Americans refer to them as “tennis shoes” or “sneakers."

Whatever you call them, these rubber-soled, casual shoes

are worn by billions of people around the world.

Originally invented in the late 19th century,

these simple canvas and rubber creations have changed a lot

since they first hit the pavement.

Today, sneaker consumption is at an all-time high.

No country buys more sneakers than the United States,

where people purchase 3 pairs a year on average.

To meet this demand, roughly 23 billion shoes are produced each year,

mostly in factories across China and Southeast Asia.

But making shoes has become more complicated, more labor-intensive,

and in some ways, more dangerous,

for the workers involved and for our planet.

Shoe manufacturing accounts for roughly one-fifth

of the fashion industry's carbon emissions.

Sneakers alone generate 313 million metric tons of carbon dioxide every year,

which is equivalent to the annual emissions of 66 million cars.

To better understand your shoe's carbon footprint,

let's dive into the anatomy of a sneaker.

For starters, the heel, insole, midsole, and upper layer

are usually made from synthetic textiles like polyester, nylon, latex,

and polyurethane.

Mining the fossil fuels that make up these materials emits tons of greenhouse gases.

And processing those raw ingredients into synthetic textiles

also uses a lot of energy, further compounding that pollution.

Some sneaker tops are made from natural sources like leather,

but tanning this material relies on chromium;

a carcinogenic chemical that can damage freshwater ecosystems.

The outer soles of most shoes are made of rubber

that's gone through a process called vulcanization.

This technique adds sulfur to superheated raw rubber to create a material

that's both elastic and sturdy.

Until recently, sneakers used natural rubber for this process.

But today, most outer soles are made with a synthetic blend of natural rubber

and byproducts from coal and oil.

Producing these materials accounts for 20% of a sneaker's carbon footprint.

But more than two-thirds of the shoe's carbon impact comes from the next step:

manufacturing.

A typical sneaker is comprised of 65 discrete parts,

each of which is produced by specialized machinery.

This means it's cheaper for factories to mass-produce each piece separately

rather than manufacturing every part under one roof.

But the transportation required to ship these pieces

to one assembly plant emits even more CO2.

Once the components arrive at the assembly line,

they undergo cutting, pouring, melting, baking, cooling, and gluing,

before the final products can be stitched together.

The assembly of a typical sneaker requires more than 360 steps,

and accounts for the remaining 20% of a sneaker's environmental impact.

The dispersion of factories fuels another problem as well: labor abuse.

Most brands don't own or operate their factories,

so the plants they work with are in countries

with little to no worker protection laws.

As a result, many laborers earn below the living wage,

and are exposed to harmful chemicals, like toxic glue fumes.

When manufacturing is complete,

the shoes are packaged and transported to stores around the globe.

For many, these shoes could last years.

But for someone running 20 miles a week,

a pair of running shoes will start wearing out after roughly 6 months.

Since the shoes are made of so many different materials,

they're almost impossible to break down into recyclable components.

20% of these shoes are incinerated, while the rest are tossed into landfills

where they can take up to 1,000 years to degrade.

So, how can we balance our love of sneakers

with the need for sustainability?

First, designers should streamline design elements

and focus on eco-friendly materials.

Factories need to develop energy efficient manufacturing processes

that consolidate steps and sneaker parts.

And consumers should support companies using clean energy

and ethical manufacturing processes.

We can also buy fewer shoes, wear them for longer,

and donate those we no longer need.

So no matter what your style, we can all take steps towards a sustainable future.