The Latent Potential of Cumulative Effects Concepts in National and International Environmental Impact Assessment Regimes

Abstract

Most modern-day environmental issues are caused by the complex aggregation and interaction of numerous actions contributing to large-scale problems, from biodiversity loss to climate change. Environmental impact assessments (EIAs) consider how projects contribute to these cumulative environmental problems. This article firstly evaluates the theoretical importance of cumulative effects concepts for EIA. It reveals their potential to spotlight values embedded in decision making and to illuminate, as a lighthouse would, types of harm from broad-ranging, typically unregulated, activities. A large-scale global survey of national EIA laws and multilateral environmental agreements then shows that cumulative effects concepts are legally relevant for most national EIA frameworks. This prevalence suggests that better implementation of cumulative effects provisions may help EIA law to deliver more significant benefits than previously appreciated. Evaluating a sample of EIA provisions shows that cumulative effects concepts can contribute to different stages of an EIA, but that using these concepts across all EIA stages would maximize their potential to achieve the theoretical benefits identified. From theoretical and practical legal perspectives, cumulative effects concepts have significant latent potential – perhaps transformational potential – to address cumulative environmental change through EIA regimes at national and international levels. However, without better implementation, the latent potential of these laws to address cumulative environmental problems is likely to remain unrealized. By shedding light on the extent of national and international legal frameworks that adopt cumulative effects concepts, and their differences, this article highlights the significant learning potential between legal regimes to aid improved implementation.

1. INTRODUCTION

Many of our most intractable environmental problems involve cumulative environmental harm, from a changing climate caused by high concentrations of greenhouse gas emissions to biodiversity lost as a result of the incremental clearing of native vegetation. These types of harm occur when multiple individual adverse environmental impacts interact and aggregate. Regulating these ‘cumulative effects’ is increasingly important for environmental protection.

Sources of such impacts include large-scale public and private projects, such as new infrastructure, resources developments or housing. Globally, waves of new infrastructure are anticipated to aid post-pandemic economic recovery,¹ renewable energy transitions,² and economic development in the global south.³ Without care and legal clarity, these projects will create serious cumulative effects.

Environmental impact assessment (EIA) offers one way of considering and controlling the impacts of major projects. EIA originated in the United States’ (US) National Environmental Policy Act of 1969,⁴ then spread to various US states, with other countries following suit in the 1970s and 1980s.⁵ The EIA process involves several stages, including ‘screening’ a project to determine the need for environmental assessment; ‘scoping’ to determine key elements of the environment expected to be impacted, relevant baseline conditions and alternatives to the project; substantive prediction and evaluation of impacts of the project (environmental assessment); public participation; the final decision; and follow-up.⁶

EIA law may require consideration of cumulative effects. A representative definition of cumulative effects – from the many that exist – is:

[effects] that result from additive effects caused by other past, present, or reasonably foreseeable actions together with the plan, programme, or project itself and synergistic effects (in combination) which arise from the interaction between effects of a development plan, programme or project, on different components of the environment’.⁷

EIA that includes cumulative effects assessment (CEA) differs from ‘regular’ EIA in important ways. It involves, at least to some extent, identifying other actors and actions in the past, present, and reasonably foreseeable future. By contrast, regular EIA does not disaggregate actions; instead, it may consider the overall effects of those actions as environmental ‘context’ or ‘existing circumstances’.⁸ Thus, CEA highlights not only the metaphorical ‘thousand cuts’, but also who wields (and has wielded, and will wield) the knife. Secondly, considering other actors in space and time expands the spatial and temporal boundaries of EIA that includes CEA relative to regular EIA.⁹ CEA also alters EIA investigations by considering whether ‘individually minor effects will be collectively significant’,¹⁰ illuminating relatively small, potentially unregulated effects that regular EIA may otherwise disregard. Finally, CEA also emphasizes non-linear responses, such as impacts that become amplified or exponentially greater as a result of other development activities and natural background changes in environmental conditions.¹¹ By contrast, ‘traditional’ EIA tends to conceptualize a single source of impact in isolation,¹² potentially misrepresenting to decision makers and the public the true extent of environmental harm. Considering cumulative effects exposes the true extent of a project's potential harm and, by revealing the full suite of contributors to the harm, also exposes more options for reducing aggregate environmental damage.¹³

At least 180 countries prescribe some type of EIA in national law,¹⁴ as do several treaties and customary international laws.¹⁵ There is increased comparative legal debate about CEA in EIA.¹⁶ However, no comprehensive survey has explored the domestic and international legal adoption of provisions that address cumulative effects or their theoretical implications. Such a survey is warranted given the widespread use of EIA and the ‘untapped potential in existing laws to address environmental change’.¹⁷ While other forms of law also consider cumulative effects, such as strategic environmental assessment (SEA) and regional-scale assessments,¹⁸ their use is comparatively rare,¹⁹ which would reduce the potential impact of including CEA in these processes as compared with EIAs.

