Here's a rather stunning chart from the US National Climate Assessment 2018, Chapter 25.It shows that since 1984, climate change has doubled the total wildfire acreage in the US west.
Note: the acreage is zero in 1984 because that's when they started counting. Results come from an ensemble of climate models.
This additional acreage comes to about 12 million acres, or 19,000 square miles. That's a little more than the area of Vermont and New Hampshire combined.
26 comments:
Articles like this one by John T. Abatzoglou and A. Park Williams turn knowledgeable people into climate skeptics. There is no fair way to assign anthropogenic climate change as the primary cause of the increase in cumulative forest area burned. It's my understanding that the PNAS has lower standards than many other journals.
Cheers
Hi DiC,
I don't know enough about this to evaluate. Why are the methods used in this paper unfair?
The total acreage per year does seem to be increasing: https://wildfiretoday.com/2019/02/02/average-size-of-wildfires-continued-to-increase-in-2018/
D in CA wrote:
"There is no fair way to assign anthropogenic climate change as the primary cause of the increase in cumulative forest area burned."
Did you read the paper?
David - I looked at the paper. I didn't read it in detail. Here's why I think it's ridiculous
1. Proving cause, not just correlation, is very difficult. The number of years was probably much too small to prove cause, even absent the points below.
2. A 1 deg C rise in average temperature is not a big factor in fires spreading.
3. Changes in rainfall patterns are much much more significant than a 1 deg rise in temperature. Nobody really knows how climate change affects rainfall. In theory, warming should increase rainfall over land, but I don't know that this is established. Some people assert that global warming causes more droughts, but that certainly is not established.
4. Another huge factor is change in land management. Here in CA more and more forests were protected from the logging companies. As a result, there was nobody to thin out the brush. This policy change was a significant factor in the horrendous fires we had here the last two years.
Having spent a lifetime analyzing data, it's obvious to me that no model could tease out the impact of higher average temperatures. IMHO, to show results like this in an impressive graph is unethical.
Cheers
DiC wrote:
2. A 1 deg C rise in average temperature is not a big factor in fires spreading.
Why or why not?
Dic wrote:
2. A 1 deg C rise in average temperature is not a big factor in fires spreading.
This is a subjective assertion, not a fact.
It's not science, just an opinion.
DiC wrote:
"Having spent a lifetime analyzing data, it's obvious to me that no model could tease out the impact of higher average temperatures."
Bullshit. Did you ever analyze climate data? Are you a climate scientist? Have you ever run a climate model?
You're trying to claim expertise in one area -- what, actuarial statistics? -- makes you an expert in climate science, because they both use "data."
And that's just crap. AND UNETHICAL. You haven't written a word about the study, but tried to evade having to read it while claiming you have valid points anyway. That's pathetic and pure bull.
David -- regarding temperature, we're all experts. When you light a match, how much difference does one degree of temperature make?
As I said, the abstract alone tells how many years of data they used. It wasn't enough.
I looked for the paper and found a long list of data that they used. See https://agupubs.onlinelibrary.wiley.com/action/downloadSupplement?doi=10.1029%2F2019EF001210&file=eft2577-sup-0001-2019EF001210-S01.pdf
Maybe the full paper itself is somewhere else. Do you know where to find it?
The data they used is extensive and interesting. However, there's nothing in their list of data about all the other possible causes of increased forest fire damage. As far as I can tell, they found a correlation with temperature and concluded that it proved causation. You can't work that way. You have to look at all the possible causes before concluding that the one you're one looking at is the cause.
I was fairly certain that they hadn't included all these other possible causes in their model, because they're not numerical values that can easily fit into a model.
Cheers
Hi DiC,
You mentioned: "A 1 deg C rise in average temperature is not a big factor in fires spreading."
Fire fighters and forest managers must have a good understanding of the conditions that are ripe for forest fires. They publish the relative risk on the side of the roads in Canada.
How much more frequent are these conditions in a 1C warmer world? To my mind you would have to have a good understanding of this before you could conclude that 1C is not a big factor.
Remember that three-sigma anomalies will increase ten fold with only a slight shift of the bell curve.
Layzej - living in CA, I'm pretty familiar with the relative risk charts. They're based on dryness. Now, a big question is how temperature rise affects dryness of the forest. One theory is that higher temperatures cause more evaporation, thus dryer forests. In that way, higher temperatures could lead to dryer forests.
Another theory is that warmer temperatures cause more evaporation over the oceans, thus more water vapor in the atmosphere, and then more rain over land areas. in that way, higher temperatures could lead to wetter forests.
IMHO these are both reasonable conjectures. However, AFAIK they have not been fully proved and certainly not quantified. That is, nobody even claims to know how much dryer a forest would be due to more evaporation or how much more rainfall would be caused by a given increase in average temperature.
In short, I think it's certainly plausible that global warming may be contributing to the increase in forest fire damage, but IMHO a precise model would not be possible. My guess FWIW, is that changes in lumbering are the biggest factor in CA. The buildup of brush is a big deal.
cheers
IMHO these are both reasonable conjectures. However, AFAIK they have not been fully proved and certainly not quantified.
If I look up "evapotranspiration response to climate change in California" it sure turns up a lot of results. Are you sure none of these quantify the relative contribution?
The IPCC also has a section on observed hydrological changes due to climate change. This outlines both detection and attribution.
I think this may be better understood than you believe. Understanding the topic may not be as simple as lighting a match.
Good points, Layzej. CO2 could also be contributing to worse forest fires. Higher CO2 is good for plants. It seems to be causing worldwide expansion of forested areas. That's good. OTOH it also contributes to more shrubbery in the forests. Dried shrubbery is a big factor in fire danger.
