Claim that wildfires are on increase due to ‘climate change’ is shown to be ‘a prescribed result’ of climate models

Read All About It! Heat Dries Things Up!


No one doubts that much of the West, especially California, has been very droughty since the turn of the century, and that heat and drought are highly correlated. So it seemed surprising that it was big news last week that forest fires, which require dry fuel, are on the increase out there.

University of Idaho’s John Abatzoglou and Columbia’s A. Park Williams used a large family of climate models to calculate various indices of western aridity (they used eight different measures), which were then related to the burned-out area every year. About half of the increase since the mid-1980s was related to climate-modelled warming. The other half, they say, was from other causes, including natural variability. The authors also note that some forest management practices may be contributing to the increasing burn.

The notion that this much drying is caused by dreaded global warming is what made the papers.

Should we use models that can’t even get close to the real-world evolution of lower atmospheric temperatures in recent decades to determine how much climate change is human-caused? That’s what they did—assuming only warming that was not modelled was “natural.” To say the least, that’s a heavy logical lift when it is so clear that the models are predicting far too much warming in the lower layers.

It is all too human to not let some else’s work get in the way of your confirmation bias. So there’s no mention of another explanation for why it’s so hot and dry there. Writing in the same journal that the fire work was published in, the Proceedings of the National Academy of Sciences (PNAS), two other western researchers, James Johnstone and Nathan Mantua, demonstrated that virtually all of the temperature changes in California and the West are related to changes in atmospheric pressure patterns that occur with or without global warming. That was first published in 2014, but there is no reference to it whatsoever in the fire paper.

Nor is there any reference to the most comprehensive study of western fires—some 33,000 of them—by Argentina’s Thomas Kitzberger showing that for centuries the distribution and frequency of western fires is related to well-known atmospheric patterns over  both the North Pacific and North Atlantic, not global warming. It too was published in PNAS, in 2007.

But we digress. Aridity is largely driven by temperature (warmth) and precipitation. Unfortunately, only two of their eight measures of dryness are very sensitive to rainfall variability.

Climate models have pretty much no skill in estimating precipitation. But they do predict warming, and western (particularly California and Arizona) temperatures are higher than they were. So, absent any precipitation data, they are guaranteed to paint a drying picture and therefore an increase in fire extent.

The six aridity indicators that are not particularly influenced by precipitation instead are primarily temperature-driven. Not surprisingly, these show much greater increases in aridity than the other two.

Here’s an example from the heavily forested northwest states of Idaho, Washington and Oregon. One of the aridity indicators is the Palmer Drought Severity Index (PDSI), an old warhorse that has been used to assess long-term moisture status since it was first published in 1965 by Wayne Palmer, a scientist at the (then) U.S. Weather Bureau.

Our first figure shows the relationship between observed summer temperatures and the PDSI.  Note that the more negative the PDSI is, the more droughty it is, and vice-versa for wetness.

Figure 1. Scatterplot of summer Palmer Drought Severity Index values vs. summer temperature in the U.S. Northwest climate region, 1895-2016 (data from National Centers for Environmental Education,

That’s the variable that the models as consistent with in their projections, and it explains about 20 per cent of the summer-to-summer behavior of the PSDI since 1895.

What about the other component—precipitation—in which model predictions are all over the map?  We show that in Figure 2.


Figure 2. Scatterplot of summer Palmer Drought Severity Index values vs. summer precipitation in the U.S. Northwest climate region, 1895-2016 (data from National Centers for Environmental Education,

In this area, about twice as much of much of the PDSI behavior is predicted by rainfall than by temperature.

A different situation obtains as one moves further south, with temperature more important because it doesn’t rain very much in the period we are looking at here (summer).  In droughty California any significant summer rain aside from occasional mountain thunderstorms is usually front-page news.  If you average across the entire area, the contributions of the two predictors are pretty much equivalent.

If dryness is driven both by temperature and precipitation, and we can’t predict the latter, then climate models guarantee a positive relationship between climate change and fire in a warming world. This is exactly what this paper shows.  Is such a prescribed result actually news?


Abatzogloua, J. T. and A. P, Williams, 2016. Impact of anthropogenic climate change on wildfire across western US forests. Proceedings of the National Academy of Sciences, doi:10.1073/pnas.1607171113.

Johnstone, J. A. and N. J. Mantua, 2014a. Atmospheric controls on northeast Pacific temperature variability and change, 1900–2012. Proceedings of the National Academy of Sciences, 111, 14360–14365.

Johnstone, J. A. and N. J. Mantua, 2014b.  Reply to Abatzoglou et al.: Atmospheric controls on northwest United States air temperatures, 1948–2012, Proceedings of the National Academy of Sciences, 111, E5607–E5608.

