Shocker: study shows past forest fires occurred mainly in humid, warm periods

Researchers at the University of Bonn used drill cores to trace back the fires of the past 600,000 years – favorable climate induced growth promoting larger fuel loads was the biggest factor.

Highlights:

  • Fire intensity and temperature were largest during warmer periods of earth history.
  • The fires did not mainly occur during particularly dry periods as assumed, but in comparatively humid and warm periods – because then the forests grew particularly lush and provided fuel for fires.
  • High seasonality led to highest fire residue input to terrestrial systems.
  • Fire activity at Lake Van followed orbital forcing during the past 600,000 years.

Lake Van in eastern Turkey is considered a unique climate archive. Several years ago, an international team of scientists led by the University of Bonn raised sediments from the bottom of the lake reflecting the past 600,000 years. An interdisciplinary group of soil scientists and paleobotanists from the University of Bonn has now evaluated the drill cores for residues of early fires – with surprising findings. The fires did not mainly occur during particularly dry periods as assumed, but in comparatively humid and warm periods – because then the forests grew particularly lush and provided fuel for fires. The results are now published in the journal “Quaternary Science Reviews“.

Every summer there are more and more reports of bush and forest fires in the south. But even long before man adapted earth’s vegetation to his purposes or started fires, large fires occurred at regular intervals. Researchers at the University of Bonn have investigated the frequency and intensity of these steppe, bush and forest fires over the past 600,000 years using drill cores from the bottom of Lake Van in eastern Turkey. During this period, rainfall washed the soil and pollen from the surrounding area into the lake, which thus became a unique archive.

In 2010, an international team of scientists led by the paleobotanist Prof. Dr. Thomas Litt from the Institute of Geosciences and Meteorology had already drilled the deposits of Lake Van with a floating platform. “In the 220-meter thick sediment profile, we were able to reconstruct the vegetation of the past 600,000 years using pollen,” says Litt. On the basis of the composition of the pollen in the individual layers, the paleobotanist determined which plants grew particularly frequently during particular epochs. Based on the temperature and water requirements of these plant species, the scientists were able to draw conclusions about the respective climate.

Together with soil scientists from the Institute of Crop Sciences and Resource Conservation (INRES) at the University of Bonn, the researchers analyzed the fire residues in the drill cores. The fire residue particles are partly microscopically small and finely distributed in the sediments. “We therefore used a method that works independently of the visibility of the charcoal residues,” explains soil scientist Prof. Dr. Wulf Amelung from INRES. Benzene polycarboxylic acids served as a biomarker for the fire residues, respectively as biomarker for Black Carbon. The age of the layers in the drill cores, the pollen contained therein and the content of benzene-polycarboxylic acids made it possible to reconstruct the predominant vegetation and the fire events.

“Our thesis was that fire activities were highest during dry climate periods,” says lead author Dr. Arne Kappenberg, who was a doctorate student of Prof. Amelung. After all, even today, fires frequently occur in summer in the dry forests and shrub heaths of the Mediterranean region, while the forests of the cool and damp temperate latitudes are largely spared.

Fires were particularly violent between the ice ages

The data of the past 600,000 years from the drill cores of Lake Van, however, show the opposite. “The forest fires increased during the phases where a lush steppe oak forest with coniferous trees grew in a relatively humid and warm climate,” summarizes Litt. It was thus not dry brushwood as tinder that was decisive for the early fires, but the quantity of plants (biomass) that was produced depending on temperature and precipitation. The biomass was particularly large in the warmer episodes between the ice ages. Since it was only about 11,000 years ago that man made a more extensive appearance in the Middle East through agriculture and livestock breeding, the fires were largely natural.

The fires show a peculiar cycle: About every 100,000 years there were particularly violent fires. This is probably related to the so-called Milankovic cycles. These refer to the regular fluctuations of the Earth’s orbit, which result in higher irradiation on our planet in this rhythm. “This is regarded as a driving force for the change between warm and cold periods,” says Amelung. The researchers suspect that these differences in irradiation led to an accumulation of forest fires not only locally, but globally. Data from Japan indicate that. “This assumption has to be tested on the basis of further studies,” says Kappenberg.

So far, there have been studies on steppe and forest fires that date back a maximum of 150,000 years. The drill cores from Lake Van cover the past 600,000 years. The data also allows derivations for the future. Litt: “If the trend of increasing summer drought continues to persist in Germany, then the danger of forest fires will also rise significantly here.” After all, there are lush forests in Germany – and according to the results of the study, the fire risk increases with the biomass.

###

The study was carried out in the Collaborative Research Center SFB 806 “Our Way to Europe” of the Universities of Cologne and Bonn and the RWTH Aachen.

