Australia and US Wildfire, Similarities and Differences: II. How Much is Due to Anthropogenic Climate Change?

Time of emergence of anthropogenic climate change for (a) the frequency of days exceeding the 95th percentile, (b) the length of the fire weather season, (c) the peak 90‐day average FWI, and (d) annual maximum FWI. Mapped is the 17‐model median date at which the anthropogenic signal emerges based on the change exceeding the standard deviation of the baseline period. Areas of light gray highlight where the signal does not emerge for at least eight models by 2050. Unburnable lands where >80% of the area is water, snow, and ice or barren or sparsely vegetated are shown in dark gray. The percent of burnable land with emergence by 2050 is denoted in the bottom left corner of each map.

The above maps are from this paper by Abatzoglou et al.

Here’s a link to a Science Brief from the University of East Anglia about climate and wildfires. It’s kind of like a scientific rapid response team when an issue comes up, which made it easy to compare the Western US and Australia in terms of ACC.

First, here’s Australia

Climate change also affects fire weather in many other regions, although formal detection does not yet emerge from natural variability. ​Abatzoglou ​et al. (2019) suggest that the anthropogenic climate change signal will be detectable on 33-62% of the burnable land area by 2050. Other global studies agree that the effect of climate change is to increase fire weather and burned area once other factors have been controlled for (e.g. Huang ​et al.​, 2015; Flannigan ​et al.,​ 2013). ​Regional modelling studies corroborate these global findings by projecting how climate change will affect fire weather:…

Australia. Observational data suggest that fire weather extremes are already becoming more frequent and intense (Dowdy, 2018; Head ​et al.​, 2014). However, the divergence between anthropogenic and natural forcing signals is weaker, and more challenging to diagnose, than in other regions due to strong regional and inter-annual variability in the effect of the El Niño–Southern Oscillation on fire weather (Dowdy, 2018; Sharples ​et al.​ , 2016). ​Other important regional weather patterns, such as the Indian Ocean Dipole (IOD) and the Southern Annular Mode (SAM) also contribute to natural variability in fire weather, but their effects are increasingly superimposed on more favourable background fire weather conditions. ​Impacts of anthropogenic climate change on fire weather extremes and fire season length are projected to emerge above natural variability in the 2040s (Abatzoglou​ etal.,​ 2019)

Then here’s the western US:

The impact of anthropogenic climate change on fire weather is emerging above natural variability. ​Jolly et al. (2015) use observational data to show that fire weather seasons have lengthened across ~25% of the Earth’s vegetated surface, resulting in a ~20% increase in global mean fire weather season length. By 2019, models suggest that the impact of anthropogenic climate change on fire weather was detectable outside the range of natural variability in 22% of global burnable land area (Abatzoglou et al., 2019). Regional studies corroborate these global findings by identifying links between climate change and fire weather, including in the following regions with major recent wildfire outbreaks:…

Western US and Canada. Models suggest that the impacts of anthropogenic climate change on fire weather extremes and fire season length emerged in the 2010s (Abatzoglou ​et al.,​ 2019; Williams ​et al​., 2019; Abatzoglou & Williams, 2016). Yoon ​et al​. (2015) similarly predicted the occurrence of extreme fire risk would exceed natural variability in California by 2020. Kirchmeir-Young ​et al​. (2017) found that the 2016 Fort McMurray fires were 1.5 to 6 times more likely due to anthropogenic climate change, compared to natural forcing alone. Westerling ​et al. (2016) found that burned area was >10 times greater in Western US forests in 2003-2012 than in 1973-1982. The 2015 Alaskan wildfires occurred amidst fire weather conditions that were 34-60% more likely due to anthropogenic climate change (Partain ​et al.​, 2016).

Note that the claims are sometimes models and sometimes empirical. For example, the increase in burned area noted by Westerling may have had many reasons besides changes in fire weather.

If we accept the Australian claim at face value (differences due to anthropogenic climate change expected to show up in the 2040’s) then they have some time to get their prescribed burning and other programs up to speed before the additional problems due to ACC surface. In that case, it looks like they have about 20 years before they get the additional problems due to ACC. However, if climate modelers don’t understand the natural cycles or anthropogenic factors well enough, though, as seems likely, conditions could be worse sooner or later than the 2040’s. So the Aussies and us, despite the difference in model predictions both need to get on with prescribed burning, building and community design, improving suppression and all that.

