Wildfire Attribution study full of smoke

December 4, 2018
Guest post by Bob Vislocky

In light of the devastating wildfires that ravished California last month, I thought it would be interesting to critically review a frequently referenced article published in the Proceedings of the National Academy of Sciences in 2016 titled “Impact of Anthropogenic Climate Change on Wildfire Across Western US Forests” by John T. Abatzoglou and A. Park Williams.

http://www.pnas.org/content/113/42/11770

In the paper, which was the first and most significant quantitative effort to link climate change to wildfires, the authors conclude that roughly 50% of the wild fire acreage in the Western United States from 1979 to 2015 can be attributed to Anthropogenic Global Warming (AGW) as displayed in the figures below:

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Not so surprisingly the article contains several serious deficiencies which will be presented below.

1) In the article, the authors create a wildfire regression model by correlating various weather parameters (temperature, humidity, etc…) to wildfire acreage. Then the AGW component of those parameters is removed from the raw weather data (using CMIP5 climate models) and the adjusted weather parameters are input to the wildfire regression model to determine the amount of acreage that would have burned without AGW.
However, the AGW components filtered out for maximum temperature in the summer and fall (which is the height of fire season) appear to be way too high (~2*C according to figure S1 in the article). In reality, the AGW component for maximum temperature during the summer and fall is closer to 0.5*C when computed from actual observations using the same baseline period as in the article (see graph below):

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The estimates of the AGW component for minimum temperature in summer and fall were also inflated by the authors, but to a lesser extent. From the same figure S1 in their article it appears that from June to November they used an AGW contribution for minimum temperature around 1.5 to 2.0*C across the region. In reality, the AGW component for the summer and fall using actual observations is closer to 0.9*C (see figure below).

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As a result of the authors’ desire to use climate models to determine the AGW component for the necessary weather parameters, their estimates of the AGW component for maximum and minimum temperature during fire season was roughly 2-4 times too high compared to trends in actual observations figured over a larger scale. Moreover, that 2-4 times factor is a conservative overestimation that assumes the entire observed temperature trend is due to AGW. For example, if the observed trend in max/min temperatures was 50% natural and 50% anthropogenic, then the authors would have overestimated the AGW component by 4-8 times. In the event the authors were to revise the study with more realistic AGW-adjusted temperatures then it is likely there would be much less attribution of wildfire acreage as a result of AGW.

2) Post-mortem attribution studies like these almost always lead to biased results. Let me explain how. Consider a variable like precipitation where the global trends over the past century are very weak or non-existent. Despite the lack of a global trend there will still always be several locations or regions where the local trend is highly positive or negative due to natural regional variability. All that is required is to select one of those regions, say New England, figure out that the number of 1+ inch rain events has increased over the last 100 years and then run an attribution study which shows the increased rains are correlated with global warming. In the end, however, that amounts to nothing more than cherry picking. Over the last century, there have been NO increases in the severity of drought during fire season when measured over a nationwide scale despite all the added CO2 (see figure below). Therefore none of the recent drought that the western US is currently experiencing can be attributed to global warming over natural regional variability.

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3) Post-mortem event attribution studies like these are also inherently flawed because they look at the research area in isolation without consideration to the weather or climate around the rest of the world. An example will be provided using hurricane Michael that destroyed parts of the Florida Panhandle this year. All that is required is to subtract out the +1*C temperature anomaly from the Gulf of Mexico region caused by AGW and to re-run the computer models using the adjusted weather & sea surface data. When the results come back that Michael would only have reached Category 2 strength without AGW the climate scientists can claim that global warming significantly contributed to the storm’s intensity and all the newspapers will pick up on the story!

However the fatal flaw is that similar but opposite attribution tests are not performed simultaneously over other the rest of the hurricane season and other areas of open water around the world to see if a strong hurricane would have developed that otherwise didn’t because there was excess global warming in the wrong places. Otherwise, attribution studies could be run on all the hurricanes in the past couple decades to show that they all would have been 25-50% weaker without AGW. However, since there is no apparent overall trend in hurricane frequency or strength, an explanation would then be required to explain the mechanism by why hurricane strength would have been decreasing so substantially over the last few decades without an AGW component. That’s why it’s important to look at the overall trend on a national or global scale rather than fixate on a certain storm or region in doing these attribution studies.

In the case of wildfires, if the west was getting lots of rain instead of arid conditions this year, then maybe Texas or Florida would have gotten more wildfires instead, or perhaps the Midwest would have had a major drought that affected their crops. There is no way an event-driven attribution test can property detect an AGW component, especially since climate models are unable to reproduce natural regional variability.

4. The authors did not include known natural contributions to arid conditions in the Western US that have nothing to do with CO2, such as the Pacific Decadal Oscillation, which has been shown in several publications to be correlated to wildfires in the Western US, as seen in the figure below.

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5) According to the US Forest Service, roughly 85% of all wild fires are started by humans. Since the population of the US has grown by 40% over their period of study, often extending into areas where previously there was less human activity, it would not be a stretch to claim that a portion of the growth in wildfires in the past several decades could be attributed to human carelessness unrelated to CO2. Moreover, over the past 20 years there has been a systematic 30-70% reduction in the fleet of large air tankers used by the Forest Service to combat wildfires. These and other human facets were not considered.
https://fireaviation.com/2018/02/16/air-tankers-cut-one-third-2018/

Now, in all fairness, the authors do provide a list of assumptions toward the end of the paper. In addition, they did provide a more conservative analysis that de-trended the burn data to account for potential extraneous correlations (such as those mentioned above in bullet points 4 & 5), and that modified analysis showed only 19% of the burned acres was due to AGW. However, this is buried in the middle of the article in a two-sentence blurb that nobody is going to read along with the assumptions, plus it still doesn’t address the first three points above. Unfortunately the near 50% contribution of AGW toward wildfire acreage mentioned in the abstract is what gets quoted when the study is referenced.