This article investigates the potential of cumulative effects concepts in EIA law to address cumulative environmental change. This investigation proceeds on two fronts, applying theoretical and practical legal lenses to two sub-questions. Firstly, as a matter of theory, how might cumulative effects concepts²⁰ help to address cumulative environmental change through EIA law? Secondly, practically, to what extent do existing EIA laws adopt cumulative effects concepts, thereby laying the legal foundations for delivering the identified theoretical benefits? To answer these questions, we cover EIA under national laws and multilateral environmental agreements (MEAs). EIA regimes at both levels are important components of the global ‘constellation’²¹ of theories and laws related to EIA, and are interlinked. Throughout, we also reflect on the impact of poor implementation in realizing the potential of cumulative effects concepts in EIA law to address cumulative environmental change. We offer several law-related methods of encouraging better implementation, with a focus on forms of cooperation and cross-regime lesson learning.

The remainder of the article is structured as follows. Section 2 considers the importance of cumulative effects concepts in major EIA theories. It finds that cumulative effects provisions ‘spotlight’ value-laden aspects of EIA and illuminate, as a lighthouse would, a broader set of potentially harmful activities beyond the activity that triggered the EIA, including activities across boundaries. The article then moves to its main contribution, a systematic global survey of EIA laws containing cumulative effects provisions. Section 3 undertakes this survey at the national level, analyzing the major areas in which these provisions vary and discussing corresponding implications. It finds cumulative effects provisions in most national EIA laws (113 national laws), which provide a wide foundation for delivering the theoretical benefits of cumulative effects concepts, though there are definitional and functional differences between these provisions. Section 4 conducts this survey and examines these factors in the context of MEAs, finding ten MEAs that adopt such provisions, then considers points of intersection between national law and MEAs. Section 5 synthesizes key findings from the theoretical analysis and global survey, and highlights opportunities for further research.

2. THEORETICAL UNDERSTANDINGS OF EIA AND THE PLACE OF CUMULATIVE EFFECTS CONCEPTS

Considering major EIA theories reveals that cumulative effects concepts significantly expand the capacity of EIA to address key theoretical concerns and achieve theoretical benefits relevant for addressing cumulative environmental change.

2.1. Rationales for EIA: Theoretical Models

EIA is traditionally considered a purely technical-rational exercise, whereby decision makers objectively,²² rationally²³ and systematically examine all the relevant information produced by the EIA process to reach the ‘correct’ decision about the acceptability of a project.²⁴ This neutrality is conveyed by impact statements that emphasize scientific techniques, using value-free terms such as the ‘public interest’.²⁵ From this apolitical view,²⁶ public participation is valued purely for producing additional information.²⁷

Over time, these assumptions of complete rationality have been increasingly questioned,²⁸ recognizing that EIA unavoidably involves political decisions²⁹ about prioritizing conflicting interests.³⁰ Determining the significance of an environmental impact is especially subjective,³¹ despite increasingly standardized practices.³² Commentators also question the resource-intensity and plausibility³³ of exhaustively compiling information to make perfect predictions ex ante,³⁴ and criticize the lack of emphasis on follow-up monitoring and adaptive responses.³⁵ These critiques aim to reconceptualize the EIA process as less positivist³⁶ and more deliberative,³⁷ potentially transforming the views of individuals, institutions, and societies.

Many EIA theories (grouped as ‘transformational theories’) recognize that EIA processes involve difficult choices and diverse participants.³⁸ Seen thus, EIA can transform stakeholders’³⁹ interests by raising awareness of broader social interests and the common good,⁴⁰ and reconfiguring their interests through deliberation to be more aligned with community-minded, environmental values.⁴¹ EIA processes can shift the values of public institutions – such as environmental agencies, planning authorities and private institutions⁴² – as well as the values of individuals.⁴³ EIA can also be seen as a domestic or international process of ‘negotiation, bargaining and compromise among organized groups’ that compete to realize their values.⁴⁴ However, transformational theories are criticized for involving time- and resource-intensive processes without guaranteeing constructive outcomes,⁴⁵ and exaggerating the potential of participatory processes to shift values⁴⁶ and drive competing interests to agreement.⁴⁷

2.2. Rationales for EIA: International Legal Principles

Another theoretical source underpinning EIA are principles of international law. Internationally, EIA is theorized to implement the no-harm principle (which requires states to take reasonable steps to prevent significant transboundary environmental harm⁴⁸) and the duty of state cooperation⁴⁹ (which requires states to notify and consult with states which may experience environmental impacts resulting from the originating state's proposed project⁵⁰). These focus on the participatory and deliberative elements of EIA processes⁵¹ and can be considered integrated rather than mutually exclusive obligations.⁵² The duty of state cooperation creates a good-faith obligation which requires states to genuinely engage in consultations and attempt to resolve other states’ objections, while stopping short of giving those other states veto power over the originating state's proposed activities.⁵³ This echoes the domestic expectation that decision makers genuinely consider environmental issues, generally without requiring them to reach a specific outcome.⁵⁴ At both the domestic and international levels, these duties are procedural.

