Migration and justice in the era of sustainable development goals: a conceptual framework

Migration and mobility are major characteristics of societies worldwide. The reasons for and pathways of migrations vary, as do perceptions of migration. Political debates are often organised normatively: the debate on the sustainable development goals presents migration foremost as a development issue resulting from global inequalities. The problems faced by particular migrants, and what a more sustainable approach to migration would look like are, therefore, often lost in political debates. We aim to address those gaps: the article conceptualizes, based on established academic debates, how sustainability in migration can be addressed systematically, which aspects are important for a more sustainable migration process and which trade-offs and injustices exist from several perspectives. We create a conceptual framework of sustainability in migration processes, building on the concepts of inter- and intragenerational justice, commonly accepted as the core of the sustainability concept. We apply this conceptual framework to empirical findings on labour migration and multilocality in Kyrgyzstan. The case enables consideration of the nested system effects of scale and translocality. This research is novel because it bridges the divided literature on migration, justice and sustainability, integrates theoretical and empirical insights and provokes a debate on which kind of migration we want to achieve.

Worldwide, more than a billion people, one out of every seven, are estimated to be one of the many types of migrants. Among them, 740 million are considered internal 1 migrants, and 272 million are counted as international 2 migrants. 3 Seventy-four percent are of working age (20-64 years) (IOM 2020). While mobility and migration have become major markers of our lives, they are characterised by deep inequalities. For some, migration is a pathway to opportunities and personal growth, e.g., by improved educational and professional opportunities. For others, migration is an experience of forced separation, loss and marginalisation, e.g., if migration is forced by external factors such as lack of work and income. Such contrasting experiences can also occur close to one another in the same individual's life, or in a family constellation across different generations, where one works under precarious conditions as temporary worker so family members might benefit from remittances. Similarly, opportunities to be mobile, and having a choice whether to migrate, where and under what conditions are also not equally distributed, but rather privileges reserved for a minority of people 1 An internal migrant is a person who moves within the boundaries of one country, but beyond administrative borders (UN DESA 2017a). 2 An international migrant is "a person who changes his/her country of usual residence". (Recommendations on Statistics of International Migration, Revision 1 (1998) para. 32). The UN DESA definition excludes movements that are due to "recreation, holiday, visits to friends and relatives, business, medical treatment or religious pilgrimages" (UN DESA 1998in IOM 2020. 3 The data bases on the UN DESA (2019) report "World Population Prospects 2019". The estimates origin from data sources in 235 countries worldwide which can be accessed online at: https:// popul ation. un. org/ wpp/ DataS ources (last access 13.11.2020).
worldwide. For example, (im)migration opportunities often depend on bilateral agreements, which are particularly controlled by wealthier countries, such as the European Union (Adepoju et al. 2010;Delgado Wise et al. 2013;Delgado Wise 2020).
During recent years, efforts have been made to acknowledge the diverse nature of migration (drivers) in reality. Also, international policies have taken up migration as a topic in relation to sustainable development debates (Lee et al. 2014;Thieme and Ghimire 2014;UN DESA 2017b). Nijenhuis and Leung (2017) report the first acknowledgement of the connection between development and migration in the 1994 UN Population and Development conference in Cairo, with subsequent UN actions following after 2000. While the topic 'migration' was still rarely present in the millennium development goals (MDGs), the topic has gained currency in the debates on the sustainable development goals (SDGs) (UN 2015), where "11 out of 17 goals contain targets and indicators that are relevant to migration" (Nijenhuis and Leung 2017, p. 53). Policymakers are increasingly addressing migration and development issues in the context of sustainability debates. Yet scholars criticize a hegemonic narrative that policies retain, with an implicit assumption of sedentary lives and only particular forms of orderly migration being relevant for sustainable development (Adger et al. 2019). That narrative still side-lines persisting inequalities in processes of neoliberal globalization (Delgado Wise et al. 2013). There is a need to consider different scales by not only integrating perspectives on national scale for countries of origin and destination, but also embedding migration processes in broader processes of neoliberal globalisation and resulting inequalities, and simultaneously addressing the perspective of individual migrants and families. This represents the point of origin for our paper. With the SDGs as current major political goals, it seems urgent to discuss what sustainability actually means in empirical cases.
Is there something akin to "sustainable migration"? How do we establish systematically what sustainability means for migration? Which aspects of justice are important during migration processes and which conflicting perspectives and trade-offs exist? These questions have resulted in the research question addressed in the present article: How can one systematically approach sustainability (trade-offs) in empirical migration processes? We propose a conceptual frame to evaluate aspects and trade-offs concerning the justice and consequently sustainability of a migration process. We thereby start a debate on what sustainability can mean for diverse migration processes, also enabling a consideration of questions and implications for policy debates. Black and Gent's (2006) conception of sustainable return inspired our discussion on what we aim to achieve in the present work. They propose a conceptual framework to assess the influences return migration has on different societal actors, and how this migration cycle can be more sustainable. Hewing close to this, our work aims to provide an analytical framework or "tool box" to systematically grasp the different aspects influencing the quality of migration processes, and how these aspects influence and partially clash across scale-for example individual, generational and national scales (trade-offs). To operationalize and systematize sustainability aspects in migration, we use the commonly accepted core of sustainability, the concepts of inter-and intragenerational justice (Anderson et al. 2016;Burger and Christen 2011;Christen and Schmidt 2012;Jahnke and Nutzinger 2003;Langhelle 2000;Ott 2003) as analytical lenses. We further integrate the perspective of different scales (e.g. Swyngedouw 2004) and places (e.g. Brickell and Datta 2011) and thereby understand processes of migration as always tied to different localities and structures on international, national, and local scale such as community, family and individual. Those scales are neither distinct nor hierarchical entities but are mutually constituted (e.g. Swyngedouw 2004), and grounded in embodied and material localities connecting different sites (e.g. Brickell and Datta 2011; Greiner and Sakdapolrak 2013).
With longstanding research experience in migration research (Thieme 2014a(Thieme , b, 2008) and sustainability conceptualizations (Janker et al. , 2019Janker 2020), we find that analytical frameworks should bridge the theory and empiricism divide present in many sustainability debates. We, therefore, "test" our framework on own empirical case work, and link it to other existing scholarly work.
We also offer a bridge between migration studies and sustainability studies. Following Rawls' conception of justice (Boone 2010;Rawls 1999), the justice concept serves particularly well as the core of our sustainability framework, allowing us to raise normative questions that represent the multitude of perspectives on what sustainability could mean in the migration context.
The paper proceeds as follows: we start by presenting the state of the art on how sustainability and migration are debated. After highlighting how justice and sustainability are conceptually related, we demonstrate how to utilize Rawls' (1999) theory of justice to assess migration processes. We apply the resulting analytical framework to the empirical field research of one of the authors on lowskilled labour migration in Kyrgyzstan. We find distinct justice issues and conflicts in these cases and discuss them in the broader migration context. As migration case studies vary strongly, the justice results cannot serve as universal sustainability aspects. But the case studies confirm that our conceptual framework presents a pathway to unveil justice aspects promoting and hindering the sustainability 1 3 of migration processes and it shows potential trade-offs between different perspectives.

