inspired by his new book “How  to Avoid a Climate Disaster.”

Earth's climate is changing rapidly. The world  is heating up. These are undeniable facts,  

and the culprit for this very recent, very rapid  change is us. With the help of fossil fuels,  

humans emit billions of tons of carbon dioxide  into the atmosphere every year. But, when you  

think of carbon emissions you probably imagine the  cars on the road, the power running your apartment  

or even the electricity in the lightbulbs above  your head. If we look at the breakdown of the  

51 billion metric tons of greenhouse gases we emit  every year, however, electricity only accounts 27%  

of the problem. It's not even the  biggest sector in terms of emissions.  

That award goes to the oft-forgotten manufacturing  sector. Emissions from manufacturing come from a  

wide range of building materials like  plastics, steel, glass, aluminum. But,  

today we're going to zoom in on one of the most  polluting materials in the manufacturing world,  

which is also one of the least mentioned  materials in terms of emissions: cement.

The Problem with Cement 

We build a lot of stuff, and a lot of that stuff,  from the Three Gorges Dam to the Sydney Opera  

House, is built with concrete, which is a mixture  of sand or gravel and a cement paste. Globally,  

we produce 4.1 billion tons of cement every single  year. The U.S. alone creates roughly 96 million  

metric tons and China develops over half of the  world's cement at 2.2 billion per year. We use  

so much of it because to be quite honest, it's the  perfect building material. Concrete is extremely  

durable, versatile, inflammable, and weatherproof.  But concrete also has a large downside. In order  

to create cement (and ultimately concrete), you  also have to emit a lot of carbon dioxide. In  

fact, for every ton of cement made, a ton of  carbon dioxide is released into the air. This  

happens because of a particular chemical reaction  that occurs when raw materials are turned into  

finished cement. After raw limestone and clay have  been ground up and mixed with other materials like  

ash, they are fed through a massive cylindrical  kiln that gets heated up to 1450 degrees celsius.  

Within these large kilns, a process called  “calcination” occurs wherein the raw materials  

are split into calcium oxide and carbon dioxide  and the final product becomes solid grey balls  

known as clinker. The byproduct of conventional  cement, then, is carbon dioxide. CO2 emissions  

from the chemical process account for 50%  of cement's total footprint. Another 40% of  

cement's emissions come from the burning of fossil  fuels to heat the kiln up to extreme temperatures,  

and the final 10% comes from mining and  transporting raw materials. In short, 90% of the  

CO2 emissions from cement come from what happens  in and around that big cylindrical kiln. As a  

result of these emissions, the cement industry  generates 2.8 billion metric tons of CO2 every  

year. That's 8% of the total global CO2 emissions.  This means that, if left unchecked, the growing  

cement industry could prove a huge obstacle  to getting to zero emissions by 2050. It also  

means that cement offers a chance to drastically  reduce global emissions quickly if done right.

Concrete Solutions: When it comes to greening the cement industry,  

there are a lot of proposed solutions. From  geopolymers that harden at room temperature,  

to using bacteria to grow concrete blocks,  innovators are all scrambling to find the  

next alternative cement. One of them, a 2013  startup called Solidia, represents an exciting  

development in the world of cement. The company  has developed an alternative chemical process for  

cement which reduces both energy use and emissions  by 30% during the manufacturing phase. But the  

most promising part about Solidia's cement is  that they use CO2 instead of water in order  

to harden their concrete blocks. This means that  not only does Solidia cement conserve freshwater,  

which, for an industry that accounts for 9%  of total global industrial water use is huge,  

but it also means that Solidia's concrete  blocks can sequester carbon. As a result  

of the decreased energy demands, reduction in  emissions in the kiln process, and the absorption  

of carbon during curing, Solidia claims they  can reduce cement's carbon footprint by 70%.

Meanwhile, in Silicon Valley a startup called  Blue Planet is approaching the cement problem  

from a different angle. They've developed  a technology to create synthetic limestone  

aggregates, which are basically just rocks, by  capturing carbon emissions from flue gas. This  

synthetic aggregate can then be used to replace  the traditional materials like sand and gravel  

in the final concrete mix. Blue Planet claims  this low-cost carbon sequestration method  

could theoretically offset all of the  emissions from the cement creation process.  

In essence, the amount of carbon that Blue  Planet's synthetic limestone captures could  

potentially equal the amount of carbon  the cement production process creates.

Pipe Dreams or Realities? These solutions, however,  

aren't without barriers. Solidia's cement  curing process can only happen at a factory,  

which means it's applications are limited compared  to conventional cement. Blue Planet's aggregate  

process only comes in after the cement has gone  through the kiln, meaning that its carbon capture  

properties are really just trying to make up for  the emissions created during the kiln process.  

On top of all of that, both these companies have  yet to really hit the market and be proven at  

scale. In short, these alternatives have a long  way to go in part because they're entering an  

industry where safety and durability are king, so  in the eyes of builders and safety inspectors the  

tried-and-true conventional cement almost always  trumps new varieties and inventions. Which means  

that without significant government backing  and policy change, the concrete industry will  

stay rigid. But we should not just wait for new  technologies to hopefully save us one day, the way  

we build and how much we build can also greatly  influence how much cement we use. According to  

a research paper by Chatham House, designing  cities based on a “capillary web system” could  

decrease car use by two-thirds and cement demand  by one-third. If employed in places like China and  

India where construction is booming, this type  of smart design could mean huge reductions in  

concrete use and ultimately emissions. At the end  of the day, developing new technologies is just  

one part of our global concrete problem. Only  combined with government policy, smart design,  

and reducing consumption, can we truly create  the building blocks of a zero carbon world.

Bill Gates's new book, “How to Avoid a Climate  Disaster,” does a great job outlining the  

technical challenges that lay ahead of us in terms  of climate change. Gates and I can sometimes take  

different approaches to climate change and that's  part of the reason why I found this book useful.  

It concisely outlines what needs to be done  in order to get to zero emissions by 2050.  

Throughout the book Gates unpacks the five biggest  emissions-causing sectors and explains how we can  

minimize the greenhouse gas footprint of  each one. There is even a whole chapter  

about how we can get zero-emissions in  the steel, cement, and plastics industry  

by 2050! You can find out more about the  book, and how we can all work together  

to avoid a climate disaster using  the link in the description below.

Hey everyone! Thanks for making it to the  end. If you've already grabbed the book,  

you can also support this channel on Patreon.  Chip in a couple of dollars a month and help  

Our Changing Climate stay afloat. Thanks  for watching and I'll see you next week!