I heat my house entirely with firewood from trees I cut from my own property, and have always prided myself on my relatively modest carbon footprint. But I'm aware that wood produces carbon dioxide when it burns, as well as particulate matter, dioxin and other serious pollutants, so the question arises: To what extent is wood an environmentally preferable fuel source, and how might it not be?

In the 18th and early 19th centuries, wood was virtually the exclusive fuel for space heating and cooking in America, and wood-derived charcoal was used for blacksmithing and other industrial processes, though some bituminous coal was imported from England. Cities such as New York were shrouded in wood smoke for much of the year. (Add to this the abundance of manure from horses and other farm animals and the primitive state of hygiene infrastructure and consciousness, and we have a not-very-pretty picture!) When anthracite coal began to compete with wood, it was widely regarded as a cleaner fuel that would greatly improve the air quality in cities. And in many respects, it did just that.

Today, we are able to see the bigger picture: Wood is a renewable resource, or can be, and coal and other fossil fuels are not. A growing forest draws carbon from the air and turns it into wood. When the tree eventually is cut down and burned, or dies naturally, its stored carbon returns to the atmosphere. This takes place quickly in the case of combustion, or slowly if the tree gradually decomposes on the forest floor, or even more slowly if the tree's wood becomes long-lasting building material.

In a very mature forest that experiences no human intervention, forest growth and rot would eventually reach a kind of stasis, in which the forest is no longer continuing to be a net carbon absorber, though the carbon locked up in the live trees would remain out of the atmosphere. But if a particular forest is being cut down at a faster rate than tree growth can keep up with, that forest can hardly claim to be a renewable resource. This is unfortunately the case with most commercially exploited forest land, whether the wood is being turned into lumber, cordwood, or into pellets for wood stoves. For the forest to truly be carbon neutral or better, the carbon released into the atmosphere both from fuel use and naturally occurring rotting of dead trees (and eventual rotting of lumber) must equal no more than the carbon sequestered from the atmosphere by new tree growth.

The most climate-friendly use of wood for fuel would occur when only natural dead (or dying) wood is burned. Or when the wood source consists of trees that were felled by others for aesthetic or safety reasons and would otherwise be ground into chips and allowed to rot, whether as mulch or simply as waste.

The traditional rule of thumb is that a reasonably mature, healthy forest can yield about half of a full cord of live-cut firewood annually and remain stable in terms of live biomass. A full cord is a stack that measures 128 cubic feet (a so-called “face cord” is only a third of this). About eight of my own ten-and-a-half acres are wooded, which allows me about four cords annually, of which I only use about two and three-quarters. So I believe my land continues to be a net carbon absorber rather than emitter. Some of my acreage was overgrown pasture as recently as 50 years ago, but has gradually evolved into a young woods. Most of my tree cutting over the years has been in the form of aesthetic forestry, felling live trees that begin blocking my view of the Shawangunks. But in more recent years, the percentage of my fuel derived from dead or dying trees (or large storm-broken limbs) has happily increased.

Of course, I happen to be lucky enough to own wooded acreage. Someone who must buy firewood would be most environmentally friendly if they can arrange to purchase “waste” wood from a tree removal business or firewood from a truly sustainably managed woodlot.

There remains the issue of wood smoke as a pollutant. Unfortunately, aside from burning dry, well-seasoned hardwood and assuring a good draft and clean stovepipe / chimney, there's not much one can do, and, at least based on a little on-line research, studies appear to show that installing a catalytic devise or EPA-certified unit accomplish nothing. For public health reasons, using wood fuel in a densely populated area should be avoided, as should burning wood in households that include persons with asthma or decreased lung capacity. External heating units, with chimneys considerably shorter than internal units (whose smoke exits higher than the house's roof peak) are especially problematic. But even young, healthy people are not immune to the potential ill health effects of wood smoke. For all these reasons, I am not a fan of pure maple syrup (despite its great taste), which is traditionally made by burning great quantities of wood fuel to produce what is, after all, basically just a sugar.

One mitigating factor when calculating wood smoke vs fossil fuel pollution is the pollution (and carbon footprint) of drilling, refining and transport of oil, or mining and transporting coal (or the myriad environmental costs of both fracking and nuclear power) compared to the almost minuscule environmental cost of running a chain saw and hauling the firewood a short distance in a pickup truck. (I should not fail to mention, however, that the process of manufacturing wood pellets involves considerable pollution!) In the case of both coal and nuclear, the problem of waste storage or disposal is also a huge factor.

The bottom line seems to be that, although truly responsible wood fuel use can lessen global warming, it may be as bad or in some cases worse than fossil fuels as a pollution source. Most usage of commercially purchased wood pellets passes neither the sustainability nor pollution-equivalency test, and burning biomass for electrical generation is a terrible idea.