Recently I came across an article in Nature magazine about the annual global consumption of concrete. Worldwide, we use about 30 billion tons of concrete[i] every year. That comes down to 12.900.000.000 cubic meters[ii] of concrete. Just to get a feeling how much that is: If all that sand-cement mix was poured into a lake, it would fill the entire Lake of Lucerne in Switzerland year after year.
Many, me included, were quick to call for a replacement of carbon intensive concrete by timber. It is carbon-neutral and could even be used to store carbon and therefore reduce the amount of CO2 in the atmosphere. While it is debatable if an industrialized wood and construction industry really allows for carbon positive effects or only for carbon neutrality, there undeniably are benefits in replacing a polluting material with a less polluting one. Timber is a material that – unlike many others, can be used in many different ways. It can be a structural material holding the whole building up, it can be a panelling material, or it can be used for insulation, flooring, roofing and many other applications. Let’s use timber then!
The Amsterdam Institute of Metropolitan Studies AMS has recently even published a document that shows that we have enough wood in Europe – now and most likely also in the future. But after careful reading, there are many caveats to that statement that show that this claim is only true in an ideal situation. The report also did not account for the changes in tree population due to climate change. With more heat, many species of trees will not survive in their current habitat. Mainly, the quickly growing softwood trees that provide a large part of the construction timber will die and be replaced by hardwood trees that grow a lot slower and are less suitable for long straight pieces of wood the construction industry likes to use.
Concrete plant – Image source: wikimeida.org
But all these problems put aside, one could contemplate replacing concrete with wood. For simplicity, I just assume that all concrete can be replaced by wood (which in reality it will not, since the physical characteristics are different). 12.9 billion cubic meters of wood a year would be needed. One tree with a trunk diameter of about 60 cm contains about 3 cubic meters of wood[iii]. If all trees were the same, then we would need 4.3 billion trees. A plantation type forest with distance between trees of 2.5 meters has about 2000 trees per hectare. It would have to be 21.500 square kilometres in size to house the wood we need. We would have to cut woodlands the size of Slovenia every year. Average growing time of trees to be usable for construction is around 40 years. That means we need a forest of 860.000 square kilometres to only replace the concrete – a forest the size of the whole of Pakistan.
Construction timber in Austria – Image source: wikimedia.org
Then we have not replaced other carbon intensive materials like brick, rock or glass wool or natural stone yet. They all will add more space to our ‘construction forest’. Add to that the need for additional wood for the packaging that we also want to change from fossil based plastic to renewables and the use of wood for carbon-neutral forms of heating, then it becomes obvious that there is a problem.
Admittedly this calculation is rough, and it does not take into account other trends like genetical modification of plants to grow faster, the development of a circular economy and the re-use of old wood or the development of entirely new bio-based construction materials that reduce the use of timber. But it illustrates that using wood alone will not do the job.
There are other problems that we now see surfacing when switching from a concrete based construction industry to a wood based one: The skill sets needed greatly differ. The machinery to process wood is completely different from the tools needed for concrete. Scaling up the wood industry takes time and cannot be done overnight, most likely leading to an under provision with timber when using it on a global scale and therefore driving prices through the roof. There is also still a significant number of applications where wood is not the right material. Long span structures, infrastructure like tunnels or pipes, very tall structures or buildings in climatically unfavourable conditions all will require concrete as a material for the foreseeable future.
How about changing the core problem of concrete instead of trying to change an entire industry? In recent years huge steps have been made to create less carbon intensive concrete and if innovation in this field keeps its pace, carbon-neutral concrete is not far away any more. Maybe it would be worthwhile to heavily invest into achieving this and making no carbon cement available worldwide at affordable prices. No new machines would be needed, the workers trained in concrete construction could keep their jobs. This would give the wood industry time to grow sustainable wood sources for the timber we need in the future, instead of destroying existing ecosystems to fulfil the wood hunger of the world.
by Markus Appenzeller
Cover image: wikimedia.org
1 ton of concrete is about 0,43 cubic meters