Let's imagine a modest-sized skyscraper...
about 100 meters and 30 stories tall.
A high rise this size was almost certainly built
with concrete, which contains cement.
In this case, about 6,000 tons of cement.
Making that cement probably emitted about 4,600 metric tons
of carbon into the atmosphere.
That's about the emissions from driving a car for 12 million miles.
Now, multiply that by all the buildings in the world.
Even that wouldn't capture cement's carbon footprint.
Think about the sidewalks we’re walking on.
Many of the streets you drive on.
A lot of our energy infrastructure.
Dams, power plants.
All that cement production accounts for 8%
of all global carbon emissions...
more than the aviation and the shipping industries combined.
Today, most of those emissions
are due to China's rapid development.
In just two years, China produced more cement than the US did
in the entire 20th century.
Other developing countries will use a lot of cement
as they build tall cities and infrastructure too.
If we want to reach net zero in a few decades
we'll have to figure out how to build a building like this...
without emissions.
It'll be hard, but there's a way.
You're looking at a typical cement plant.
One like this is currently operating
in nearly every region of the world.
This rotating tube, a kiln, and this tower, a pre heater
are where all cement's emissions take place.
About 40% of cement's emissions
are a result of burning fuel to heat the kiln.
It reaches around 1450 degrees Celsius near the heat source.
The preheating tower is where limestone, clays
and other additives are dropped.
The 850 degree temperature here
causes limestone to release its stored carbon dioxide
and those are the other 60% of emissions.
The first question about decarbonizing cement
is whether we can just use less concrete altogether.
We typically use up to 2 to 3 times too much concrete in design.
Architects and structural engineers just use lots of it.
It doesn't hit the bottom line and it makes the thing more reliable
and they're less likely to get sued and kill people
and what have you.
In a building, concrete is valuable for its compressive strength:
its ability to hold up under a lot of weight.
So it's hard to substitute its use in places like
foundations and columns.
But elsewhere, we should minimize it.
I was in the new Parliament building in Scotland
and it was obviously designed with greenhouse gases in mind.
Concrete was only used where needed.
Steel was only used where needed.
And they used laminated wood for the roof
for a lot of structural materials
things that weren't load bearing.
Carbon conscious design can certainly chip away
at cement's emissions.
But replacing concrete altogether
won't be possible in the near term.
So cutting down on excess concrete can cut emissions
on our high rise by roughly 26%, according to one analysis.
We'll have to do more
and the next place to start is how cement is made.
Looking at the 40% of emissions
that go into firing the kiln is one place to start.
Typically, cement plants use coal or petroleum coke
or natural gas to heat the kiln to 1450 degrees Celsius.
You could electrify that
but it's really hard to achieve
that high of a temperature with electric heat.
Though some startup companies like this Finnish one are trying.
Until we get there
cement plants have started to just burn different things.
The high heat makes cement plants a good place to incinerate
industrial waste, trash, or used tires.
The limestone basically scrubs out any nasties
that are produced in the flame here...
and stops them being emitted into the atmosphere.
Switching fuels can cut emissions by roughly 7%.
We've still got a ways to go
so let's look at the other way cement causes emissions:
The chemical process.
This is the carbon released from the heated limestone.
Once it goes through the kiln
it becomes a material called clinker:
the key binding ingredient in cement.
And cement binds together the rocks and sand and water in concrete.
Cement is about 10% of concrete
but accounts for a majority of its emissions.
So one strategy is to find a substitute for the clinker.
Startups have been in a race
to develop a new kind of green cement
that avoids clinker altogether.
But so far, nothing is as abundant
and commercially viable as the limestone-based stuff.
And adjusting concrete formulas
takes a lot of time and safety testing.
For good reason.
The events in Turkey recently,
there was a lot of substandard cement being used there
and there was a lot of substandard building practices.
In North America
clinker accounts for about 90% of cement
due to safety standards.
But North America is overly cautious
compared to the rest of the world.
The average clinker-to-cement ratio globally
was about 72% in 2020.
That's made possible by clinker-like substitutes.
We could reduce the clinker ratio even more.
Experts emphasized one new cement mixture
that gets the clinker ratio safely down to 50%
by supplementing it with more clay and unprocessed limestone.
So that’s with an existing technology that meets existing building codes.
That'll cut half the emissions
from the cement and concrete industry.
These reductions will help in reducing emissions...
but until we find a scalable, zero-emission cement,
any clinker production at all
will inevitably have process emissions.
Which brings us to the last piece of decarbonization.
The cement industry will need to use
carbon capture and storage to get there.
There's no way around it.
This would mean capturing the carbon emitted
from the heat and chemical processes here...
and storing it deep underground in a geologic deposit.
A cement company in Norway is piloting
one of the first cement plants in the world to capture carbon.
And they'll store it under the North Sea
in their oil and gas deposits.
Some new companies are also finding a way to inject
stored carbon back into cement and concrete during production.
This takes advantage of rock's natural ability to reabsorb carbon.
And potentially one day we may even see our built environment
become a carbon sink
which we don't usually think about when we think about large
concrete cities and large buildings
and our roads and all of that.
So this is the scenario
in which we get this building to net zero emissions.
And the goal right now is to get there by 2050.
That requires us to start now and aggressively.
Especially in China, the world's biggest producer.
But experts told me there's some good news there.
So in the US, the average age of a cement plant
is about 34, 35 years.
In China, it's 15, which means that many of their plants
are actually more energy efficient
than the plants that we have here.
China uses less clinker in their cement than the global average
and they have at least one carbon capture project in the works.
But there's a long way to go.
Last year, they pushed back
their peak building emissions deadline from 2025 to 2030.
Changes to design in the concrete and cement processes
will be the easiest to implement...
but carbon capture and storage is at very early stages.
And all this will be expensive.
It's estimated that the cement used in this building
will cost somewhere between 70 to 115% more.
The cost of cement or concrete
is a very small fraction of the overall cost of a project.
So it's relatively easy
and cost effective for a government agency
to commit to pay
a little more for the material to absorb that green premium.
The US Inflation Reduction Act
is helping create a market for carbon capture and storage
by increasing tax credits to $85 per metric ton of carbon stored.
For a long time, heavy industries like cement
seemed like unsolvable climate problems.
But today, we know how to fix them
and we can't afford not to try.
Thanks for watching the video.
As a follow up to this one,
I'd recommend checking out my coworker, Phil Edwards’s
great video on the world's tallest mass timber building
in Milwaukee, Wisconsin.
He was able to film the building under construction
and he gives a great explanation about how changing
from traditional materials
like steel and concrete
to wood changes the entire building process.
Wood probably can't replace
concrete in all the world's buildings.
One expert I interviewed told me we'd probably have to triple
the amount of wood harvested
in order to scale it up and do that
and that would come with its own environmental problems.
But our big concrete problem requires
a lot of different solutions
and using wood when possible is definitely one of them.
And as you can see from Phil's video, it looks really cool, too.