A while back I thought I had linked to this WaPo story “Massive wildfires helped fuel global forest losses in 2021” but I got totally sidetracked and so am posting it now. I’m sure it’s an interesting story. But this is how I got sidetracked.
The article said:
In a recent assessment, the Intergovernmental Panel on Climate Change found that human-caused emissions have significantly increased the area burned by wildfires the American West and British Columbia.
So I wrote the reporter,because the link wasn’t to the IPCC, and the reporter replied that the link is the study that the IPCC referenced. So let’s take a look at that study.
First, the study was of BC, not BC and the American West. The authors don’t make that claim, as far as I can tell. It’s about weather (affected by climate and AGW) and how that impacts fires. And I think it’s worth looking at the authors’ own set of caveats.
The result is dependent on the regression model being realistic. Our regression model assumes that nonclimatic variability in the natural log of area burned is stationary in time and does not account for the possible influence of human factors such as changes in forest management or human ignition sources. Humans have long had a direct influence on fire activity (Bowman et al., 2011), and trends in some regions have been strongly impacted by human intervention (Fréjaville & Curt, 2017; Parisien et al., 2016; Turco et al., 2014). Syphard et al. (2017) demonstrated that climate influence on fire activity becomes less important with a strong human presence. We also do not consider directly the impacts of repeated suppression over time, which could result in larger fires, nor do we consider the pine beetle infestation that has affected BC (Kurz et al., 2008), although such a disturbance did not impact large-scale area burned in the United States (Hart et al., 2015). Nonetheless, consistency of our finding with attribution of an increase in fire risk and previous studies demonstrating that climate change is an important driver of changes in fire behavior in many regions of North America (Gillett et al., 2004; Littell et al., 2009; Morton et al., 2013) supports the finding of a substantial contribution of anthropogenic climate change to the risk of a burned area as large as that in 2017.
My bold. It appears the links to the cited papers in the paper itself work, but not from this excerpt. So if you want to go to a cited paper you have to go back to the original paper . This from the conclusions was also interesting:
While we find no evidence that anthropogenic influence contributed to the risk of extremely dry conditions, we find that it has substantially increased the risk of warm conditions, elevated wildfire risk, and large area burned comparable to those observed.
The Syphard et al paper (2017) I hadn’t seen before (or have forgotten?) and was interesting.. here’s an excerpt from the results:
Of the 10 different variables we explored to explain the variation in the strength of fire-climate relationships, none were statistically significant at P ≤ 0.05 except for the anthropogenic variables (Table 1 and Figs. S1 and S2). In the federal data, regions in close proximity to either roads or developed areas had weaker fire-climate relationships; and in the FPA FOD data, regions with a higher mean human population and proportion of developed land had weaker fire-climate relationships.
More folks around, less direct relationship between climate and fire. It raises many interesting questions, as the authors say in the discussion. Hopefully the authors are continuing to explore them.