Migration, sustainability and justice: state of the art
In the following, we provide a short overview how the topics of migration and sustainability, as well as sustainability and justice, have been addressed in contemporary debates.

Migration and sustainability debates
The affirmation of sustainable development registered on the international political agenda in 2015 through the SDGs, with 11 out of 17 goals explicitly relevant to migration (UN 2019). Attached to these 11 goals are many indicators addressing conditions of migration (Adger et al. 2019). Additionally, international documents such as the Global Compact for Safe, Orderly and Regular Migration (UN 2018) and the Issues Brief on Migration and sustainable development (UNCSD 2012) analyse problems associated with migration-for either host or receiving countries, or for migrating individuals themselves. Within development discourses, assessments of the relationship between migration and development have varied over time. For sending countries, migration has long been seen as failure of internal development, where lack of employment and infrastructure forces migrants to leave, causing 'brain drain' and preventing innovation in home countries (e.g. Docquier et al. 2007;de Haas 2010). In receiving states, the economic contribution of migrants has tended to be appreciated, but a perception of immigration pressure has led to increasingly restrictive and selective migration policies (Faist 2008;Nyberg-Sørensen et al. 2002). During the last 2 decades, policy debates on migration have again become optimistic. Discussions of 'brain and manpower drain' have shifted to notions of 'globalisation of labour' and 'brain circulation': there is a change in perception of migrants, from mere low-skilled labourers and hence financial remitters, to people with skills and knowledge (social remittances) and agents conveying these remittances, often to home and to some extent to the host country, as well (De Haas 2010;Levitt and Lamba-Nieves 2011). At the same time, we find polarized and politicized debates about increasing 'irregular' migration, 'refugee crises', and 'bogus' asylum-seeking. Authorities react with enforcement of sovereign powers, controlling human mobility and residence of noncitizens within national territories (e.g. de Genova 2002;Anderson 2011). Therefore, despite a certain positive acknowledgement of migration as an integral part of society, migration is still overall framed as development issue causing problems for either host or receiving countries (Pécoud 2015;Røpke 2006), and challenges accompanying migration are highlighted in the international political debate on sustainable development (Al-Husban and Adams 2016; McDowell and de Haan 2017). A debate on migration and global inequalities has thus also been taken up in scholarly work on SDGs (Hackl 2018). Scholars have criticized the framing of migration within the SDGs as territorially fixated Nijenhuis and Leung 2017). They have questioned the gendered character and experiences of migration as underrepresented (Gammage and Stevanovic 2018;Hennebry et al. 2018;Holliday et al. 2019) and describe how irregularity (Elias and Holliday 2018) and discrimination (Thompson and Walton-Roberts 2018) have been inadequately addressed by the global development goals. Adger et al. (2019) fundamentally question the representation of migration in the SDGs, as still seeing migration as an exception rather than a normality. However, apart from addressing the SDG policy discourses, only few authors (Al-Husban and Adams 2016; Jackson et al. 2008;Lewis and Runsten 2008) have conceptually linked the migration and sustainability debates. For example, Al-Husban and Adams (2016) connect refugees and sustainability thinking, while Jackson et al. (2008) portray amenity migration as part of sustainable regional development. Winkels and Adger (2002) and Thieme and Siegmann (2010) analyse the role of social capital and vulnerabilities of livelihoods in the context of migration; Lewis and Runsten (2008) connect migration and sustainability issues in the context of the production of fair trade coffee.
Recurring migration issues, such as labour rights violations, marginalized living conditions, continuing inequalities in access to free mobility (UN 2018) and potentials to improve migration conditions contained in the SDG implementation process are certainly highly relevant. Nonetheless, an overall vision or a framework to analyze what makes migration in/just and potentially sustainable and where trade-offs lie is rarely discussed. Individual migrants' rights and the effects of migration on a national scale are both under debate, but often separated from each other (e.g. Delgado Wise et al. 2013; Delgado Wise 2020). We therefore, want to contribute to a more holistic discussion on the sustainability of migration processes, by integrating perspectives from different scales and places as well as intergenerational aspects during migration processes in our conceptual framework.

