Impact Assessment Frameworks for Nature-Based Climate Solutions: A Review of Contemporary Approaches

Abstract

This study provides a comparative analysis of ecological impact assessment (EcIA) guidance for the design and approval stages of carbon sequestration and emission reduction projects, which are rapidly proliferating in response to the global need for climate change mitigation. Previous reports of negative effects on biodiversity from such projects suggest a need for more robust project design and assessment processes to improve synergies with conservation. Using a content and thematic analysis methodology, we compared four published frameworks that guide the assessment of carbon projects in natural environments. The results showed considerable variation in environmental assessment components including the level of attention to ecosystem services and the identification of areas of high conservation value that may require specific protections. There was a general lack of guidance on the inclusion of indirect and supply chain effects despite their relevance to ecological impacts. Critically, guidance in common use in the climate mitigation sector shows differing applications of the baseline and counterfactual scenarios that are used to quantify impacts. We discuss the need to focus assessment and reporting on comparisons with recent baselines to identify the contributions of individual projects and enable adaptive management and show how aligning with the concepts of Nature-based Solutions and nature-positive could be used to reimagine the role of EcIA to achieve these objectives. If these current weaknesses can be improved, EcIA has the potential to become an important implementation pathway for the conservation–climate change nexus due to its pivotal role in project design and approval processes. Conversely, a failure to reliably address these aspects will undermine the utility of EcIA as a decision support tool for sustainable development. We encourage the further exploration of EcIA practices in this direction and highlight the pressing need for reliable comparisons to support more strategic and sustainable solutions for both the conservation and climate change agendas.

1. Introduction

Climate change mitigation is a rapidly expanding area of human endeavors and innovation that is being catalyzed globally by the 2015 Paris Agreement. As a legally binding instrument, the Paris Agreement commits its parties to identifying and delivering Nationally Determined Contributions (NDCs) to the collective goal of “holding the increase in the global average temperature to well below 2 °C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 °C above pre-industrial levels” [1,2]. The need to develop methods for achieving NDCs has a cascading effect on domestic policies which may vary from country to country despite having the same general objective of decarbonization. These policy developments generally aim to reduce carbon emissions from reference levels or sequester additional carbon as a “negative emission”, with both strategies contributing to the lowering of atmospheric carbon [3,4]. The rapidly proliferating landscape of carbon sequestration and emission reduction initiatives (hereafter “carbon projects”) also includes incentive schemes such as carbon pricing and trading mechanisms that serve as implementation pathways for climate policies [5,6]. Carbon markets can be stimulated by direct finance (e.g., government funding) or by statutory requirements that impose mitigation requirements on polluters, especially where these allow for the purchase of carbon offsets as a means of complying with an emissions cap or target [6,7]. The expansion of carbon markets is also driving demand for carbon sequestration and emission reduction projects that can be accounted for and traded as carbon credits [8]. However, it is critical that these carbon-centric developments are well integrated with other societal objectives such as those encapsulated in the Sustainable Development Goals (SDGs) and Convention on Biological Diversity (CBD) [9,10].

Carbon projects that take place in natural environments or have the potential to affect them include the so-called nature-based climate solutions (NbCS) and closely related concept of natural climate solutions (NCS) [11,12,13,14,15] and clean energy developments that can reduce emissions in comparison to fossil fuels [16]. Across all sectors of carbon projects and financing, the energy sector is by far the largest area of activity since it accounts for around three-quarters of current emissions and, with the difference in carbon emissions between clean energy projects and incumbent energy sources, forms the basis of the benefit for climate mitigation [16]. Another prominent group of climate mitigation initiatives involves demand-side management in the energy sector, which provides a pathway towards reducing the emissions associated with energy consumption [17]. Outside of the energy sector, a wide range of other climate-wise strategies are being developed for various industries (e.g., construction, waste management) and land uses such as agriculture and forestry [16]. At the same time, solving the challenge of rapid decarbonisation while reversing biodiversity decline is one of the most critical modern-day conundrums (Box 1), since many adverse impacts on biodiversity and ecosystem services have been identified in studies on existing clean energy developments and other forms of carbon projects [8,18,19].