As the authors state:

Nonetheless, wildfire occurrence is moderated by a range of factors including land management practises, land-use change and ignition sources.

7 thoughts on “Australia and US Wildfire, Similarities and Differences: II. How Much is Due to Anthropogenic Climate Change?”

  1. More to read: The NY Times has an article today (S): “Reducing Fire, and Cutting Carbon Emissions, the Aboriginal Way.” Subhead: “As blazes rage in southern Australia, Indigenous fire-prevention techniques that have sharply cut destructive bushfires in the north are drawing new attention.”


    At a time when vast tracts of Australia are burning, Violet Lawson is never far from a match.

    In the woodlands surrounding her home in the far north of the country, she lights hundreds of small fires a year — literally fighting fire with fire. These traditional Aboriginal practices, which reduce the undergrowth that can fuel bigger blazes, are attracting new attention as Australia endures disaster and confronts a fiery future.

    Over the past decade, fire-prevention programs, mainly on Aboriginal lands in northern Australia, have cut destructive wildfires in half. While the efforts draw on ancient ways, they also have a thoroughly modern benefit: Organizations that practice defensive burning have earned $80 million under the country’s cap-and-trade system as they have reduced greenhouse-gas emissions from wildfires in the north by 40 percent.

    These programs, which are generating important scientific data, are being held up as a model that could be adapted to save lives and homes in other regions of Australia, as well as fire-prone parts of the world as different as California and Botswana.

    • Steve, that’s pretty interesting.. when I was working at the FS, EPA questioned the argument that prescribed burning would lead to fewer particulates and less carbon in the future from wildfires. This was from the EPA comments on a project that involved prescribed burning.

      A. I wonder whether EPA has changed its institutional mind on this from 10-15 years ago?
      B. I wonder whether different cap and trade systems treat prescribed burning differently?
      C. Hopefully EPA and California’s cap and trade system are not at cross purposes.
      D. But perhaps cap and trade systems only look at carbon, and regulators such as EPA also look at particulates?

      Does anyone from California understand how this all fits together?

      • One can argue that thinning and Rx burning in old-growth stands in the PNW, including LSRs, are climate-friendly, over the long term.

  2. Sharon: “So the Aussies and us, despite the difference in model predictions both need to get on with prescribed burning, building and community design, improving suppression and all that.” That’s exactly why I tend to tune out the arguments about “how much is due to anthropogenic climate change” or how accurate climate models are. That doesn’t matter to what we need to do now. (What matters is what is most effective.)

    • I agree with tuning out.. however, there are reasons folks may want to amplify the climate angle.. one is “it’s not our fault” as in PG&E or governments.

  3. WA Today, an Australian newspaper, has this article, “These scientists think we’re in a ‘bushfire spiral’. They have a plan.” The plan? Fuels management. The article looks at the argument.

    Also, note that WA Today says that “Our coverage of the bushfire crisis is free for all readers. Please consider supporting our journalism with a subscription.” An example I’d like other news outlets to follow.

  4. Op-ed by two Aussie scientists:

    Why prescribed burning has never been so important to Australia

    “The purpose of a fuel-reduction burning program is not to stop bushfires, but to assist with their safe suppression. To understand this properly it is necessary to understand the complex and dynamic process of bushfire suppression.”

    “Of the elements that make up the bushfire triangle – fuel, weather and oxygen – only fuel can be managed. But this must be done the right way.

    “It must be underpinned by good science, well planned and well executed by trained, experienced people who are well resourced.

    “Prescribed burning is costly and comes with an element of risk, but the alternative – a cycle of bushfires – is far more costly to humanity, to communities and to the environment.”

    Dr Neil Burrows has 42 years experience as a bushfire scientist, fire investigator, fire policy advisor and fire behaviour analyst in Incident Management Teams.

    Rick Sneeuwjagt has 50 years experience in bushfire research and management at district, regional, state and national levels.


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