Understanding the Effect of Climate Change on Human Migration – The Contribution of Mathematical and Conceptual Models




Perch-Nielsen, S.


Understanding the Effect of Climate Change on Human Migration – The Contribution of Mathematical and Conceptual Models



Academic dept

Department of Environmental Sciences – ETH Zürich


ETH – Zürich


In the last two decades, several researchers have predicted mass migrations as a consequence of climate change. They pictured millions of people fleeing from rising sea levels and drought, leading to serious consequences for both migrants and receiving societies. These images have fuelled recent research on climate change as a push factor for migration. This diploma thesis contributes to the understanding of this topic by (i) investigating the possibilities of connecting existing mathematical models of climate and migration; (ii) developing four conceptual models of the most important mechanisms linking climate change to migration; and (iii) assessing the contribution of both approaches. In a first stage, the possibility of linking existing mathematical models of climate and migration was investigated. An overview of models showed that the types of models used in climate and migration research are very different. Climate models are mostly complex three-dimensional and dynamic mathematical models, based on physical and chemical laws. In contrast, migration models, if mathematical at all, are of empirical nature and independent of time and space. In addition, migration studies are characterized by the fact each theory and model focuses on one specific type of migration. Significantly, the type of interest for this diploma thesis, i.e. migration pushed climatic hazards, has not been integrated into migration models. Therefore, exisiting climate and migration models cannot be simply linked. First, climate-related migration has to be studied in order to determine whether it is similar to other types of migration from which models could be adopted, or whether new migration models have to be created. Given a suitable migration model, the task of connecting such different components of natural and social system lies in the domain of Integrated Assessment Modelling. In this context, one model was found that mathematically connected climate change and migration. However, due to limitations of the sub-models and an accumulation of uncertainties through integration, such integrated models cannot fulfil the predictive function often expected from mathematical models. Thus, the value added in comparison to conceptual models was assumed moderate. Therefore, in a second stage, the emphasis was shifted to conceptual models as an alternative approach. An overview of previous research on this topic revealed that the most urgent need was to explicitly demonstrate the linkages between climate change and migration. As a result, conceptual models addressing these linkages were developed for four climatic hazards that are likely to be increased or intensified by climate change (sea level rise, floods, tropical cyclones and droughts). These models were termed “connection models” and proved successful in demonstrating the major (direct and indirect) impacts of the respective climatic hazard on the affected community. However, migration could not be explicitely linked to specific impacts but could only be connected to the climatic hazard in a very general way. This is due to a large knowledge gap regarding the extent and specific causes of migration in this context. Owing to this knowledge gap, it is presently not possible to make an overall assessment of the potential effect of climate change on migration. With regard to tropical cyclones and floods, the results suggest that these hazards cause only little permanent migration and that accordingly, climate change is not likely to trigger mass migrations. Drought, in contrast, can lead to considerable migration in some cases and to none in others. What factors determine the extent of migration is presently not known. Concerning sea level rise there is no knowledge base of migration on which to base an assessment. In thelight of the large amount of people potentially at risk of loosing their land and thus of migrating, high priority should be given to further research in this area. An important insight gained during the development of the connection models was the significance of vulnerability for the topic studied. While there are indications that climatic hazards can be a trigger for migration, it depends largely on the vulnerability of the community affected, whether such an indirect effect as migration in fact takes place. How vulnerable people are to climatic hazards is determined by a complex interaction of social, economic, and political processes. The connection models proposed in this diploma thesis proved an appropriate tool to give an overview of the relevant processes and to offer a framework to structure knowledge, facilitating the identification of knowledge gaps, the search for solutions and the communication between researchers from different disciplines. For future improvement, the models have to be developed in an interdisciplinary team and should adequately include vulnerability. The central and indispensable contribution of mathematical models in the entire climate-migration chain is seen to lie in the analysis of the underlying subjects and connections, particularly climate change, its effects on the climatic hazards, and the direct effects of these hazards.


Perch-Nielsen, S. (2004). Understanding the Effect of Climate Change on Human Migration – The Contribution of Mathematical and Conceptual Models. Zürich : ETH, Department of Environmental Sciences.