gotten bigger in recent years, and the trend is likely to continue" Data from
    National Interagency Fire Center data since 1983. Here is article from Wash. Post

  72. Cliff, why indeed did you limit this to California, and why do you emphasize number of fires over area or severity, and why the period 1900-2010 when it's the current decade's fires that really confirm the trend?
    I think including the first half of twentieth century introduces error because so many things changed besides climate and fuels; method of counting acres, for one. (see post by TW B early in this thread.) if you want to go before 1950, then look at the Holocene charcoal records of western North America, like Marlon et al 2012, who wrote "Burning generally increased when temperatures and drought area increased, and decreased when temperatures and drought declined."
    If you want to look at California more recently, I found a 1950-2017 chart based on CalFire data that shows a dramatic upward trend that I don't think you can miss.
    Keeley is a chaparral guy, and comes up with different conclusions than all the other fire ecologists in California because he insists on lumping together chaparral with forest with grassland with exurbs. I think he likes to provoke. He says one reason fires on USFS land in CA have gone up is that USFS backed away from fire suppression policy, unlike CalFire. I don't think anyone else agrees with that. USFS still suppresses 99%—until they can't.

  73. I am both amused and frustrated by the articles stating that this is the worst fire season in California's history. Read past the headlines, and that claim is based on records kept since 1905. Need I say more?

  74. Mass, do you read the comments?

    Interesting article, posted a year ago:
    “Our summers are getting hotter and they’re getting drier and they’re getting windier. And the fire season is now 40 to 80 days longer each year. Because of this, climatologists are predicting that the area burned since 2000 will double or triple in the next three decades.

    “And we’re building houses in the middle of this. Two recently published studies tell us that more than 60 percent of all new housing starts are being built in this flammable and dangerous mess.”

  75. Interesting, and apparently factual, presentation. Are there any studies that include effects of "climate change" that causes warming and changing the precipitation patterns (both wetter and drier) that influence fire frequency and size?

  76. Starting the "season" of fires, and politicians looking elsewhere, meanwhile the criminals incendiary-religious come again

  77. We are all so reliant on our high-quality of life: appliances, air conditioning, big homes on the brink of the forest, mixed with crazy weather, and progressive climate policies that make a tinder box... Whats the future?


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