Spatial and absolute environmental sustainability assessment with a focus on marine eutrophication

Research output: Book/ReportPh.D. thesis


Environmental impacts caused by human activities threaten the planet's stability and habitability. The leading sustainability strategy to decouple environmental impacts from economic growth through increased eco-efficiency has failed to limit total environmental impacts. To reverse this development, we need to recognise Earth as a finite system with a constrained capacity. We should shift the focus from merely reducing environmental impacts per product to actual sustainable development. This calls for methods that can address environmental impacts in relation to the level of impacts the Earth can sustain, and not solely in relation to a reference product or activity. In the past decade, methods have emerged to support this type of assessments, collectively termed Absolute Environmental Sustainability Assessment (AESA) methods. These methods involve comparing the impacts or pressures of human activities to environmental boundaries that define the safe operating space (SOS). AESA methods can guide policymakers, the private sector, and citizens in sufficiently reducing environmental impacts.

However, knowledge gaps and limitations currently exist in AESA methods. Three key limitations are: 1) limited knowledge and guidance on how to define environmental sustainability boundaries, 2) none or low spatial resolution creates uncertainties due to regional variability of environmental processes, such as marine eutrophication, 3) limited knowledge on implications of different approaches to aggregate regional boundaries and their current states across spatial scales. This PhD project aims to contribute to advancing the field of AESA by reducing uncertainties and biases, focusing on defining environmental boundaries, spatial aggregation and marine eutrophication impacts. The thesis summarises the work of four scientific articles in four core chapters.

Chapter 2 revolves around approaches to define environmental sustainability boundaries, including a comprehensive review of existing boundary approaches. The literature review identified and categorised 110 original environmental sustainability boundaries into thirteen approaches used in assessments or policies. Along with assessing the boundary approaches, a framework to facilitate defining, analysing, and adopting environmental sustainability boundaries in assessments was developed. The framework's application to existing boundary approaches revealed shortcomings, notably that few approaches consider temporal variations and indicator interactions. Moreover, inconsistencies in managing value judgments within approaches that encompass multiple boundaries, such as the Planetary Boundaries, were identified, potentially introducing bias. Demonstrating the versatility of the developed framework, it was applied to identify suitable environmental boundaries for an AESA case. Its use not only increased transparency but also provided a systematic way to weigh the benefits and drawbacks of potential boundary approaches. In addition to the recommendations provided with the framework, future research should address limitations such as quantifying dynamic interactions between boundaries and increasing the spatial resolution where this is relevant.

Chapter 3 presents the development of a complete and spatially resolved marine eutrophication AESA method. The new method is a result of integrating recent advancements in marine eutrophication in LCIA and AESA methods, along with outputs from models representing state of the art of their fields. Beyond the modelling improvements related to the coupled methods, such as enhancing resolution in the inland fate component, the new method addresses additional existing limitations. These limitations include poor data on fate in the coastal compartment and insufficient spatial resolution for identifying local exceedances of SOS. Moreover, previously missing marine regions were included in the method by rerunning models underlying the combined methods. Additionally, the atmospheric fate component in the new method was improved by including denitrification and plant uptake of nitrogen deposition on land.

Chapter 4 covers a demonstration and validation of the new marine eutrophication AESA method described in Chapter 3 and developed in this PhD work. The method was validated against observational data on low oxygen levels in coastal bottom layers. By addressing limitations of existing methods, the new method shows an exceedance of SOS closer to observations than previous methods. The chapter also demonstrates how the method has the potential to improve AESAs related to nitrogen emissions by comparing its performance with an established method by applying both to a case study. Here, it was shown that the increased spatial resolution of the inland fate component is important as the spatial variability within river basins greatly influences the results. Moreover, by incorporating fate components previously omitted in existing methods in the air emission pathway, the new method has significantly reduced the uncertainties associated with modelling marine eutrophication impacts. While the method altogether substantially improves the basis for modelling marine eutrophication impacts and their SOS, limitations remain which should be addressed in future research. For instance, expanding the temporal scope of simulations in the source models for both inland and air fate components is recommended.

Chapter 5 explores the spatial aggregation of regional occupations of SOS and implications for the interpretation of AESA results. In a literature review, 23 studies spatially aggregating 41 regional environmental boundaries and their current state were identified. These were further classified into five spatial aggregation approaches and according to four types of adjustments. These approaches were labelled as moderate or conservative based on their value judgements about precaution and acceptance of regional transgressions. We found that prominent studies covering multiple environmental boundaries often employ different spatial aggregation approaches across their boundaries. This can introduce biases in comparisons across environmental processes of the global risks posed by current regional impacts. Through a case study applying the identified spatial aggregation approaches, it was demonstrated that the choice of spatial aggregation approach significantly influences the resulting occupation of global aggregated SOS and may affect conclusions about whether aggregated boundaries are exceeded. Future AESA methods should transparently communicate the underlying assumptions of their spatial aggregation approaches and avoid inconsistencies across environmental processes. Meanwhile, there is a need for a better scientific understanding of the mechanisms by which transgressions of regional SOS can propagate to global effects.

Altogether, this PhD thesis contributes to advancing the field of AESA, by proposing how to consistently manage value judgements in approaches to define boundaries and in the spatial aggregation of occupation of regional SOS. Moreover, an improved and comprehensive absolute impact assessment method for marine eutrophication is provided, also contributing to the underlying field of life cycle assessment. These outputs, decreasing uncertainty and the risk of introducing biases, improve the basis for decision-making for sufficiently reducing environmental pressures to levels within the SOS and hence support the transition towards actual sustainable development.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages195
Publication statusPublished - 2023


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