Sustainability and justice
As a reaction to the SDGs, studies from a wide range of disciplines have arisen (e.g., Christen and Schmidt 2012;Frantzeskaki et al. 2012;Hopwood et al. 2005;Jahnke and Nutzinger 2003;Kajikawa et al. 2014;Keitsch 2018;Holden et al. 2017) that conceptualize sustainability from a theoretical point of view. Within the diversity of conceptualizations, scholars mainly agree on the definition of sustainable development by the World Commission on the Environment and Development of the UN (WCED) (WCED 1987, p. 24) as foundational. This definition refers to the ability of humanity to fulfil the needs of present generations without affecting future generations' chances at a decent life. It, therefore, contains two normative imperatives, often called intergenerational and intragenerational justice (Hopwood et al. 2005;Keitsch 2018;Langhelle 2000;Soini and Birkeland 2014). Intergenerational justice, in general terms, refers to the fulfilment of needs between present and future generations (Barry 1997;Roemer 2005), whereas intragenerational justice means justice for all members of a society (Padilla 2002). The latter can imply justice for every person in a society, but also for all countries across the globe. As one or both of these two imperatives represent the common element of sustainability in most policy and scientific debates, the question of justice seems central to better understanding the notion of sustainability. However, few sustainability scholars (Anderson et al. 2016;Burger and Christen 2011;Jahnke and Nutzinger 2003;Langhelle 2000;Ott 2003) have drawn on the theoretical foundations of both types of justice to develop an analytical sustainability framework (Christen and Schmidt 2012), although a large portion of the sustainability literature does mention the concepts of justice or equity at some point. 4 We agree, however, with scholars such as Klinsky and Golub (2016) who argue that the integration of both discourses is needed for a more holistic approach to sustainability. For example, the systems thinking inherent in the sustainability literature can lead to multi-scale, multidimensional, and cross-generational concepts that are transferable to multiple regions, whereas environmental justice is more proactive and case-study specific (Boone 2010). On the other hand, the action-oriented nature of the justice conception (Boone 2010) and the inherent normativity of this concept can show where context-specific challenges exist regarding the sustainability of migration processes. Seeing inter-and intragenerational justice as the core of sustainability (e.g. Glotzbach and Baumgärtner 2012; Vasconcellos Oliveira 2018; Baykara-Krumme and Fokkema 2019), we utilize these concepts as analytical lenses to approach what sustainability may mean in migration processes and what trade-offs potentially occur.
The central ideas of sustainability and of justice are highly strongly aligned: the major aspiration is the good life for all, with the moral legitimation being the fairness principle (Spangenberg 2018). According to Rawls (1999), it is up to social systems and institutions to define the concept of right and what justice means, and how fairness is institutionally implemented. Specifying his idea, Rawls describes distributive, or intragenerational justice as the main component of justice within a fairness regime: "All social values-liberty and opportunity, income and wealth, and the social bases of self-respect-are to be distributed equally unless an unequal distribution of any, or all, of these values is to everyone's advantage" (Rawls 1999, p. 54). "Those who have gained more must do so", he adds "on terms that are justifiable to those who have gained the least" (Rawls 1999, p. 131). Hence, the distribution of goods must be fair for everyone, depending on how much they contribute to a just society. Rawls also addresses intergenerational justice as a central aspect of a just society: "(…) persons in different generations have duties and obligations to one another just as contemporaries do. The present generation cannot do as it pleases but is bound by the principles that would be chosen in the original position to define justice between persons at different moments of time" (Rawls 1999, p. 258). Rawls' understanding of societal justice is closely related to the commonly accepted sustainability definition, with distributive or intergenerational justice at its heart, and the further consideration of future generations. Hence, our analytical frame uses the two types of justice as a basis for classification to determine just and unjust aspects of migration, and trade-offs, with a particular emphasis on multiple generations and societal scales. We are, therefore, building on the Rawlsian tradition and extending it to migration cases, each within their specific normative regimes. Relying on the extensive scholarly debates outlined above, we perceive the justice perspective as one crucial way to approach sustainability in migration.

