Hemp versus cotton: Which is better for the environment?

Illuminating answers to environmental questions.
April 12 2011 5:11 AM

High on Environmentalism

Can hemp clothing save the planet?

A worker touches plants at a cannabis greenhouse. Click image to expand.
Both hemp and marijuana are classified as Cannabis sativa L

I keep hearing about how beneficial hemp is for the environment, and what a shame it is that U.S. farmers aren't allowed to grow it. Is hemp really that eco-friendly?

With the possible exception of soy, no plant has managed to spawn so many different products, and as much controversy, as hemp. You can buy hemp clothing, hemp paper, hemp milk, hemp oil ... the list goes on. A Canadian company has even built an electric car out of hemp. Advocates talk about the leafy plant like it's going to reverse global climate change. Opponents think it's merely a Trojan horse packed with potheads hoping to get your children stoned.

The legal problem for hemp is that it's visually and taxonomically identical to marijuana. Both are classified as Cannabis sativa L, and the only difference between them is the concentration of delta-9-tetrahydrocannabinol (THC), the psychoactive substance in pot. Marijuana contains at least 3 percent THC by weight, whereas hemp falls below that threshold. Some hemp advocates think there are also visible differences. But as far as Uncle Sam is concerned (PDF), the only way to distinguish marijuana from hemp is by taking it to the lab, or rolling it up and smoking it.

The plant is a Schedule 1 controlled substance in the United States, which means you need special permission to grow it regardless of THC content. Canada and several European countries now allow their farmers to grow hemp with THC content below 0.3 percent—one-tenth as strong as the weakest marijuana. (These countries require hemp farmers to pre-register their plots for cultivation and use certified low-THC seed. The government also checks their crop periodically for THC content.) The United States has held off, largely because a government helicopter that flies over a farmer's field can't tell the difference between hemp and marijuana. For this reason, raw ingredients for all U.S.-manufactured hemp products must be imported.

Hemp is so versatile in part because it can be grown for either seed or fiber. The seeds yield milk, oil, and other food products, and are particularly popular among vegans, who have trouble working omega-3s (PDF) into their diets. The fiber is used for paper and clothing. Sailors have been using hemp rope and sails for centuries, and the crop's abundance was crucial during the Revolutionary War.

Patagonia Men's Migration Hemp Shirt. Click image to expand.
A shirt made using hemp

So is hemp the answer to all our environmental problems, or just boring pot? It depends on what you want to use it for, and what you compare it to. For now, let's focus on textiles, the most traditional and common use.

A 2005 report (PDF) by the Stockholm Environment Institute compared the water, land, and energy requirements of cotton, polyester, and hemp textiles. While the study is the most comprehensive investigation of this issue, the results were unsatisfyingly mixed.

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Producing the raw ingredients for any textile consumes more energy than any other stage in the process. Different production techniques, however, can significantly increase or reduce the impact. Since pesticides and herbicides account for more than one-half of the energy in farming either hemp or cotton, organic methods are responsible for less carbon-dioxide emissions. Overall, organic cotton required less energy than organic hemp, but the margin was fairly small. Polyester, a petroleum-based synthetic fabric, was the clear loser by a 3-1 margin, because it takes so much energy to extract the oil required to make it.

While cotton requires less energy to grow and process than its competitors, it uses a lot of land. The "fabric of our lives" needs approximately twice as much territory as hemp per ton of finished textile, the land-use miser of the bunch. Further complicating matters is the inverse relationship between chemical use and land requirements. While organic farmers can save on energy by cutting synthetic pesticides and herbicides, their yield per acre drops. Polyester, a synthetic fabric made from petroleum, does almost as well as hemp on land use. Apparently, you can get more fabric from an oil field than a cotton field.

Cotton is the big loser, once again, when it comes to water. The cotton plant needs about 50 percent more water per season than hemp, which can grow with little irrigation. (It's so prolific that the overwhelming majority (PDF) of cannabis plants uprooted by the Drug Enforcement Administration every year are a wild relative of hemp. It's no coincidence they call the stuff weed.) Cotton also tends to be grown in parts of the world where water is scarce. More than one-half of the world's cotton fields rely on irrigation, because it grows in some relatively dry regions, like Egypt, China's Xinjiang province, California, and Texas.

When you add processing into the equation, cotton uses more than four times as much water as hemp. Polyester is difficult to compare, because it's not an agricultural product. But some studies suggest it's the least water-intensive of the bunch, using just one-thousandth as much water as cotton. (In fact, water is a byproduct of polyester processing.)

So where does all this leave us? Without a clear winner, unfortunately. There's an argument to make for polyester, but the nonrenewability of synthetic textiles raises serious concerns. Overall, hemp appears to be slightly easier on the environment than cotton, considering it's superior on water and land requirements, and only slightly worse for energy use. But is the DEA responsible for all of our environmental woes? Hardly.

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