The wall is close to 200m long and 40m tall. If it were made of 4000 cubic meters of concrete, it might weigh 10,000 tons, and the whole building might weigh 4

The wall is close to 200m long and 40m tall. If it were made of 4000 cubic meters of concrete, it might weigh 10,000 tons, and the whole building might weigh 4 times that amount. 2.5 tons is a rounding error! Unfortunately, the chemistry and energy use to make a cubic meter of concrete releases about a third of a ton of CO2. So this building, implemented in concrete, would extract 9 tons of CO2 annually and take more than 1,000 tons of CO2 to pour. Edit: I now see that the images (especially [1]) describe a more expensive steel-and-glass building. It will probably still include lots of concrete, but 2.5 tons across the whole building is not a big concern. (Not to mention they'll likely have to do some gardening occasionally). [1]: https://www.ianvisits.co.uk/blog/wp-content/uploads/2019/10/citiscape-house-05.jpg https://www.ianvisits.co.uk/blog/wp-content/uploads/2019/10/...