They call them plyscrapers: the sudden emergence of tall buildings constructed almost entirely from timber. Vancouver, Vienna and Brumunddal in Norway have all claimed recently to have the tallest wooden building in the world, and now Tokyo has its own designs on the informal title.

Making buildings from wood may seem like a rather medieval idea. But there is a very modern issue that is driving cities and architects to turn to treated timber as a resource: climate change.

Concrete is the second most used substance in the global economy, after water – and one of the world’s biggest single sources of greenhouse gas emissions. The chemical process by which cement, the key ingredient of concrete, is created involves large quantities of carbon dioxide.

Q&A What is Guardian concrete week? Show Hide This week Guardian Cities investigates the shocking impact of concrete on the planet, to learn what we can do to bring about a less grey world. Our species is addicted to concrete. We use more of it than anything else except water. Like that other manmade wonder material, plastic, concrete transformed construction and advanced human health. But, as with plastic, we are only now waking up to its dangers. Concrete causes up to 8% of global CO2 emissions; if it were a country it would be the world's worst culprit after the US and China. It fills our rubbish dumps, overheats our cities, causes floods that kills thousands of people – and fundamentally changes our relationship to the planet. Can we kick our addiction, when it's so hard to imagine modern life without it? In this series of articles, Concrete Week will explore the impact of the material on our environment and us, and look at alternative options for the future. Chris Michael, Cities editor



The UN estimates that there will be 9.8 billion people living on the planet by mid-century. They will need somewhere to live. If concrete is the only answer to the construction of new cities, then carbon emissions will soar, aggravating global warming.

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And so scientists and builders have started innovating with other materials, in a scramble for alternatives to a universal commodity that has underpinned our modern life for centuries.

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The problem with replacing concrete is that it is so very good at what it does. Chris Cheeseman, professor of materials resources engineering at Imperial College London, says the key thing to consider is the vast extent to which concrete is used around the world, and is likely to continue to be used. “Concrete is not a high-carbon product. Cement is high-carbon, but concrete is not. But it is the scale on which it is used that makes it high carbon. The sheer scale of manufacture is so huge, that is the issue.”

Not only are the raw materials for concrete available cheaply and in abundance in most places around the globe, but the stuff itself has marvellous properties: Portland cement, the vital component of concrete, is mouldable and pourable, but quickly sets hard.

Cheeseman also notes another advantage: concrete and steel have similar thermal expansion properties, so steel can be used to reinforce concrete, making it far stronger and more flexible as a building material than it could be on its own. The steel used can be recycled, reducing its carbon impact, but Cheeseman says the combination of steel and concrete – giving enormous strength to buildings, while being mouldable and widely available – is hard to beat. “It is amazing stuff. Making anything with similar properties is going to be very difficult.”

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Using wood, for example, is not straightforward. Wood absorbs moisture from the air and is susceptible to rot and pests, not to mention fire.

But treating wood and combining it with other materials can improve its properties. Cross-laminated timber is engineered wood, made from gluing layers of solid-sawn timber together, crosswise, to form building blocks. This material is lightweight but as strong as concrete and steel, and construction experts say it can be more versatile and faster to work with than concrete and steel – and even, it seems, quieter.

Stora Enso is Europe’s biggest supplier of cross-laminated timber, and Markus Mannström, the executive vice-president for biomaterials, reports that the company is seeing increasing demand globally for building in wood, with climate change concerns the key driver. The Nordic countries, where Stora Enso is based, with their large forest resources, have been leading the way, but the company is seeing increasing demand across the world, including in Asia. It plants two or three trees for every tree used, which has contributed to Sweden doubling its rate of forest cover in the past century. Of course, using timber in a building also locks away the carbon that it has absorbed as it grew.

Facebook Twitter Pinterest ‘If construction goes ahead on a project in Japan, the W350: that will reach 70 storeys, and be made of 90% wood.’ Photograph: Sumitomo Forestry Co

Even treated wood, however, has limitations. In Norway, the Mjøstårnet building is planned to be the tallest in the world with a wooden frame. It will rise 88 metres tall, with 18 storeys, and will be used for offices, hotel rooms and apartments. Mjøstårnet may not hold its crown for long, if construction goes ahead on a project in Japan, the W350: that will reach 70 storeys, and be made of 90% wood. But it is still in the early stages of planning.

