Climate & Cities
Concrete Is A Climate Problem Because It Is Cheap
The emissions from cement come from a chemical reaction rather than from fuel, and concrete's low price is why cities use enough of it for that to matter.
Concrete is the most used construction material by volume, and its climate impact follows directly from that scale. The chemistry sets a floor that efficiency cannot remove.
The emissions are chemical, not just thermal
Making cement involves heating limestone until it releases carbon dioxide, which is a reaction rather than a by-product of the fuel used to heat it.
Switching the kiln to a cleaner fuel therefore removes only part of the total, because the rest comes from the rock itself.
This is why cement is described as hard to abate. The obvious decarbonisation route addresses a fraction of the problem and leaves the chemistry untouched.
Cheapness drives the volume
Concrete is made from widely available materials, mixed near the point of use, and it can be shaped without specialist labour or long lead times.
Because it is inexpensive per unit of strength, it is used generously, and structures are often designed with more material than strictly necessary because that is cheaper than optimising.
The total impact is the product of a moderate figure per tonne and an enormous number of tonnes, so the volume is where the leverage sits.
Substitution reduces cement rather than replacing it
Industrial by-products can replace part of the cement in a mix, cutting emissions without changing how the material is handled on site.
Supply of those by-products is tied to industries that are themselves shrinking, so the availability of the cheapest substitutes is falling rather than rising.
Alternative binders exist but face the difficulty that a structural material needs decades of evidence before insurers and codes will accept it routinely.
Design decisions move more than material choice
Using less concrete achieves what a better mix cannot. Voided slabs, longer curing times, precise structural analysis and shorter spans all reduce quantity.
Reusing an existing frame avoids the material entirely, which is why retention of structure has become a central argument in redevelopment decisions.
These choices are made early, when the building's shape and grid are still open, and they close off quickly once a scheme is fixed.
Cities lock in the decision for a century
A concrete frame outlasts several rounds of tenants, uses and even facades, so the emissions were spent once and the asset persists.
That durability is an argument for building carefully rather than for building less, since a structure demolished early wasted everything it embodied.
Treating existing frames as a resource rather than an obstacle changes what a city does with the material it has already paid for.
Questions readers ask
Do green roofs save energy?
Modestly, and mostly on poorly insulated buildings. On a well-insulated roof the thermal effect is small. Run-off attenuation is the benefit that reliably justifies them.
Are green roofs maintenance free?
No. They need outlet clearance, occasional weeding and inspection, and they need access to do it. Most failed installations were neglected rather than badly built.