Humans can affect wildfire patterns in a number of ways, from starting fires to managing fires (e.g., prescribed fire or fire suppression) and via changes in the abundance and continuity of fuel through land use decisions. For example, humans alter native vegetation through agriculture, urbanization, and forestry management practices. Although their geographical subdivisions were coarser than those used here, regions where lightning-started fires dominated in a recent nationwide analysis (27) show some alignment with areas here where fire-climate relationships were stronger, largely in the interior, northwestern part of the country. Nevertheless, although human-caused ignitions predominate across most of the country, there are also regions like the interior Southeast where fire-climate relationships were relatively strong but the cause of ignitions was nevertheless dominated by humans.This suggests that human influence goes beyond just starting fires, and there is some combination of factors that leads to a dampening of the effect of climate on fire activity. This may be due to effective lengthening of the fire season (27), or starting fires in areas where naturally occurring fires are rare. On the other hand, fragmentation of fuels via land use and urban development may interrupt the spread of fires that would otherwise occur in a less human-dominated landscape. In this case, the climatological factors that might otherwise lead to fire spread are overridden by human-created landscape patterns. This dual effect of humans either increasing fire where it would not otherwise occur, or decreasing it where it would occur, may be why the overall amount of fire in a region was not significantly related to the importance of climate. A couple of other studies performed at smaller extents also suggest that human influence [i.e., suppression policy (40) or land use (33)] in addition to fuel quantity or quality (31, 33) can potentially mediate or dampen fire-climate relationships across different temporal scales.One of the most consistently important variables for explaining strong fire-climate relationships was prior-year precipitation, which is similar to results in other studies (e.g., refs. 28, 30, and 35). This relationship is often found in grasslands and savannahs where fire activity is fuel-limited. High precipitation appears to have a dampening effect on current-year fires but leads to high fuel loads in subsequent years, and the production of fine-fuel biomass that dries by the following year is conducive to fire spread (41). In forested ecosystems, this relationship has been shown to be present in forest types with herbaceous understories and absent in ones with understory fuels comprising litter and other downed material (42)An important caveat to this study is the fact that the variance explained for the differences in strength of fire-climate relationships was not particularly high, and there was substantial variability in the data (Figs. S1 and S2). Therefore, despite evaluating the role of climatic or topographic variability, or variation in vegetation or forest biomass, differences in strength of fire-climate relationships may be due to additional factors. For example, temperature or precipitation patterns may be less variable in some regions than in others, meaning there is less annual variability in fire activity due to these variables. Another reason may be that the fire-climate models do not include essential factors such as localized fire-weather events, long-term drought, or lightning density, nor do they account for variable interactions or more complex variable combinations.
Maybe “fire activity” and “acres burned” are different measures?
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If for some reason you are still interested in this topic. I went to the 3500 or so page IPCC report and searched on Kirchmeier-Young, the first author of the paper. And much to my surprise and delight, I found these paragraphs (page 2-53) which summarize how sure the IPCC is, and which sources they cited. I’m fascinated by how the authors got from the caveats in the KY et al. paper to robust evidence- high agreement. Plus the differences in dryness as a factor. I suppose it’s mostly a function of different conditions in different places.
Since the IPCC Fifth Assessment Report and the IPCC Special Report on Land, published research has
24 detected increases in the area burned by wildfire, analysed relative contributions of climate and non-climate
25 factors, and attributed burned area increases above natural levels to anthropogenic climate change in one part
26 of the world – western North America (robust evidence, high agreement) (Abatzoglou and Williams, 2016;
27 Partain et al., 2016; Kirchmeier‐Young et al., 2019; Mansuy et al., 2019; Bowman et al., 2020b). Across the
28 western United States, increases in vegetation aridity due to higher temperatures from anthropogenic climate
29 change doubled burned area from 1984 to 2015 over what would have burned due to non-climate factors,
30 including unnatural fuel accumulation from fire suppression, with the burned area attributed to climate
31 change accounting for 49% (32-76%, 95% confidence interval) of cumulative burned area (Abatzoglou and
32 Williams, 2016). Anthropogenic climate change has doubled the severity of a southwest North American
