Normally, about this time of year, I’d start burning my way through two cords of wood, over the course of the winter.
This year, I’m not.
It’s complicated.
Soot uncertainty.
I went through the biggest global environmental problem in heating with wood back in Post G22-058.
In a nutshell, when I burn firewood for heat, the C02 that goes up my chimney came out of the air an average ten years ago. For that reason, firewood is very close to a carbon-neutral fuel, when viewed over (say) a decade of time. Over that time period, atmospheric C02 is neither increased nor decreased by the process of growing wood, then burning that wood.
As opposed to say, burning natural gas. Typically, that was produced some time in the last half-a-billion years or so, and trapped underground. The C02 from that source definitely adds to the current level of atmospheric C02.
But along with wood burning comes soot. And even though that soot resides in the atmosphere for just a brief period (typically, two weeks), soot is incredibly effective at capturing the heat from the sun. Dispersing a microscopic black powder through the atmosphere allows the atmosphere to absorb more light energy? Who would have guessed that?
Source: Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza,
T. Nakajima, A. Robock, G. Stephens, T. Takemura and H. Zhang, 2013: Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United
Kingdom and New York, NY, USA.
Back in 1995, nobody quite knew what the net effect of soot was. Even through 2014, estimates were uncertain enough that the confidence interval around the point estimate included zero.
That said, you have to go with the most recent evidence. Based on the 2014 5th report (AR5) of the Intergovernmental Panel on Climate Change (IPCC), I estimated that the warming effect of the soot from my wood stove was just about large enough to offset any benefit from wood burning. That’s the gist of in Post G22-058.
And that’s why I skipped the firewood purchase this year.
The IPCC sixth summary report was released in its entirety earlier this year. So it’s worth taking a peek at that, as the estimate for black carbon involved a lot of uncertainty.
(First, though I have to note how different the public debate is now, for the IPCC 6th report, compared to nine years ago, for the 5th report. For the IPCC 5th report, climate-change denialists went over it with a fine-toothed comb and found an actual substantive error, in a sentence, in a section of the technical portion of the report. This had to do with the rate of melting of Himalayan glaciers. And, as is their habit, the climate-denial industry then proceeded to play the game of This Changes Everything, So Believe Nothing You Have Heard. For the sixth report, by contrast, the release was uneventful, and nobody tried to fabricate some made-up stink about it. It’s almost as if everyone with sense now realizes that climate change is real, man-made, and causing problems. And so there is little value in trying to generate new disinformation, because those who still deny that climate change is a real threat are more-than-satisfied with continuing to believe disinformation that was debunked decades ago.)
Interestingly, they’ve revised their estimate of the warming impact of soot way downward, compared to the 2014 report. (Though still within the 95% confidence interval of the 2014 report).
The best estimates of ... attributed to ... black carbon is substantially reduced. The magnitude of uncertainty in the ... due to black carbon emissions has also been reduced relative to AR5. (Section TS.3.1)
Source: Page 42, IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2391 pp. doi:10.1017/9781009157896.
And, in fact, it looks like the estimate of the warming impact of soot is back about where it was in 1995. Which is about when I decided it would minimize my global warming footprint if I burned wood for (at least some of) my home heating.
Source: Page 92, reference cited just above.
Without getting further into the details, at face value, the upshot of this most recent change is that heating your house with wood, in a modern air-tight low-emissions wood stove, probably offers significant net benefit in terms of global warming footprint. Based on this most recent estimate of the impact of the resulting soot. Assuming I did my calculations correctly last year.
Local air pollution
This year’s air pollution alerts from Canadian forest fires have made me a lot more sensitive to the issue of air pollution from wood fires. In the past, I’ve just turned a blind eye to that, mostly because as far as I can tell, I’m the only person within blocks that actually burns wood for heat.
Air pollution from an isolated wood stove does not have the same public health implications as air pollution from Canadian forest fires. That’s because you have to be in the exhaust plume from my stove to be affected by it. By contrast, you were breathing Canadian soot no matter where you were, and no matter when. It’s the difference between a brief exposure, walking past my house (say), and breathing it 24 hours a day.
So, really, it’s more a question of what I’m doing to the air that I and my neighbors breathe. And for that, the key question is how particulates generated by my wood stove, at my property line (i.e., entering the public domain) compare to the particulate levels we saw during the Summer 2023 air pollution alerts?
I suspect that the only way to tell, with this one, is to measure it. Which I will, the next time I light a fire in my stove.
For now, let me work through the basics, given that this stove is EPA rated to produce no more than 2 grams of soot per hour. A good round number for “too much soot in the air” is, say, 100 micrograms per cubic meter for total particulates. That would trigger an “unhealthy” reading for PM 2.5. To get down to that level, an hour’s worth of soot from my stove would have to be diluted into … 20,000 cubic meters of air per hour.
Or about 333 cubic meters of air per minute. In order to dilute the smoke from my wood stove down below the “hazardous” level for particulate matter. That’s a cube of air roughly 18′ on a side. That seems like a high-but-plausible rate of dilution.
There is also a sense that if you can smell wood smoke, you are breathing in pollutants. And that may well be true — the smell must come from somewhere. That said, a quick look at some scholarly papers suggests that there isn’t a tight correlation between the smell of smoke and the density of particulates in the air. (As evidenced, I guess, by the Canadian forest fires, where there was no smell of wood smoke in the air, but particulate levels were high).
So, before I even lay my first fire of the season, and get out my recently-purchased air quality meter, I’m guessing that this is an open question. I can surely smell wood smoke, at ground level, at least part of the time that I’m buring wood. The next step is to measure it and see if I’m pushing unhealthy levels of particulates out into my adjacent neighborhood.
