Climate impact

Wood is not CO₂-neutral

Wood burning is politically defined as carbon neutral because trees accumulate almost same amount of CO2 throughout their lifetime as the amount released when wood is burned. In other words, assuming that the reforestation is adequate and that wood is burned as slow as the growth of new trees, wood burning does not lead to net increasing CO2 levels in the atmosphere.

However, in practice this means that if you cut down a fully-grown 60-year-old tree then you need to plant a new tree and slowly burn the wood over 60 years as the new three grows up. Since the wood would be burned much quicker in a stove this would cause a net accumulation of CO2 in the atmosphere for decades thereby contribute significantly to global warming.

In the short run, the direct CO2-emissions from chimneys in homes heated with wood are larger than if the same houses burned fossil fuels. However, the solution is neither wood nor fossil fuels but energy efficient buildings heated with real carbon neutral energy.

Forests, forest floors and trees should be seen as a solid permanent carbon sink and storage increasing biodiversity and protecting groundwater and surface water from agricultural pollution. Increased use of wood as high value building material providing long-term storage of CO2 - and as well replacing CO2-inten-

Wood burning is not CO2-neutral and can prevent energy efficient homes

sive building materials – would be climate efficient.

Waste biomass from forestry and sawmills should not be burned but used to create high value products and fuels as input to sectors where there are limited renewable alternatives.

Cheap wood makes it unattractive to insulate buildings, replace old windows, and to use cleaner heat sources (cf. page 25). Thereby, cheap wood burning prevents the transition towards a climate-neutral low emission society with clean air.

Soot increases global warming

UNs Intergovernmental Panel on Climate Change has approved that black carbon (soot) has a Global Warming Potential (GWP) of 900 (100-year time horizon) and 3,200 (20-year time horizon). Meaning that one ton of black carbon causes the same warming as 900 tons of CO2 (100-year time horizon) and 3,200 tons of CO2 (20-year time horizon).

The annual black carbon emission from wood burning in Denmark is about 1,900 tons. This causes same global warming as 1,710,000 tons CO2-equivalents per year (100-year time horizon) and 6,080,000 tons CO2-equivalents per year (20-year time horizon). The energy content in the wood burned in Denmark is about 25,000 TJ per year. This gives the following contribution to global warming: 86.4 tons CO2-equivalents per TJ (100-year time horizon) and 243.2 tons CO2-equivalents per TJ (20-year time horizon). Co-emission of organic carbon (global cooling effect) will not change this warming effect significant (less than 5 %). To comparison, the CO2-emision from fuel oil is 77.4 tons CO2 per TJ. Thereby soot particles from wood burning cases around the same global

Soot particles make wood burning as bad – probably even worse – than fossil fuels from a climate point of view

warming per energy unit as CO2 from an oil-fired boiler (100-year time horizon) and about three times more global warming than an oil-fired boiler (20-year time horizon). The latest reports from the UN clearly underlines that we need to reduce global warming as quick as possible. Hence, a 20-year time horizon is most relevant. Thereby it is clear, that even if we consider wood as completely CO2-natural, soot particles from wood burning will significantly contribute to global warming. The right way forward is to eliminate both the emission of CO2 and black carbon by energy renovation of buildings and use of cleaner heat sources (c.f. page 25). For creating a cosy atmosphere for specific occasions, electrical fireplaces and gas stoves can be used.

Ignoring these facts, firewood sellers, stove manufacturers and chimneys sweepers keep on praising wood burning as carbon neutral heating in their marketing. Without mentioning that black carbon from wood burning (in addition to being health hazardous) makes wood burning as bad – and probably even worse – than fossil fuels from a climate point of view.

Expensive CO₂ reduction

Let’s assume a best case for wood burning: We assume that wood burning is CO2-neutral and completely ignore global warming from black carbon. Furthermore, we assume that all wood burning replaces fuel oil (even though fuel oil only covers 5 % of the energy use in Danish one-family houses). Finally, we assume wood is free. Then wood burning could maximally save 1.8 million tons of CO2 per year. The health damages are 1,225 million euro per year (cf. page 22). Thereby, reduction costs would be almost 700 euro per tons avoided CO2. This would make wood burning an extremely expensive way of reducing CO2-emissions. Most other reductions have a price less than 70 euro per ton CO2 reduced.