There is a growing need to ensure that climate mitigation developments are designed to avoid adverse environmental impacts and maximise potential benefits given the rapid proliferation of carbon projects in many sectors and jurisdictions [16,20,21]. Consequently, there is an increasing level of interest in the identification and avoidance of potential downsides through approaches such as the application of minimum standards and safeguards that can account for co-costs and co-benefits that are additional to a focus on carbon [7,22]. In this context, impact assessment models and practices can play a key role in improving outcomes through their role in the approval of carbon projects as a beneficial form of development. To date, however, there has been only limited research on the impact assessment tools that are being applied to the conservation–climate change nexus, leading to the potential for wide disparities in the outcomes they are driving. In this study we provide an initial characterization of these needs by evaluating current guidance for the design and execution of ecological impact assessments (EcIA), as applied to project types that feature prominently in climate mitigation actions.

Box 1. The Conservation–Climate Change conundrum.

Global warming is driving the displacement of natural ecosystems, posing a significant risk to biodiversity conservation and natural resource management objectives, even though some species may benefit from a warming climate [22,23,24]. Ecosystem-based adaptation that supports nature conservation is also expected to be more challenging in rapid or extreme climate change scenarios, especially at sensitive locations [25], leading to the expectation of highly variable effects on nature across localities and time periods [16]. Insufficient climate change mitigation can be identified as a contributing risk factor that may be reduced through the upscaling of climate mitigation ambitions and actions. However, it is important that natural ecosystems are not lost, either intentionally or un-intentionally, in the pursuit of climate mitigation, since this would undermine the fun-damental objective of protecting natural ecosystems and resources. Solving this conun-drum requires solutions that can simultaneously address global warming and protect ecosystems from further degradation.

2. Materials and Methods

We reviewed contemporary academic and grey literature to identify published guidance for ecological impact assessment (EcIA) processes for the design and permitting stages of carbon projects in natural environments (i.e., as opposed to urban environments and demand-side initiatives). We applied two key criteria to guide our selection of frameworks for evaluation. The first was the specific attention to natural environment outcomes as communicated by the stated scope and intended applications of the framework or guidance. The second was the specificity of the framework for project-scale assessments as our main area of interest. We selected four frameworks for comparison that met these criteria and emphasize different aspects of the assessment context in their structure and stated purposes. As described further below, the Verra Climate, Community, and Biodiversity Standards (CCB) and the International Association for Impact Assessment’s guidelines for EcIA provide explicit assessment frameworks for project-scale impact assessments. The IUCN’s Global Standard for Nature-based Solutions (NbS-GS) and the draft IUCN Nature-Positive measurement framework (NP) are higher-level frameworks that have an accompanying set of assessment criteria which can be applied to a range of project-based, institutional, or sector-wide evaluation contexts. In combination, we expected that these frameworks would provide a thorough treatment of our objective of identifying a reliable and comprehensive EcIA framework for improving the alignment between climate mitigation and nature conservation in a format suitable for practitioners involved in the design, permitting, or evaluation stages of carbon projects.

Other frameworks we considered that may inform EcIA practice include the System of Environmental Economic Accounting (SEEA) [26] and ecosystem services classifications such as CICES [27]. These frameworks deal with the recognition of nature’s contributions to people and have an important interaction with the scope of EcIA, particularly where the EcIA framework requires attention to ecosystem services, natural capital, or socio-cultural benefits associated with natural ecosystem components. We regarded these frameworks as providing support for EcIA processes as they generally provide detailed guidance for the identification and measurement of these considerations. We also noted considerable variation in the level of detail that is identified. For example, the Common International Classification of Ecosystem Services (CICES) provides a highly detailed set of ecosystem services classes in comparison to other ecosystem services classifications [27].

To facilitate a comparative analysis of the four selected frameworks, we conducted a detailed content analysis (sensu. [28]) of the assessment requirements found in the published frameworks and supporting guidance materials and then applied a thematic analysis to the coding results following Boyatzis [29] and Miles and Huberman [30]. The initial round of coding was completed independently by two researchers. Discrepancies between unique codes were resolved in a second round of coding to identify a set of themes and categories that collectively describe the components of all four frameworks. The primary objective of the analysis was, first, to identify the unique assessment concepts and targets that are presented by these frameworks and, second, to assess the degree of representation and any discrepancies between the treatment of each component across frameworks. We present a nature-based impact assessment framework that combines the key strengths of the assessment concepts found in the source materials and conclude by discussing opportunities to reimagine the role of EcIA frameworks in the design and permitting of climate mitigation actions and related development contexts.