Publication: Arne Kappenberg, Eva Lehndorff, Nadine Pickarski, Thomas Litt, Wulf Amelung, Solar controls of fire events during the past 600,000 years, Quaternary Science Reviews, DOI: 10.1016/j.quascirev.2019.02.008Highlights

https://www.sciencedirect.com/science/article/abs/pii/S0277379118306048?via%3Dihub

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40 thoughts on “Shocker: study shows past forest fires occurred mainly in humid, warm periods

  1. Lots of forest growth during wetter warmer climate, but it is safe to assume the forest fires still occurred after a couple of weeks of dry weather. Forestry guys know this already…

    • Yup.

      It takes only a matter of weeks, sometimes only days, for a forest to dry out in the presence of warm dry winds.

      Here in southwest Florida where I live, one of the wettest states in the US (average annual rainfall here is 56 inches per year), wildfires are a huge concern every year. Our thick vegetation, both forest and ground cover, dries out in just a few days of low humidity and elevated winds like we typically experience in the springtime. Our local TV stations report daily on fire risk, along with temperature, humidity, and rainfall, because with the right conditions, we can easily go from very low fire risk to extremely high risk in just a couple of days.

      • 1 Hour fuel takes just that 1 hour to dry completely-relative to dry weight. High RH (Relative Humidity) will retard drying. 1 Hour fuels, burning, carry fire from one spot toward another receptive fuel spot (fire fighting this is called “spotting”). Incineration is driven by excess oxygen – well above the norm. Slope and or Wind may drive a fire beyond any ability to control. Extreme spread is much beyond man’s ability to extinguish. Similar to the Camp Fire Nov 2018. Fire Breaks and Fuel Breaks.

        1 Hour – fine fuels up to 1/4 inch
        10 Hour
        100 Hour
        1000 Hour
        100,000 hour

    • That’s the trouble. Just because a year was warmer or wetter according to proxies, that doesn’t mean the whole year was warm and wet. WUWT The local vegetation will also adapt to the fire regime, so that’s another thing.

      • There is also the small problem that the wind has the biggest effect on danger of a bushfire, it doesn’t matter if it’s cold if you have wind and dry fuel you have a problem.

    • Aye. They also admit to not seeing charcoal fragments in the sediment, so this was likely either airborne ash from very far away or the cycles in BPA was caused a general increase in oxidized organic matter. They are comparing precipitation derived locally from lake sediments and trying to tie that to global climate. I’m not convinced, they need other evidence of increased wildfires during interglacials, like macroscopic charcoal and other polycyclic aromatic hydrocarbons.

  2. Little grows in dry climates. Look at the deserts.
    So, of course it is the wet climates that have fires. During the dry seasons or the frequent dry periods.

    • In a related story … EVERYTHING in my yard, shrubs, trees … are ALREADY showing extraordinary Growth this year. Hmmm? I wonder why? Perhaps we need a “study model” to figure it out …

      https://www.latimes.com/local/lanow/la-me-ln-california-rain-cold-20190219-story.html

      However! The official “Drought” Monitor says CA is just BARELY out of Jerry Brown’s official perpetual drought. The State is experiencing only SLIGHTLY greater than “normal” snowfall and rainfall. BullSHITE! My own eyes, my own soil, my own vegetation say otherwise. Take your charts and graphs and shove em.

      By October … I expect a MASSIVELY greater than “normal” Fire DANGER. Duh.

  3. Fuel.
    Who knew?
    That fires need fuel, lots of fuel, to burn hotter and longer.

    Sarcasm aside at least these researchers published results that KOed their thesis.
    Obviously not team players,from the IPCC.

    Funny how those alarmed by the concept of a warmer world seem oblivious to what kind of climate was necessary to feed the mega sized animals of our past.

    Water water everywhere but not a drop to compute….
    Warm humid environment..add good soil and adequate minerals plus increased CO2…equals
    Doom.
    Unless you like to eat.

    • I have never understood how the warmer world of the Cambrian explosion of life seems to get lost in the noise.

    • with respect to the antarctic as a control study area … have you ever seen or had anyone try to tell you (why) your logic is not valid?

  4. There’s no surprise to this. Natural cycles occur without any interference from us. And they will continue to occur, despite us and long after we are gone.

  5. I am not sure that the trees themselves supply the increased fuel.

    In my area (central Kansas) it is the weeds and shrubs that explode in the wet period that follows a mild drought. As soon as there is another brief dry period, or the plants move into seasonal dormancy, there exists an incredible fuel load that is spatially well connected.

    Any spark, or lightning strike, during a windy day quickly becomes an inferno. This type of undergrowth fire can easily become a crown fire for our patches of “forest”.

