The SiOO X Story – Protecting the Planet - Book - Page 25
Chapter 1
The Carbon Question and Climate Change
Is it really possible to get these emissions down to zero?
This is where the use of timber in construction can help.
Trees absorb atmospheric carbon dioxide as they grow and this
carbon is stored in the wood (biogenic carbon). Eventually, the
tree will die and the carbon will be returned to the atmosphere
as the wood decays. In plantation forestry, this wood is harvested and can be used in harvested wood products (HWPs), which
will store the atmospheric carbon for the lifetime of the product.
Meanwhile, the harvested tree is replaced with new growth, so
that the process of sequestration continues. The Intergovern
mental Panel on Climate Change (IPCC) provides guidance on
how to record carbon stocks in the different pools (forest, HWP).
The principal is shown diagrammatically, below.
IN SEPTEMBER 2020 Ursula von der Leyen, the newly elected President of the European Union, in her State of the Union
speech stated: “Our buildings generate 40% of our emissions.
They need to become less wasteful, less expensive and more
sustainable. And we know that the construction sector can
even be turned from a carbon source into a carbon sink, if organic building materials like wood and smart technologies like
AI are applied.” According to the World Green Building Council,
of this 40% of global carbon emissions, 28% comes from the
operational carbon and 11% from the embodied carbon of the
construction materials. In order to keep the global temperature increase below 2ºC, all sectors of the economy must rapidly
decarbonise. The vision of the WGBC is that by 2030 all new
buildings, infrastructure and renovations will have at least 40%
less embodied carbon and that by 2050 the embodied carbon
should be net zero. These are extremely ambitious targets.
What does this mean and is it achievable?
The embodied carbon is the total of the greenhouse gas emissions that are associated with the extraction, processing, manufacture and transport of a product from the point of the raw
resource in nature to the product leaving the factory gate. This is
usually known as cradle to gate (modules A1 to A3 in EN 15804).
Because different greenhouse gases have different impacts, the
total emissions are converted into a common factor, known as
the global warming potential (GWP), which is reported in carbon
dioxide equivalents (e.g., kg CO2e). Sometimes, these are direct
emissions; for example, the release of fossil carbon as CO2 during
the conversion of limestone to clinker in cement manufacture.
Quite often, these emissions are indirect, such as the release of
carbon dioxide by power stations in the generation of electricity.
This shows the carbon cycle, with storage of atmospheric carbon in the forestry and built environment carbon pools with
incineration at end of life and return of the carbon back to the
atmosphere. The question is – if the carbon returns to the atmosphere at end of life, is there really any extra climate change
mitigation benefit obtained from using timber in construction?
The answer is a resounding yes – provided that you look at the
built environment as a whole. Many such studies have shown
that there is a climate change mitigation benefit and that the
Photo: Alan Coultas.
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