Conclusion: There is little question that recent drought conditions enhanced the spread of November’s wildfires in California. However, due to the many considerations expressed above it would likely be a huge over-reach to conclude that CO2-induced climate change is responsible for anywhere close to the 50% of the wildfire acreage estimated by the authors over the last few decades in the western US. Regrettably, results from their article spread like a wildfire through the media and has appeared in publications like the New York Times, Scientific American, and most recently the Fourth National Climate Assessment.

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68 thoughts on “Wildfire Attribution study full of smoke

  1. Environmental conditions may explain the severity of the fires but not the randomness or frequency. That is because there are are many man-made fires and the main-stream press ignores what the U’S. Forest Service discussed in a recent conference on PYROTERRORISM. Look that up on Google. There is a fatwa to hurt the United States by using remote-controlled incendiary devices. Instructions on how to make these devices are on Arabic language internet sites. You can read all about this on Google. You won’t read about it in the MSM because of political correctness and the worry of creating fear in the populace. But the people must be warned.

    • THIS IS SERIOUS AND if this continues it will skew the statistics on wildfires to the point that the alarmists will be able to prove that wildfires are increasing. They will blame it on CO2 and skeptics will have a hell of a time parsing out the drought correlation from the temperature correlation to be able to disprove the CO2/ temperature meme. Up to now it has been easy to laugh off the “Climate change causes wildfires” meme by pointing to the stats that say there aren’t any more than there used to be.

  2. They onlr real connection is that the nutty Green so called enviorements stop the timber workers from reducing the fuel load on the ground, so making it much harder to control the fires when they start via lightnine strikes.

    MJE

  3. Wildfires highly correlate with week long plus stretches of dry weather, and do not correlate with weather averaged over 30 years. No matter whether you believe in AGW or not.

  4. US Forest Service, roughly 85% of all wild fires are started by humans.

    I recall that “started by” is not the correct manner of saying ‘relating to the activities of humans’.
    There is a big difference between deliberate arson, young males lighting fireworks in dry woods or leaving a campfire unattended, and equipment failure.
    In dry central Washington (last 2 years) there have been 3 or 4 fires started when vehicles catch fire and the driver pulls off the pavement into grass at the edge. A friend had a pickup catch fire. She parked it in the middle of the road. The truck was totaled but the forest did not burn.
    The problem with the word “started” is that it makes the solution sound simple. All we humans have to do is not start fires. Problem solved.

    I also recall the study arrived at 84%, but that’s really not an issue.
    Good post otherwise.

    Cliff Mass has a good post on this issue regarding the “Camp Fire” fire.

    • I think it was 13% definitely deliberate and 37% suspicious with 35% accidental. 5% was reignition so really 90% started by humans. Whether intentional or not, you can’t pretend to eke out a AGW signal in a variable so highly dependent on the whims of humans.

      I might as well add what I wanted say here. 1998 had the third lowest acreage burnt for the contiguous US but Aug-Sep was the highest maximum average on record, about 2C above the mean for all years on record. Acreage burnt was a quarter of that for 2000 that had the coldest August – Sep since 1965. You even can’t argue that its investigating only increasing the probability of a large fire when whether a fire starts is dependent on something so random as accidents and someone getting p_ssed off, or park management practices.

      • Back in the early days when Toyota Land Cruiser and Nissan Patrol started with 4WD vehicles that later were SUVs, we discovered that parts of the fuel supply pipes were plastic. In Australian deserts, dry spinifex grass would clump in the chassis next to hot exhaust pipes and melt the plastic petrol line. We lost a vehicle spectacularly this way at about this location 20 degrees south, 133 degrees east. (Very approximate, from 1977 memory). The windscreen glass melted and flowed like syrup.

    • It’s a very distant memory, but on my first bicycle tour out west in 1974, I remember reading that in the west, about 35% of wildfires were human-related and most of the rest were due to lightning.

      With the population increase since then, I assume the figure is significantly higher now.

  5. “However, the AGW components filtered out for maximum temperature in the summer and fall (which is the height of fire season) appear to be way too high (~2*C according to figure S1 in the article). In reality, the AGW component for maximum temperature during the summer and fall is closer to 0.5*C when computed from actual observations using the same baseline period as in the article (see graph below):”

    Their data: western us
    Your chart: all of Conus

    You need to be a bit more clear on the actual data used. Especially when you make bold claims.

    For example, what observations did they actually use? PRISM? ERA? ECMWF? what?
    and you cant just paste a chart and say they are wrong.

    you have to demonstrate.

    • Indeed, claiming CONUS temperatures refute the carefully assembled data in the paper for the actual area of western US is very bad for the credibility of this review. Same for PDSI. And it would be good to have a proper reference for the Littell plot. I can’t find it in his papers.

      • And it would be good to have a proper reference for the Littell plot. I can’t find it in his papers.

        Agreed.

        It would also be nice if WUWT stories consistently provided titles and figure numbers for illustrations. It would make it much easier to refer to them in the comments.

      • Okay you 2 alarmists win for now (until somebody drags up the relevant charts 1 and 2 for western US.) However you don’t win on points 3, 4 and 5. Also the whole concept of using unproven components of AGW in computer models to then subtract them out and model the resultant fires is the worst case of circular reasoning that I have come across. They assumed that there is an AGW component to wildfire acreage. They then subtracted that out of the acreage burned equation. They then redid the simulated computer runs of burn acreage to arrive at a non CO2 caused burn acreage.

        With that sort of reasoning, I could prove anything.

        • Alarmists?