Others argue that EIA contributes to the non-discrimination principle,⁵⁵ obliging a state to ‘apply their environmental laws without discriminating between internal environmental harm and environmental harm to areas external to the state’.⁵⁶ Related to this is the equal access principle, which states that all potentially affected people should have equal access to participatory decision-making processes regardless of whether they live inside the state or not.⁵⁷

The non-discrimination principle does not directly act to strengthen environmental laws, but rather ensures that existing environmental laws and decision-making processes are applied to transboundary situations.⁵⁸ Conversely, the no-harm principle provides more scope for improving existing environmental laws and standards, as it focuses on the possibility and existence of environmental harm.⁵⁹

2.3. Theoretical Contributions of Cumulative Effects Concepts: A Spotlight and Lighthouse in EIA

Cumulative effects concepts in EIA carry benefits across these different theoretical rationales for EIA: the technical-rational approach, the transformational approach, the no-harm principle, and the non-discrimination principle. Cumulative effects improve EIA as a technical-rational exercise by producing more comprehensive information about the circumstances surrounding a proposed project, better informing how a decision maker evaluates central EIA concepts like environmental significance.⁶⁰ Courts have found that even a relatively small amount of additional environmental impact on an already degraded environment should be considered cumulatively significant, given existing levels of harm.⁶¹

The existing literature focuses largely on the technical-rational benefits of CEA, but is beginning to recognize its transformational potential:⁶² we build on the latter discussion here. By expanding the temporal and spatial boundaries of EIA under the requirement to consider relevant past and future activities, CEA forces a decision maker to transparently consider matters that are central to value judgements implicit in EIA and conceptualize the common good. A broader temporal view encourages more explicit consideration of appropriate historical baselines (for example, past ecological conditions in ‘pristine’ pre-colonial times versus contemporary pre-project conditions) to consider whether effects are significant, and may reveal value judgements about desired resulting ecological conditions.⁶³ An extended future orientation speaks to a broader focus on future generations and intergenerational equity. Australian judges have recognized this link in cases interpreting the principle of intergenerational equity to require decision makers to consider cumulative impacts,⁶⁴ and reduce the cumulative effects of climate change.⁶⁵ Through requiring more explicit decisions (relative to ‘regular EIA’) related to value-rich issues, such as baselines and the interests of future generations, cumulative effects provisions invite deliberation about environmental values and the common good in a way that the transformational approach theorizes may shift the values of the public and institutions – or at least expose differences for contestation.

In theory, the wider spatial scope that inheres in cumulative effects concepts also expands geographically the public wishing to participate in EIA, potentially in national and transnational contexts. This may engage more diverse values and visions of the common good in line with the transformational theories outlined above. In the national context, this could arise if, relative to ‘regular EIA’, cumulative effects-inclusive EIA recasts the impacts of a project as extending over a wider area and potentially having an impact on more diverse populations. The theoretical implications of this geographic expansion would be most profound in the case of a project that would be conceived as having effects confined to a single jurisdiction under regular EIA, but where applying cumulative effects concepts triggers a geographic expansion in scope that recasts that proposal as having transboundary effects. This spatial revision of the understanding of affected people occurs, for example, where an emissions-intensive project is conceived to contribute to cumulative emissions causing climate change that affects other states. For example, the Federated States of Micronesia challenged rebuilding a coal power plant in the Czech Republic, reasoning that it required a transboundary EIA.⁶⁶ Recasting the effects of the Czech power plant as transboundary would imply that the Micronesian state or public should participate in the EIA process. This would bring in a different culture and values, and perhaps thereby boost the deliberative and transformational potential of the EIA process, whether it is conceived to be underlain by the no-harm principle (conceptualized in combination with the duty of state cooperation)⁶⁷ or the non-discrimination principle (linked to the equal access principle).

In sum, nationally and internationally, cumulative effects concepts have the potential to act as a metaphorical spotlight because they force assessments to identify more explicitly ideas about baselines and environmental significance used in the assessment, revealing underlying values that can remain hidden in regular EIA. Not only can cumulative effects better reveal these values, they magnify the theoretically transformational potential of EIA by potentially spotlighting and including more spatially and temporally diverse communities than ‘regular’ EIA, increasing opportunities to contest the revealed values and visions of the ‘common good’ embedded in decision making.

