Environmental impacts and co-benefits
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CDR can require land, water, energy, and other inputs, which may be associated with resource competition or depletion, raise pollution concerns, and impact ecosystem quality. To appraise CDR options, we must go beyond assessing their potential role in climate change mitigation, also investigating their wider environmental impacts and co-benefits. We consider impacts along the entire supply chain — from resource extraction and processing to transport and waste disposal — to identify environmental concerns of a given CDR and opportunities to improve its processes and enhance co-benefits.
As many CDR approaches involve large-scale land-use, much of the environmental assessment comes down to the impact of different land cover and land management practices. For example, it is important to consider how the agricultural practices in growing ‘biomass’ crops for bioenergy with carbon capture and storage (BECCS) compare with current crop production, or how the impacts would change if there was a risk of natural vegetation being converted to biomass crops. In some cases, these impacts may be positive: some land-based GGRs deployed in appropriate locations have the potential to assist in biodiversity recovery, ecosystem restoration, and climate adaptation, alongside their climate benefits.
To account for the environmental co-benefits and impacts potentially related to deploying and scaling up CDRs, we are recommending the following environmental indicators.
CO₂RE’s environmental indicators
To track and assess impacts of material flows and processes along the CDR supply chains, we use the principles and methodologies of Life Cycle Assessment (LCA). This involves constructing a ‘life cycle inventory’ which collects all material and energy flows and related emissions to air, water and soil. The data collected in this inventory is then aggregated into relevant impact categories. For instance, the volume of water utilised (reported in the inventory) is assessed against the amount of water available in the watershed at the time of water use, resulting in an indicator of water scarcity.
Natural resource use: Land use and water use
To appraise land-use impacts, we use a range of methods including local data collection and environmental modelling. This requires location, state and time-specific data and methods. For example, soil erosion risk could be assessed based on agricultural practices for bioenergy crops or tree-planting, incorporating site-specific data on soil type and precipitation. Even more detail may be considered in biodiversity assessments, where different land-uses and management intensities affect ecological functioning relative to an intact ecosystem.
Where possible, this site-specific detail on land-use and environmental impacts is also extended across the entire supply chain, in addition to the main on-site CDR assessment. This requires as much specificity in the life cycle inventory as possible.
Land use
A fundamental indicator, with important implications across many other environmental impacts, is the amount of land required for a CDR project. If the project is assumed to scale-up in the future, then the amount of additional land needed to enable the larger project should also be considered.
Usually, the amount of land is reported as a generic total area footprint.
We recommend a more detailed land reporting, including:
- Location of the land-use as it determines other impacts resulting from land-use and land-use change;
- The type of land used or converted as it has important consequences for the environmental impacts and for the type of farms and farmers that could be affected, e.g. a CDR could be deployed on ‘marginal’ agricultural land vs prime agricultural land;
- CDR land management, to highlight where practices can be integrated with other land-uses, e.g. agriculture or ecosystem protection/recovery and the co-benefits provided.
Water use
Water use by CDR considers water usage in the area in which the CDR methods are directly applied, and the water embedded or utilised in ‘upstream’ areas required to produce inputs to CDR, e.g. the water utilised in a nursery for tree saplings. To reflect the impact of water usage onto the local water availability, LCA best practice recommends applying a water scarcity weighting onto the amount of water consumed. The weighting factor accounts for variation in water availability across different locations.
Biodiversity change
To quantify biodiversity change, we need to anticipate (and, ideally, eventually measure) how species diversity and abundance changes in response to CDR deployment. Measuring biodiversity is not straightforward. Biodiversity indicators could include a range of simpler metrics monitoring the diversity of life, from genetic diversity within individual species, to changes in population size and ecosystem species composition. There are also ongoing attempts to develop indicators that link biodiversity change and ecosystem health to ecosystem functioning, i.e. provision of ecosystem services such as pollination.
LCA methods typically report impacts on biodiversity as the ‘Potentially Disappeared Fraction’, determined primarily by land conversion and usage, with more recent versions including type of land use and its intensity. In some cases, climate change and ecotoxicological impacts from greenhouse gases and other emissions are included. Where there are more specific regional or national scale biodiversity concerns, or particular risks associated with a given CDR, more specific biodiversity indicators and modelling may be useful or even legislatively required.
The most robust approach is to combine biodiversity indicators and/or modelling approaches with on-the-ground monitoring of biodiversity. Ideally, species diversity and abundance would be measured before the project started and monitored over time. With further development, this approach can be complemented with indicators of ecosystem functioning, i.e. translating biodiversity change to ecological stability and resilience which can affect the long-term store of carbon.
Water, air and soil quality
Different land uses and managements have implications for water, air and soil quality. For example, fertilisers applied for CDR, e.g., for growing biomass crops, may be lost to water. Excessive nutrients in water could cause dense algal blooms, which can kill all life beneath them.
As an initial approach to generating water, air, and soil indicators, we recommend using LCA characterisation factors to determine the eventual impacts of fertilizer loss on air or water quality. These can be developed with more detailed and location-specific environmental modelling, considering as well how land is managed, e.g., erosion risk based on soil type and field operations. Considering land management may also reveal co- benefits. For example, increasing soil carbon may also enhance soil stability and reduce nutrient losses.