Australians call them “runners."  The British know them as “trainers." 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.