Bridger Foothills Fire: The shifting bell-curve (climate change)

Before I start, all my education work via the Geogramblings’ “Life Geographic” blog is done all in my spare time, at my own cost but is free for you to access and enjoy. Usually here I mention how you can support my work; on this occasion, please instead consider contributing in some way to fundraising efforts to help those impacted by the Bridger Foothills Fire. Details are found in the previous blog post about the fire. Thank you!

Some important context

For those of you whom these Bridger Foothills Fire articles are first of mine you are reading, I have a degree in Environmental Science with a focus on meteorology, climate change, environmental risk and scientific communication. After over a decade as a high-school teacher, I have since worked directly with climate scientists from NOAA, the Met Office and various other agencies across the world. I have seen both the data and the methodologies to collect and analyse them which makes up robost and reliable climate science. I have an understanding of what is meant by terms such as ‘uncertainty’, ‘projections’ and ‘modelling’. I am also a trained and practiced critical thinker who delievers teacher training and student learning on that skill. With all that said, human-influenced (or ‘anthropogenic’) climate change is real, and we are now entering a period where stories of its impacts are no longer from far-off shores or something that happens to someone else.

When climate scientists say that it is difficult to attribute a single extreme event such as a wildfire or a tropical storm to climate change, and talk in probabilities and likelihoods rather than absolute definitives, it is because they are being accurate in their reporting and know it is unscientific and unethical to mislead. The are simply following the data. Uncertainty is actually very useful and important in science. It gives confidence levels that help policy makers and decision makers – you would put more resources into managing something that you’re 95% confident will happen than something that is 50%, but you wouldn’t disregard the latter either. Uncertainty also indicates where further study, investigation and analysis is needed. Reducing uncertainty is not always the aim, accounting for it is just as important and as it can further understanding of both the issue itself or other issues that may be connected. Knowing uncertainty can help find missing pieces of the puzzle.

The second thing to bear in mind is the difference between weather and climate. Wildfires are essentially weather events. They are short-term, last days or weeks, and cover small areas. Climate on the other hand is the averaging of these events and all the ‘norms’ in between – so over a longer period and over wider areas. One way we know the climate is changing is simply by looking at weather observations that have been taken for over a hundred years.

One study which actually uses ‘probability’ to good effect was led by James Hansen in 2012, and was summarised in a NASA brief here. Put simply, if you were to take Northern Hemisphere summer temperatures recorded in the decades of 1951-1980 and plot them as a frequency distribution, you would get a bell-curve, with the coldest ‘anomalous’ observations (meaning they were unusually cold) on the left and the warmest (unusually warm) observations on the right. Now, press ‘play’ on that plot, and compare each decade’s worth of temperature observations. Look what happens:

The bell curve moves to the right. The ‘normal’ for the decade of 2001-2011 is mostly what would be considered as ‘abnormally warm’ for 1951-1961. Long-story-short, ‘unusally warm’ summers are becoming more common, and ‘unusually cold’ less so.

But what does this mean for wildfires in Montana? As mentioned in the previous blog post about the Bridger Foothills Fire:

Fires are a result of arid conditions, but particularly drought, which is defined as a prolonged period of time in which an area experiences less than normal precipitation (e.g. rainfall). When temperatures are high, then evapotranspiration (which takes moisture out of the ground and vegetation) is greater than precipitation.

So we need two things: warmer temperatures and less precipitation. Was that the case for the Bridger Foothills Fire? Yes it was, again as described in the previous post. But were those conditions due to climate change?

Was the Bridger Foothills Fire a result of climate change?

This is where the ‘difficult to attribute a single event’ bit comes in. But to take that as a straw-man argument to beat down climate change is to misunderstand and dismiss the science of climate change attribution. I won’t tread over old ground here, but instead refer you to my first vlog and accompanying blog article on the science of climate change attribution, relating it to the devastating Australian Bushfires of 2019-2020. In that article you will find plenty of robust further reading.

It would be irresponsible and inaccurate for scientists to say that a particular event was definitely due to climate change unless they had irrefutable evidence to suggest so. That’s why they talk in probabilities and likelihood. We saw from the changing bell-curve above that summers in the Northern Hemisphere are getting hotter, and what was once ‘extreme heat’ a few decades ago is now becoming more normal. So that is one pre-condition for drought and fire conditions being met right now.

Warming Stripes for Montana from 1895-2019, generated at

When we look into the future, we simply play these scenarios into complex climate models over and over and over again – tweaking the conditions (e.g. more or less carbon emissions) and let the modelling of physics do the work).

Climate models today are so robust, complex and detailed, that we can now look at potential changes in specific areas. So let’s look now specifically at Montana, and we’ll also look at precipitation too.

The 2017 Montana Climate Assessment report is the result of two years of effort by university faculty and students, state and federal agency researchers, non-profit organisations, resource managers, and citizens from across Montana.