          I’d love to see you make a reasonable argument with citations explaining how Mosher is an alarmist.

          I suspect the best we’ll see is a few cheap throw away lines before you abandon the subject.

        • I was going to make the same point as Steve and Nick, plus point out that there is variation in the temperature maps – saying it’s 2 C seems an exaggeration. Besides, it’s not about the observed change, it the change attributable to AGW. That could theoretically be greater than the observed change if natural factors were driving temperatures down.

          Alan, you don’t seem to understand the analysis. The authors ran a regression analysis to estimate the portion of burned area attributable to ACC, they didn’t “simulate” the fires. “Model” can be used to describe statistical analyses in general; maybe that’s what confused you?

          Point 2:
          “All that is required is to select one of those regions, …nothing more than cherry picking. Over the last century, there have been NO increases in the severity of drought during fire season when measured over a nationwide scale…Therefore none of the recent drought that the western US is currently experiencing can be attributed to global warming over natural regional variability.”

          This is backwards. If you select a region as an illustration, then run the test, that is not cherry-picking. It would be cherry-picking if you ran tests on a variety of regions, and selected those which showed “desired” results to report.

          The fact that different regions show different patterns is expected from ACC (AGW). When you find a trend in a region that supports the models of ACC for that region, that is not “natural regional variability.” Looking at global or national averages for precipitation, for example, is not informative as to whether climate change is occurring since it’s predicted that some regions will get more rain and others less. This kind of generalization seems to be a common error.

          Point 3
          …makes a similar error; the interpretation of the analysis wrong from the beginning. The change that is being subtracted is an emergent property of the models – it is not the observed temperature change, but the temperature change due to AGW. And because “climate models are unable to reproduce natural regional variability” is blatantly false, it’s hard to find credible any of this argument. Regional factors matter. (But maybe I’m missing something? I’m writing in a rush.)

          Point 4.
          I don’t know about the research into the relationship between PDO and fires, but the graph shown is not convincing; the PDO index does not correlate well with the acreage burned except in the broadest terms, which could be attributable to other factors. But at any rate, the climate models do incorporate the PDO, and since the changes are based on the ACC signal from modeling, that would include PDO. (Interesting graph, though – shows the figures for western U.S. alone, unlike many of the graphs used in this debate.)

          Point 5.
          Population has increased, sure, but most population increase is urban and people are educated to put out fires. It’s a huge assumption to think that fires weren’t started by people back then any less than they are now.

          All in all, this rebuttal doesn’t seem convincing. That doesn’t mean the research is correct, but it would take a better argument to show it’s “full of smoke.”

          • Kristi, thanks for your detailed comments. I will try to address them below.

            Point 1. I wish the authors would have provided more precise numbers for the ACC component rather than a color chart that has to be eyeballed. Nonetheless, looking at their figure S1 again I still feel that 2* representative of what the authors used for the max temp ACC component in summer (Jun-Aug) and fall (Sep-Nov) which was the focus of my analysis since since that’s when the largest wildfires seem to occur. On both of those charts the western US is solid red or even higher. For min temp in summer & fall their ACC component seems to vary more, between 1.5 & 2.0*C depending on the state (say an average of 1.7*). I don’t think either of these is an exaggeration by any means.

            The change attributable to AGW may be more than the observed warming, but it’s not relevant to my point because of the way the authors computed the ACC components. The authors defined the ACC component for any location as the smoothed multi-model (27 CMIP5) monthly temp anomaly vs. 1901 baseline. I’m basically defining ACC the same way as the authors except using observed data instead of climate model output, which I think is the more accurate approach of the two given a choice. However my fiance have disagreements on color with me all the time, LOL!

            Point 2. Couldn’t disagree more. It’s cherry picking by proxy. Climate scientists wait for a disaster and then try to find an AGW fingerprint in that event in isolation without regard as to whether there is any net effect over the whole globe.

            I had the same discussion with a colleague when he tried to blame the October tornadoes in PA on climate change, whereby their historical tornado numbers for autumn tripled in one day. Sure increasing temperatures can shift the region to where tornadoes don’t normally occur, but the national statistics clearly show no increase in tornado frequency or strength. So if one area gets more tornadoes and another area gets less, the main conclusion to make is that global warming has no overall impact on tornadoes. That’s what counts the most when doing cost/benefit analysis regarding the impact of CO2. However you, and many climate scientists, would rather conclude that climate change is increasing tornadoes in the Northeast and that the whole world is coming to an end. This is a systemic error often made by climate scientists when they try to do event-driven attributions. In the case of drought, if AGW causes one area to get more droughts than normal and another to get fewer then AGW has no net overall impact.

            Point 3. The authors did not subtract the change due to AGW, but rather the change over time in the monthly mean temp anomalies output from CMIP5 models (as discussed in more detail above & below). Climate models certainly can try to reproduce natural regional variability, but not very well. The errors at individual grid points are huge, only through the averaging in space & time do the individual errors cancel out, resulting in a decent global simulation/forecast.

            Point 4. The authors didn’t base their ACC signal the way you’re thinking. That is, they didn’t run one set of climate models with anthropogenic forcing and another set without the forcing and take the difference. Rather, as explained above they took the ensemble of CMIP5 simulations and defined the ACC signal at any location as the difference between the time smoothed monthly temp anomaly and the 1901 baseline. So any multi-decadal natural oscillations get lumped into the ACC signal, which was the point I was trying to make. The authors acknowledge this drawback in their article too “The lack of fuel aridity trends during 1948–1978 and persistence of positive trends during 1979–2015 even after removing the ACC signal implicates natural multidecadal climate variability as an important factor that compounded anthropogenic effects during 1979–2015.”