Only when these concepts have been proven in practice will it be possible to see wood as a widespread alternative to concrete in constructing tall buildings.

Concrete is tipping us into climate catastrophe. It's payback time Read more

Concrete examples

Fly ash is a possible alternative. It is a byproduct of coal-burning power plants – cinders, the unburnt parts of the coal that used to be allowed to disperse into the air, or fall to the bottom of power station chimneys, but in modern power plants are collected instead. It can be incorporated into concrete mixes to make up as much as 15% to 30% of the cement, without harming the strength or durability of the resulting mix.

A byproduct of the iron-ore processing industry, ground granulated blast-furnace slag, can also be of use in a similar way. This is incorporated into concrete mixes, and has the potential to reduce greenhouse gas emissions.

But Anna Surgenor, senior sustainability adviser at the UK’s Green Building Council, which is currently engaged in educating its construction industry members on the availability of cement replacements, notes that although these waste products can save carbon in the concrete mix, their use is not always straightforward.

“It is possible to replace the cement content in concrete with waste products – a built asset could also use alternative materials [such as timber] in construction to lower the overall carbon impact. But there are several calculations that need to be considered across the entire life cycle of the building – these include factoring in where these materials are being shipped from. If they are transported over long distances, using fossil fuels, the use of alternative materials might not make sense from an overall carbon reduction perspective.”

Fly ash from coal and slag from iron ore are abundant in some of the areas where concrete is most needed, including rapidly developing countries such as China and India. But they are heavy and that means it is not only carbon-intensive to transport over long distances, but also expensive.

Other mooted materials have pros and cons. Magnesium silicates are not as widely available as the building blocks of concrete, for instance, limiting their appeal. Calcite clays show promise, according to Cheeseman, but will reduce concrete emissions only by about a third – worth doing, but not a comprehensive solution.

Carrots and sticks

Research at Lancaster University has found that adding vegetable particles – yes, carrots or sugar beet – can strengthen concrete while reducing the volume of cement required. Similar work is being conducted with bamboo and other fibres.

Facebook Twitter Pinterest The flooring structure of this student hall of residence at the University of British Columbia is made from cross-laminated timber panels and the exterior cladding is also mostly made of wood. Photograph: University of British Columbia

Graphene, a wonder material invented in the UK early this century, is also coming into play. Experts at the University of Exeter have used graphene in concrete construction to create a new composite material that is twice as strong as traditional concrete and four times more water-resistant. Monica Craciun, professor of nanoscience in the university’s engineering department, called the new material “an absolute game-changer”, and work is continuing on how to develop it further. Commercial introduction is still some way off.

While these technologies are all promising ideas, they are either expensive, unproven or based on materials that are not abundant. Thinktank the Royal Institute of International Affairs at Chatham House produced an overview last year of innovation in the industry, which reached the gloomy conclusion: “Some novel cements have been discussed for more than a decade within the research community, without breaking through. At present, these alternatives are rarely as cost-effective as conventional cement, and they face raw-material shortages and resistance from customers.”

Given the slow take-up of alternatives to concrete and their limitations, attention has turned to solutions such as capturing and storing, or even using, the carbon dioxide that results from its production.

CarbonCure, a Canadian company, recycles carbon dioxide in its products. Liquefied carbon dioxide is captured from industrial processes and injected into concrete while it is being made, which helps with the process of cement incorporation. The company has so far reduced carbon emissions through its products roughly equivalent to taking about 5,000 cars off the road.

But carbon-capture technology remains very expensive and only a handful of projects have been trying to innovate in this way to reduce the emissions from cement.

• Fiona Harvey is an environment correspondent for the Guardian

This article is part of a series on possible solutions to some of the world’s most stubborn problems. What else should we cover? Email us at theupside@theguardian.com