US scientists have a new green solution to urban construction: chop down trees and use the wood for buildings. Good strong timber buildings – and there are plans for 30-storey skyscrapers built of wood – would save on concrete and steel, save on carbon dioxide emissions and cut the use of fossil fuel.
The argument may seem counter-intuitive: that is because a substantial component of climate change stems from changes in land use and the loss of forests. And some researchers have demonstrated that even the most mature trees, the forest giants, can go on absorbing carbon dioxide from the atmosphere.
But Chadwick Oliver, a forester at the University of Yale and colleagues make the case in the Journal of Sustainable Forestry. They argue that if the world stepped up the harvest of the forests and used the wood efficiently then economies could save on fossil fuel, reduce carbon dioxide emissions and give people a reason to value the forests.
It works like this. Overall, trees add 17 billion cubic metres of new wood to the planet’s biomass each year. Right now, humans take about 20 per cent of this new growth – that’s 3.4 billion cubic metres – and a lot of that is burned, inefficiently as cooking fuel, or just burned.
The savings on concrete and steel happen because about 16 per cent of global fossil fuel consumption is accounted for by the manufacture of steel, concrete and brick. Factor in the need to transport building materials and that brings the fossil fuel share to between 20 per cent and 30 per cent. So wood-based construction consumes less energyfoss
Savings outweigh emissions
If humans stepped up the wood harvest to 34 per cent and used it for construction, they could reduce the use of steel and concrete, and cut between 14 per cent and 31 per cent of global carbon dioxide emissions (the authors count methane and nitrous oxide emissions as carbon equivalents in this calculation).
And of course, carbon would stay locked up in the wood in permanent structures. This would also save between 12 and 19 per cent of annual global fossil fuel consumption: the wood left over from construction could be turned into energy.
The savings on concrete and steel happen because about 16 per cent of global fossil fuel consumption is accounted for by the manufacture of steel, concrete and brick. Factor in the need to transport building materials and that brings the fossil fuel share to between 20 per cent and 30 per cent. So wood-based construction consumes less energy.
The loss of forests represents the release of carbon dioxide, but as long as the harvesting is efficient, more carbon emissions are saved overall.
Better than agriculture
But, of course, this makes forests valuable. “The study shows still another reason to appreciate forests,” says Professor Oliver, “and another reason not to let them be cleared for agriculture.
“Forest harvest creates a temporary opening that is needed for forest species such as butterflies and some birds and deer before it regrows to large trees. But conversion to agriculture is a permanent loss of all forest biodiversity.”
So suddenly, in every sense, wood is cool. Wooden skyscrapers and apartment buildings are already being designed and tested in Sweden and in Canada. Selective harvesting of forests could help protect stands of timber against the spread of wildfire, benefit wildlife and maintain wealth.
“Forests historically have had a diversity of habitats that different species need,” says Professor Oliver. “This diversity can be maintained by harvesting some of the forest growth. And the harvested wood will save fossil fuel and CO2 and provide jobs — giving local people more reason to keep the forests.”
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