Residential wood smoke is an important source of short-lived climate pollutants.

Wood Burning and Our Climate

There is a belief that wood burning doesn’t contribute to climate change. But this simply isn’t true.

 

Living trees absorb carbon dioxide (CO2) from the air as part of the photosynthetic process and store the carbon as cellulose and other carbon-containing carbohydrates.

 

When wood is burned, the CO2 that was absorbed over years while the tree was alive is released back into the atmosphere all at once, along with short-lived climate pollutants (SLCP) such as black carbon.

 

We need to emit less in the short term, not more.Photo of clouds in the sky spelling out CO2In the sense that trees can be replanted, wood burning has been described as renewable. After decades, or even centuries, new trees will eventually reabsorb the carbon that was emitted when their predecessors were burned. However, we need to reduce our emissions now.

 

The harvest, storage and transportation of the wood also results in greenhouse gas emissions from fossil fuels.

 

It’s Not Just About CO2

But CO2 isn’t the only problem. Burning wood also emits short-lived climate pollutants including soot, carbon monoxide, and volatile organic compounds such as methane.

 

Soot, of which black carbon is a major component, is the second largest contributor to global climate change, and methane is the third. CO2 concentrations are now about 50% above pre-industrial levels, while methane concentrations have tripled.

 

Preventing Climate Destabilization

Short-lived climate pollutants (also called super pollutants) are responsible for about half of global warming. They remain in the atmosphere from a few days to a couple of decades, compared to the much longer time CO2 stays there.

 

Three experts — a Nobel prize-winner, a renowned climate scientist and a sustainability guru explain: “The best and fastest way to prevent immediate climate destabilization lies in cutting back on emissions of super pollutants that make outsize contributions.” The three experts warn, “Cutting CO2 emissions remains imperative, and cannot be delayed … the parallel strategy of reducing super pollutants is perhaps even more important to avert disastrous consequences in the near-term.”

 

UN: Phase Out Log-Burning Stoves to Reduce Global Warming

The next few decades will be critical. If we are to meet the targets set by the 2015 Paris Agreement and limit global warming to well below 2ºC, it is crucial that we lower both CO2 and SLCP emissions. Phasing out log-burning stoves in developed countries was one of a package of 16 measures recommended by the UN Environment Program and World Meteorological Organization to improve health and help keep the global temperature rise below 1.5ºC.

 

Black Carbon

Particles in the air can absorb light from the sun or scatter it, depending upon the particles’ characteristics. Particles that absorb light warm the earth, whereas particles that scatter light help cool it.

 

The terms black carbon and elemental carbon both refer to a similar type of carbon particle. The difference in terms reflects the different methods used to measure them.

 

Image: US EPAGraphic comparing elemental carbon and black carbonBlack carbon is the most strongly light-absorbing component of particulate matter. Per unit of mass in the atmosphere, black carbon can absorb a million times more energy than CO2. In the atmosphere, it warms clouds and affects the size and distribution of cloud droplets, which in turn can affect rain patterns and alter the amount of solar energy that is reflected back into space.

 

Once black carbon particles have fallen back to earth, they absorb the sun’s energy on the ground. If they land in areas covered with snow or ice, the resulting darkening of the snow’s surface and the absorption of the sun’s solar radiation promotes melting. This is an especially serious problem in Arctic nations, but can affect all snow-bound places.

 

Wood burning is a significant source of black carbon emissions. For example, a study from Switzerland found that, at the sites that were measured, wood burning contributed up to 33% of black carbon emissions. It was noted that, “This is a noticeable high fraction as the contribution of wood burning to the total final energy consumption is in Switzerland less than 4%.”

In Canada, an official black carbon
emissions inventory found that residential wood burning is responsible for 90% of black carbon emissions from non-industrial stationary fuel combustion, which includes electrical power generation by utilities. In 2014, all of Canada’s electric generation, including coal, was responsible for 0.5% of Canada’s black carbon emissions, while residential wood burning was responsible for 27%. All industrial sources, including petroleum production, were responsible for 8.5% of Canada’s black carbon emissions, while vehicles on the highway contributed 20% (2% for gasoline cars and 18% for diesel).

 

Brown Carbon and Organic Carbon

When wood is burned, it also produces organic carbon, which is a complex mixture of compounds. Recent research shows that some organic carbon particles are highly absorbing in the near-UV spectrum, and that this affects the global climate balance. For example, this study in coastal California provided evidence that the light-absorbing properties of organic carbon “in atmospheres burdened with residential wood smoke” are secondary to those of black carbon, “but not insignificant.”

 

These near-UV-absorbing particles are also known as brown carbon.

 

Another study in the United Kingdom looked at atmospheric nitrated phenols from residential wood burning. It was determined that although nitrated phenols may make up a small portion of the total organic aromatics measured in the air, they are nonetheless a potentially important contributor to light absorption in the near-UV spectrum by brown carbon from wood burning. “They can thus affect atmospheric radiative transfer and photochemistry and with that climate and air quality.”

 

Methane

 Letters spelling out CH4 - methaneAccording to the Intergovernmental Panel on Climate Change (IPCC), methane will cause 88 times as much global warming in the first 20 years after emission as the same amount of CO2 and 34 times as much over 100 years. In the US, residential wood burning accounts for over 45 percent of methane emissions from stationary combustion.

 

According to law professor Christopher Ahlers, methane emissions from the residential burning of wood are four times greater than those of industry, in spite of the fact that greenhouse gas emissions from residential burning are half those of industry. This suggests, according to him, that “the industrial sector is more efficient at extracting or limiting the emissions of methane,” which is a valuable commercial product. “This highlights the wasteful nature of residential wood-burning.”

 

 

Air free of wood smoke is goodfor both people and the planet.A smiling girl holding a globeNewer Wood Stoves Won't Fix the Problem

Switching to a newer wood stove will not fix the problem of short-lived climate pollutants. It has been shown in at least one study that newer stoves do not emit less elemental (black) carbon than conventional stoves, and other studies have provided evidence that hotter combustion temperatures, which newer stoves have, actually raise the ratio of light-absorbing carbon. For example, this study found the relative fractions of black carbon in PM emissions rose by as much as 12-fold higher from an “eco-labeled” stove with more efficient combustion.

 

Save Lives as Well as the Planet

Stanford climate scientist Mark Z. Jacobson has written that brown carbon from burning biomass has a greater impact on health than fossil fuel soot emissions, and controlling it will reduce human mortality. According to him, deaths from biomass emissions are 8 times greater than those from fossil fuels, in large part because solid biomass fuels such as wood are used in close proximity to where people live. Controlling both fossil fuel and biomass emissions, such as from wood, “may help to reduce Arctic ice loss and global warming faster than any other control option available, including control of CH4 (methane) or CO2 although controls of all chemicals are needed.”

 

According to Dr. Jacobson, levels of soot emissions from fossil fuels can be improved with better engines, fuels, filters and other changes in technology. However, the only practical method of mitigating solid fuel emissions, such as from wood, is to eliminate them entirely.

 

Environment and Climate References

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