            Point 5. Without hard data I agree it’s an assumption. But on the other hand I think it’s an even bigger assumption on the part of the authors to conduct their primary research under the assumption there was no human contribution, leading to the conclusion that AGW was responsible for 50% of the burned area.

          • Bob,

            And I thank you for the detailed comments! Sorry, mine below aren’t arranged point-for-point.

            “However you, and many climate scientists, would rather conclude that climate change is increasing tornadoes in the Northeast and that the whole world is coming to an end.”

            I don’t thank you for this insulting and completely ridiculous assumption. The example is rotten – I would never make any such conclusion and I doubt many climate scientists would, either. I think you underestimate their general intelligence.

            It’s not simply a matter of some regions getting more droughts, for instance, and some getting fewer, so that it all balances out. The predictions are that areas that are dry historically will get drier, and areas that are wet now will get wetter, which is to some extent borne out in the U.S. patterns. And wetter isn’t always better, since more intense precipitation episodes are also expected – and that, too, seems to be the pattern. This can mean more flooding and bigger snowstorms, both of which have an economic cost. When any of these patterns are averaged over the whole globe in absolute numbers, they are less evident because of regional variability. They would also be less evident if one region got a lot more tornadoes (for instance) and the rest of the world remained the same – but as I understand it, their isn’t a strong signal in the models for more tornadoes, anyway. (I did read that there has been a trend toward more “cluster” tornadoes, but that’s a tough thing to verify and I don’t give it much weight.)

            “So if one area gets more tornadoes and another area gets less, the main conclusion to make is that global warming has no overall impact on tornadoes. That’s what counts the most when doing cost/benefit analysis regarding the impact of CO2.”

            Depends on the areas (more or less populous) and strength, but in general that’s true. Tornadoes aren’t a good example, though, since they are naturally much more common in some regions and don’t show a trend.

            It’s very hard to detect patterns in weather if it is simply getting increasingly unusual (e.g. if there were more F3+ tornadoes in Europe). The media make everyone more aware of these oddities and detection methods are better, so that it could easily be perceived that they are happening more when they aren’t. On the other hand, many skeptics seem to think that extreme weather events have little to do with climate, so that any individual event is NOT part of climate change. I am of the opinion that in the next couple decades it will be more obvious that some of these events really are part of patterns, but that the signal is not yet clear – partly be cause they are regional. We tend to average across climatologically artificial boundaries, such as CONUS, which could obscure meaningful patterns.

            “The authors defined the ACC component for any location as the smoothed multi-model (27 CMIP5) monthly temp anomaly vs. 1901 baseline.”

            From the article:
            ‘The ACC signal is obtained from ensemble members taken from 27 CMIP5 global climate models (GCMs) regridded to a common 1° resolution for 1850–2005 using historical forcing experiments and for 2006–2099 using the Representative Concentration Pathway (RCP) 8.5 emissions scenario ”

            From the Supplemental Materials:
            “We appended historical model simulations for 1850–2005
            with simulations for experiment RCP8.5 for 2006–2099 (72).
            CMIP5 models were used to obtain an anthropogenic climate signal
            that could be removed from the observational record. ”

            I took this to mean that since they were using “historical forcing experiments” they were getting the ACC signal from these, then converting the data to a meaningful and useful format for the study. At any rate, the baseline is not 1901 – it would be very poor research to have any single year as a “baseline.”

            “Couldn’t disagree more. It’s cherry picking by proxy. Climate scientists wait for a disaster and then try to find an AGW fingerprint in that event in isolation without regard as to whether there is any net effect over the whole globe.”

            Show me a single example of this. You can’t do attribution based on one event in isolation, it has to be part of a pattern.

            But it’s not what you said. You said, take a region, calculate the data (1″ rainfall), and than analyze it for attribution – not starting with a single event.

            The “net effect” on the whole globe is only relevant to the science in that when we calculate averages, we could be missing important patterns. If one region has a trend toward more rainfall and another has a trend toward less, that’s still a pattern that could be due to AGW.

            You are making a great error, it seems, by conflating AGW patterns with the net effect in cost/benefit analysis, which is an entirely different issue, one that is informed by science but not a scientific question. The global climate isn’t about “net effects,” or you might as well characterize every place on Earth as having the same temperature.

            The tendency to get policy issues mixed up with scientific ones is a real problem in climate science. It predates the IPCC, although that sure hasn’t helped. It’s not limited to skeptics, but to me it seems like many around here see climate science through its impacts on economics and policy. The fact that these issues are such a large component of WUWT posts exacerbates the problem – it would be much better if there were different parts of the site dedicated to science, policy, energy, etc., and the discussions of them kept appropriate to the topic.

            “So any multi-decadal natural oscillations get lumped into the ACC signal, which was the point I was trying to make. The authors acknowledge this drawback in their article too “The lack of fuel aridity trends during 1948–1978 and persistence of positive trends during 1979–2015 even after removing the ACC signal implicates natural multidecadal climate variability as an important factor that compounded anthropogenic effects during 1979–2015.”

            The quote itself contradicts what you say. “…even after removing the ACC signal” is hardly lumping it in with natural oscillations! The quote says that there are not mid-century trends, and that there are both natural and ACC trends later that act together, compounding the effect. It’s not a problem with the study – not judging by this quote, anyway.

            Oh…coming back to your first point…there can be no “precise numbers” for the temperature anomalies. There could be an average and a range, but neither is very meaningful in real terms, any more than an average for 11 states is meaningful for determining a relationship with fire. You just want a number you can compare with what you think it should be.