  6. Something strange is going on with this site, I wonder if anyone else is seeing it. If I load it up with my IE browser, it works and looks just like it always has, and that’s how I’m posting now. However, if I load it up using Chrome, I get this mess with text running over the margins that I can’t even use – but Chrome was working here up until a couple days ago. & my Chrome browser is still loading up every other site I look at with no trouble, so the issue seems site specific.

    • I get that weirdness in various sites on and off with firefox also. What is happening is your browser is not properly applying the Cascading Style Sheets code. Sometimes I have to get so drastic as to re-boot the computer. There are a few sites (very few thank god) where the developers are so lazy that they set it up to only work with one browser (usually I.E.) and their sites look like garbage to every other browser.

    • However, if I load it up using Chrome . . .

      Using Chrome Version 72.0.3626.119 (Official Build) (64-bit) with no problems here.

  7. So nature causes forest fires, who would have thought.

    Seriously what about us clearing the undergrowth, yes I know, we must not interfear with nature, but if we allow housing and other buildings to be built in forested areas, then what is is wrong with us minimising the risk of fires by such measures.

    Its called adapting.

    MJE

  8. The comment below was made at climateaudit dot org
    The study showed how the sequoia national forest has had significantly more fires during the MWP, yet arent used in the NH temp reconstruction. While they may not be good temp proxies, the are an indication that other “peer reviewed temp proxies” dont reconcile with known historical events.

    “I mentioned in a post a few years ago that there’s a fascinating library of
    tree rings in cold storage at the University of Arizona…

    combined with actual FIELD observations this got us:

    https://www.nps.gov/seki/learn/nature/sequoia-fire-history.htm which is

    Multi-Millennial Fire History of the Giant Forest, Sequoia National Park, California,
    by Swetnam, et al.

    You can get to the PDF of this report from the little “here” embedded in the
    National Park Service precise of the main study.”

    A goodly number of Sequoia trees sampled by Swetnem were mighty near some of
    the bristle cones used by Mann, et al.

    I’m amazed no one seems to want to make use of this “library” the goes back
    almost 3,000 years.

  9. The fires show a peculiar cycle: About every 100,000 years there were particularly violent fires. This is probably related to the so-called Milankovic cycles. These refer to the regular fluctuations of the Earth’s orbit, which result in higher irradiation on our planet in this rhythm. “This is regarded as a driving force for the change between warm and cold periods,” says Amelung.
    ___________________________________________________

    OK –

    Sun intensity change – https://www.google.com/search?client=ms-android-samsung&ei=XgxvXLvyLPTQmwXakbrIAw&q=Sun+intensity+change+-&oq=Sun+intensity+change+-&gs_l=mobile-gws-wiz-serp.

    has to get studied further.

    Milankovic cycles

    https://www.google.com/search?client=ms-android-samsung&q=Milankovitch+cycles+influence&sa=X&ved=2ahUKEwiPutSs2M3gAhXiyaYKHbrBCosQ7xYoAHoECAsQAg&biw=360&bih=560

    have to get studied further.

    Lots of work waiting.

  10. Anyone who lives around prairie fires is well aware of this. The worst fires are in years where it’s wet for two or three months, then summer arrives and it get warm, dry and windy. A dry spring yields less fuel. Funny how that works—fires need fuel loads. Who would have guessed?

  11. Many years ago, when I first realized the significance of El Ninos and the Pacific Decadal Oscillation in climate cycles, the Florida Forestry service published a graph with an excellent time-lagged fit of El Nino occurance to acres burned. The extra El Nino moisture grows lush underbrush that doesn’t go up in flames until the following dry La Nina.

  12. I have long wondered if there is often a fundamental lack of understanding of the relationship between production, biomass, and mortality. Producing oyster reefs (biomass) is now a big fad with a certain amount of justification, but the “fire”equivalent (mortality/consumption) is dependent on amount of production, not always adequately comprehended. I learned the basics working for a grocery store in high school. Details do get complicated. I did once meet a botanist studying a desert fire who understood.

    Also in a fair amount of living and camping in desert or near similar dry places, fire danger was usually based on amount of vegetation, modified by wind and moisture. As noted above really dry deserts don’t burn much, plants too far apart. Really wet places like oyster reefs don’t much either. Very productive Louisiana brackish marshes are burned in dry times for management reasons and for otherwise impossible access.

  13. The article seems like a circular firing squad.
    Our thesis was that fire activities were highest during dry climate periods.
    The data of the past 600,000 years from the drill cores of Lake Van, however, show the opposite.
    “If the trend of increasing summer drought continues to persist in Germany, then the danger of forest fires will also rise significantly here.”
    How do dry climate periods differ from droughts? Do droughts happen in wet climate periods?

  14. In Oregon, forest fire fighters have known for at least a century that wetter fall, winter and spring mean a worse fire season, thanks to more fuel. The summer in our climate is going to dry out no matter what.

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