Conceptual approach
In the following section, we explain the construction of our conceptual framework to analyse justice and sustainability in migration processes. Based on the section about migration studies, we first define the different levels of our research object, what we call a migration system. Second, we introduce the analytical lens of inter-and intragenerational justice, our "sustainability metric" for these migration systems. The framework will be applied thereafter and "tested" on empirical cases based on one author's empirical work and related scholarly debates.

3
First, migration processes are defined as the point of origin for our framework. Migration, here, means a (temporary) physical relocation of a person (cf. Black and Gent 2006). Our framework, therefore, starts from an individual perspective of a person migrating (migrant), who is moving through different stages of migration. Those stages include pre-migration: the decision-making process and preparation; the migration process, including departure, travel and transit and arrival; the period of remaining in the host context; and eventually a stage of return. Return can be interpreted in various ways, as a definite return back to the place of origin, but also temporary return, or even going elsewhere (further migration) (Thieme 2014c).
Second, starting from an individual perspective, we integrate different scales and how they are connected, which altogether can be called a 'nested migration system'. Processes and structures affecting individuals, families (or other households), communities, national and international scales are neither distinct nor hierarchical entities but are mutually constituted, produced and contested (Swyngedouw 2004, p. 34). These aspects have been also taken up more recently Household and family members live in different places, so how they sustain their relationships between places, and the flow of goods, money, information, values and ideas between those places strongly affect the migration process and its potentials, but also its vulnerabilities (Black and Gent 2006;Levitt and Lamba-Nieves 2011;Zoomers 2018). We hence differentiate the migration effects schematically between the migrant's place of origin and new places of work and living (place of destination) and well as the connections between the different places (acknowledging that more than two places could be involved in migration processes (e.g., Thieme and Murzakulova 2019).
After establishing the framework with all its levels ( Fig. 1)-what one can call the nested, translocal migration system-the 'sustainability metric' is introduced: inter-and intragenerational justice. Applying this sustainability metric means identifying justices and injustices for (1) the individual migration process, (2) as well as for the household, the region(s) and nation(s) (only aspects affected by the migration process), and (3) both for the place of origin and the place of destination. Intragenerational justice or distributive justice in the framework means that everyone, independent of national borders, should have the same rights and duties (Rawls 1999). For the sustainability of the migration system, this would imply the premise that each migrant and migration system actor should be treated equally fairly or have the same rights and conditions during the entire migration process, independent of the place of living and origin. Intergenerational justice, which explicitly focuses on justice between generations (such as between parents and children, or for future generations) should be guaranteed as well. This means that conditions fostering justice should be enhanced over time (Bornemann and Strassheim 2019), such as for children of migrants, or future generations of a society.
However, with the levels of a nested system and at least two places being connected through migration, trade-off problems appear. While, for example justice among individuals can be increased for migrants moving abroad for better employment conditions, persons in the household of a different generation may be adversely affected (e.g. lack of labour, emotional distress), therefore, diminishing intergenerational justice. Particularly in cases of labour migration, justice is often problematic, because migrants often experience marginalisation and precarity, whereas their households may gain from the remittances (Thieme 2014a). These tradeoffs are also captured by our framework.
The resulting conceptual framework, as applied to the empirical cases, is shown in Fig. 2. We apply this sustainability framework or "tool" to empirical cases to "test" its applicability. It should be acknowledged that we do not see this conceptual framework as a one-size-fits-all solution to compare individual migration cases. We consider it a pathway to systematically approach what might be sustainability in specific cases of migration processes by showing justices, injustices and trade-offs fostering or hindering the sustainability of migration processes.

