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27.01.2020 A material revolution that replaces cement and steel with wood in urban construction can have double benefits for climate stabilisation. This is now shown by the study of an international team of scientists. First, it can avoid greenhouse gas emissions from cement and steel production. Secondly, it can turn buildings into a carbon sink, since in the construction timber the CO₂ is stored. Although the required amount of wood is theoretically available, such an expansion would require very careful sustainable forest management, the authors emphasize.

"Urbanisation and population growth will create huge demand for the construction of new buildings for housing and commerce - so the production of cement and steel will remain a major source of greenhouse gases unless we act," says the study's lead author, Galina Churkina, who is affiliated with both the Yale School of Forestry and Environmental Studies in the US and the Potsdam Institute for Climate Impact Research in Germany (PIK). "However, these risks to the global climate system can be turned into an effective means of mitigating climate change if we greatly increase the use of engineered wood in the global building sector. Our analysis shows that this potential can be realised under two conditions. First, the harvested forests are managed sustainably. Second, the wood from the demolition of buildings is reused."

Four scenarios of wood use as a contribution to climate stabilisation

Four scenarios were calculated by the scientists for the next thirty years. Assuming "business as usual", only 0.5 percent of new buildings will be built with wood by 2050. This share could rise to 10 percent or 50 percent if mass timber production increases accordingly. If countries with currently low industrialisation also make the transition, even 90 percent wood in construction is conceivable, the scientists explain. This could result in storing between 10 million tonnes of carbon per year in the lowest scenario and almost 700 million tonnes in the highest scenario. Furthermore, the construction of wooden buildings reduces the cumulative emissions of greenhouse gases from steel and cement production by at least half in the long run. This may not seem like that much compared to the current amount of about 11,000 million tonnes of global carbon emissions worldwide per year (for ease of comparison, these figures are given here in carbon, not CO₂). But switching to wood would make a difference for achieving climate stabilisation goals of the Paris Agreement.

Assuming that construction continues with concrete and steel and the floor area per person increases according to the current trend, by 2050 cumulative emissions from mineral building materials could account for up to one fifth of CO₂-emissions budget - a budget that should not be exceeded if we want to keep warming to well below 2°C, as governments promised in the Paris Agreement. Importantly, in order to reduce greenhouse gas emissions to net zero by mid-century, the countries of the world must reduce CO₂-sinks. Only with these can they offset the remaining emissions that are difficult to avoid, especially those from agriculture.

Buildings could be such a sink - if they are made of wood. A five-storey residential building made of glulam can store up to 180 kilograms of carbon per square metre, three times more than in the above-ground biomass of natural forests with high carbon density. Nevertheless, even in the 90 per cent wood scenario, the carbon accumulated in wooden cities over thirty years would be less than one tenth of the total amount of carbon stored above ground in forests worldwide.

"Protecting forests from unsustainable logging is crucial".

"If the use of timber is to be greatly increased, protecting forests from unsustainable deforestation and a host of other threats is critically important," emphasises co-author Christopher Reyer of PIK. "However, our vision for sustainable management and regulation could actually improve the situation of forests worldwide, as they will then be assigned a higher value," emphasises Christopher Reyer of PIK.

The scientists summarise several chains of evidence, from official statistics on timber harvests to complex simulation models, and determine on this basis that theoretically the currently untapped potential of the global timber harvest would cover the demand of the 10 percent timber scenario. It could even meet the needs of the 50 and 90 per cent wood scenarios if the floor area per person in buildings worldwide did not increase but remained at the current average. "There is quite a lot of uncertainty here, as well as a strong need for policies to enhance the value of forests and their products, but basically it looks promising," says Reyer.
"In addition, plantations would be needed to meet demand, including the cultivation of fast-growing bamboo by small landowners in tropical and subtropical regions."

In addition, if the use of logs as fuel were reduced - currently about half of logs are burned, which also leads to emissions - more of them could be made available for building with processed wood materials. In addition, reusing wood after buildings have been demolished can expand the amount of wood available.

The technology of trees - "to build us a safe home on earth".

Wood as a building material has a number of interesting characteristics, which are described in the analysis. For example, large timbers are comparatively fire resistant when used correctly - their inner core is protected when burning by the charring of their outer layer, making it difficult for a fire to destroy the supporting structure. This is in contrast to the widespread assumption of the fire hazard of timber buildings. Many national building codes already recognise these properties.

"Trees offer us a technology of unprecedented perfection," says Hans Joachim Schellnhuber, co-author of the study and Director Emeritus of PIK. "They extract CO from our atmosphere.₂ and convert it into oxygen for breathing and into carbon in the tree trunk that we can use. I can't think of a safer way to store carbon. Mankind has used wood for building structures for many centuries, but now we are talking about a whole new order of magnitude given the challenge of climate stabilisation. If we process the wood into modern building materials and manage the harvesting and building wisely, we humans can build ourselves a safe home on Earth".

Articles: Galina Churkina, Alan Organschi, Christopher P. O. Reyer, Andrew Ruff, Kira Vinke, Zhu Liu, Barbara K. Reck, T. E. Graedel, Hans Joachim Schellnhuber (2020): Buildings as a global carbon sink. Nature Sustainability [DOI:10.1038/s41893-019-0462-4]

Web link to the article:
www.nature.com/articles/s41893-019-0462-4

The Potsdam Institute for Climate Impact Research (PIK) is one of the world's leading institutes in research on global change, climate impact and sustainable development. Natural and social scientists develop interdisciplinary insights here, which in turn provide a robust basis for decisions in politics, business and civil society. PIK is a member of the Leibniz Association www.leibniz-gemeinschaft.de/start

Source: Press release of the Potsdam Institute for Climate Impact Research, 27.1.2020

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Building materials / Construction, DE-News, Research, Wood construction, Climate protection, Sustainable management, New books and studies, News Blog Europe (without DE), Resource efficiency, SDG 2030, Environmental policy, Life cycle assessment