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Wood Stoves Hot Things Up and Cool Things Down

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News

Wood Stoves Hot Things Up and Cool Things Down

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Norwegians love to heat with wood. That’s easy to see when driving around the Norwegian countryside in the winter. Stacks of wood line the walls of houses and smoke rises from the chimneys, especially on cold days. There was even a national “wood night programme” on NRK, the Norwegian Broadcasting Corporation, which ran for 12 hours and attracted international attention because of its unusual theme.

According to figures from Statistics Norway (SSB), 1.2 million Norwegian households heat with wood. They burned 1.1 million tonnes of firewood in 2016 that provided 5.34 TWh of direct heat – and that might have affected the climate more than you think.


“Our findings show a complex picture. This form of heating has a significant warming effect on the climate, which is cause for concern. But at the same time, burning wood also causes significant cooling, which is encouraging,” says Anders Arvesen, a researcher in the Industrial Ecology Programme at NTNU.


Major study published


The Scientific Reports for Nature Publishing Group recently published a major study on climate impacts in Norway. The study analysed so-called stationary bioenergy systems based on heat from wood-burning stoves and from wood biomass-based district heating.

“A lot of research has been done on this topic, but until now we’ve never had such a comprehensive study of various effects on a national level. This is the first time we’ve considered all the different factors in a single study,” says Francesco Cherubini. He is a professor in NTNU’s Industrial Ecology Programme.


The FME CenBio research project carried out the study, which was supported by NTNU in cooperation with SINTEF Energy, the Norwegian Institute of Bioeconomy Research (NIBIO) and the Norwegian University of Life Sciences (NMBU).


Temporary warming


The 35 countries of the OECD (the Organisation for Economic Co-operation and Development) decided in 1991 that CO2 emissions from biomass combustion would not count in CO2 emission accounting. The theory was that nature would reabsorb the carbon dioxide released by burning, yielding a net balance of zero. Unfortunately it’s not quite that simple.


“Bioenergy from forests is carbon neutral in the sense that forests are a renewable resource. The trees will absorb CO2 as they grow, but temporarily there will be a greater amount of CO2 in the atmosphere,” explains Arvesen.


Logging areas have a cooling effect


Logging can adversely affect the climate, including from emissions from the heavy logging machinery. But the logged areas themselves can actually have a cooling effect, because open areas reflect more of the incoming sunlight back into the atmosphere than wooded areas.


“The cooling effect varies depending on where in the country the logging takes place, since different parts of the country have varying snow conditions and forest density,” says Arvesen.


The research project CenBio has taken these factors into consideration in the calculations for the study.


Soot heats up the climate


The CenBio study has also analysed how other emissions from burning wood affect the climate. Methane gas and assorted particles also flow out of Norwegian chimneys. These particles can both absorb and reflect solar radiation. Whereas organic carbon particles have a cooling effect, black carbon – also known as soot – has a warming effect on the climate.


Black carbon also destroys some of the snow’s ability to reflect sunlight because it changes the colour of the snow landscape and contributes to increased snowmelt.


More research needed


Black carbon from biomass combustion accounts for 1.6 million tonnes of CO2 in Norway, according to the study.


“Our analysis indicates that black carbon is the main reason for climate warming. I was surprised how important the effect of soot was, although it wasn’t completely unexpected. Burning wood creates a lot of dust emissions,” says Arvesen.


Cherubini thinks more research is needed in this area. He points out that reducing black carbon emissions will also have a positive health effect due to improved air quality.


So should we stop heating with wood?


“It’s still better to heat with wood than to burn fossil fuels,” says Cherubini.


He emphasizes that more technological possibilities are being developed that will result in new and better furnaces. Until they come on the market, people can reduce particle emissions by replacing their old stoves.

Nano-sized particles


Many Norwegians have already replaced their old woodstoves with newer and cleaner-burning stoves, which has more than halved soot emissions since the early 2000s.


By 2016, 730 000 wood-burning households were using new technology. Overall, heating with wood in Norway has decreased slightly. The amount of wood burned in furnaces with old technology has decreased by more than 75 per cent in the past 20 years, according to Statistics Norway.


Old woodstoves emit more black carbon than new ones. And if the positive development continues, woodstove emissions should drop to the same level as pellet stoves in the near future. The challenge lies in the smallest particles, according to SINTEF scientist Morten Seljeskog.


“Soot is made up of particles as small as nanosize. These emissions are the most difficult ones to get rid of. Researchers are working to figure out what physical measures need to be taken in the combustion chamber to minimize soot emissions in all furnaces,” he says.

This article has been republished from materials provided by the Norwegian University of Science and Technology. Note: material may have been edited for length and content. For further information, please contact the cited source.

Reference
Cooling aerosols and changes in albedo counteract warming from CO2 and black carbon from forest bioenergy in Norway. Anders Arvesen, Francesco Cherubini, Gonzalo del Alamo Serrano, Rasmus Astrup, Michael Becidan, Helmer Belbo, Franziska Goile, Tuva Grytli, Geoffrey Guest, Carine Lausselet, Per Kristian Rørstad, Line Rydså, Morten Seljeskog, Øyvind Skreiberg, Sajith Vezhapparambu & Anders Hammer Strømman. Scientific Reportsvolume 8, Article number: 3299 (2018), doi:10.1038/s41598-018-21559-8.

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