            Consider this: if the models were way off-base in simulating temperatures compared to the observed ones, do you think they would use them? If they are good enough to use for simulating historical data (which takes into account CO2 effects), would they not be good enough to use for simulations that remove the anthropogenic CO2 component? We are talking about estimates, here – no one is saying they are exact. Climate scientists are aware of this. It is in the nature of science to quantify, but those who deal with these things on a daily basis would presumably be quite aware of the fact that numbers can seem more “certain” or “concrete” than they are, and come away from reading this with the general message, “AGW is having an effect on fires in the West” rather than, “Increased fire is due to AGW” – two very different statements.

            “These anthropogenic increases in fuel aridity approximately doubled the western US forest fire area beyond that expected from natural climate variability alone during 1984–2015.”

            The period of doubling is only 30 years; I don’t think population changes are the 40% you quoted. I think their estimate seems awfully high, but if it’s even half what they say it’s pretty impressive. I agree with others that management is an issue, though I disagree with many about the solutions. It’s a complex question. I would imagine that the same amount and aridity of fuel on the ground could burn differently in cleared areas vs. forested ones simply because there would be more ground-level wind in cleared areas, for instance.

            But now I’m rambling.

      • I googled |”area burned in 11 western states”| and got closer:

        https://slideplayer.com/slide/5071636/ slide 3

        Adding Littell got me to one .pdf that’s hard to get the link for, but also:

        https://www.frames.gov/files/4213/8879/7024/Littell_AFSC_25Nov13.pdf – Powerpoint, but mentions Littell et al 2009 Ecological Applications

        http://adaptationpartners.org/bmap/docs/BMAP_Workshop_kerns_kim_peterson.pdf – reference, but slide 18 has the PDO overlay.

        https://www.fs.usda.gov/nfs/11558/www/nepa/61203_FSPLT2_028699.pdf – This might have the real reference:

        Exhibit:
        Attachment Littell et al 2009 fire climate.pdf
        Littell, J.S., et al. 2009. Climate and wildfire area burned in western U.S. ecoprovinces,
        1916-2003. Ecol. Appl. 19(4):1003-1021.

        Here it is – paywalled: https://www.ncbi.nlm.nih.gov/pubmed/19544740

        • “might have the real reference”
          But that is a 2009 paper, and the graph goes to 2012. Mainly I’m curious as to whether the PDO speculation is in the original, or has been added by someone.

    • Steven, I used national trend for max/min temp because I would think that would be more representative of an AGW signal than that for a smaller region. For example, if the local trend in sea level was 6 mm/year but the rest of the coast or the globe averaged 3 mm/year, would it really be defensible to argue that that the entire 6 mm/year at my location was all due to AGW? Instead, wouldn’t it be more accurate to claim that 3 mm could be from AGW and the other 3 mm is due to local effects or natural regional variability?

      Consequently, if I had global observations of max/min temp for the past 100 years readily at hand I would have used them over the national trends. As for the study, they didn’t use actual observations to filter out the AGW components. Rather, they used CMIP5 trends which I don’t think is very tenable.

      Notwithstanding the above, I went back to the NOAA/NCDC site and computed the temperature trends for just the western US. Results showed an increase of 1.2*C for both max and min temp over the same 115 year time period as in their figure. So evem in this case the article overestimates the AGW component by 40-70% which would still have a significant impact on their results.

      • BV
        I think your reasoning and approach are reasonable but in error because of the acceptance of the premise that most of recent warming is caused by ACO2. No more than 15% of the atmospheric CO2 is from human sources (Harde 2017, Salby, and Berry) so no more than 15 % of CO2 caused warming can be human caused. It is very unlikely that all of the recent warming is from increased CO2 as the correlation with solar activity is very strong. The excellent new video by Salby
        (https://www.youtube.com/watch?time_continue=4414&v=rohF6K2avtY) addresses this and the efforts to keep this information out of general knowledge.

        • DMA, yes I agree and it was actually addressed at the bottom of bullet point #1 in my review where it says the AGW component used by the authors would be an even greater overestimation if some of the warming trend could be attributed to natural processes. So the “error” only goes to discredit the authors’ work even further.

          I only stipulated all of the warming trend was AGW in the review because that’s what the publication assumed and I didn’t have a need to go down that road to critique their article as it’s a whole other discussion point. In reality, whether the authors overestimated the AGW component by 50%, 200% or 600% is largely irrelevant since any of those should have caused the article to get rejected in the first place.

        • In order to get ECS three times higher than the probable actual figure, models have to assume that more CO2 increases water vapor, far and away the main GHG, in the air.

          So why then should the West be drier than average now for the Holocene?

        • DMA,

          That would mean that warming attributable to atmospheric carbon dioxide would be happening even if there were no anthropogenic constituent – or if there were any CO2 up there at all. Makes no sense.

      • Bob, you are assuming that AGW predicts geographically uniform trends. It does not.

        Are the NOAA/NCDC results just for summer and fall? I don’t see where you get your 40-70%.

        Observed temps aren’t what they are looking at in the figure, anyway. You don’t seem to understand why they used CMIP5 simulations rather than observations to get their estimates. The differences over time due to ACC could be larger than the observed differences if the natural component alone results in a decrease in temperature. There seem to be some key features of this analysis that you are missing.

        See my comment above regarding regional variability.

        • Kristi, thanks for your feedback. You make good points which I’ll try to address.

          I understand AGW does not mean geographically uniform trends. However, while climate models seem to be OK reproducing global temperature anomalies, there is a great amount of uncertainty as to their ability to simulate/predict regional variations or for their use in attribution studies. Consequently, I still think for this applciation using a national/global trend based on observations is a more justifiable representation of the AGW component than climate model output, at least for now.