Cumulative effects concepts also provide wide-angled illumination akin to a lighthouse, revealing otherwise potentially overlooked sources of harm and aggregate harm. This boosts the power of EIA to trigger deliberation that may influence environmental law beyond EIA – for example, habitat protection, natural resources permitting, or pollution control rules. Cumulative effects provisions inherently facilitate revelations about environmentally harmful actors beyond the proponent (‘other past, present and reasonably foreseeable future activities’). This may trigger transformational political agitation and contestation to regulate these broader actors differently, for example, by introducing new permitting processes. ‘Regular’ EIA may also produce this effect, as in Australia, where EIA for a major coal mine in the habitat of an endangered finch species highlighted how wider environmental laws had failed to constrain vegetation clearing that had led to its decline.⁶⁸ However, cumulative effects provisions would arguably produce this effect more reliably as, by definition, they involve examining the effects of other activities beyond the instant proposal. This influence of cumulative effects concepts also helps to address criticism regarding EIA, which focuses on a single proposed project rather than considering the regulation of harmful projects more generally.⁶⁹

For developing economies where EIA is the sole or major environmental law,⁷⁰ cumulative effects concepts have special value in enabling agitation for expanded environmental controls.⁷¹ Other processes might also build awareness about harmful unregulated activities, but cumulative effects provisions within EIA may enable enforceable requirements⁷² and involve large projects of an attention-grabbing nature to drive public interest and debate.

3. CUMULATIVE EFFECTS PROVISIONS IN NATIONAL EIA LAWS

While the ‘spotlight’ and ‘lighthouse’ potential of cumulative effects provisions could constitute significant ‘untapped potential in existing laws to address environmental change’,⁷³ this potential is affected by the extent of the adoption of these provisions and their precise content. Here we explore the national legal foundations for delivering these benefits, reporting the results of a systematic global assessment of the prevalence of cumulative effects concepts in national EIA laws.

3.1. Prevalence of Cumulative Effects Provisions in National EIA Laws

Using a methodology similar to other large, global-scale comparative law surveys,⁷⁴ our search examined national EIA laws that apply to physical projects and that require CEA or otherwise include cumulative effects concepts⁷⁵ (both, for brevity, ‘cumulative effects provisions’). We researched the laws of 195 nations (or equivalent), excluding the following: provincial and local laws; laws for strategic or regional environmental assessment; sector-specific laws;⁷⁶ and laws not available online.

We consulted the ECOLEX database⁷⁷ by inputting relevant keywords in appropriate languages;⁷⁸ national legislative websites, such as government gazettes;⁷⁹ international legal encyclopaedias⁸⁰ and other international materials;⁸¹ and other secondary legal sources to confirm our understanding. We required access to primary sources to confirm the presence of cumulative effects provisions, as secondary sources⁸² do not always differentiate between EIA and SEA.

Recognizing the importance of methodological reflection,⁸³ Appendix 1 details thoroughly our search process and its limitations. In summary, as with similar studies, the scope of this study precludes in-depth doctrinal analysis beyond a general discussion of key elements,⁸⁴ and we cannot confirm that a nation lacks a cumulative effects provision if we locate none (though our methodology raises this presumption).⁸⁵ Ultimately, we are likely to have underestimated the adoption of cumulative effects provisions because of the exclusions already mentioned. Appendix 2 summarizes the relevant provisions of national laws.

We found that most national EIA laws include a cumulative effects provision (‘adopting jurisdictions’, being 113 of the 186 countries that we confirmed to have a national EIA law, or 61%). Adopting jurisdictions are found on all inhabited continents, and across all major legal traditions (Figure 1): common law (as in the US, United Kingdom (UK)), civil law (as in France, Italy), Islamic law (as in Saudi Arabia, Mauritania), and mixed systems (as in Malta, Zimbabwe). Asia and Australasia have noticeably less legal coverage of the concept at the national level.

Figure 1 Nations with National-level Cumulative Effects Provisions in their EIA Laws (‘Adopting Jurisdictions’)

The high number and widespread nature of adopting jurisdictions are significant factors for the doctrinal, theoretical, and practical reasons outlined above. The prevalence of cumulative effects provisions could be argued to construct internationally accepted practice in EIA, influencing EIA practitioners and the interpretation of national EIA laws that requires a project proponent to apply international best practice.⁸⁶ If well implemented, these widespread provisions should produce better information for EIA in a technical-rational sense.⁸⁷ Applying a transformational theoretical model of EIA, cumulative effects provisions in these countries have the theoretical potential to produce agitation for improved environmental protection both within and outside EIA.⁸⁸ Though poor implementation of these provisions probably prevents them from reaching this potential,⁸⁹ identifying adopting jurisdictions is a step towards realizing the potential. Knowing where cumulative effects provisions are adopted facilitates improving implementation through lesson learning between national legal regimes (including through civil society litigants learning about challenges to the adequacy of cumulative effects provisions, which is common in its original US context⁹⁰), especially between regional neighbours (see Figure 1) with similar environmental and social contexts and legal traditions.

