﻿The temple you're looking at survived longer than the civilization that built it.
Even through Barbarian invasions and the collapse of the Roman Empire, the Pantheon
is standing after nearly 2000 years.
That's because of this super material here: concrete.
It's simple, it's strong, it's cheap and it lasts long.
Across the world, concrete has become the foundation of modern cities and high living standards.
But it's also a climate killer.
The cement and concrete industry is responsible for about 8% of the world's carbon pollution.
And even though it's all around us,
we don't talk about it nearly enough.
So how can we make concrete clean?
How can we build cities
without destroying the planet?
The ancient Romans were master engineers.
They made a special mortar out of wet lime and volcanic ash
which they used to bind small stones and bricks.
They used it to build some of the greatest wonders of the ancient world.
But when the Roman Empire fell, so did these secrets of making volcanic concrete.
It wasn't until the 19th century that English bricklayer
Joseph Aspdin invented Portland cement — a fine powder
made by heating limestone and clay in a kiln and grinding it down to a powder.
This was the precursor to the modern cement industry.
Soon concrete was at the heart of a global construction
boom of everything from cities and houses to roads and dams.
But the concrete we use today isn't fundamentally that different from what the Romans had.
It's still made of just a few key ingredients:
cement, water and cheap filler rocks like sand and gravel.
The cement is what gives concrete both its incredible strength and toxic emissions.
At super high heat the calcium carbonate of the limestone
and silicon dioxide of the clay join to form strong calcium silicates.
But the reaction also releases carbon dioxide that heats the planet.
The calcium and silicon ions in the silicates disassociate when cement is added to water.
As the mixture dries, these form crystals that fill gaps
and glue material tightly together.
By mixing cement with sand and gravel, you can make
what is essentially a strong, durable
artificial rock — for very little money.
That's why this ancient invention is now the most widely used material in the world after water.
The concrete industry expects emissions will rise
from 2.5 Gigatons per year to 3.8 by 2050.
They actually need to go down to zero
to stop the planet heating.
But the emissions from concrete are hard to get rid of.
It's not just the carbon dioxide from the chemical reaction we saw earlier.
It's also because manufacturers burn fossil fuels to
heat kilns to the 1400 degrees Celsius they need to break down the components.
All that means making one ton of concrete releases more
than 600 kilograms of carbon dioxide into the air.
"It is incredibly carbon-intensive, it is a definite problem,
and yet we probably will continue to use more of it."
This is Johanna Lehne, an expert in decarbonizing
industry at the environmental think tank E3G.
She says cement is harder to fix than
pollution from, say, cars or coal plants.
"You can't simply make sure that your energy consumption
is more efficient, you can't simply change the fuels that you use,
there is a fundamental technical challenge."
But wait...
If concrete is so hard to make without hurting the climate,
shouldn't we just stop using it altogether?
Well first of all, the rich world has been
building with concrete for more than a century.
People in lower income countries have a right to build affordable
housing and infrastructure that can stay strong in the face of extreme weather.
But the second problem is that alternatives
to concrete aren't necessarily better.
In some parts of the world, sustainably sourced timber has huge potential
to replace concrete and store carbon dioxide at the same time.
But building entire cities out of trees would put too much
pressure on forests that are already struggling.
"Concrete is not the problem.
Concrete is actually the solution."
This is Jorge de Brito,
a civil engineering professor at the University of Lisbon.
"Most people think concrete has a huge impact
on the environment, and they are right."
But concrete has that impact
because it's the most used material."
So if concrete is here to stay,
then how exactly can we make it green?
In October 2021 the industry took a huge step forward
and unveiled its plan for doing just that.
A big chunk of the savings by 2050
basically boils down to efficiency.
For instance, 11% comes from industrializing the process of making concrete.
Then there's heating kilns with alternative fuels,
perhaps from burning rubbish in waste incineration plants,
or making cement with leftover material
from steel and coal plants.
It also includes some carbon dioxide that concrete
naturally absorbs over time.
It's a process the construction industry could speed up
by recycling crushed concrete from old buildings and injecting it with CO2.
Another 22% of the planned savings come from
designing more efficient buildings and extending their lifetimes.
Now this isn't entirely in the hands of the cement industry.
It's also about how architects and engineers design our cities.
They could retrofit old buildings instead of
knocking them down, and design new ones to last longer — just like the Romans did.
The Pantheon went from a Pagan temple to a Christian church.
But the big question mark is the final third:
capturing carbon dioxide after it's emitted and then storing it.
The technology broadly exists in plants like this —
just not cheaply or at scale.
So can the industry guarantee that enough carbon will be captured by 2050
when the first trials in cement plants are only just happening now?
"The thing is that, you know,
in the next 10 years, we have to, as you say,
make that technology mature, and prove
the industrial scalability and the
commercial scalability of the technology."
This is Thomas Guillot, CEO of the cement industry lobby group
that authored the roadmap.
By the end of the decade they want 10 cement plants
fully equipped to capture carbon for reuse or storage.
"It's not something that would be easy. I mean, we need to commit.
We need to work on it.
That's why we call on particularly local government
and the other actors of the value chain to help us
to embrace that initiative, to really make it work."
But despite putting on a green face in its advertising,
the concrete industry has not yet made detailed commitments
as to how it will stop polluting.
It says that will come later in the year.
"What we want to do is to really 'walk the talk'
and to transform commitments into actions,
global visions into local requirements."
Experts say a big part of the solution would be incentivizing the industry
to change by taxing carbon and subsidizing emerging technology.
Because cement is so profitable and alternatives are still in the early stages of development,
governments would need to push it along the right track.
"It is a very capital-intensive sector.
It is a sector that has been very conservative, that has been reluctant
to move in the past. It hasn't faced a lot of policy pressure.
People don't really think about it.
This is also part of it being hard to abate."
There are already pockets of good news.
A British company has successfully captured CO2
from a cement plant in France
and turned it into materials that can be used in construction.
In Sweden, a pilot study has shown cement
can technically be made out of electricity
without using fossil fuels — though this would also mean even more
demand for clean energy.
In Norway, a cement factory is set to open a carbon capture facility
in 2024 that should single-handedly halve the plant's emissions.
The common thread behind all these solutions is making low-carbon concrete cheaper.
And that takes policies, investment and research.
"The average consumer doesn't think about
their cement and concrete consumption...
The place where those decisions sit
are really with governments."
That doesn't mean you don't have a voice.
Sure, you can't choose how much concrete is in your home.
But the more attention the cement industry gets,
the more pressure it will face to go green.
"Concrete is one of those climate problems that nobody is
talking about, but a massive amount needs to be done.
And as we've just seen, there are actually solutions.
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