Kitzberger, T., Brown, P.M., Heyerdahl, E.K., Swetnam, T.W. and T.T. Veblen, 2007. Contingent Pacific-Atlantic Ocean Influence on multicentury wildfire synchrony over western North America. Proceedings of the National Academy of Sciences, 104, 543-548.


29 thoughts on “Claim that wildfires are on increase due to ‘climate change’ is shown to be ‘a prescribed result’ of climate models

      • Bloke, Case in point:
        We had a fire about 13 years ago that started with a single lightening strike and was left to smolder for a few days. It happened to be in a park area that was completely left alone and had build up ( in some place 3-4 ft deep) dead debris from the usual pine and spruce needles.
        The park was directly next to a growing town. The interface was never controlled because the protocol was not to interfere with “The Natural Beauty” of the park.
        Due to series of unforeseen weather events ( But also the terrain) the fire erupted , destroyed hundreds of homes and tens of thousands of people evacuated and were out of their homes for weeks( Thank God nobody died). In a way you are right but in this case it was non interference. The human interference was, in this case, doing nothing while the problem stared them right in the face and they were warned by many a disaster was waiting to happen.

  1. It’s worse than that. One of the base assumptions of AGW theory is that humidity will increase, not decrease.

    CO2 won’t do all of the warming they predict – the calculations need a big lump of extra water vapor (in a huge positive feedback loop) to make things a lot warmer. If the water content of the atmosphere drops on average, or even stays about the same, catastrophic AGW can’t happen. According to science, anyway.

  2. It doesn’t help that the Obama administration crippled the USFS’s aerial firefighting capability. In fact, it appears that President Obama has been doing his best to worsen the wildfire problem.

    That sounds like a joke, but it’s not. In the summer of 2011 the Obama Administration abruptly canceled the contract for the U.S. Forest Service’s use of P-3 Orion firefighting planes, “the backbone of the aerial firefighting arsenal.” That irresponsible action gutted the U.S. Forest Service’s aerial firefighting capability.

    The Administration’s reasons are mysterious. They claimed it was due to safety concerns, but the planes, though old, had excellent safety records, they were up-to-date on their maintenance and inspections, and they were much cheaper than getting new planes.

    The USFS was left with eleven smaller P-2 Neptunes. They went shopping for other planes, mostly BAe-146 jets, but the Orions are still sorely missed.

    The company which operated the Orions was called Aero Union. The Obama Administration’s action put them out of business. Their six big four-engine P-3 Orion tankers (plus a 7th that was scheduled to enter service on the very day the contract was cancelled) were the core of America’s aerial firefighting capabilities. They were the “big boys,” with about twice the payload of the two-engine P-2 Neptunes, and 1.5x the payload of the new BAe-146 jets. I think the USFS also has access to a few Canadian CV-580s, but they’re smaller yet.

    Putting Aero Union out of business not only deprived the USFS of most of the large firefighting planes they used, it also jeopardizes the maintenance of the MAFFS systems that Aero Union built, which are used on other firefighting planes.

    The loss of the P-3 Orions drastically reduced the aerial firefighting capability of the USFS, and increased the risks faced by firefighters on the ground. I expected that problems with wildfires out west would worsen as a result. To my surprise, that didn’t immediately happen.

  3. Back in the 90s when I was working on my PhD studying ground squirrel population genetics, I had to survey golden mantled ground squirrel population distribution in the sierra nevada mountains. What I found was an increase in population density of Spermophilus lateralis around campgrounds. This was due to man creating a perfect environment for the squirrels by clearing trees, placing concrete tables and benches and because people frequented these areas, the squirrels normal predators were kept out. Populations exploded also due to management practices not allowing people to use broken limbs or needles from the trees that were on the ground for their campfires. Massive amounts were on the ground and gave the squirrels easy access to nesting materials. Several things happened because of this:
    1. Golden mantled ground squirrel populations increased and with that cases of bubonic plague increased especially in domestic pets.
    2. This closed many campgrounds for extended periods resulting in an increase in undergrowth at these campgrounds
    3. The policy at the time and it may still be in place was once the undergrowth was established you were not allowed to clear it out.
    4. As a result when fires did happen they burned much hotter and killed the ponderosa and other pine trees. This allowed colonizing species of trees to become established, incense cedar and white fir. These trees are by far more highly susceptible to fire and spread it faster.

    The increase in wildfires has very little to do with global warming in my opinion.