33 drought from 2000 to 2020 that has reduced soil moisture to its lowest levels since the 1500s (Williams et
34 al., 2020), driving half of the increase in burned area (Abatzoglou and Williams, 2016; Holden et al., 2018;
35 Williams et al., 2019). In British Columbia, Canada, the increased maximum temperatures due to
36 anthropogenic climate change increased burned area in 2017 to its highest extent in the 1950-2017 record,
37 seven to eleven times the area that would have burned without climate change (Kirchmeier-Young et al.,
38 2019). In Alaska, USA, the high maximum temperatures and extremely low relative humidity due to
39 anthropogenic climate change accounted for 33‒60% of the probability of wildfire in 2015, when the area
40 burned was the second highest in the 1940-2015 record (Partain et al., 2016). In protected areas of Canada
41 and the United States, climate factors (temperature, precipitation, relative humidity, evapotranspiration
24 detected increases in the area burned by wildfire, analysed relative contributions of climate and non-climate
25 factors, and attributed burned area increases above natural levels to anthropogenic climate change in one part
26 of the world – western North America (robust evidence, high agreement) (Abatzoglou and Williams, 2016;
27 Partain et al., 2016; Kirchmeier‐Young et al., 2019; Mansuy et al., 2019; Bowman et al., 2020b). Across the
28 western United States, increases in vegetation aridity due to higher temperatures from anthropogenic climate
29 change doubled burned area from 1984 to 2015 over what would have burned due to non-climate factors,
30 including unnatural fuel accumulation from fire suppression, with the burned area attributed to climate
31 change accounting for 49% (32-76%, 95% confidence interval) of cumulative burned area (Abatzoglou and
32 Williams, 2016). Anthropogenic climate change has doubled the severity of a southwest North American
33 drought from 2000 to 2020 that has reduced soil moisture to its lowest levels since the 1500s (Williams et
34 al., 2020), driving half of the increase in burned area (Abatzoglou and Williams, 2016; Holden et al., 2018;
35 Williams et al., 2019). In British Columbia, Canada, the increased maximum temperatures due to
36 anthropogenic climate change increased burned area in 2017 to its highest extent in the 1950-2017 record,
37 seven to eleven times the area that would have burned without climate change (Kirchmeier-Young et al.,
38 2019). In Alaska, USA, the high maximum temperatures and extremely low relative humidity due to
39 anthropogenic climate change accounted for 33‒60% of the probability of wildfire in 2015, when the area
40 burned was the second highest in the 1940-2015 record (Partain et al., 2016). In protected areas of Canada
41 and the United States, climate factors (temperature, precipitation, relative humidity, evapotranspiration
change accounting for 49% (32-76%, 95% confidence interval) of cumulative burned area (Abatzoglou and
32 Williams, 2016). Anthropogenic climate change has doubled the severity of a southwest North American
33 drought from 2000 to 2020 that has reduced soil moisture to its lowest levels since the 1500s (Williams et
34 al., 2020), driving half of the increase in burned area (Abatzoglou and Williams, 2016; Holden et al., 2018;
35 Williams et al., 2019). In British Columbia, Canada, the increased maximum temperatures due to
36 anthropogenic climate change increased burned area in 2017 to its highest extent in the 1950-2017 record,
37 seven to eleven times the area that would have burned without climate change (Kirchmeier-Young et al.,
38 2019). In Alaska, USA, the high maximum temperatures and extremely low relative humidity due to
39 anthropogenic climate change accounted for 33‒60% of the probability of wildfire in 2015, when the area
40 burned was the second highest in the 1940-2015 record (Partain et al., 2016). In protected areas of Canada
41 and the United States, climate factors (temperature, precipitation, relative humidity, evapotranspiration)
accounted for 60% of burned area from local human and natural ignitions
33 drought from 2000 to 2020 that has reduced soil moisture to its lowest levels since the 1500s (Williams et
34 al., 2020), driving half of the increase in burned area (Abatzoglou and Williams, 2016; Holden et al., 2018;
35 Williams et al., 2019). In British Columbia, Canada, the increased maximum temperatures due to
36 anthropogenic climate change increased burned area in 2017 to its highest extent in the 1950-2017 record,
37 seven to eleven times the area that would have burned without climate change (Kirchmeier-Young et al.,
38 2019). In Alaska, USA, the high maximum temperatures and extremely low relative humidity due to
39 anthropogenic climate change accounted for 33‒60% of the probability of wildfire in 2015, when the area
40 burned was the second highest in the 1940-2015 record (Partain et al., 2016). In protected areas of Canada
41 and the United States, climate factors (temperature, precipitation, relative humidity, evapotranspiration)
accounted for 60% of burned area from local human and natural ignitions
1 from 1984 to 2014, outweighing
2 local human factors (population density, roads, and built area) (Mansuy et al., 2019).
