TCoPS - 39

using a discount rate (the authors used the social discount
rate of 2%), this gives less weight to costs that will occur in
the long term future. This estimated the lifetime cost per
tonne imposed by plastic in the ocean as ~US$204,270408,541,
with 85% of this cost made up of costs that
societies and governments will face in the next 100 years
(or 95% in the next 150 years).
Step 5: To calculate the proportion of plastic waste
that becomes waste, the authors summed the tonnes of
plastic leakage from municipal solid waste and primary
microplastics from Breaking the Plastic Wave294
(9.8 million from MSW and 1.3 million from primary
microplastics) with the annual tonnes of at-sea sources
of leakage (~923,076295
). This estimated annual leakage
into the ocean in 2016 as ~12 million tonnes. They then
divided this by total plastic waste generation in 2015 (302
million tonnes) which estimated the proportion of plastic
waste entering the ocean as ~4%. This estimate includes
the simplifying assumption that plastic waste generation
in 2015 can act as a proxy for plastic waste generation in
2016. This estimate is an underestimate because it does
not include leakage from non-municipal solid plastic waste
or secondary microplastics. However, studies have shown
that plastics from electronics, building and construction,
and transport are not often observed as ocean debris296
. As
such the authors are comfortable using their estimate as
a conservative estimate of the proportion of plastic waste
that enters the ocean.
Step 6: To calculate the total tonnes of the plastic
produced in 2019 that will enter the ocean, the authors
multiplied the tonnes of plastic produced in 2019 (368
million) by the proportion of plastic produced that
becomes waste (70%), then multiplied that result by
the proportion of plastic waste that leaks into the ocean
(~4%). This estimated the tonnes of plastic leaking into the
ocean attributable to the plastic produced in 2019 as ~10
million.
Step 7: To estimate the ecosystem service cost induced
by the plastic produced in 2019, the authors multiplied
the plastic produced in 2019 that will enter the ocean
(10 million tonnes) by the lifetime impact on ecosystem
services per tonne of plastic entering the ocean
(US$204,270-408,541). This estimated the ecosystem
service cost imposed over the lifetime of the plastic
produced in 2019 as ~US$2.1-4.2 trillion. While
research indicated 2% as the most relevant discount
rate value (as explained above), the authors also ran
scenario analyses to confirm how the figure would change
under a higher discount rate, which would place an even
lower weight on long term future costs. As the authors
used the perpetuity net present value formula, doubling
the discount rate to 4% would mechanically half the
ecosystem service cost imposed over the lifetime of the
plastic produced in 2019, to between ~US$1.0-2.1 trillion.
However, an important nuance should be observed:
while this total is halved, the costs occurring future are
significantly less impacted. If current decision-makers
focus on the costs that will occur within the next decades,
the difference in the estimates from an increased discount
rate is less significant. Taking the period between now and
2050, which is frequently used timeline for climate action,
using a 2% discount rate leads to cumulative discounted
costs of ~US$938 billion by 2050 and using a 4% discount
rate still leads to cumulative discounted costs of US$724
billion by 2050, only 23% lower.
Step 8: The authors then estimated the median ecosystem
service cost imposed over the lifetime of the plastic
produced in 2019 as ~US$3.1 trillion.
4. Cost of lifecycle GHG emissions:
● The following inputs were used to estimate the
cost of lifecycle GHG emissions from the plastic
produced in 2019:
plastic lifecycle in 2015 provided by Zheng & Su. ◦ Input 1: Total GHG emissions from across the
297 These
figures are limited by the fact that they do not provide
estimates for the use phase of the plastic lifecycle or
from mismanaged plastic waste. However, data on these
components is currently not comprehensive enough
to provide robust estimates. Therefore, the authors
were comfortable in using the Zheng & Su figures as
a conservative estimate for GHG emissions from the
plastic lifecycle. These figures also do not include
the displacement of carbon intensive virgin polymer
production by recyclates. The authors chose to use the
Zheng & Su298
by CIEL (0.8Gt)299
estimate rather than the estimate provided
because it included the conversion
process and a breakdown of the emissions from each of the
lifecycle stages: GHG emissions across the plastic lifecycle
in 2015.
Table 2: GHG emissions across the plastic lifecycle in 2015.300
Lifecycle
Stage
Resin
Production
Conversion
Description
Includes all activities
from cradle to polymerproduction
factory gate
Covers the
manufacturing processes
that turn polymers into
final plastic products
End-of-Life
Total
Includes the treatment
and disposal processes of
plastic waste
535
Emissions
1,085
161
1,781
◦ Input 2: Cost of carbon estimated as US$100 in
line with the average price from IPCC based on IAMs used
in the IPCC SR15 report301
. This is based on the required
cost to reach a certain temperature reduction under given
abatement technology.
◦ Input 3: Plastic production in 2015 estimated by
Geyer et al.302
as 380 million tonnes.
by Geyer ◦ Input 4: Plastic waste generated in 2015 estimated
et al.303 as 302 million tonnes.
◦ Input 5: Proportion of the plastic produced in
2019 that becomes waste estimated as 70%. This is based
on a study by Geyer et al.304
that estimated 70% of the
cumulative plastic produced between 1950-2015 has
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