3.2. Definitions and Functions of Cumulative Effect Concepts in National EIA Laws

Legal and scientific scholars have long highlighted problems in defining cumulative effects. Many condemn laws that fail to define cumulative effects for allowing excessive agency discretion and diverging judicial interpretation, which can confuse practitioners.⁹¹ They note that existing definitions vary, as can their interpretation,⁹² even within a single jurisdiction.⁹³ Some note that diversity borne of detail potentially carries advantages: it encourages ‘sharpening’ of concepts,⁹⁴ reduces ambiguity,⁹⁵ reduces the potential for inadvertently inconsistent interpretations between jurisdictions, and reveals important underlying values.⁹⁶ Conversely, overly simple definitions encourage imprecision and inconsistent implementation over time.⁹⁷ Others argue that consistency in at least some definitional elements is desirable.⁹⁸

One might expect similarity among cumulative effects provisions as a result of the standardizing effect of initiatives to promote good EIA principles by non-governmental organizations (NGOs) and others,⁹⁹ particularly pressure from Western donor agencies on ‘developing’¹⁰⁰ countries and countries in transition.¹⁰¹ EIA principles and training materials endorsed by the United Nations (UN) promote consideration of cumulative effects,¹⁰² as do the Equator Principles advanced by financial institutions.¹⁰³ However, these materials take a no-frills approach, merely listing cumulative impacts among the kinds of impact that an impact assessment should consider without defining the term.¹⁰⁴ Several African nations¹⁰⁵ use similar legislative language to that used in the UN principles,¹⁰⁶ though insufficient information on relevant legislative dates means we cannot confirm an international lineage.

Other adopting jurisdictions provide more detail but reveal significant definitional differences in the process of doing so. Analyzing a sample of the laws collated for this study suggests that definitions may diverge on core conceptual features of cumulative effects. Cumulative effects concepts theoretically expand the temporal scope of EIA, but while some definitions refer explicitly to effects accumulating with other ‘reasonably foreseeable’ actions,¹⁰⁷ others are silent on this future temporal component.¹⁰⁸ Identifying foreseeable future activities is labour-intensive,¹⁰⁹ and selecting an appropriate temporal scope requires careful consideration;¹¹⁰ this legislative silence, therefore, is undesirable.

Definitions also vary in the ‘accumulation’ of effects that they foresee. Scientists consider that ‘cumulative effects’ include simple linear aggregation and ‘synergistic effects’ (namely, ‘[t]otal effects that are qualitatively or quantitatively different from the sum of the effects of the individual disturbances’).¹¹¹ The legal picture is muddier, as has previously been noted in a small number of jurisdictions.¹¹² Some legislative provisions reflect the scientific view,¹¹³ but others use the terms ‘cumulative’ and ‘synergistic’ as distinct and separately defined concepts,¹¹⁴ and some use the term ‘synergistic’ exclusively.¹¹⁵ This may affect the basic scope of the concept: narrow, if it encompasses only simple additive effects or complex and interactive effects; or wider, if it includes both.

Taking a narrow view of the nature of accumulation, or a truncated or unclear temporal horizon, eschews the key scope-expanding benefits of cumulative effects provisions for EIA law,¹¹⁶ including its ‘spotlight’ function. Definitional inconsistencies also increase the complexity and cost for proponents acting in multiple national contexts,¹¹⁷ and invite disagreements about transboundary EIA processes. Just as importantly, inconsistencies may cause adopting jurisdictions or proponents to produce environmental data that is difficult to collate and compare, creating an obstacle to cooperative transboundary EIA as well as strategic assessments.¹¹⁸ This is significant, as insufficient environmental data is a major barrier to implementing cumulative effects provisions.¹¹⁹ International frameworks could help to encourage consistent definitions and reduce such difficulties.¹²⁰

Definitions aside, the concept of cumulative effects performs different functions in the EIA processes envisioned by various legislative schemes (Figure 2, adopting generally accepted stages in EIA¹²¹). This fact appears to have gone unremarked in the literature thus far, but may affect the practical influence of the concept. Firstly, cumulative effects may be a screening criterion, which must be considered in determining if a project requires any form of environmental assessment at all. EIA may be required, for example, if a project falls within a named category (such as a power plant) or is likely to create cumulative effects.¹²² An alternative formulation is to require EIA for a development proposal that is likely to ‘significantly’ affect the environment, which requires considering, among other things, ‘whether the action is related to other actions with individually insignificant but cumulatively significant impacts’.¹²³

Figure 2 Functions of Cumulative Effects Concepts in National EIA Laws by Stage of the EIA Process

As a screening criterion, cumulative effects provisions could have high impact: they could expand the use of EIA outside its usual bounds if they trigger EIA requirements for activities of a category or scale that is usually exempt. Indeed, on one view of cumulative effects, causing minor harm to an already degraded environment should automatically be considered significant.¹²⁴ This supports the transformational significance of cumulative effects provisions for EIA if projects are considered significant and caught by a screening test only because the screening includes cumulative effects, as this triggers greater public participation and contestation about activities that usually escape such scrutiny.