          That said, I’ll explain how I got the 40-70% when using data specifically for the Western US. I charted the max & min temp graphs at the NOAA/NCDC site & uploaded them to the following links:
          https://drive.google.com/open?id=1OFYsenXPmCjeSgf_ZWdjxrBsj49OMMdd
          https://drive.google.com/open?id=1Y6zdmIwRBqscuU36hq4iy3oERomCDhuB

          The plots are just for summer & fall (Jun-Nov, which is when the worst wildfires occur), and show about a 1.1-1.2*C trend from 1901-1915 (same period as the figure in the article). Eyeballing their color chart (unfortunately they don’t give the actual numbers) it looks like they have about a 2.0*C & 1.7*C AGW component for max & min temp, respectively for Jun-Nov. So their AGW component for max/min temp during the most violent portion of the wildfire season is still 40-70% greater than actual observed trends for the western US over the same period.

          Now your point is well taken about the AGW allocation could actually be more than the observed warming. However, it’s not going to be 40-70% greater, at least there’s nothing published I’ve seen to suggest that much. I’ll try to address the other bullet points you addressed in the other post after a night of sleep!

        • Kristi, your point about ACC being larger than observed differences would be applicable in this discussion if the authors defined the ACC component as the difference between two two sets of climate model runs: one with anthropogenic forcing and one without. However, they didn’t do that. Rather the authors defined the ACC component for any location as the smoothed multi-model (27 CMIP5) monthly temp anomaly vs. 1901 baseline. I’m basically defining ACC the same way as the authors except using observed data instead of climate model output, which I think is the more accurate approach of the two given a choice.

          • Bob,

            I think I see now where you get the 1901 “baseline” – it’s from the caption. As I understand it, they are subtracting the AGW signal at 2015 from the signal at 1901 (following processing, i.e. smoothing etc.). That’s a bit different from what you are saying, isn’t it?

    • Actually, those making the “bold claims” are the ones saying that 50% of wildfires are due to AGW.

      This is important to remember in all the myriad of catastrophic AGW claims. The skeptic supports the null hypothesis and isn’t making any claims at all. The burden of proof lies with Chicken Little

  6. Forest management practices are much more likely to have exacerbated the wildfire situation.

    Additionally a 2015 study by the University of California at Berkeley concluded that the present extremely high level of vegetation now fueling California wildfires has occurred because of fire fighting forest management policies over the last century which have allowed an unsustainable amount of vegetation to accumulate. WUWT

    Globally, forest fires are in decline. What’s special about California? I would cite forest management practices. The graph above, Area Burned in 11 Western States, directly mentions forest management practices to wit: “Period of active fire suppression and fuel accumulation”.

    Any purported AGW vs. wildfires relationship is likely a spurious correlation.

    • CommieBob,
      I agree, forest management practices exacerbated “the situation.” The does not contradict the idea that climate change was part of “the situation.”

      It’s hard to see how they got a regression (not a correlation) in which 74% of the variation is explained by fuel aridity if the relationship is entirely due to something else. The “Period of active fire suppression” is just as likely to be a “spurious correlation,” since it is also a fairly distinct climatic period.

  7. “Conclusion: There is little question that recent drought conditions enhanced the spread of November’s wildfires in California.” Except that 2016-7 winter was a very wet West Coast El Nino year, and 2017-8 was also modestly wet. A drought has to last longer than a single dry Mediterranean climate summer, as all such climatic summers are dry. The rains have come in starting mid November and so is shaping up a normal water year. A fire caused by a microburst of downslope winds on the lee side of the Sierra, downing power lines that started the fire, is hardly a drought induced event.

    • Willis has written an excellent story in which he tries to parse out the effect of seasonal rainfall. Some comments to that story are very informative to those of us unfamiliar with the local California climate.

    • Good comment, Donald.

      Currently California is worrying about getting too much rain and accompanying mudslides.

      Where do these scientists get the idea that 50 or 100 percent of the current-day warmth is caused from CO2? They get this idea mostly from looking at bogus, bastardized Hockey Stick charts that make it look like today is warmer than any day in the recent or distant past.

      The Hockey Stick fraud is what this study is based on.

      One of these days we will have to figure up the true cost of this Hockey Stick fraud. It’s going to be HUGE!

    • A wet fall, winter and spring with nothing to eat the extra fuel thus grown raises fire danger during the following summer.

      CA Indians burnt the grass in woodlands to improve habitat for game they hunted. The Spanish and early Americans grazed the savannah and forests.

      Only imbecilic “Green” resource mismanagers could have produced the conditions which fed Western fires in this century. CA’s climate is usually a mix of drought and flood of longer or shorter lengths. “Climate change” isn’t the cause of devastating wildfires. More people, roads and idiotic mismanagement are.

  8. In Australia were are blessed to have a Dr David Karoly who writes amateur science papers with pop-science conclusions to scare the pyjama pants off 6 year old kids.
    Here is one of his (joint) statements.

    “From 27 January to 8 February 2009, a severe and prolonged heatwave
    (12–15 °C above the seasonal average of 28–32 °C) resulted in 374 more
    deaths in Victoria than would normally be expected during this time.4”
    http://www.cawcr.gov.au/projects/Climatechange/wp-content/uploads/2015/11/Weather_Extremes_Report-FINAL.pdf

    Karoly seems to have a signature in his alarmism, being the number of significant figures used to express disaster levels and the absence of error bounds around the figures. (Here he quotes 384 deaths from a Victorian Government report when a more reasonable science effort might say “300 +/- 300 deaths”.

    The whole methodology of arriving at these assertions that ‘climate change caused zyx additional deaths’ is laughable in terms of the exclusion of plausible alternative mechanisms.

