Using Metrics to Support Co-Investment in Ocean Plastics and Climate Change Mitigation

There will be less need for beach cleanups with a circular plastics economy as it results in reductions of both plastic waste and greenhouse gas emissions. Photo credit: ADB.

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Life cycle assessments and complex value optimization are holistic approaches in measuring investment impacts.


Ocean health and climate change are inextricably linked in their impact on the capability of the planet to sustain life and in the approaches to their effective management. However, a significant disconnect exists in terms of the funding available to address these challenges. As with many conflicts throughout history, the gap causing the issue is not as big as it appears.

The climate change sector was arguably the first to gain awareness and the capacities to support necessary actions. Adopted in 1997, the Kyoto Protocol operationalized the United Nations Framework Convention on Climate Change (UNFCCC). That same year, yachtsman Charles Moore, returning to California from Hawaii, sailed through an area of plastic debris, which would later be called the Great Pacific Garbage Patch.

Fast forward to 2015 when the UNFCCC 21st Conference of Parties called for developed countries to commit $100 billion per year toward climate change mitigation. That same year, a landmark study led by University of Georgia’s Jenna R. Jambeck, Plastic Waste Inputs from Land into the Ocean, was published in Science journal and catalyzed the ocean plastics sector. Solid links are increasingly being used to identify and challenge the major producers of single-use plastic.

By 2020, leading experts were beginning to raise concerns that focus on ocean plastics, or plastic in general, was detracting from the bigger environmental threats of greenhouse gases (GHG) and ocean acidification. Unlike GHG emissions, where the impacts are not as immediate, ocean plastics provide a more visual impact that elicits public interest and opinion. Two important environmental missions addressing the preservation of the same planet are suddenly in competition.

Gases and solids

The issues go deeper to a more fundamental facet as impact investing. Funds committed to climate change measure success in terms of tonnes/CO2e (gas) mitigated, while ocean plastics projects were originally evaluated against how many tonnes (solid) were diverted from the ocean.

As understanding of ocean plastics grew from 2015, areas of intervention in the plastic value chain have also shifted. The framework has moved from “How do we remove plastic waste from the oceans?” (as seen in the work of non-profit The Ocean Cleanup, one of the first projects) to “How do we stop plastic from reaching the ocean?” This highlights the need to manage plastic products upstream at their origins—in consumer disposal choices and even earlier by delving into manufacturing, materials technology, and consumer behavior spaces. Connections between plastic producers and the fossil fuel industry have been recognized, and pressure is being brought to bear through both sustainable investment policies, legal action, and shareholders who focus on environmental, social, and governance (ESG) performance.

The result of this shift has aligned plastic management much more closely with the GHG management sector. However, the units of measurement are still creating a challenge for ESG investing and reporting. This article discusses the data, metrics, and calculations to bridge the gap between assessing the performance of plastic waste and climate change mitigation.

Developing Upstream Metrics

The common unit of measurement in the Kyoto Protocol and the carbon industry is tonnes of carbon dioxide equivalent (CO2e). There is a well-tested set of conversion factors, both from the UNFCCC and other sources, for the major GHGs that allow their reduction to be converted easily into CO2e. In this way, projects with GHG emissions, whether focused on methane, carbon dioxide, or hydrofluorocarbons, have a common unit of measurement and reporting.

The predominantly inert nature of plastic waste in the environment means that ocean plastics do not have a measurable GHG emission profile. Their damage to the environment through interactions with marine life and ecosystems can be measured, but it cannot be easily converted into CO2e. As the ocean plastics sector expands further upstream, the ability to attach CO2e figures to environmental impact, either directly or through conversion, becomes more achievable.

Not only does attaching CO2e figures to the production and disposal of plastic benefit the alignment of ocean plastics management with GHG emission management, but it can also support the sector in addressing questions about its net environmental impact.

For example, glass bottles and bio-degradable substitutes help reduce plastic use. However, a life cycle analysis shows a glass bottle has a much higher environmental impact, and bio-degradable plastic in some cases produce up to 80% more CO2e than the conventional plastic.

Calculating Plastic's Carbon Footprint

UNFCCC methodologies provide the simplest way to calculate CO2e for plastic management. One such methodology, AMS-III-AJ (which is part of the Approved Methodology for Small-Scale Carbon Development Mechanism project), focuses on recovery and recycling of materials from solid wastes. Data on the reduction in overall energy consumption and resource usage achieved by recycled plastic is used to calculate how much CO2e is avoided compared to business as usual.

The AMS-III-AJ methodology for calculating greenhouse gas emission reductions from recycling plastics provides the following equation:


For the purposes of this example the equation may be more simply written as follows,


the inference being that, for every tonne of plastics recycled, the emissions resulting from the virgin production process are avoided. The exact emission reductions are influenced by many factors, such as the plastic being recycled/produced, the type of electricity generation used and its emission factor, or the process by which the polymer is manufactured from the fossil fuel-based natural resource.

The following table provides an example of this calculation in practice:


PET = polyethylene terephthalate, HDPE = high-density polyethylene, LDPE = low-density polyethylene, PP = polypropylene.
T/CO2e = tonne of carbon dioxide equivalent, MWh/t = megawatt hour per tonne.
Source: Author.

