With the rising desire for a cosy and comfortable life full of ‘hygge’ has come a rising demand for the warm glow of a household fire to gather around. But, at what price for our health?
Dr Mikko Savolahti, senior research scientist at the Finnish Environment Institute, and colleagues published detailed research investigating the emissions from residential wood combustion in Finland. The models demonstrate that the climate impacts of wood burning need to be fully included in policy making.
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In this episode we will be discussing the impact of residential wood burning both on our personal health and on the environment. People are often aware that pollution from wood burning stoves has a negative impact on air quality (especially if used in urban areas) and, therefore, respiratory health. But because they involve the burning of a “renewable” fuel rather than a fossil fuel such as coal, gas or oil, they are often advertised as a carbon neutral method of home heating. So how true are these assumptions and why is this such a hot topic today?
The popularity of wood burning stoves has increased across Europe over the last four decades, and particularly in Finland where the research we will be discussing has taken place. In Finland, 23% of detached homes have wood burning appliances as their primary heat source, as well as wood being burnt in most other houses for supplementary heating, recreational purposes or in sauna stoves. Almost 90% of new built houses in Finland have at least one wood burning stove installed in them. With the rising desire for a life that is more ‘hygge’, aka cosy and comfortable, has come a rising demand for the warm glow of a household fire to gather around. But, at what price does this idyll come at for our health?
Exposure to fine particles in ambient air has been suggested as one of the leading environmental health risks both globally and in Finland, where residential wood combustion is the largest domestic source of fine particles. Estimations indicate that around 1600 annual deaths in Finland result from fine particle air pollution, which is 80% of the total air pollution disease burden. In 2019, Dr Mikko Savolahti, senior research scientist at the Finnish Environment Institute, and colleagues published detailed research investigating the emissions from residential wood combustion in Finland and the resulting concentrations of fine particles in the air. They were then able to estimate the disease burden of these specific emissions. They hope that such investigations can better inform policy makers aiming to reduce air pollution and improve national health.
The authors modelled concentrations of the fine particles resulting from the primary particle emissions from residential wood combustion, with calculations made for 2015 and projections made for 2030. They report that, in 2015, the number of deaths attributable to residential wood combustion was 200 for that year and the disease burden was 13% of the total attributable to fine particles air pollution. Most of this health impact was a result of wood being burned as supplementary heating in residential homes. The burning of wood for as the primary heating method, or for heating recreational buildings, which more commonly take place in rural areas, were much less harmful. In the 2030 projection, the authors found that disease burden and death is forecast to reduce by 8% due to renewal of the appliance stock and new heaters being less polluting in general. In an ambitious emission reduction scenario, the potential to mitigate health hazards was estimated to be 63%.
These results raise serious points for Finnish policy makers – should wood burning stoves be allowed as secondary heat sources in urban areas? Should new houses be built so that they rely on supplementary wood heating? What is the most effective policy to reduce the overall environmental impacts of heating homes?
Savolahti and colleagues’ studied a set of possible emission reduction measures, though no single measure seemed to be a ‘silver bullet’. Unsurprisingly, the most effective measure to reduce negative health impacts was urban combustion bans. However, a more holistic study regarding compensatory heating methods is needed before the viability of such action can be assessed, and the authors considered it a measure of last resort. Other measures included flue gas cleaning technologies installed to chimneys, a legislation that sets emission limits for sauna stoves and informational campaigns about better burning practices. The most cost-efficient measure was estimated to be informational campaigns targeted to urban areas. Other, more costly measures would be needed for more significant impact on total emissions. However, the only effect of informational campaigns was assumed to be improved burning practices that lead to less smoke. In reality, it’s possible that such campaigns might also reduce peoples’ willingness to burn wood, which could lead to significant additional benefits.
These conclusions probably don’t come as a surprise to most people – campaigns encouraging better operation and reduced use of wood and multi-fuel stoves, especially in urban areas, have been increasingly widespread in Europe in the last decade as a means to reduce air pollution. What may come as more of a shock is the effect that residential wood combustion may be having on climate change.
Savolahti and colleagues have been challenging the assumption that wood burning stoves are a ‘greener’ solution to warm our homes. In another paper published in 2019, they reported on the results of a second study, the first to assess the climate impact of residential wood burning emissions of a whole country.
It is already acknowledged in the scientific community that residential wood combustion is a major source of ‘climate-impacting emissions’. These emissions include ‘short-lived climate forcers’ or SLCFs – emissions with relatively short atmospheric durations compared with CO2 , such as black carbon (also called soot), methane and ozone. Combustion of wood also releases notable amounts of carbon dioxide, although biogenic in origin.
It is these particular emissions that Savolahti and colleagues are interested in. Based on the current data, the team made projections for these emissions in Finland from 2015 to 2040, and then calculated the climate impact of the same using figures called ‘regional temperature potential metrics’. Emissions from residential wood combustion had a significant warming impact on climate when compared with Finland’s reported and projected greenhouse gas emissions.
One issue affecting the general public’s understanding of the impact of residential wood combustion is the fact that the short-lived climate forcers and biogenic carbon dioxide emissions are not usually included in the greenhouse gas emission estimates of a country’s energy sector. The authors report that including the SLCFs from home wood burning in projections increases the warming impact of Finland’s overall emissions by 28% in global response and 170% in Arctic response; accounting for the biogenic carbon dioxide would significantly further increase the warming response of wood burning. In comparison to district or electric heating, the warming impact of wood burning on the climate was estimated to be several times larger in a 25-year timespan.
With black carbon and other SLCFs, the geographical location of the emissions, as well as the studied timespan plays a bigger role than with well-mixed greenhouse gases like carbon dioxide: Black carbon is notably more potent as a climate warming agent when emitted near the Arctic area.
What is made apparent in Savolahti and colleagues’ research is the fact that the calculation method utilised has a huge impact on how ‘green’ each heating method appears to be. This is something that needs to be made clear across society, from within the scientific community to the general public and policy makers. Taking biogenic carbon as equal to fossil-fuel derived emissions, as the authors chose to in this model, significantly increases the warming impact of wood burning. While the findings may be alarming, they may be closer to the truth than past projections: when taking into account changes in forest carbon stocks in a 25-year timespan, CO2 emissions related to harvesting and burning wood might total twice as much as those from burning the same energy content of coal.
The authors conclude their study by stating that: “When assessing near-term impacts, wood heating is likely the least climate-friendly option of the common heating methods in Finland, if all relevant emissions are taken into account… It should not be promoted as beneficial for the environment”. It should also be noted that whilst emissions from residential wood burning have more of an impact on personal health in urban areas, the effect on climate warming is the same in both densely and less populated areas.
It is clear that whilst a growing number of public health campaigns and legislation around the globe have discouraged residential wood burning in urban and populace areas, it has also been advertised in some quarters as ‘a green way to heat your home’. The models and projections presented by Savolahti and colleagues demonstrate that this contradiction must be resolved, and the climate impacts of wood burning need to be fully included in the analyses that support policy making. While there are merits to wood heating, such as energy security, cheap fuel prices and physical activity, shifting to more wood burning in the housing sector cannot be viewed as a viable strategy to mitigate climate change.
In situations where wood heating remains a reasonable option, the cleanest available combustion appliances should be used, and attention paid in proper operating practices. Having a wood stove is a reliable back-up heating option in cases of power failures or disruption in energy supply, but house owners should consider their stove using habits, especially in urban areas: If possible and practicable, the less wood burnt, the better for the health of people and the environment.
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