In/justices and migration across scales and places: empirical examples
In the following section, we exemplify our analytical framework with empirical work. We start from longstanding research of one of the authors 5 on low-skilled labour migration and multilocality in Kyrgyzstan (Thieme), which we extend by and relate to other scholarly work. We thereby exemplify the diversity and complexity of individual migration processes as well as their effects on actors beyond nested system scales. We acknowledge that we cannot take all different forms of migration into consideration, but that we explore the possibilities to highlight aspects of intra-and intergenerational justice in the places of destination and origin, and, therefore, illuminate a new pathway to approach sustainability in migration. Our sustainability framework does not provide a final definition of sustainability beyond the justices/injustices in each empirical example but it provides a pathway which can be applied to a high variety of Fig. 2 Framework to assess intra-and inter-generational justice of a nested migration system to approach the sustainability of migration processes migration cases. Because of the complexity of the empirical cases, we can only present a summarized version of the main forms of justice and injustice in the following section, but we will draw particular attention to the connections of different scales and places. The chapter is structured as follows: we explain the nested migration system with all scales of labour migration in Kyrgyzstan, schematically differentiated into first intragenerational justice, both at the place of origin and the place of destination and second, intergenerational justice, in regards to the effects on the country of origin. Our findings are related to similar studies in the international context throughout this chapter.

Labour migration from Kyrgyzstan (and beyond) as nested migration system
If remittances are viewed as a percentage of GDP, with 33.6% Kyrgyzstan is among the top five remittance-receiving countries worldwide (IOM 2019, p. 36). According to official statistics (IOM 2019), about 13% of Kyrgyzstan's populations seeks employment abroad, mainly in the neighbouring countries of Kazakhstan and Russia. Those figures represent a common global characteristic of labour migration, where mobility of people is mainly regional and driven by search for a more secure and better income. Remittances are sent and migrants sometimes return, but often also put down roots in other places (e.g. Zoomers 2018; Thieme 2008). Livelihoods become multilocal, responsibilities more complex, and inter-and intragenerational justice issues cut across different places within and across national borders.