    But,as the old saying went, it sells newspapers. Frankly, I do not know how to stop the drivel.
    Here is a quick and amateur attempt of my own to show the severity of past higher-than-normal temperatures in some of Australia’s major cities over the last 100 years or so. I readily admit that it is simplistic analysis, but then again, if the simple method excludes the hypotheses that heatwaves are becoming longer, hotter and more frequent, then why invent horribly complicated new definitions to torture this historic data to portray alarmism?
    http://joannenova.com.au/2015/02/heatwaves-in-australia-not-longer-not-more-common-why-wont-bom-and-abc-say-that/

    While this WUWT article is about wildfires, there is methodology in common with heatwaves, so the heatwave figures are relevant.

    Geoff

  9. Does no-one have a problem with how a ‘well mixed gas’ and ‘global change’ can cause such impressively local events?

    With any luck, you should see a video from the BBC:
    https://www.bbc.co.uk/news/av/world-us-canada-46485267/flooding-and-snow-as-storm-hits-california

    I actually have a wry sort of smile on my face as Jeff Masters referred to this as ‘Blessed Rain’ when it fell and put the fire out.
    Maybe. Yes.

    But look at the colour of the water in those floods.
    Various shades of grey. See the back-hoe shovelling up more grey/black ‘stuff’

    Gross isn’t it. Horrible. Dirty. Muck.
    Pure yuck, get rid of that shyte ASAP

    That disgusting muck stuff is Pure Concentrated Life Blood for forests, trees and plants. It comprises all the nutrient(s) they need and use. Ambrosia for plants.
    And is swilling away into the ocean from where it will never return, not in our lifetimes anyway.

    Is anyone going to assert that there is an infinite supply of that stuff – the finely divided rock powder/flour, the water soluble (and insoluble) nutrient, the soot, ash & charcoal soil conditioners? Any remaining organic material for bacteria to digest, the bacteria themselves.

    All gone and thus not available to any future plants/trees/forest that fancies recolonising the place.
    Yet ‘some’ forest *will* recolonise the burned areas but will be so much the poorer/weaker because of the loss of all that ‘muck’
    So it wont accumulate water, within the plants themselves but most importantly, in all the trash/junk that falls out of trees and dead plants.

    And so, it will burn so much more easily than the previous forest.
    And more ‘muck’ will wash away, weakening the *next* forest which will burn etc etc etc until all the ‘muck’ is lost and you’re left with a landscape that will neither burn nor grow plants.
    Silica sand and bare rock.

    Until someone/anyone/everyone realises that, the (childish) squabbling will continue and as the forest weakens and burns ever more, the squabbling will intensify..
    until…
    we hear about ‘Pyroterrorism’
    and, does matter whether such a thing is actually real or not?

    Such an idea spread amongst a population, a population that depends on a Fat Fifty pickup truck loaded with mind bending chemicals just to get through an average day, cannot have a happy ending.

    Already we see the blindness, dumbness and ignorance:
    Some here recently mentioned ‘The Carr Fire’
    In my book, a ‘Carr’ is a patch of permanently waterlogged ground – a swamp, a moss, moor, muir or mire. Typically growing mosses and low-growing rushes/reshes.
    What differentiates a Carr from a ‘normal’ moor, mire or moss, is that a few trees are starting to grow out of it – but still a waterlogged mire.

    And yet we hear that The Good People of California have managed to set fire to such a thing and even worse, don’t seem to realise how baaaaaaad that is.

    Amazing.

  10. Although the article is generally true, this part strikes me as an overstatement:
    “Over the last century, there have been NO increases in the severity of drought during fire season when measured over a nationwide scale despite all the added CO2 (see figure below). Therefore none of the recent drought that the western US is currently experiencing can be attributed to global warming over natural regional variability.”

    Reduction in drought nationwide does not mean that AGW is not increasing drought anywhere in the US. It seems to be a factor in increasing drought in West Coast states (along with decadal/multidecadal oscillations), and decreasing drought in the rest of the country.

  11. Droughts and wildfires have always been a part of California. What’s new is the very low moisture fuel load in the form of closely spaced homes that are not hardened against wildfires. One catches fire and they all go.

    The first wave of retiring, cash-flush baby boomers began in 2011, who in large numbers are building homes, or installing mobile homes, in remote places like Paradise, thus increasing the ultra-dry, densely packed fuel load. It really doesn’t matter if the temperature is a few degrees warmer, or if the humidity is a few percent less, because embers flying at 50+ mph are going to turn these types of environments into unstoppable conflagrations.

  12. No mention of fuel load in the article, which is a major factor. With the cessation of logging in the late 1970s, fuel loads are up at least 60% per USFS inventory records

  13. The pop. of California was 23 million in 1980 and now nearly 40m. Counties like Butte are the fastest growing. There is your correlation.

  14. What boggles the mind is the lack of discussion on the massive increase in fuel for wildfires being caused by atmospheric fertilization in the forests from CO2!

    The earth has seen an incredible, widespread greening from this effect as CO2 is well mixed in the global atmosphere.
    https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fertilization-greening-earth

    When it turns dry for an extended period(which has always happened in the West), a lot of the green stuff on the forest floors becomes brown stuff.

    The increase in dried vegetation that was once green makes for an ideal environment for large wildfires. More fuel=higher potential.

    Does this make a case for the increase in CO2 from 280 ppm to 410 ppm being detrimental?

    To answer that fairly, we should balance it with the fact that the increase in CO2, along with the benefits of modest warming are allowing us to feed 1 billion more people today than would be possible with atmospheric conditions from a century ago………..the law of photosynthesis has not been repealed!

    https://www.marketforum.com/forum/topic/14777/

    • The greening effect of CO2 is most pronounced in dry regions, such as the Sahel. Most of CA isn’t quite that dry, especially the north.

      But more plant food in the air surely has had some effect, especially with trees, which are all C3 plants. Common among native CA grasses are fescues (Genus Festuca), which are also C3.