2.1. Verra Climate, Community, and Biodiversity Standards

Verra is one of the largest global platforms in the voluntary carbon markets and has undertaken several initiatives to ensure greater rigor and quality assurance in the awarding of carbon credits. Verra has specialized in the development of voluntary standards in a diverse range of sectors, but with an emphasis on climate action and sustainable development. The core approach for awarding credits under Verra’s Verified Carbon Standard (VCS) requires a project to demonstrate its contributions to sustainable development, as assessed against the SDGs. For these purposes, the VCS requires the reporting of gains in at least three SDGs (selected by the project). This emphasis on co-benefits is supported by two additional standards, the Sustainable Development Verified Impact Standard (SD VISta) and the Climate, Community, and Biodiversity Standards (CCB). Of these the CCB Standards have been developed for projects in the land-use sector and provide quality assurance for the delivery of tangible climate, community, and biodiversity benefits.

Verra promotes the use of the CCB Standards for project developers and local communities, project investors and offset buyers, and governments, and they are in widespread use in the voluntary carbon markets [31]. The CCB Standards are applied to a project’s design and implementation stages in separate processes. These are the ‘validation’ of a proposed project and ‘verification’ for an implemented project where project deliverables and monitoring results are considered. However, the same assessment framework is used in both processes (see Supplementary Material Table S1). Biodiversity-related requirements of the CCB Standards are separated into four categories which consider the formulation of assessment baselines, the net positive impacts of the project, the evaluation and mitigation of offsite impacts, and biodiversity impact monitoring. Additional criteria are provided for projects that affect sites of global significance for biodiversity conservation as identified in the Key Biodiversity Area (KBA) framework [32,33]. Other sections of the CCB Standards also address impacts on communities and climate mitigation and adaptation outcomes.

In addition to Verra’s CCB Standards, several other guidance materials and frameworks have been developed for use in the voluntary carbon markets. In comparison to the CCB Standards, these mainly provide high-level principles as recommendations for consideration when developing assessment processes or setting targets. Examples include the “High-Quality Blue Carbon Principles and Guidance” produced by Conservation International and partners [34]. Such principles are incorporated to varying degrees in the other frameworks we considered.

2.2. International Association for Impact Assessment (IAIA) Best Practice Principles

The International Association for Impact Assessment (IAIA) is a global network of researchers and practitioners who aim to lead best practice approaches for impact assessment to enable informed decision-making of policies, programs, and plans. The International Best Practice Principles for Biodiversity and Ecosystem Services in Impact Assessment (BES-IA) provide a core set of guidelines which aim to ensure that sustainable outcomes for biodiversity, ecosystems, and ecosystem services are promoted during impact assessment [35]. We included the BES-IA guidance in our review because these practices are in widespread use and have been specifically designed to set out practices for project-based impact assessment and strategic environmental assessment (SEA). The BES-IA principles address nine key topic areas, each with associated implementation guidance (see Supplementary Materials Table S2). The principles are specifically designed to align with international environmental agreements, including the Convention on Biological Diversity (CBD), the Ramsar Convention, and the Convention on Migratory Species (CMS) [35]. Due to its leadership role in international impact assessment, guidelines produced by the IAIA and similar guidance from affiliated organizations (e.g., national impact assessment associations) have helped to shape practices that are often a requirement of statutory processes for environmental management. Consequently, they have the potential to be highly influential over outcomes that are managed and regulated in these settings and may also drive innovation in the design of development projects and programs. Current best practice within the impact assessment community is an important area of focus at the conservation–climate change nexus since many mitigation projects are assessed for regulatory approval in these processes.

2.3. IUCN Global Standard for Nature-Based Solutions

Several versions of the nature-based solutions (NbS) concept have found their way into national and international policy, all of which have a focus on working with nature to address societal challenges. However, the variety of interpretations of what constitutes NbS has resulted in the potential for inconsistent applications that could include the greenwashing of projects which contribute little to solving the sustainability issues that are the focus of the NbS concept. IUCN’s Global Standard for Nature-based Solutions (NbS-GS) was developed to address this context by fostering a common understanding of core principles and guiding the implementation of high-integrity NbS in a consistent manner [36].

The NbS-GS is designed to assess interventions that address one or more societal challenges (Figure 1). Its eight core criteria and associated sub-criteria can be applied to identify the scope of relevant considerations for many project and program evaluation contexts. Although biodiversity conservation is one of the identified societal challenges, criterion three of the standard also requires that all NbS result in a net gain to biodiversity and ecosystem integrity (see Supplementary Materials Table S3). Therefore, the need to assess these aspects is common to all projects that are evaluated against NbS principles, as encapsulated by the standard, and it is readily applied to climate change adaptation and mitigation challenges [37]. Using the NbS-GS framing, nature-based climate solutions (NbCS) can be understood as interventions that are designed to address the challenge of climate mitigation using approaches that are consistent with all eight NbS criteria. This focus is particularly well matched to our framework selection criteria due to its mandatory focus on the degree of alignment with biodiversity conservation objectives.