The report gives a very clear and very stark assessment when it comes to fire risk:

An increase in fire risk (i.e., probability of occurrence)—including an increase in size and possible frequency and/or severity (i.e., tree mortality)—is expected in the coming century as a result of a) prolonged fire seasons due to increased temperatures, and b) increased fuel loads from past fire suppression. [high agreement, robust evidence]

2017 Montana Climate Assessment Executive Summary: “Impact to Montana’s Forests”

‘High agreement, robust evidence’ is the scientific way of saying that there is very little doubt, so you better deal with it or get ready for it. The statement also makes a recognition that other non-meteorological factors are at play (namely land management*).

*NB: An article regarding land-management that is very worth-while to read is the piece “They know how to prevent megafires. Why won’t anybody listen?” piece published in the MinnPost (thanks to my father-in-law for making me aware!)

How did they come to this conclusion, particularly when it comes to the changing climate? Two indications are the results from climate models that show changes in temperature and precipitation during the summer months, particularly between July and September, which is currently fire season (you’ll see later why I say ‘currently’).

The South West of Montana, which is where Gallatin County (containing Bozeman and the southern part of the Bridger mountain range) is located, has been warming an average of 0.35*F per decade since 1950 (p28). And a warming trend will continue into the near-future. Even under a ‘moderate’ carbon emission scenario, temperatures in SW Montana could increase by an average of 2.5-3*F for the 2040-2069 period (from a baseline of the average recorded between 1970-2000). Preciptiation changes historically, across the whole year, have not been very significant, But looking specifically at SW Montana in summer, July and August could see an average of 5 inches less precipitation from the 1970-2000 baseline (with September seeing little change, if not slightly wetter).

Whitlock C, Cross W, Maxwell B, Silverman N, Wade AA. 2017. 2017 Montana Climate Assessment. Bozeman and Missoula MT: Montana State University and University of Montana, Montana Institute on Ecosystems. 318 p. doi:10.15788/m2ww8w.

But note that June is expected to get a little drier and warmer too, thus potentially bringing the official start of the fire season a little earlier. Since Montana is already prone to drought, these warming trends and seemingly small drying trends increase the risk of persistent drought conditions. Evapotranspiration rates will be higher, and more vegetation becomes cured and tinderous.

So, was the Bridger Foothills Fire caused by climate change? No. It was likely caused by a natural weather event (reportedly a ‘hold-over fire’ from a lightning strike). Was it probable that, thanks to climate change, the conditions that allowed the fire to ignite and consume the eastern side of the southern Bridgers? Yes, probably. And the final question: will climate change make fires in the area more likely, less likely or have no difference? Studies suggest – more likely, with a high degree of confidence.

Tree of climate signals relating greenhouse gas emissions to the wildlifes in the western US. Source: Climate Signals, from their article “Western Wildfire Season 2020“.

You see, concluding as above does not invalidate the climate change argument in any way. I would actually argue that stamping a definite ‘yes’ is more crazy, more irresponsible and very much unscientific. Does it mean that because we can only talk about probabilities that we shouldn’t therefore do anything to mitigate or adapt for human-caused climate change? Of course not, that’s ridiculous. If a team of engineers reported to an airline company that as a group they are in ‘high agreement’ that their data ‘robustly’ tells them that a plane will suffer a catastrophic failure if it is put into service without repair, would that airline company allow passengers on it? It’s a simple analogy, but you get the point.

Getting closer to home for more of us

When I was in high-school in the 1990s, my Geography teacher taught us climate change is a thing in the future, plenty of ‘ifs’ and ‘buts’ and ‘maybes’. When I first started teaching Geography in the mid-2000s, I was saying that climate change ‘will, if’… Then throughout the next ten years the language changed from ‘will’ to ‘is’, giving examples of the most vulnerable in the world suffering from impacts, such as sea-level rise in low-lying countries, crippling drought in the Sahel or melting permafrost in Alaska and Siberia etc. But now, it’s coming home.

The current fire situation in the western USA is absolutely terrifying, and the number of studies that have looked into the relationship between wildfires and climate change is becoming more and more conclusive. So there’s the Bridger Foothills Fire which came within a kilometer of buring my family’s home down, and there’s also the fires which are choking friends and family we have in California. One particular fire, the CZU August Lightning Complex fire, started to burn parts of the Henry Cowell Redwood State Park, a place I visited in 2010 and which is a matter of miles from a close friend’s house in Santa Cruz.

Wildfire’s aside, in April of this year, I ran an online teacher-training webinar for a conference regarding climate change. One participant told me that some of her students who were already vulnerable were at risk of homelessness due to the flooding of the River Don in Sheffield in November 2019, an event in which the evidence suggests is attributable to climate change. Then you have more ‘obvious’ events like the European heatwaves of June and July 2019 and the persistently hot weather of this summer.

As a teacher, my concern for this is very high when it comes to safeguarding the children in our care. In the upcoming Geographical Association GA Magazine (Autumn 2020 issue), you can read my thoughts and arguments why I strongly believe climate change should be considered a safeguarding issue in our schools.

The impacts of climate change change are now at our doorstep, whether it be fires, floods or heatwaves. Now that more of us here in the western world are being directly impacted, are we as a society finally going to do something about it?


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