    • Mike Maguire
      You said, “… lack of discussion on the massive increase in fuel for wildfires being caused by atmospheric fertilization in the forests from CO2!” However, from the pictures I have seen, the pine trees in Paradise survived better than the houses. Except for the occasional lone surviving building, the homes burned to the ground. However, the trees appear to primarily be scorched on the trunks. It didn’t look like a crown conflagration. What was probably more important were all the exotic ornamental shrubs and trees,along with the native ceonothus, manzanita, and oaks that are slow growing, but burn very hot.

      • Wooden houses are made of kiln-dried lumber.

        Live, standing trees are green, and many species have anti-fire chemicals. Pine forests rely on low fires to open the cones and release the seeds.

        Back when we had healthy, normal forests, it was common to see signs of surviving past fires on tree trunks.

  15. California’s massive wildfires in the past few years are due to a combination of a cyclical regional climate change pattern, covering the entire American Southwest with the cycle going back thousands of years if not the entire Holocene Era, and the better known human mismanagement of the past century or so.

    The regional climate change cycle involves precipitation. We’ve just ended the wettest hundred year period in the past 2000 years, and the regional precipitation is returning to at best the long-term normal of 2/3 that amount. Paleo-climatalogists have warned for years that it looks more like we’ve started a real regional drought period of 1/3 the precipitation what we’ve had in the past hundred years, and that this drought might last for several centuries.

    See the book and article cited below for more information on the Southwestern regional climate change cycle:

    http://www.amazon.com/gp/product/B00D4EWHPU/ref=oh_aui_d_detailpage_o02_?ie=UTF8&psc=1

    The West without Water: What Past Floods, Droughts, and Other Climatic Clues Tell Us about Tomorrow, Ingram, B. Lynn, and Malamud-Roam, Frances, 2013, University of California Press

    http://ngm.nationalgeographic.com/2008/02/drying-west/kunzig-text

    Drying of the West, (February 2008), National Geographic, Kunzig, Robert

  16. I think it was fifth grade when we learned that fire needs a triangle of things: fuel, air, ignition. In premodern times, the Indians prevented damaging conflagrations by frequent small burns in places where tinder had accumulated. In the 19th and 20th Centuries the logging industry prevented fires by clearing areas and removing brush so they could access useful timber. The “environmentalists” destroyed the logging industry to “protect the environment”. Now we have conflagrations.

    The real hidden variable needed to understand wildfires is laws, regulators, judges, and lawyers.

    When the last lawyer is strangled with the entrails of the last environmentalist, then we will have peace.

  17. So much of the above post and comments are braindead. It’s the fuels, stupid. Fuels grow because they are alive. They accumulate. Fuel increases over time. No patch of vegetation is constant. There is no such thing as a “normal” forest. Green trees burn, too. Your town is next, because you did nothing but blame the wrong thing. With or without global warming.

    • The post is far from “stupid”. The author is a meteorologist and dealt with the meteorological aspects of the issue not the fuel aspect.

  18. the authors create a wildfire regression model by correlating various weather parameters (temperature, humidity, etc…) to wildfire acreage. Then the AGW component of those parameters is removed from the raw weather data (using CMIP5 climate models) and the adjusted weather parameters are input to the wildfire regression model to determine the amount of acreage that would have burned without AGW.

    What could possibly go wrong. The fact that authors have a whizbang theory of AGW is superfluous to the causes of wildfires. There are more humans living in the woods, as the opening post notes, and more occasion for all kinds of accidents, malign intent and just plain stupid. There are more miles of electrical wire through wooded areas, more cars, more campfires… There are millions of lightning-strikes to the earth every night, and millions during the daytime. https://www.youtube.com/watch?v=6RRkcn_CvVA

    Whatever the level of belief of AGW, critics of the opening post would still likely agree that there have been decades of fire suppression. They will never agree upon the size of that problem. Gullies and arroyos and sere mountainsides ready to go up in flames … and who doesn’t want a cabin in the woods?

    AGW-ers are doing something about this. They are appropriating the term “Adaptation”. We are adapting. Along their journey to taking over the power industry (see California), they are all now aware of what adaptation really means, even if they want to infer global warming is the cause. It is just an expansion of the precautionary principle to fireproof their own houses in those protected glades in the woods, cut back the encroaching brush, pay higher government and service taxes, limit tourism, teach the kids to feel very bad…

    https://www.cbsnews.com/news/paradise-lost-inside-california-camp-fire-60-minutes/

    A few residents who fled the Campfire reported that they knew the problem was there and even saw it coming. Some took tentative steps to protect themselves, but were limited in what they could do outside of their own property. Of course, they were overwhelmed. No one in city state or local government can feign ignorance now. The 60-Minutes clip above shows very clearly how the flames of Campfire raced across the greenery covering the forest and chaparral at a rate of a football-field per second, but it also shows the areas outside of Paradise still unaffected by this particular fire. One doesn’t have to scroll out far from a Google satellite close-up of Paradise – to a scale of 10 miles to an inch – to fill the entire screen with greenery, and at that scale, the 153,000 acres that was Paradise is a dot on the hillsides along the west-facing 500 mile scarp of the Sacramento Valley. That whole valley can be an offering to the CO2 gods or (instead of shaking their fists at the sky) they can turn their hands to reversing the policies leading to their predicament. They can call it adaptation, because that’s what it is.

  19. We’ve had two major fires and many, many minor fires here recently in Colorado Springs, CO. All of them were cases of arson. All were set during extremely hot, dry, windy conditions which whipped the fire into an inferno. The public – esp. those living near forest areas or wilderness areas need to be extremely vigilant about making sure that they have mitigated their living space and prompted those around them to mitigate their areas. This is not a cure-all but reduces the potential damage by half.

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