2.4. IUCN Measuring Nature-Positive Framework

The concept of nature-positive (NP) has been defined as “halting and reversing biodiversity loss by 2030 from a 2020 baseline and to set the path for full recovery of nature by 2050” [38]. While there is also a need for attention to the socio-cultural and economic interactions with nature which, inter alia, require the differentiation of implementation pathways and mechanisms for resolving conflicts [39,40], the nature-positive concept promotes a biocentric view that seeks to reverse the decline of nature as a priority [38,41]. The key strategies for achieving this are the avoidance of or reduction in pressures on the environment coupled with investments in the restoration and regeneration of nature that exceed any residual degradation from pressures that cannot be effectively avoided. In this sense, NP is consistent with the NbS principles, which require a net gain for nature (i.e., criterion 3), with the major difference being the setting of an explicit target date for achieving these gains and their measurement against a fixed-date baseline. As with NbS, there is also a danger that this aspirational framework may fail to achieve tangible outcomes in the absence of effective implementation, with considerable potential for greenwashing [42].

For each specific project or institution, to assess its contribution to NP, there is a need to evaluate both its positive and negative impacts [43], consistent with the traditional focus of impact assessment. Additionally, it is important to consider how these contributions are influencing outcomes across the many dimensions of nature. This suggests the need for a common assessment framework that can facilitate a consistent approach to evaluation across key measures and metrics. To support these needs, the IUCN has recently developed a draft framework for measuring NP progress [44], and this is an active topic of discussion globally (e.g., see https://www.naturepositive.org (accessed on 20 December 2024)). The IUCN framework contextualizes the NP concept in a format suitable for impact assessment and builds on the existing principles of other net gain approaches (e.g., [45,46,47]). Points of difference between the proposed framework and earlier net gain formulations include the need to integrate the combined effects of gains at project and institutional scales to facilitate their alignment with NP targets at larger national and global scales. Also notable is the abovementioned use of a fixed-date baseline against which impacts must be measured. To improve the alignment between the measurement of NP and monitoring of the Kunming-Montreal Global Biodiversity Framework (KMGBF), the IUCN’s framework proposes a fixed-baseline and net-positive target date of 2022 and 2032, respectively, marking a small change from the original baseline (2020) and decadal NP target proposed by Locke et al. [38] (Figure 1).

Figure 1. Linkages between major societal challenges addressed by Nature-based Solutions (NbS) and the concept of nature-positive. The first six NbS challenges were identified in the IUCN definition of NbS [48,49], while the seventh (environmental degradation and biodiversity loss) was an outcome of public consultation on the draft standard. In practice, achieving net gains for nature are a requirement of all NbS. In comparison, the nature-positive concept highlights the key targets of a net positive trend by 2030 and full recovery of nature by 2050. Adapted from [50,51] with permission from Nature Positive Initiative, building on the original visualization from Locke et al. [38].

Figure 1. Linkages between major societal challenges addressed by Nature-based Solutions (NbS) and the concept of nature-positive. The first six NbS challenges were identified in the IUCN definition of NbS [48,49], while the seventh (environmental degradation and biodiversity loss) was an outcome of public consultation on the draft standard. In practice, achieving net gains for nature are a requirement of all NbS. In comparison, the nature-positive concept highlights the key targets of a net positive trend by 2030 and full recovery of nature by 2050. Adapted from [50,51] with permission from Nature Positive Initiative, building on the original visualization from Locke et al. [38].

3. Results

3.1. Framework Comparison

Detailed content analysis of the selected frameworks revealed 20 discrete concepts that provide guidance for EcIA practitioners. They are clustered under five major themes which address (i) the assessment process and knowledge sources, (ii) criteria for assessment, (iii) the use of offsetting and the mitigation hierarchy, (iv) outcomes verification, and (v) baseline concepts used for comparison (Table 1, Supplementary Material Figure S1). Criteria for the assessment of biodiversity and ecosystem components were grouped into six classes (impacts on species, ecosystem condition/integrity, areas of high conservation value, connectivity and evolutionary processes, ecosystem services, and socio-cultural associations with biodiversity and ecosystem service changes). These topics together account for the collective scope of all four frameworks. It can be noted that the last of these overlaps with the scope of social and cultural impact assessments while also requiring an understanding of ecological changes and thereby contributing to the notion of integrated impact assessments [52]. Comparisons between frameworks (Table 1) show that most of the frameworks require attention to all six classes. However, only the BES-IA and NbS frameworks emphasize the need to consider connectivity and ecological context changes, and the NP framework does not specifically require attention to ecosystem services. Despite this, all frameworks require the assessment of socio-cultural impacts associated with ecological changes. Another important nuance concerns the identification of areas of high conservation value. This is generally required by all frameworks, yet the specified assessment concepts and criteria differ considerably. As a result, there are a wide range of high-conservation-value concepts that might be addressed in IA processes and a notable lack of information on the choice of such concepts and the justification for their selection within each individual framework. We therefore flag this as a topic that requires more specific attention in the interests of promoting consistency across EcIA practitioners and jurisdictions. In contrast, all frameworks emphasize the need to incorporate traditional knowledge, recognize different forms of knowledge, use participatory assessment approaches, and ensure transparent communication and reporting to stakeholders, illustrating the universal importance of these assessment practices and elements (Table 1).