See https://www.carbonbrief.org/rising-co2-has-greened-worlds-plants-and-trees
Cheers
Could be. Is there any research that supports the idea that increased greening is contributing to forest fires? Are the greening areas experiencing a larger growth in forest fires than the browning areas?
P.S. we've had the "nobody knows whether climate change will cause an increase or decrease in precipitation" discussion before.
JoeT concluded:
It's not just that evaporation increases in warmer weather and that the atmosphere can hold more water vapor. It's that the atmospheric circulation changes as a function of a warming climate. Some regions in the world will have less precipitation and other regions will have more. As I now realize, even Manabe and Wetherald realized back in 1975 that the circulation changes. It's why local regions in north Africa, southern Europe, the SW part of the US and locations in Australia will dry out in a warmer world, but other parts of the planet will get wetter. The expression that in a warming world the dry parts get dryer and the wet parts get wetter is too simple, but basically true.
As a starting point, take a look at a map of the world's deserts
https://www.quora.com/Why-are-most-of-the-world%E2%80%99s-deserts-located-on-the-Western-margins-of-continents-in-the-subtropics
Notice how the world's deserts more or less line up with the 30 degree parallel north and south of the equator? That's your Hadley circulation in action.
From what I gather, M&W knew over 40 years ago that the circulation will expand poleward.
Layzej - Here's a quote:
Scan the lower elevations of mountains across Southern California, and you'll see that they're covered in bunches of grass, bursting from hillsides like small tufts of wayward hair. Dense amounts of grasses have squeezed in between the native coastal sage brush and chaparral. The grasses are invasive and have provided the perfect fuel to start the fires that have torn through the of mountains of Ventura, Los Angeles and Santa Barbara counties, destroying habitats and homes.
"The invasive grasses have had a major role in most of the fires this year," said Richard Minnich, professor in the department of earth sciences at UC Riverside. "The fires have largely been at low elevations where exotic annual grassland is most abundant. And the amount of grass and biomass was unusually high this year because of the heavy rains last winter."
https://www.scpr.org/news/2017/12/12/78789/the-invasive-flammable-plants-making-california-s/
Cheers
Interesting. Thanks David.
David in Cal said...
As I said, the abstract alone tells how many years of data they used. It wasn't enough.
Another assertion with no evidence given at all.
You have to look at all the possible causes before concluding that the one you're one looking at is the cause.
from the paper:
"We constrain our attention to climate processes that promote fuel aridity that encompass fire behavior characteristics of landscape ignitability, flammability, and fire spread via fuel desiccation in primarily flammability-limited western US forests by considering eight fuel aridity metrics that have well-established direct interannual relationships with burned area in this region (1, 8, 24, 25). Four metrics were calculated from monthly data for 1948–2015: (i) reference potential evapotranspiration (ETo), (ii) VPD, (iii) CWD, and (iv) Palmer drought severity index (PDSI). The other four metrics are daily fire danger indices calculated for 1979–2015: (v) fire weather index (FWI) from the
Canadian forest fire danger rating system, (vi) energy release
component (ERC) from the US national fire danger rating system,
(vii) McArthur forest fire danger index (FFDI), and (viii) Keetch–
Byram drought index (KBDI)."
So what did they miss?
David in Cal said...
"Layzej - living in CA, I'm pretty familiar with the relative risk charts. They're based on dryness."
They're also based on wind.
"IMHO these are both reasonable conjectures. However, AFAIK they have not been fully proved and certainly not quantified."
Did you even read the paper?
Be honest.
They use 8 aridity metrics. Did you read this part?
"We constrain our attention to climate processes that promote fuel aridity that encompass fire behavior characteristics of landscape ignitability, flammability, and fire spread via fuel desiccation in primarily flammability-limited western US forests by considering eight fuel aridity metrics that have well-established direct interannual relationships with burned area in this region (1, 8, 24, 25). Four metrics were calculated from monthly data for 1948–2015: (i) reference potential evapotranspiration (ETo), (ii) VPD, (iii) CWD, and (iv) Palmer drought severity index (PDSI). The other four metrics are daily fire danger indices calculated for 1979–2015: (v) fire weather index (FWI) from the
Canadian forest fire danger rating system, (vi) energy release
component (ERC) from the US national fire danger rating system,
(vii) McArthur forest fire danger index (FFDI), and (viii) Keetch–
Byram drought index (KBDI)."
"Higher CO2 is good for plants."
How so, specifically?
Higher temperatures from higher CO2 decrease crop growth in many cases, often more drought, protein and nitrogen concentrations decrease, more CO2 decreases plant nutrition, there are more pests, weeds do better as well which compete with crops.
BTW, a greener world is a positive feedback on global warming, by decreasing planetary albedo.
David - I never found the paper. Can you post the link?
Regarding CO2 and plant growth, see CO2 is making Earth greener—for now
https://climate.nasa.gov/news/2436/co2-is-making-earth-greenerfor-now/
Cheers
The paper is linked in the original post: https://www.pnas.org/content/113/42/11770
Thanks Layzej. I overlooked it. Here's a sentence:
Climate influences wildfire potential primarily by modulating fuel abundance in fuel-limited environments, and by modulating fuel aridity in flammability-limited environments
Apparently, the assumption that global warming causes dryness is key.
Cheers
I apologize for severely criticizing the paper, based on reading only the Abstract, but not the paper itself.
Cheers
David, regarding temperature -- When you light a match, how much difference does one degree of temperature make?
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