  4. Don’t forget the fire fighters, and others who work in the “elements”, as in construction and agriculture.(We are actually concerned about people,aren’t we?) Their health/survival depends on the heat index, a combination of temperature and humidity. If temperature goes up but humidity goes down, we have to look very carefully at the combination. Hence the need to go beyond mere temperature changes and look at heat index and wind chill records.

  5. At least in the northwest – and I imagine probably California too, although I don’t live there – the majority of this problem is caused by basically banning logging – and pretty much any activity outside the city limits that touches a blade of grass – and so none of the loose brush is cleared away, resulting in an entire forest full of dried out kindling.

  6. I’ve always hated the PDSI as a drought indicator. It seems intentionally derived to prove a connection between climate change and drought because temperature is one of the inputs. Only the temperature signal changes — the soil moisture content has zero change with respect to drought. There are dozens of different drought indices. PDSI has become the primary indicator for climate change because it shows a response.

    In the end, they are effectively proving that when it gets warmer, the temperature increases. Not really very scientific.

      • Obviously, you haven’t noticed much climate studies. They all fit this level of agreement. The point of such regressions is that they are supposed to compare independent variables. However, PDSI is not independent of temperature — temperature is one of the inputs to the index.

        There are all sorts of errors associated with the PDSI, including the point that the index was designed for the American Midwest and does a poor job representing the more arid southwest.

        (BTW — I was in a technical meeting once where a technician presented data that was a scatter plot with one outlier. He drew a straight line between the scatter plot and the outlier and was excited to report a 98% correlation.)

  7. Figures 1 and 2 remind me of shotgun blasts with a skewed choke. Better go back and fix the gun. Lots of poor quality guns out there.

  8. Poor forestry practices led by environmentalist and bureaucrats have been a major factor in increased wild fires. Couple this with stupid regulations passed by cities/counties/states and you have a recipe for major fire disasters.

  9. In 1933 John Steinbeck published “To A God Unknown” in which the cycles of rain and drought in California underlie and drive the story. The cycles of rain and drought have been known by California’s varied human populations for thousands of years. And suddenly its “caused” by climate change as if it never happened before?

    I lived in California for several years and one spring commented to my land lady about how the winter rain had made everything so green. She shook her head and “This is bad”. Come the summer we will have wildfires.”

    Eugene WR Gallun

  10. Excellent articles that exposures the climate model bs that drives these latest alarmist wildfire headlines.

  11. There is an interaction between precip and temperature. The evaporation of water cools the air. In a drought, this cooling is less so the temperature gets higher than it would have otherwise. Note that the climate models can’t do local/regional precip to save their lives.

  12. Managing healthy forests through the original schemes of “cut it flat, burn it black, plant it back” have given way to old growth mania where even bug-killed trees cannot be harvested. Combine that with the fact that people are now living in areas of the “whispering pines” where wildfire suppression (funded solely by tax dollars) is now driven by the need to save private property…when did that become the number one reason for the USFS to fight fire? Original “settlers” of the land (you know, people that needed to make a living off the land) in the western states did not build their houses / ranches in the forest; long ago recognizing that forests burn.

  13. Greg, if you are interested, the approximate probability level for Fig 1 is 0.0264. I had to count the dots to get this, and may have got it a bit wrong, but it’s near enough. Thus, depending upon your standards the correlation is indeed “significant”. Not much good for guessing the next value in the relationship, though!

  14. What I find interesting about the temperature plot is that if you exclude the points that are above 64 and below 60 you basically remove all correlation. My sneaking suspicion is that those were also particularly wet/dry years so that the entirety of the temperature correlation is actually related to cloud coverage – rainfall.

  15. It looks to me like you scatterplots will both have relatively low F-statistics, suggesting that the null hypothesis cannot be rejected at any useful level of confidence. I would have to looks at the raw data and perform the math to tell for sure.

  16. The fuel needed to sustain a wildfire and determine it’s severity can either be accumulated quickly as is happening now in Australia with above average rains across wide areas, or slowly over a period of time as over prolonged periods of below average rains. Either way it doesn’t really matter, if nothing is done in controlling that buildup, perhaps by grazing, sooner or later all the conditions that form part of the fire triangle, oxygen, heat and fuel are going to coincide.
    Whilst fuel reduction burns concentrate mainly on protecting areas occupied by humans and their assets, it is the putting out of fires outside such areas that eventually lead to major environmental damage when fuel levels have been allowed to build up to extreme levels such that when a wildfire does start, the chemical chain reaction, part of the fire tetrahedron, becomes the equivalent of a runaway nuclear reaction on a massive scale.
    Most fires in Australia occur in northern areas and are largely left to burn unchecked and burn themselves out if they pose no danger to life or assets. Perhaps more study needs to done to determine just what environmental damage those fires do, if any at all.

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