Requirements for the assessment of cumulative and residual impacts differ considerably between frameworks, with marked variance in the content and level of prescription for applications of the mitigation hierarchy. For example, the CCB Standards include specific attention to components for which adverse effects should be avoided in the mitigation hierarchy, including genetically modified organisms (GMOs) and impacts on areas of high conservation value, which are defined by additional sub-criteria (Supplementary Material Table S1). The BES-IA guidance also includes details on biodiversity and ecosystem components for which adverse effects should be avoided but points to a largely different set of concepts for assessment and consideration [35]. The NP framework contains more detailed guidance on the use of offsetting in comparison to other frameworks. This may reflect an intention to ensure that offsetting principles are applied consistently when determining residual impacts (i.e., post-mitigation) as a precursor to measuring the degree to which outcomes are “nature-positive” [41]. However, it can be noted that the same considerations are also required when assessing project outcomes against an objective of no-net-loss (instead of net gain), as is common in many jurisdictions [53].

The choice of comparison point (i.e., baseline or counterfactual) is a major source of difference between frameworks. It is a key matter because of its influence on the recognition and quantification of impacts. These differences may affect both the process and result of impact assessments that are required under statute with direct consequences for the environmental outcomes associated with permitting or already permitted activities. The CCB Standards, NbS-GS, and NP frameworks all specifically require a net gain, in contrast to the no-net-loss focus of the BES-IA, which represents a more traditional formulation of the mitigation hierarchy. The NbS-GS specifically requires a net gain against the “current state of the ecosystem” [36], in comparison to the CCB Standard’s use of a without-project counterfactual scenario and the NP framework’s focus on a fixed-date baseline. These frameworks essentially represent three different approaches to the measurement of impacts and they may well result in three different answers.

Table 1. Comparison of the assessment components found in four contemporary guidance sources that inform the practice of ecological impact assessment (EcIA) for climate mitigation projects. CCB = Verra Climate Community Biodiversity Standards [54], BES-IA = Best Practice Principles for Biodiversity and Ecosystem Services in Impact Assessment [35], NbS-GS = IUCN Global Standard for Nature-based Solutions [36], NP = IUCN Measuring Nature Positive framework, Version 1.0 [44].

Themes	Assessment Components or Criteria	CCB	BES-IA	NbS-GS	NP
Knowledge sources and stakeholder engagement	Use participatory assessment approaches	x	x	x	x
	Incorporate traditional knowledge	x	x	x	x
	Ensure transparent reporting to stakeholders	x	x	x	x
Biodiversity and ecosystem components	Assess: - Species-level impacts	x	x	x	x
	- Ecosystem condition/integrity changes	x	x	x	x
	- Areas recognized for high conservation value †	x	x	x	x
	- Ecological connectivity and supporting evolutionary processes		x	x
	- Ecosystem services changes	x	x	x
	- Socio-cultural impacts of biodiversity and ecosystem service changes	x	x	x	x
Offsetting and mitigation hierarchy	Incorporate mitigation hierarchy in assessment process	x	x		x
	Avoid impacts on high conservation values	x	x	x	x
	Avoid impacts that are not possible to offset				x
	Ensure offsets are like for like				x
	Avoid genetically modified organisms (GMOs)	x
	Overall outcome for biodiversity and ecosystem components is positive at appropriate scales			x	x
Monitoring and outcomes verification	Outcomes are long-term/permanent			x	x
	Establish monitoring to inform adaptive management and demonstrate long-term outcomes	x	x	x	x
Comparative concept/assessment baseline	Adopt fixed reference date as baseline				x
	Adopt current ecosystem state as baseline			x
	Develop without-project counterfactual (i.e., baseline that reflects state of the environment without project)	x	x

† concepts used to determine high conservation value include global, regional, or local significance (e.g., for natural patterns of distribution and abundance), uniqueness, irreplaceability, vulnerability, and rarity.