For projects that require EIA, cumulative effects influence a second function – scoping – by affecting the type of environmental assessment required. For example, a project that ‘generates cumulative and/or indirect and/or synergistic effects’, may trigger a requirement to carry out an environmental impact study involving deeper analysis.¹²⁵ If considering cumulative effects results in an ‘upgrade’ to a more publicly contestable and more scientifically rigorous form of assessment, it improves both the technical-rational credentials and the transformational capacity of EIA law.

The third, and most obvious function of the concept of cumulative effects is that of CEA, which influences the substantive content of the environmental assessment. This is expressed in diverse ways in different statutes: the EIA must (or may) require a description of the ‘cumulative impacts’ of the proposed project;¹²⁶ the ‘cumulative and synergistic properties’ of the project;¹²⁷ the ‘cumulative and synergistic impacts and the induced risks’ of the project;¹²⁸ or ‘any accumulation of environmental impacts as a result of current or future activities’.¹²⁹ This variation may have the same practical implications as the definitional inconsistencies described earlier.¹³⁰ Theoretically, this is the stage at which the deepest inquiry into cumulative effects would be expected, setting the stage for the ‘spotlight’ and ‘lighthouse’ functions.

Finally, cumulative effects may be included in an EIA law's definition of environmental harm,¹³¹ impact¹³² or effect.¹³³ This has potentially further-reaching application not only to all stages of EIA but also the post-EIA process. For example, where a proponent must monitor the ongoing impacts of a project, this could require analysis to understand these impacts in the light of the cumulative effects of other projects on the ground. Practical matters are likely to influence the real-world potential of this function. From the technical-rational perspective, post-approval monitoring data needs to be aggregated with other relevant data to understand relative contributions to environmental decline, but administrative structures like data warehouses are not always in place to facilitate this aggregation.¹³⁴ From the transformational perspective, post-approval monitoring data must be accessible to allow for public oversight of cumulative impacts but, equally, this is not always the case.¹³⁵

The varying potential legal functions of cumulative effects concepts are at least as significant as varying definitions of cumulative effects, for similar reasons: the depth of analysis might vary significantly, lessons learned in one jurisdiction may not translate to another to help to improve implementation, and differences may obstruct productive intersections among national and international laws (Section 4.3). Differences in national approaches may also produce different expectations about EIA content among contracting parties to MEAs, which may require resolution.

4. CUMULATIVE EFFECTS PROVISIONS IN MULTILATERAL ENVIRONMENTAL AGREEMENTS

The adoption of cumulative effects provisions in MEAs further builds the legal foundations for realizing the theoretical potential of cumulative effects concepts. MEAs that adopt cumulative effects provisions could also help to improve national implementation by collecting and diffusing states parties’ experiences of implementing cumulative effects provisions.

4.1. Prevalence of Cumulative Effects Provisions in MEAs

EIA law began its migration from domestic contexts to the international realm during the 1970s¹³⁶ in early international statements on EIA.¹³⁷ The most broadly ratified EIA treaty – the Convention on Environmental Impact Assessment in a Transboundary Context (Espoo Convention)¹³⁸ – which contributes to customary international law as regards EIA,¹³⁹ is silent on whether its EIA obligations extend to cumulative effects:¹⁴⁰ the Convention appears to assume that national laws will supply EIA procedures.¹⁴¹ International jurisprudence is silent on the matter of cumulative effects, and international EIA scholarship tends to discuss it only in passing,¹⁴² noting the occasional presence of cumulative effects provisions in some international EIA instruments¹⁴³ and suggesting that their implementation may be weak.¹⁴⁴

The prevalence and operation of cumulative effects provisions in MEAs appear to be understudied, and this is an important gap. While some consider that international EIA obligations are not intended to be prescriptive,¹⁴⁵ we suggest that cumulative effects concepts are not mere procedural detail. Rather, they are a central factor that influences whether EIA can reach its theoretical potential (see Section 2): at minimum, cumulative effects concepts ought to inform debates about the content of international EIA obligations.