3
4 In summary, field evidence shows that anthropogenic climate change has increased the area burned by
5 wildfire above natural levels across western North America in the period 1984-2017, at global mean surface
6 temperature increases of 0.6ºC -0.9ºC, increasing burned area up to 11 times in one extreme year and
7 doubling burned area over natural levels in a 32 year period (high confidence).
2 local human factors (population density, roads, and built area) (Mansuy et al., 2019).
3
4 In summary, field evidence shows that anthropogenic climate change has increased the area burned by
5 wildfire above natural levels across western North America in the period 1984-2017, at global mean surface
6 temperature increases of 0.6ºC -0.9ºC, increasing burned area up to 11 times in one extreme year and
7 doubling burned area over natural levels in a 32 year period (high confidence).
There is indeed a lot of uncertainty around the exact outcomes from climate modeling. In termps of total precipitation, will some places become wetter or dryer? How much warmer will they be? What places will warm the most? What places will warm the least or even get cooler? Etc. etc.
But, there is not a lot of uncertainty about the fact that globally it is getting warmer, there is more evaporative loss of water, earlier snowpack melt, and even without decreases in precipitation this means dryer fuels and more stressed plants for longer. Also, there isn’t uncertainty that greater global temperature will lead to extreme weather events happening more often- which leads to more wind, and wind drives fires. Overall, is going to lead to more, and more intense, fire (at least until fuels become limiting aka places become a desert). Unfortunately, that is pretty certain. I’d love to be wrong.
Focusing on the uncertainty in the exact outcomes misses the big picture. Scientists need to get better at communicating this, because as soon as people who don’t write peer-reviewed journal articles for a living see ‘uncertainty’, many think the whole thing is up for debate.
Kristen, I think the difference is that adaptation (say forest management, prescribed fire or reducing ignitions) is done at the local level. So if you are trying to help people adapt you need to understand all the causes, and the uncertainty associated with predictions of human, animal and plant behavior at that level, as well as those uncertainties of weather and climate.
Policy makers deal with uncertainty all the time and it doesn’t keep them from acting. Do we know, for example, how long the war in Ukraine will last? It is one (popular in some circles) idea that “if everyone believed” then somehow (magically?) we would all agree on solutions and rapidly implement them. I think California is an example of how, even if elected officials all agree on the importance of the problem, they still disagree about specific solutions and timing. See discussions of keeping Diablo Canyon open.
More importantly, perhaps, is that if you mix authority based on impartiality (science or journalism) with open advocacy, you lose trust. You have lost the long game (building trust and relationships) hoping to “win” the short game. But people have inherent “truth detectors” and use those. For example, “AGW is the ultimate threat to humanity” contrasted with “we are going to have a humongous meeting about it and all fly there.” As a wise forest economist once told me “you have to go by what people do, not what they say.” That’s just one signal people use to discern how much you yourself believe what you say.
I wonder if even the term ‘uncertainty’ is worth some attention. It seems to have both a general or generic meaning, as in “huh, I’m uncertain about that”, and a scientific meaning that comes from Statistics and is about research design, confidence intervals, and Measures of Central Tendency.
In the later, uncertainty refers to how certain you are that the statistics associated with the sampled, measured population and those of the actual, entire population are the same. Using the same term to discuss statistical uncertainty and something like uncertainty associated with a specific, local effect of climate change seems problematic. The former is a statistical measure, while the later seems more about a prediction, something not yet measured.
Goes to Kristen’s point about the importance of scientists focusing on some of these communication questions. I remember a discussion years ago between economists and social scientists about the term ‘value’ or ‘values’, each using the same term in an entirely different way: monetary value v beliefs and other core values. And if scientists in similar fields can have such different meanings of the same word, imagine why communication deserves such attention when dealing with issues like climate change.
My question about uncertainty has to do with scale. Should uncertainty at a “local” level should be imposed as an obstacle to achieving broader scale desired outcomes?