While this methodology is a valuable first step, its scope is limited in not only addressing four primary types of plastic (low-density polyethylene, high-density polyethylene, polyethylene, and polyvinyl chloride) but also in representing the true CO2e mitigation impacts of plastic management. The UNFCCC calculation captures only a small segment of the circular plastics economy, which is outlined below (red dotted line):


Source: Author.

More recent calculations and databases from private groups are in development or were recently launched, increasing the accuracy and scope of CO2e assessments to include more emission points seen in a circular economy. These allow greater accessibility, accuracy, and coverage for project teams when drawing links between plastics management and CO2e mitigation. They do not, however, benefit from the credibility and recognition of UNFCCC methodologies.

Life cycle assessment (LCA) methodologies allow analysts to explore a more holistic representation of the climate impact for individual plastic products. While targeted calculations, such as AMS-III-AJ, are in the minority, using LCA identifies the energy inputs for the product, and its impact matrix gives a much more complete “carbon footprint” for products, their components, and their varied fates in the circular economy. GHG methodologies and calculations exist for a wide range of production processes and inputs used in the manufacturing, transport, disposal, and recycling of plastic.

Scope is a key foundation of LCA calculations, and this is especially true for Complex Value Optimization for Resource Recovery modelling, which looks at multiple values of materials: environmental, social, economic, etc. LCA guidelines suggest three steps from the target product; however, this still requires a large amount of work to achieve comprehensive and accurate figures.

By considering additional emissions from transport and disposal, the climate change impact of plastic can be estimated more completely using existing tools. By including the reuse and recycling loops, analysts can form a complex value modelling process. This in-depth process, though resource intensive, will also allow analysts to effectively compare product lifecycles in the circular economy.


As we can see, there are existing tools that are sufficient in allowing an effective conversion of plastic tonnes managed to CO2e. The depth of investigation and scope of study for the meaningful estimation of life cycle GHG emissions from a product are covered by international standards for LCA activities. The final step in drawing together an integrated model representative of circular economy behaviors can be found in complex value modelling that captures both the GHG emissions of plastic in a “business as usual” context and the impact on GHG emissions resulting from mitigation activities. While this process will struggle to bridge every investment metric gap, it does allow a meaningful process to support interaction between climate and plastic management investments.

In the short term, these basic calculations can provide credible guidance for project design and project comparison to investors and governments, who have relied on established metrics and calculations that provide indicative results but cannot fully present the positive and negative impacts of policy or investment decisions.

In the medium term, more advanced CO2e mitigation models, which can capture more of the life cycle emissions and other environmental impacts, are available. However, they will need to address perceptions of credibility to be fully integrated into large-scale policy and investment decisions.

Policy and investment decision makers benefit from a range of information sources to support their due diligence process. There are established links to bridge the perceived gaps between ocean plastics initiatives and GHG reduction activities. In addition, significant developments are under way, such as through Indonesia’s National Plastics Action Partnership metrics task force activities, to further clarify and model these interactions in order to provide more consistent decision-making support. By embracing these innovations in life cycle understanding and measurement, decision makers can ensure that future projects and policies are inclusive of both plastic and GHG impacts rather than treating them as separate challenges.

The ADB regional technical assistance (TA), Promoting Action on Plastic Pollution from Source to Sea in Asia and the Pacific, supports developing member countries in reducing marine plastic pollution and enabling a transition to a circular plastics economy. It focuses heavily on upstream interventions as do many other plastic management initiatives. Among its activities, the TA works with regional and global programs to drive the collation and validation of metrics related to terrestrial and ocean pollution, as well as map the flow of plastic through the linear and circular economies. By working with groups developing advanced tracking and modelling systems, ADB’s projects and specialists are closing the gap between established data sets and the more widely available, but less proven, data being generated by more recent activities.

Ongoing knowledge products and project development research highlight areas where existing data can be harnessed to better support investment and policy teams in addressing overall sustainability, rather than individual segments of the ecosystem.


Asian Development Bank. Technical Assistance for Promoting Action on Plastic Pollution from Source to Sea in Asia and Pacific..

J. R. Jambeck et al. 2015. Plastic Waste Inputs from Land into the Ocean. Science. 347 (6223). pp. 768–771.

International Organization for Standardization. 2006. ISO 14044:2006 Environmental Management—Life Cycle Assessment—Requirements and Guidelines.

Indonesia National Plastic Action Partnership. 2021. Indonesia Metrics Roadmap.

United Nations Framework Convention on Climate Change. 2020. Clean Development Mechanism CDM Methodology Booklet (Twelfth Edition).

University of Leeds. Complex Value Optimization for Resource Recovery.

James Baker
Senior Circular Economy Specialist (Plastic Wastes), Climate Change, Resilience, and Environment Cluster, Climate Change and Sustainable Development Department, Asian Development Bank

James leads the regional marine plastics reduction program and supports operationalization of Strategy 2030 Operational Priority 3 and the Healthy Oceans Action Plan. He also supports country programming and sovereign and private sector project teams in identifying and promoting circular economy activities within their programs and investments. Prior to ADB, he was in senior project development and investment roles, and his background was in industrial recycling. He is studying for his PhD at University of Leeds.

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