Which bag should you use? - Luka Seamus Wright and Imogen Ellen Napper
You’ve filled up your cart and made
it to the front of the grocery line
when you’re confronted
with yet another choice:
what kind of bag should you use?
If you’ve seen the images of plastic bags
strewn across the ocean,
it might seem obvious that plastic
is bad for the environment.
Surely a paper bag or a cotton tote
would be the better option.
But is that really true?
Each of these three materials
has a unique environmental impact
that’s determined by its carbon footprint,
its potential to be reused and recycled,
and its degradability.
So, to get the full story
on these grocery bags
we need to look at how they’re made,
how they’re used,
and where they ultimately go.
Let’s start with plastic.
The typical thin and flimsy plastic bag
is made of high-density polyethylene,
commonly known as HDPE.
Producing this material requires
extracting petroleum from the ground
and applying extreme heat.
The resulting polymer resin
is then transported
alongside additional ingredients
like titanium oxide and chalk
to a bag manufacturing plant.
Here, coal powered machines
melt the materials down
and spin them into sheets of plastic,
which are then folded into bags.
By the time a bag reaches
its final destination,
it’s contributed an estimated 1.6 kg
of carbon dioxide to the atmosphere.
That’s the same amount of carbon
a car produces,
driving a little over 6 kilometers.
But the alternatives actually possess
a much larger carbon footprint.
Paper is made from wood pulp,
and when you account for the carbon cost
of removing trees from their ecosystems,
a single paper bag can be responsible
for about 5.5 kg of carbon dioxide.
Meanwhile, growing cotton is an extremely
energy and water intensive process.
The production of a single cotton tote
emits an estimated 272 kg
of carbon dioxide.
When we compare carbon footprints,
plastic bags are the clear winner.
But environmental impact
is also determined by how the bag is used.
Reusing or recycling these bags
significantly offsets
their environmental toll
by reducing demand for new production.
To quantify that offset, we can divide
the bag’s carbon footprint
by the number of times it’s reused.
For example, if a typical paper bag
is reused three times,
it has a lower net impact
than a single-use plastic bag.
The carbon footprint of a cotton tote
can similarly be lowered,
if it’s reused 131 times.
Of these three options, durable cloth
totes are most likely to be reused.
Evidence shows paper bags are quickly
discarded due to their tendency to tear.
This issue plagues HDPE
plastic bags as well.
But even when they’re made
to avoid tearing,
their widespread availability makes
it easy to treat them as single-use items.
Fortunately, researchers estimate
that 40% of HDPE bags
are reused at least once
for throwing out waste.
Recycling these bags also offsets
their carbon footprint,
but it’s not universally possible
for each material.
Many countries lack the infrastructure
to efficiently recycle plastic bags.
Cotton totes are perhaps even more
difficult to breakdown and process,
but since they’re often reused
for long periods,
they’re still least likely
to end up in landfills.
Whenever these bags aren’t recycled,
the third factor in calculating
environmental impact comes into play:
degradability.
Since HDPE bags are heat-resistant
and insoluble,
they stick around long after we’re done
with them.
Partially broken down plastic
can circulate in ecosystems for centuries.
Cotton on the other hand degrades
substantially in a matter of months,
and paper bags break down
completely in just 90 days.
So, which bag should you use?
It turns out the most
environmentally friendly bags
have features of several materials
we've discussed.
They’re durable and reusable, like cotton,
but made of plastic,
which has a lower carbon footprint
than cotton or paper.
These sturdy shopping bags consist of
polyester, vinyl and other tough plastics,
and are already used worldwide.
Most importantly,
they should last a lifetime—
making them the best option
for the planet, and your groceries.