Analogous to our investigation of domestic laws, our study sought to understand which nations have consented to consider cumulative effects under the terms of an MEA, and the prevalence of those MEAs. We also reflect on the extent to which parties to these MEAs have adopted national cumulative effects provisions and implications for implementing the relevant MEAs and creating productive national-international links.

We searched for references to cumulative effects concepts in the text of MEAs housed on the International Environmental Agreements Database Project (University of Oregon (US)),¹⁴⁶ which is often used for large-scale environmental law research.¹⁴⁷ Similar limitations apply to those discussed above for the analysis at national level.¹⁴⁸ Appendix 1 further details our search methods. Appendix 2 provides agreement- and nation-specific information about entry into force, signature and ratification.

We found that 102 of the 195 nations investigated are bound by one or more of the 10 MEAs (or corresponding protocols) that are in force and contain a cumulative effects provision.¹⁴⁹ This expands the suite of nations bound to consider cumulative effects: 30 nations lack a cumulative effects provision in their national EIA law, but are bound by at least one MEA that includes such a provision.¹⁵⁰

MEAs adopt cumulative effects concepts in two forms. The first type applies to projects generally, mirroring the national EIA laws discussed in Section 3. Most notable is the Regional Agreement on Access to Information, Public Participation and Justice in Environmental Matters in Latin America and the Caribbean (Escazú Agreement),¹⁵¹ which entered into force in April 2021. Like the 1998 Convention on Access to Information, Public Participation in Decision-making and Access to Justice in Environmental Matters (Aarhus Convention),¹⁵² the Escazú Agreement applies Principle 10 of the 1992 Rio Declaration on Environment and Development, which covers public access to environmental information and public participation in decision-making processes.¹⁵³ In its relevant part, Article 7(17)(b) of the Escazú Agreement requires parties to make public ‘a description of the main environmental impacts of the project or activity and, as appropriate, the cumulative environmental impact’. A clear way to implement this article in national EIA law would be to adopt a CEA provision — our national legal study (Section 3) suggests that 12 of 33 eligible state parties presently lack any national cumulative effects provision,¹⁵⁴ demonstrating the potential influence of this Agreement.

The CEA provision in the Escazú Agreement may also influence other international EIA initiatives. These include Aarhus Convention guidance and the non-binding Bali Guidelines,¹⁵⁵ both of which cursorily address cumulative effects.¹⁵⁶ The Espoo Convention includes cumulative effect concepts only in the context of SEA rather than regarding EIA.¹⁵⁷

The second type of MEA containing cumulative effects provisions in the context of EIA applies to specific regional environments or contexts, such as marine and coastal environments; these include addressing marine pollution generally,¹⁵⁸ coastal zone management in the Mediterranean,¹⁵⁹ the biodiversity of the Black Sea,¹⁶⁰ the Caribbean,¹⁶¹ the Carpathian Mountains,¹⁶² the environment of Antarctica,¹⁶³ and the Baltic Sea.¹⁶⁴ The geographic limitation of these MEAs is arguably a strength, not a weakness: focusing on a specific mountain range or sea aligns with scientific aspirations that CEA occur at an ecologically relevant regional scale,¹⁶⁵ capturing the extent of a distinct environment that experiences adverse effects. Regional MEAs also offer benefits for intersecting national and international regimes through tiering,¹⁶⁶ and allow for the implementation of tailored thresholds of acceptable harm.¹⁶⁷ To fulfil this promise, regional MEAs should offer policy guidance on considering cumulative effects,¹⁶⁸ which addresses capacity building in the 30 nations that are bound by an international cumulative effects commitment but lack an equivalent national provision, in addition to settling any existing divergent national cumulative effects definitions and functions (Section 3.2).

4.2. Definitions and Functions of Cumulative Effects Concepts in Multilateral Environmental Agreements

Cumulative effects provisions are far less detailed and varied in MEAs than in national EIA laws. No relevant MEA defines ‘cumulative effects’, or ‘cumulative’ generally.¹⁶⁹ In terms of function, the vast majority of MEAs use cumulative effects concepts in the context of CEA as a required or suggested¹⁷⁰ component of the substantive environmental assessment,¹⁷¹ but apparently overlook the other functions identified in Section 3.2. An exception is the Protocol on Environmental Protection to the Antarctic Treaty.¹⁷² As well as requiring cumulative effects in a substantive environmental assessment,¹⁷³ it uses cumulative effects concepts to categorize areas for protection and proposed activities for control,¹⁷⁴ and inform a duty to consult and cooperate with other parties about activities.¹⁷⁵ By generally omitting cumulative effects concepts from screening, scoping and post-assessment processes, MEAs may have reduced opportunities to gain the theoretical benefits outlined in Sections 2.2 and 3.2. They may even contribute to confusing variation in these concepts vis-à-vis their national use.

