[♩INTRO] We all want to make greener choices and help
the environment but sometimes what’s best for the planet
can be counterintuitive. Like, single-use plastic shopping bags seem
to quickly be going extinct. They’re now banned by stores, cities...even
entire countries! And in their place are sturdier, reusable,
supposedly greener bags so problem solved, right? Well, when you look at the entire lifecycle
of a product, what’s best for the environment can get…
complex. Case in point: By some measures, plastic bags
can be the best option. At least, if you leave out one important factor. There are all kinds of bags out there, but here, we’ll focus on five of the most
popular: single-use plastic bags, single-use compostable
or biodegradable plastic bags, brown paper bags, and two kinds of heavyweight
bag: thick, reusable plastic ones, and the classic
cotton tote bag. From that list, you might think you know which
bag is best. But sometimes, our intuition does not line
up with reality. And that becomes clear when you look at Life
Cycle Assessment for this. A Life Cycle Assessment is a study that looks
at the full environmental impact of a product. In it, researchers study and add up each step
in how a product is made, used, and disposed of. Several studies have been done like this, and the overall conclusions tend to be the
same. But one major report was prepared in 2018 by the Danish Environmental Protection Agency. This report looked at two types of impact: climate change, and total environmental impact. The climate change bit was pretty straightforward. They added up all the greenhouse gases emitted throughout the lifetime of these bags. Now, not all greenhouse gases are equal; each has a unique potential to warm the planet. But for easy comparison, this team converted
all the gases to the equivalent amounts of carbon dioxide. Meanwhile, the total environmental impact
was a lot more complicated. Here, the researchers looked at 15 effects
— everything from ozone depletion, to toxicity, to water and resource use...
and a lot more. By putting a number on these things and adding
them up, they could compare a broad range of impacts
at the same time. The downside is that this is a big oversimplification, and they couldn’t fit in some important
variables. We’ll get to those later. But for now, the big question is, what did
this study find? Well, the first thing to consider is what
it took to make the bags because producing them is the stage with the
biggest impact. Single-use plastic bags are made of petroleum
— also known as oil. Specifically, this study looked at a type
called low-density polyethylene. And the majority of the impact there came
from turning the oil into the plastic material itself. For biodegradable plastic bags, they looked
at a material called a starch-complexed biopolymer basically, a plastic that incorporates plant
starches. Overall, manufacturing these bags releases
a similar amount of greenhouse gases as making plastic bags
that aren’t biodegradable. But there are also some additional effects
of the agriculture involved in making the plant starches, like more water,
fertilizer, and pesticide use. So just from a production standpoint, biodegradable plastic is actually worse than
single-use stuff. Similarly, to make a paper bag, you need to
start with a tree. How a specific forest is managed is hard to
capture in this sort of comparison, but either way, the process of turning wood
pulp into paper can emit a lot of greenhouse gases! This depends on what kind of fuel is used
by the paper mill, so different studies can come to different
conclusions about paper bags. According to the Danish researchers’ calculations, they have a similar climate impact to single-use
plastic. Now, if you’ve been holding out for the
reusable bags to come in and blow everyone away… well, they do. But not how you might think. See, thick, reusable plastic bags are also
made from oil, and you need more of it to make a thicker
bag — so there’s a bigger impact. Heavier bags also need more fuel to transport
them to the grocery store. And cotton tote bags? These might seem like a green option, but
growing cotton requires a huge amount of land, water, fertilizer,
and pesticides. On top of that, processing cotton is an energy-intensive
process. So, when it comes to making the bag, single-use
plastics win by almost every measure. In this study, paper edged out single-use
plastics slightly when it comes to greenhouse gas emissions but others have disagreed with that and calculated that paper bags can be worse. And either way, when it comes to production,
the worst material by far is cotton! But that said, just how something is produced
doesn’t really reflect real life. It’s not like we’re just making bags and
watching them sit around in a warehouse. And that brings us to how the bags are used. Using a shopping bag doesn’t cause pollution, but it does affect how we compare these materials. Because like, ideally, you don’t use your
nice cotton bag once and then throw it away. Here, an easy way to compare different materials is by looking at how many times you would
need to reuse them to offset their impact, compared to using
a new plastic bag every time. If we just consider the climate change impact,
paper bags and biodegradable plastic bags are roughly
the same as a single-use plastic bag. Meanwhile, heavier reusable plastic bags need
to be reused at least six times to make up for their climate change impact
compared to single-use plastics. And cotton bags need to be reused at least
149 times. And this isn’t just something the Danish
report found: These numbers are similar to the findings of a 2011 study from the Environment
Agency in the UK. To offset climate change impact relative to
a single-use plastic bag, they found you’d need to use a paper bag
three times, a reusable plastic bag 11 times, and a cotton
bag 131 times. But! All those numbers change if you look at the
total environmental impact if you add in the other 15 categories with
toxicity, ozone effects, runoff, and everything else. In that case, in order to be greener than
a single-use plastic bag, biodegradable plastic bags, paper bags, and
reusable plastic bags need to be used about 40 to 50 times each. And cotton bags need to be reused 7100 times! That means even if you grocery shop three
times per week, you need to use that same cotton bag for the
next 45 years to have the same impact as using over 7000
single-use bags! And this estimate was even higher for organic
