Capture the Carbon
Target audience: Accessible to average people on the street. Northen Ontario Mayors likely use this to talk to elementary school students about the importance of the forest sector and related benefits. Slides are part of a more comprehensive presentation put together by Dean Caron.
Initial questions:
How much carbon is utilized per cubic (m3) of wood harvested in a typical forest operation (harvest to mill) in the boreal forest.
How much carbon is utilized per m3 of wood when the wood is put through a milling process (sawmill or pulpmill).
How much carbon is stored per m3 of wood when harvested and utilized in a milling process.
An indication of what age of trees (boreal forest trees preferred) produce the most oxygen (very young, young, middle aged or old growth).
GHGs like CO2 and methane are emitted when fossil fuels are burned, organic matter decomposes, etc. It is a prerequisite for life to exist on earth as we know it. CO2 is the main GHG accounting for about 80% of all GHGs, methane is a smaller share but is about 25 times more potent. According to Global Carbon Project (GCP) burning fossil fuels and producing cement is the leading cause of increased CO2 concentration in atmosphere. The safe level is 350 ppm (parts per million), we’re now at 400 ppm which could push 2 degrees above current global temperatures (global warming) and results in more extreme climatic events.
Global warming refers to the recent and ongoing rise in global average temperature near Earth's surface. It is caused mostly by increasing concentrations of greenhouse gases in the atmosphere. Global warming is causing climate patterns to change. However, global warming itself represents only one aspect of climate change.
Climate change refers to any significant change in the measures of climate lasting for an extended period of time. In other words, climate change includes major changes in temperature, precipitation, or wind patterns, among other effects, that occur over several decades or longer
http://www3.epa.gov/climatechange/basics/
Image Credited By: Nexans -- https://infogr.am/Global-Warming-Facts-and-Effects
Image: http://mmd3semspring2012.mmd.eal.dk/group7/pa/environment.html
Forest capture CO2 from atmosphere
Harvest logs with smaller branches left in the forest
Decomposition of branches releases carbon over time; if material is burned for energy, carbon is immediately released.
CO2 emissions occur during harvest especially when machinery using diesel / gasoline / natural gas / heavy oil are used
Carbon is stored for as long as product is in service
At end of service life, product be reclaimed, reused, recycled or burned for energy
Cycle continues….
Wood is a renewable resource. In Canada, harvested forests will regrow over 70-80 years.
Harvest is different from deforestation "permanent removal of forest cover and withdrawal of land from forest use, whether deliberately or circumstantially." Similarly, the IPCC Guidelines emphasize the conversion of forests (to pasture, cropland, or other managed uses): "Conversion of forests is also referred to as 'deforestation,' and it is frequently accompanied by burning."
http://www.ipcc.ch/ipccreports/sres/land_use/index.php?idp=49
- This is a graphic representation of LCA.
- It is a process of quantifying and analyzing environmental impacts over the life of a product.
LCA is a method applied to evaluate environmental footprint of a product. Rigorous accounting of flows to and from nature related to a product over its lifecycle, i.e. from extraction to disposal.
North American Average lumber emissions: 73 kg / m³
Canadian lumber is cleaner than US, electricity is cleaner.
Cradle to gate LCA: emissions resulting from the extraction, transport and sawmilling.
Excludes distribution, use and landfilling, recycling, burning.
1,970 MJ of energy required.
1,970 MJ is 55% renewable, i.e. mainly biomass used in drying and some electricity (++ hydro)
Renewable: biomass is carbon neutral: CO2 emissions from burning = CO2 forest uptake
Excluded is 8,300 MJ of energy contained in product (if burned)
1 m³ = 424 bft nominal or 630 bft real– difference is due to 2’’x4’’ being really 1.5’’x3.5’’ (only 66% of real volume)
2’’x4’’x8’ = 5.33 bft nominal
Gate to gate LCA: only includes what happens in the sawmill
Varies by species: Softwood is bit higher + Hardwood is bit lower
Service life, forest growth and payback
There is some uncertainty around how much wood decomposes in landfills, but it is generally believed that about 3% of lumber decomposes. This 3% is emitted 50/50 CO2 and methane (CH4)
It is important to recognize 1 m³ of wood is different from 1 m³ of concrete. Depending on what you use it for, you’ll need more or less material to get the job done. Relevant to look at footprint at the building level.
This is comparison of CLT building with a concrete slab and steel wall 4 storey apartment building. 4060 m2 (43 700 sq ft) floor area.
Making the materials for the wood building generates 40% less GHG than making the same building using a concrete structure with steel infill walls. Concrete has a large footprint relative to wood, so it is important to use it judiciously.
*Excludes energy used to heat building units. Both buildings use the same energy.
Wood building is 280 tons of CO2 emissions avoided. Equivalent to yearly emissions of 13.6 Canadians or 94 average cars.
A key opportunity involves displacing products with a higher carbon footprint:
-180 kg CO2 eq substitution benefit for CLT building derived from 1410 m3 wood in CLT building and assumes 10% construction waste (1410*110% = 1550 m3):
substitution benefit = ((722000-440000 kg CO2 eq)/1550 m3 / wood) = 180 kg CO2 eq
http://changingclimate.osu.edu/features/accounting-for-carbon
https://apps-scf-cfs.rncan.gc.ca/calc/en/calculateur-calculator (Pierre Bernier)
La réponse à ta question est toute simple… La biomasse (et particulièrement le bois) est composée à 50% par masse en carbone. Donc ta question revient à dire à quelle taille les arbres accumulent-t-ils le plus de biomasse.
La réponse à cette question pour un arbre individuel est évidemment que plus un arbre est gros, plus sa croissance individuelle nette en biomasse est importante. Je dis nette car un arbre produit plus de matière qu’il n’en retient : à chaque année, il perd des feuilles/aiguilles, fruits, pollen, racines fines brindilles, etc.. La croissance nette en biomasse est décrite par les équations allométriques à l’échelle de l’arbre individuel telles que celles utilisées sur notre site de calcul : https://apps-scf-cfs.rncan.gc.ca/calc/fr/calculateur-calculator
Mais, à moins qu’on ne soit en ville, les arbres poussent ensemble et on calcule alors la croissance par unité de surface de sol. Dans ce cas, la croissance nette par unité de surface de sol inclut aussi la perte de biomasse par mortalité des arbres, ce qui fait que le peuplement arrête d’accumuler de la biomasse (vivante) à un certain point. En fait c’est ce la courbe que décrivent les tables de rendement… Évidemment, le transfert de carbone accomplit son œuvre et les autres réservoirs de l’écosystème, dont particulièrement le sol minéral, peuvent continuer à accumuler lentement du carbone pendant des siècles, voire des millénaires. Sur le site indiqué plus haut, tu trouveras aussi des équations allométriques à l’échelle du peuplement.
Dont, si je reviens à ta questions à savoir si les petits arbres capturent plus de CO2 que les gros, la réponse est NON si on compare des arbres individuels, mais OUI si on compare un peuplement juvénile par rapport à un peuplement en fin de maturité.