More positively, contracting parties to an MEA that includes cumulative effects provisions could improve implementation of CEA by encouraging cooperative exchange of best practices between contracting parties, as others have suggested.¹⁷⁶ It would also be beneficial to identify best practices across MEAs, including ways to resolve different national approaches to CEA that may use different definitions and functions of cumulative effects concepts (Section 3.2).

4.3. Cumulative Effects Concepts between National and International Regimes: Five Areas of Intersection

National and international EIA regimes are mutually influential,¹⁷⁷ with several implications for cumulative effects provisions. Firstly, extensive national adoption of such provisions justifies greater consideration of cumulative effects concepts in articulating customary EIA obligations and general principles of law,¹⁷⁸ including required assessment procedures and the criteria relating to the significance of any likely adverse transboundary impact.¹⁷⁹

Secondly, national laws could provide ‘exemplars’ for MEAs¹⁸⁰ on formulating and implementing cumulative effects provisions.

Thirdly, and conversely, non-adoption of cumulative effects provisions in national law may affect how a state performs its international obligations relating to transboundary harm. At the extreme, in the absence of these provisions, a state may not consider a project to have transboundary effects or may overlook a project's potential to have a significant transboundary impact, in that considering a project in isolation may mean using a higher threshold for a finding of ‘significant’ impact.

Fourthly, MEAs that include cumulative effects concepts may influence national EIA practices, directly when they are implemented domestically,¹⁸¹ or indirectly if domestic EIA legislation engages international conventions as a decision-making consideration.¹⁸²

Fifthly, regional MEAs can influence national-level EIAs by formally linking or ‘tiering’ with cumulative effects provisions in national EIA laws, or encouraging more informal cooperation between contracting parties, who may require information from other states to complete CEAs. Valuable information, such as regionally adopted data standards¹⁸³ and thresholds of acceptable environmental harm,¹⁸⁴ can flow from regional plans to project assessments, and assessments can identify policy concerns for regional attention.¹⁸⁵ Though tiering is considered EIA best practice,¹⁸⁶ disagreements about methodology and a lack of good model examples obstruct implementation.¹⁸⁷ Regional MEAs could address these challenges by encouraging cross-regime learning through processes among contracting parties for formal deliberation, coordination about data sharing, agreed methods, and potential links to regional plans under MEAs.¹⁸⁸

5. CONCLUSION

Cumulative effects concepts are widely adopted in national laws – by at least 113 nations, 61% of nations that have national EIA laws. They are adopted internationally, to a degree previously unremarked, in 10 MEAs that bind 102 nations. This prevalence establishes a solid foundation for these regimes to deliver important theoretical benefits collectively in two ways: (i) as a ‘spotlight’ on value judgements tied to time and space, including thresholds of significance for environmental effects; (ii) as a wide-beam ‘lighthouse’ that illuminates the adverse effects of ‘other’ actions that contribute to the same types of harm as the proposed project, potentially triggering political agitation for wider environmental regulation.

From theoretical and practical legal perspectives, therefore, cumulative effects concepts have significant latent potential – perhaps transformational potential – to address cumulative environmental change through EIA regimes nationally and internationally. However, without better implementation, the latent potential of these laws to address cumulative environmental problems is likely to remain unrealized. Methods to encourage improved implementation are needed.

One potential challenge to implementation is the variety of definitions and functions of cumulative effects concepts in EIA processes among national jurisdictions. These differences pose challenges for forming clear, consistent, internationally and regionally applicable principles, and forming links between legal regimes. Differences also complicate compliance efforts by project proponents who operate across jurisdictions. These differences also limit the potential for useful diffusion of experience.

Cumulative effects provisions are understudied in a transnational context, and merit further research. A future research agenda could encompass empirical investigations of the benefits of cumulative effects provisions theorized here; experience in implementing treaty-based cumulative effects provisions; the implementation of guidelines for considering cumulative effects under MEAs; and bilateral approaches to EIA.¹⁸⁹ Empirical research on the practical significance of cumulative effects-inclusive EIA laws could also consider the number of assessments made under them and other measures of the strength of their implementation.¹⁹⁰ An investigation is also warranted of the flow of legal concepts between the national and international contexts (or the reverse), which appears to defy the caution of comparative lawyers against a ‘cut and paste’ approach to transplanting legal provisions.¹⁹¹ The roles of non-state actors also emerge as ripe for future exploration, including the potential role of advocacy organizations in political agitation in response to revelations emerging from cumulative effects provisions, and the extent to which financial institutions adopt cumulative effects concepts in their operational procedures and approaches to policy conditionality.¹⁹² While EIA law is unlikely to supply a complete solution for cumulative environmental change, lessons from cumulative effects concepts in diverse EIA contexts nationally and internationally will be an important part of the evolving legal picture.