Intragenerational justice in Kyrgyz labour migration
Migration can be an opportunity to fulfil aspirations, provide access to better education, escape from family obligations such as early marriage or just to 'explore the world'. At the centre is the desire for better job opportunities and the possibility to secure an income for one's own and the family, due to a lack of paid work in rural areas. What is officially categorised as freely chosen "economic migration" dismantles high vulnerabilities, potential exploitation and elements of force (Delgado Wise et al. 2013). Achieving sufficient income or an improved working environment that suits the skills of the migrant is not guaranteed. On the contrary, own empirical work has shown that many individual migrants who move to Kazakhstan and Russia in the hope of work and improved income to provide for their families face injustices in the new place of work and living, such as precarious working and living conditions, lack of social security and low wages. If the migrants' work is irregular, they face the daily risk of deportation and can experience high pressure from authorities and workplaces. Many migrant workers of middle age experience a devaluation of their earlier professional skills, which persist for the rest of their working lives. Depending on their work and living conditions, the migrants have little opportunity to bring family members, including children, to join them, and thus experience a longterm separation from children and close family members (Thieme 2014a).
This example stands for what Delgado Wise et al. (2013) discuss as dialects of unequal development, forced migration, and human rights in relation to neoliberal globalisation. Unequal development in Kyrgyzstan, as in all former Soviet (and all socialist) countries is embedded in a political transformation process resulting in multiple changes and continuities, a blending of persisting socialist elements and an internalisation of neoliberal doctrine (Hatcher and Thieme 2015). Part of this process was the incorporation of the socialist countries and China in the global economy, resulting in aggravated disparities within and between countries and a large available workforce with new hierarchies and divisions of labour, as well as people who benefit from mobility and others who do not (Delgado Wise 2020). Those asymmetries within and between countries can, therefore, not be described with a unidirectional understanding of international migration but have to take into consideration a complex system of multi-or translocality of livelihoods, connecting rural and urban spaces within and across countries (Schmidt-Kallert 2009; Thieme 2008; Brickell and Datta 2011). Political and economic reforms in Central Asia have also been highly gendered. Women were not only more affected by declining public infrastructure such as public schools, health care and social services (Thieme 2014a, b), but also increasingly migrated in search of work (Thieme 2014c). In so doing, they became part of the now globally equal number of women and men migrating for work (Rodriguez and Schwenken 2013; Holliday et al. 2019).
Under conditions of precariousness, the place of destination may profit at the community and national scale. Migrant workers contribute to a decrease in labour shortages, to brain and workforce gain and to diminishing labour costs, particularly in low-paid segments of the workforce (Delgado Wise et al. 2013) such as agriculture, service sectors, care and domestic work (e.g. Ambrosini 2015). Even if those migrating are well skilled and are able to fulfil their professional aspirations, countries receive workers with their skills without investing in professional education, a fact particularly debated for, e.g., health care not only in Central Asia but around the globe (e.g. Bradby 2014; Ammann et al. 2020). This outflux of skilled workers may have adverse effects on the sending countries' domestic population.
In the best case, the mobility of workers also brings accompanying technical, economic, and social innovation from the knowledge and experience of migrants. In some cases, migrants also develop inventive economic niches and create new jobs. At the same time, migration from Kyrgyzstan also makes evident how many people are selfemployed in the whole region, straddling between formality, informality and uncertainty, often running several businesses at once (Alff 2015(Alff , 2016Berner et al. 2012). In regions with a population deficit or decreasing population, immigration is also a way to ensure critical population size to maintain social services and generate an influx of economic resources and investments. Migrants, therefore, contribute to the national economic and social development of a country, because they are an important workforce and pay taxes.
On the other hand, labour migration can lead to social segregation and diminished possibilities for integration (Delgado Wise et al. 2013). The co-author's own fieldwork has shown how many people from Kyrgyzstan face a lack of acceptance or even discrimination in Russia and Kazakhstan, fostered by national policies restricting residency and work permissions as well as societal participation. Immigration can also cause debates on pressure on available jobs and salaries, other (natural) resources, and social and technical infrastructure, which may raise potential for social conflicts and exacerbate social and economic disparities.
For the place of origin, effects on the household scale mostly concern family members, those not being part of the migration process. Children and grandparents, especially, tend to remain at the place of origin, and often receive remittances essential to secure their livelihoods. In Kyrgyzstan, and also worldwide, large portions of the remittances are invested in family subsistence (e.g. Schoch et al. 2010;Thieme and Ghimire 2014;Hoang and Yeoh 2015;Kakhkharov et al. 2020). Received money goes into better nutrition and medical care, is invested in a car, housing and livestock, as well as education for children or to repay existing debts. While financial problems may be alleviated, emotional stresses such as separation issues for children and parents are difficult to balance, as has been shown during research in Kyrgyzstan and elsewhere (e.g. Madianou and Miller 2011;Mazzucato et al. 2017).
Similar to household-scale effects, remittances can contribute to improve conditions and facilitate investment in community projects (e.g. schools, food depots, religious sites, infrastructure, roads etc.), and hence benefit the local community of the place of origin-particularly if family members remain abroad. Social remittances include knowledge circulation upon return, and potential technical, social and economic innovation.
From a critical perspective, we argue that in countries with high remittances, new disparities are created in communities when, for example, the poorest usually do not migrate. From an international and national perspective discourses about remittances are also seen very critically. National and international policies promoting migrants as development agents and intentions to manage remittances as more productive reduces described complex translocal practices to development logics (Faist 2008;Thieme and Ghimire 2014;Schwertl 2016). Misleading "win-win" rhetoric depoliticises migration and conceals how neoliberal governments and global hierarchies enforce severe restrictions for many migrant workers, and that international companies and receiving states benefit the most (Delgado Wise et al. 2013;Geiger and Pécoud 2012;Kunz 2011).
If migrants do not return for a longer time period, however, the community of origin faces a loss of labour and brain drain, or imbalance in the remaining population in terms of gender and age (mostly women, children, and elderly people). A lack of labour can further increase the workload for those remaining, impair agricultural production and lead to land abandonment (e.g. Radel et al. 2019). Migration may also lead to a long-term population shrinkage and jeopardizes delivery and maintenance of social services and infrastructure in sending communities, an impact that as has been also found in rural areas of Kyrgyzstan.
Governments also have to take less responsibility for economic development, as emigration causes a high monetary influx, thus compensating for the loss of younger workers and unsuccessful economic sectors. Or, to the contrary, emigration could be presented as negative for the domestic economy and thus reduce political support, advancing policies to prevent dual citizenship, or eliminate rights to keep land or participate in an international framework such as transferable social security.