Table 1. Comparison of the assessment components found in four contemporary guidance sources that inform the practice of ecological impact assessment (EcIA) for climate mitigation projects. CCB = Verra Climate Community Biodiversity Standards [54], BES-IA = Best Practice Principles for Biodiversity and Ecosystem Services in Impact Assessment [35], NbS-GS = IUCN Global Standard for Nature-based Solutions [36], NP = IUCN Measuring Nature Positive framework, Version 1.0 [44].

Themes	Assessment Components or Criteria	CCB	BES-IA	NbS-GS	NP
Knowledge sources and stakeholder engagement	Use participatory assessment approaches	x	x	x	x
	Incorporate traditional knowledge	x	x	x	x
	Ensure transparent reporting to stakeholders	x	x	x	x
Biodiversity and ecosystem components	Assess: - Species-level impacts	x	x	x	x
	- Ecosystem condition/integrity changes	x	x	x	x
	- Areas recognized for high conservation value †	x	x	x	x
	- Ecological connectivity and supporting evolutionary processes		x	x
	- Ecosystem services changes	x	x	x
	- Socio-cultural impacts of biodiversity and ecosystem service changes	x	x	x	x
Offsetting and mitigation hierarchy	Incorporate mitigation hierarchy in assessment process	x	x		x
	Avoid impacts on high conservation values	x	x	x	x
	Avoid impacts that are not possible to offset				x
	Ensure offsets are like for like				x
	Avoid genetically modified organisms (GMOs)	x
	Overall outcome for biodiversity and ecosystem components is positive at appropriate scales			x	x
Monitoring and outcomes verification	Outcomes are long-term/permanent			x	x
	Establish monitoring to inform adaptive management and demonstrate long-term outcomes	x	x	x	x
Comparative concept/assessment baseline	Adopt fixed reference date as baseline				x
	Adopt current ecosystem state as baseline			x
	Develop without-project counterfactual (i.e., baseline that reflects state of the environment without project)	x	x

† concepts used to determine high conservation value include global, regional, or local significance (e.g., for natural patterns of distribution and abundance), uniqueness, irreplaceability, vulnerability, and rarity.

The considerable differences in the scope of assessment guidance evaluated in this study suggest that there is currently no common framework to support EcIA practice for carbon projects, and the same is likely to be true for other development sectors. These findings also suggest that the relatively recent NbS and NP frameworks have the potential to drive new and beneficial changes to established EcIA practices. It is particularly notable that the CCB Standards have adopted a without-project counterfactual as the comparison point as opposed to the current ecosystem state or fixed date reference state baselines that are recommended by NbS and NP. This presents an overt consideration for Verra and other actors in the voluntary carbon markets, particularly those who are interested in developing safeguards and robust standards for ensuring that their carbon credits also represent demonstrable co-benefits for nature. Moreover, the same considerations also apply to other government and public sector agencies who provide similar functions for carbon markets under their control—for example, where carbon credits can be purchased to comply with the emissions quota in government-led Emissions Trading Schemes (ETS).

3.2. Synthesis of Frameworks

The IUCN’s Global Standard for NbS is arguably the central touchstone for applying a holistic ecosystem-based approach to impact assessments (e.g., [55]), due to its focus on providing an overarching set of requirements for interventions to societal challenges [36]. By design, it considers all of the central principles of ecosystem management and also functions as an umbrella concept for many established ecosystem-based approaches including ecosystem-based adaptation, climate mitigation, and disaster risk reduction [49,56]. However, other frameworks offer important additional guidance and contextualization for the purposes of project-scale impact assessment through attention to aspects such as the treatment of cumulative and residual impacts and acceptable standards for their management. Other important contributions come from explicit attention to the supply chain and decommissioning or disposal implications of material requirements over the full life cycles of development projects. These aspects are most clearly articulated in the NP framework in keeping with its origins in the corporate sector [40] and are also emphasized in the CCB Standards [54]. In comparison, the NbS-GS provides a more generic set of criteria, while also indicating entry points for stakeholder input and involvement for specific contexts (e.g., in the identification of agreed biodiversity values for improvement against benchmarks as a method for implementing net gain under criterion three). Combining the strengths of these frameworks provides a useful checklist for comprehensive and inclusive EcIA processes.