cotton because organic crop yields tend to be lower. You’d need to reuse that bag 20,000 times! So there’s clearly an issue with some of
these materials. Like, the numbers for reusable plastic bags
are well within the expected lifespan. I have reusable plastic bags that I have been
using since 2004. But for biodegradable plastic, paper, or cotton
bags, the number of times you’d need to reuse
them is well beyond how long you would expect an individual bag
to last. Now, only the Danish report calculated the
total impact like this, so we don’t yet have multiple studies to
support those numbers. Still, just based on that, it might seem like
plastic comes out ahead. And the plastics industry is happy to use
this logic and these comparison studies to lobby against the regulation of single-use
plastics. But there is one more key variable: disposal. Here is plastic’s Achilles’ heel: there’s
no good way to dispose of it. So, if you add in litter and impacts on marine
ecosystems, single-use plastics look a lot less green. It’s hard to get good data on what fraction
of plastic bags are recycled, but we know it’s low, possibly around one
to three percent. Many recycling programs don’t accept them
for the simple reason that they get caught in sorting machines. And bags that aren't recycled sit in landfills,
clog sewers, and pollute waterways. Plastic bags are especially bad since they’re
easily picked up by the wind and strewn across a large area. They also take a long time to break down and
pose a direct threat to wildlife. They can become wrapped around creatures,
mistaken for food and eaten, and even spread invasive species that hitch
a ride. And this is one area that life cycle assessment
studies fall short: they don’t have a way of comparing the effects
of litter on ecosystems. Regardless, new materials like biodegradable
or compostable bags are supposed to solve this problem. But while a 2019 study found that these are
better than traditional plastics, after three years, none of the bags tested
broke down in all environments. Paper bags are biodegradable, so the impact
of litter is low. And they’re recyclable! But left to break down in a landfill, they
release methane, a potent greenhouse gas. For the heavier reusable plastic and cotton
bags, disposal should be a smaller part of the overall
footprint since hopefully they’ve been reused many
times. Both can be recycled, but that doesn’t mean
that they always are. For example, only around 15% of textiles a broad category that includes cotton bags
— end up recycled. And now, after three intense rounds, and a
surprisingly long episode of SciShow, the greenest bag of them all is… it’s
complicated. The best material depends on many factors,
including your individual habits, like how many times you reuse each type of
bag and how you dispose of your bags. Overall, making single-use plastic bags has
a relatively low environmental impact, but waste is a massive
problem with no good solution. The best option for the end of a plastic bag’s
life is to reuse it as a trash bag. Presumably, you’d be using something to
contain the trash anyway, and if nothing else, the bag is a lot less
likely to float away if it’s weighed down by all the stuff inside
it. Meanwhile, manufacturing paper or biodegradable
plastic has higher impacts, but these materials reduce the problem of
litter. And heavier reusable plastic bags are a great
option if you reuse them enough. Cotton tote bags have by far the biggest environmental
impact. They look very green when you’ve got them
on your shoulder… turns out, that’s kind of a lie. They need to be used hundreds of times to
counteract their climate footprint and possibly thousands if you consider multiple
environmental impacts. So, we’re not saying plastic bags are good. They’re not. But it is important to remember that all the
alternatives have an impact, too. It’s not worth going out to buy a snazzy
new reusable product if you already have one that works. So, no matter what your bags are made of,
the best way to minimize their impact is to reduce how many you use and reuse them
as many times as possible. And when you can’t use a bag anymore, do whatever you can to make sure it doesn’t
become litter. It’s also worth keeping in mind that despite
all the attention grocery bags get, they’re only a small part of our impact
on this planet. But looking at the entire life cycle of a
product can be a useful way to analyze nearly any aspect of our lives. From the clothes we wear, to the food we eat,
to how we get around by thinking through the full effects of daily
decisions, individuals and corporations can get a better idea of the best way to reduce
our environmental footprint. Here on SciShow, we love exploring questions
like these because often, the things that seem the most
simple are actually really nuanced and fascinating. And we wouldn’t be able to do things like
this without the support of our Patreon community. So to all our patrons: Thank you for helping
us make videos like this. If you’re not a patron but want to learn
more about supporting free science education on the internet, you can head over to patreon.com/scishow. [♩OUTRO]
I’m using my aunts old cotton bag from the 60’s, and will most likely pass it on to my kids too because of how beautiful and well made it is. Quality, not quantity.
What I appreciated about this video is that it took a look at the whole life cycle of different bag. Personally, I have been using the same bags my whole life. I could see myself passing them down to my child - should I have a child.
I've been using the same bag since the 90s.
I thought technology was supposed to enable us, not make us more dependent. Humans lived without shopping bags for hundreds of thousands of years. How did we become so entitled and helpless?
Very thought provoking. It's clear we need to do more work, measuring the effects of disposal. Would be good to see the impact of different straws or cutlery too.
I just got bagless, makes stealing easier if you're into that sort of thing, and better for the environment. Then when I get to my car I use old Amazon boxes to keep things from tumbling around. Sam's really deserves more credit for using old boxes for packaging.
Just wondering how this would change if other fabrics than cotton could be used for those bags. I feel like I've seen infographics on the env impacts of different fabrics, including things like water use for example, but I can't find any of them right now. Would appreciate it if anyone knew of any resources on this.