Intergenerational justice in labour migration
Intergenerational justice means the fulfilment of needs across all present generations and future generations. Looking at intergenerational justice, we have to consider that most labour migrants are of working age, between 20 and 55 years. They, therefore, include age groups spanning two generations (Thieme 2014a).
One author's own research on multilocal livelihoods in Kyrgyzstan has shown that in most cases the migrants' young children (up to school age), elderly relatives, and one working-age son stay at the place of origin. Justice effects of migration at the place of origin of the migrants are often connected to the living conditions of the generations staying at home. Today, two generations of labour migrants exist: In Kyrgyzstan, the older migrant generation (a), who grew up in Soviet times and now are approximately 45-60 years old, often experienced a devaluation of education and professional skills and experience, particularly through migrating for labour, resulting in social downward mobility in professional terms. Many took on lower qualified jobs abroad to secure their families' livelihoods at home and to be able to invest in education and a better future for their children. The parents of these older-generation migrants have become grandparents and take care of their grandchildren as long as they can. If there are several siblings that can migrate, some typically leave for migration and one family member's household, such as the youngest son and his wife, could be obliged to stay and take care of all the other family members. There is also a younger migrant generation, around the age of 20-30 years (b) that may have somewhat better education and may not experience the same devaluation as the "original labour migrants". But also these younger migrants show ambivalences of multi-or translocal family arrangements due to labour as well as distinct local and regional differences. All family members have to (re)negotiate their positions and needs, which can open up opportunities but also create and reinforce roles, identities and power imbalances (Thieme 2008(Thieme , 2014aHoang and Yeoh 2015;Sharma 2018;Uprety 2020).
At the community and national scales of the place of origin, migration encourages further migration. The embeddedness of migration in social networks is not particular for the case of Kyrgyzstan, but rather has been widely acknowledged (Tilly and Brown 1967;Boyd 1989;Pries 1999;Thieme 2008). While facilitating migration, networks have ambivalent roles. They can be exclusive and also hinder social mobility by facilitating handing over jobs and related structural inequalities (e.g. Thieme 2008). Benefits of these networks could be knowledge and ideas to establish economic activities and thus provide the opportunity for future generations to be able to stay in the country. Similarly, they may establish structures that support labour migration and ensure better migration conditions for future migrant generations, and facilitate circulation of knowledge and experiences. Furthermore, kin-and friendship-networkbased mobility has in many cases accorded with a professionalisation of services and with development of migration infrastructures comprised of technologies, institutions and actors facilitating and conditioning mobility (Xiang and Lindquist 2014;p. 124;Gammeltoft-Hansen and Sørensen 2013;Thieme 2017;Uprety 2020).
For the place of destination, future generations may profit from the increased availability of labour and economic income through a flourishing economy and, in the best case, also a more open society. However, these effects are not causal and thus simply illustrate a positive scenario. As outlined above, such increased economic wealth has, then, been partly built on underpaid and undervalued workers, often but not always with a migration background, and on subsequent social exclusion processes which could even worsen the preconditions for future migrants (e.g. Delgado

Discussion
The entry point of the paper was the question of how to systematically approach aspects and trade-offs regarding justice and consequently sustainability of a migration process.
The empirical case work shows multiple instances of justice and injustice in migration processes. To approach sustainability in migration, avenues for justice, such as enhanced living and working conditions, should be fostered, and injustices, such as adverse labour conditions for migrants, should be diminished. The framework sets itself apart from policy frames such as the SDGs but rather relates conceptual debates with empirical findings allowing the researcher to analyse and highlight potential opportunities, challenges, risks and trade-offs in migration processes. However, those findings can certainly inform political debates on the implementation of the SDGs. As the cases show, issues are complex, when explored on several scales and across different places, which are often not adequately equally considered by international political frameworks.
Having presented the conceptual frame and applications to empirical examples, we now turn to discuss questions of trade-offs between (in)justices, and hence to the sustainability of migration along three lines: Justice across scales from individuals to nation states; international migration and trade-offs between countries; and intergenerational justice and sustainability of migration over time.