4. Discussion

4.1. Key Roles for Assessment Frameworks

As climate mitigation initiatives are evolving and proliferating, insights from their implementation are pointing to the need for improved attention to their potential downsides, particularly those associated with the destruction or displacement of existing ecosystems. Potential threats to existing values may include effects on legally protected species, ecosystems, or resources that are not the initial focus of the carbon project [7,8,57]. This implies a key role for assessment processes that have the responsibility of detecting such issues, ideally at the project design and planning stages. To improve synergies between objectives across the conservation–climate change nexus, there is an essential need for comprehensive assessments that can guide the selection of appropriate sites for carbon projects or, indeed, choices between the various opportunities and technologies for climate change mitigation. Importantly, misalignments and maladaptation issues are not restricted to the pitfalls of clean energy sector projects and may also manifest in NbCS and NCS projects despite their framing around working with nature. For example, Panfil and Harvey [58] reviewed 80 REDD+ projects and found that their biodiversity management goals typically lacked specificity and were seldom matched with logical conservation activities or outcomes monitoring requirements. Similarly, studies on afforestation projects have frequently reported the displacement of existing ecosystem types of high conservation value [8,13]. These displacement effects are analogous to poorly situated clean energy sector projects such as hydroelectric power projects that destroy existing river ecosystems [59], illustrating the importance of evaluating the losses to natural environment values that are associated with all such new developments. Importantly, EcIA processes are an important mechanism for improving the reliability, value, and durability of NbCS, as with other carbon projects.

4.2. Influence of the Assessment Baseline or “Counterfactual”

Consequential differences between the frameworks we reviewed include differences in the conceptual basis of the assessment counterfactual or baseline scenario that is used as the comparison point for identifying the impacts of a given proposal. The specification of this comparison point has a direct influence on the perceived (and reported) benefits that are associated with a project (Figure 2). The Verra standards and IAIA guidance both recommend the development of a counterfactual scenario which reflects the expected state of the environment without the implementation of the project (“without-project counterfactual”). This form of counterfactual is commonly used in conservation assessments, where it is related to expectations of continuing decline in ecosystem health or threat status—for example, in the IUCN’s Green Status of Species methodology [60]. It provides a means for gauging the expected benefits of a conservation intervention in terms of the achievement of “less worse” outcomes, such as where decline is continuing from many pressures but can be reduced by targeting a manageable stressor. However, this also means that natural ecosystems can continue to decline while project-scale assessments are reporting a net gain in ecological outcomes (Figure 2B) [53,61].

In contrast, the NbS and NP concepts take a conceptually distinct approach by requiring that policies and projects deliver an overall improvement. This is arguably a simpler and more robust alternative to developing a “without-project” counterfactual scenario that requires the estimation of future rates of decline and their considerable uncertainties. A notable feature of the NP framework is its reference to a fixed-date baseline as the comparison point for these purposes. This is seen, for example, in the IUCN (2023) principle on offsetting, which requires the use of the mitigation hierarchy to deliver “at a minimum in situ, measured, equivalent, net gains compared to the 2022 reference year”. This objective presents several nuances when applied at the scale of individual projects or institutions. These include the expectation of improving ecosystem health by 2030 due to the collective effect of other NP efforts, which suggests that post-2030 projects will need to provide baseline measurements at their project start date to determine their specific contributions for the metrics of interest (Figure 2C). Additionally, the same principles might be applied to monitoring and reporting periods beyond their project start dates (i.e., with the expectation that projects should continue to deliver net gains in each reporting period), which implies that a new baseline should be established at the beginning of each such period. From this perspective, the measurement of a current baseline, as required by the NbS-GS, can be regarded as a more generally applicable impact assessment model for all time periods.

4.3. New Directions for Impact Assessment

As shown in our analysis, renewed commitments and heightened global ambitions for improving the state of nature will require progressive improvements against a current baseline. This objective also implies that current actors will take a share of responsibility for past actions that have driven environmental degradation and may continue to exert influences today [62]. This aspect ushers in a new era of social and shared responsibility nuances that have yet to be fully internalized in the assessment models we reviewed. However, they are very likely to manifest as decisions on the choice of metrics that are used to assess a project’s impact and the scale at which they are required to be measured and managed (e.g., under guidelines or standards). As suggested by our results, systems for measuring supply chain impacts on biodiversity are only just becoming mainstream and require greater adoption through fiscal and regulatory incentives. However, these same considerations have a long history of attention within the context of Corporate Social Responsibility [63] and Ecologically Sustainable Development [64] and include the need for full life cycle responsibilities and supply-chain considerations (e.g., [65]). Incorporating these dimensions within impact assessment frameworks provides a practical route towards defining the limits of individual projects or institutional responsibilities and presents a promising new frontier for EcIA practice. The process of developing such metrics can also offer value above and beyond a role in tracking progress by providing the scaffolding for the setting of agreed outcomes between stakeholders.

A broadening of the EcIA scope promotes the recognition of a fuller range of pressures that more closely approximates the biophysical processes which drive environmental changes [52,66,67]. Importantly, it needs to do this at the scale of the individual projects or institutions that are contributing to these pressures. At the same time, new indicator frameworks are being developed for reporting collective progress at global scales using metrics that are widely measurable. Examples include the headline, component, and complementary indicators that are required by the KMGBF’s monitoring framework (e.g., Red List of Ecosystems assessments [68]) and several proposed indicators and metrics for measuring collective progress towards NP (

Table 2. Example of indicators or metrics that have been proposed for the measurement of nature-positive.

Proposed Indicator or Metric
Nature Positive Initiative †
Natural processes	hydrological integrity sediment transport and the integrity of estuaries migration patterns carbon sequestration and storage integrity of tidal zones natural fire regimes vegetative cover that supports rainfall patterns
Ecosystems	extent of habitat ecological integrity of the habitat function of species in their ecosystems
Species	extent and abundance of species extinction risk of species genetic diversity
IUCN Measuring Nature-Positive ‡
Extinction risk	Species Threat Abatement and Restoration (STAR) metric derived from the IUCN Red List of Threatened Species
Risk of ecosystem collapse	IUCN Red List of Ecosystems [69] Ecoregion intactness index Q’ [70] Critical Ecosystems Area metric [71] Mean Species Abundance metric derivatives (sensu. Schipper et al., [72]) Ecosystem Integrity Index (in development)

^† Nature Positive Initiative (2022) [51], ^‡ IUCN (2023) [44].

). As these international workstreams are progressing concurrently, there is an emerging need to clarify the relationship between NP measurement contexts and global reporting under international conventions such as the KMGBF. We suggest that NP measurement is best suited to institutional and project-scale contexts, which implies that its metrics would be contextualized and downscaled appropriately. Such contexts are directly supported by existing EcIA processes and consistent with corporate sustainability applications (e.g., [43]). Furthermore, it seems unnecessary for NP measurement frameworks to emulate the existing global frameworks for tracking collective progress towards high-level objectives such as those that are the focus of National Biodiversity Strategies and Action Plans (NBSAPs) under the CBD. Instead, NP assessments could become a new frontier for ecological, social, and cultural impact assessments and project-scale monitoring and evaluation.

5. Conclusions

With the majority of global carbon emissions originating from the energy sector [8,16], the development of lower-emission energy sources will remain a key focus for climate mitigation action into the foreseeable future [73]. It is becoming increasingly important that energy sector projects are rigorously designed and evaluated to meet multiple objectives, and the same principles also apply to the so-called “nature-based” and “natural” climate solutions. Despite our focus here on ecological impacts, the same information is also often relevant to the assessment of cultural and social impacts, particularly those involving relationships with natural resources. In this sense, carbon storage and removal projects are broadly similar to other development proposals that are the subject of impact assessments.

Our objectives were to review and compare contemporary guidance and assessment frameworks that can be used at the design and approval stages of climate mitigation projects. We found that EcIA frameworks in current use have considerable variation in core assessment components such as the consideration of ecosystem services or areas of high conservation value. There is also a general lack of guidance on the inclusion of indirect and supply chain effects despite their relevance to ecological impacts. Additionally, we highlight the considerable variation and critical role of the baseline or counterfactual scenarios that are used to determine impacts. We conclude that the specification of this baseline in different contexts must become a key focal point for clarification. Recommended actions include the immediate need to review international guidance for EcIA and assessment standards used in the voluntary and government-regulated carbon markets. We also suggest that refocusing measurement and reporting on comparisons with recent baselines is essential to identify the contributions of individual projects and enable adaptive management. It is also likely that existing projects that were established and approved under the prevailing EcIA paradigm may not have been required to demonstrate net-positive outcomes for nature and may be contributing to ongoing decline, albeit more slowly than previously. Lastly, we propose that moving EcIA practice towards the assessment of positives could facilitate and solidify its role as an implementation pathway for global conservation objectives and their associated in-country commitments. With climate mitigation projects primarily reporting on their carbon benefits, there are bright prospects for impact assessment processes to help identify and optimize outcomes for other values. This role will only become more important as the world increases its commitment to climate action.