Justice across scales from individuals to nation states
The fairness premise behind the empirical examples of labour migration provided is one of achieving better working and living conditions. The main justice trade-off is the discrepancy between the migrants' well-being and the wellbeing of the household (or family) in the place of origin. If the migration is successful, justice means better working conditions for the migrant, and increased income and enhanced opportunities for the family or household-such as enhanced opportunities for education, social networks and many more advantages. However, on the individual and household scale, these effects often cannot be observed. Low-skilled migrants, especially, face difficulties entering another countries' economic sector, often experiencing marginalized working and living conditions, and even repression. In these cases, justice for the individual is decreased through the migration process. On the other hand, migration influences the older and younger generations remaining 'at home'. Typically, older generations such as the parents take care of the migrant's children, and thus are ascribed responsibilities of another generation. Children finally, can suffer emotionally from the separation from their parents.
While personal aspirations are an important aspect of justice at the individual scale, labour demand and economically unequal conditions for the migrant compared to the permanent population set the (justice) context for migration at regional and national scales. If both countries benefit from migration processes, and equally improve economic and knowledge capacities (through knowledge/work import and knowledge/financial circulation), one could speak of justice in the migration process. But challenges such as decreased labour potential in the country of origin and migrants' precarious working and living conditions in the country of destination create justice challenges, and potentially even increased dependency and prolonged inequalities. However, decreasing dependencies between countries does not necessarily contribute to fulfilling individual aspirations: for example, improving socio-economic conditions of the country of origin might not necessarily lead to less mobility of people (and, therefore, keeping human resources in the country of origin) but could instead lead to more migration opportunities. People could migrate with less pressure and exposure to risks, more seed capital and better information, fulfilling aspirations rather than or as well as pure livelihood needs.
Further, there are trade-offs between the individual and the national scales. For example, migrants may be appreciated in the place of destination (national effects) because they work for wages below the national average, and face violations of labour and human rights, and precarious working and living conditions (individual effects). Then, justice on the individual level does not correspond to the national level. A further justice issue is an issue of political decisions in terms of access to this kind of mobility, and to long-term migration. People from the global South, particularly, have much higher entry barriers to and constraining conditions in both temporary and permanent international migration.
Some of these issues are already being discussed in the migration livelihoods literature (e.g., McDowell and de Haan 2017;Thieme 2008). The debate on the losses and gains of migration should continue, nonetheless, to enhance the framing conditions of migration and individual choice. But at the moment, that debate predominantly takes place at the national scale, and the individual experiences of justice and injustice are often outweighed by the economic benefits and losses of countries. The utilitarian argument of the majority benefiting at the expense of individuals is still given too much weight; trade-offs by individual households, therefore, remain a 'private matter'.
At the national scale, migration has often been explained as problem of global territorial inequality that people attempt to overcome by relocating from one place to another (Hackl 2018;Israel and Frenkel 2018). Therefore, national and international stakeholders should discuss how these inequalities manifest and how they can be overcome, as well (Nijenhuis and Leung 2017). Adger et al. (2019, p. 442) further propose, "incorporating realistic scientific insights on migration and mobility would (…) identify the conditions under which migration could contribute to positive outcomes for many arenas of sustainability". Further, we should consider that people may not want to migrate, and should also have the right and opportunity to stay: to not migrate (Delegado Wise et al. 2013;Cook and Butz 2019), and still live fulfilled lives. Our framework can provide insights on conflicts and trade-offs relevant for this debate, by showing the specific effects of different types of migration processes at and between different sclaes.

International migration justice and trade-offs between countries
In international migration debates, responsibility is often attributed to national governments. In addition, Rawls' justice principles are based on the premises of institutions such as the state enabling justice. While national governments should take on this responsibility, the reality of migration is complex, with multiple affected locations beyond national borders. Binational and international agreements are missing, for example concerning protection of migrants in terms of labour rights, social rights and access to social security such as pension schemes. This gap extends to acknowledgement of degrees and credentials, as well as differing perceptions on the state's responsibilities to provide migrants the possibility to become integrated and participate in societal life.
The inherent difficulty in understanding migration processes and guiding them towards greater sustainability lies in the many and multiscalar trade-offs between territories, actors' interests, structural preconditions and assumptions about future developments. The SDGs can be seen as symbolic in this regard, as migration is not addressed as one specific development area, but as part of a number of the international development goals. But if one aims to approach sustainability of migration, the reality of cases of migration must be understood better in all its complexity, which is what our framework aims to enable. As Agder et al. (2019, p. 442) argue "a more encompassing view of migration would (…) lead to more appropriate targets and indicators for the SDGs". Finally, we might "need to move beyond the implicit assumption that sedentary lives are the norm" (Agder et al. 2019, p. 442).

Intergenerational justice and sustainability of migration over time
From the case study above, one inherent challenge of sustainability has become apparent that needs to be examined: the challenge of intra-and intergenerational justice in practice.
With justice at the core of sustainability, one difficulty is the strong overlap and causality between inter-and intragenerational justice concerns, and the partial contradictions among aspects of justice. As noted in the sustainability literature of other research areas, considering future generations' needs without neglecting the needs of present generations represents an inherent difficulty (Bornemann and Strassheim 2019;Janker 2020;Jerneck et al. 2011;Yoshihara 2007). The human rights debates on the right to mobility have not led to congruence on how this goal should be achieved in the present. While it is difficult yet possible to determine which injustices have occurred in present and past generations (Golub et al. 2013), it seems almost unattainable to adequately consider the rights, in 20 years, of those who are now children, or even unborn generations. We can only anticipate needs from our standpoint, so the consideration of future effects of migration will always remain somewhat vague. The SDGs, therefore, have named specific goals and indicators to be achieved within a specific time frame. However, these goals operate at a conceptual meta-level and lack the differentiation necessary to depict the reality of migration (cf. Agder et al. 2019). Our conceptual framework can add to debates on sustainability in migration, as it reflects the opposite scalar perspective (starting from the individual reality) on which injustices need to be overcome in the future to approach sustainability in migration. However, our framework is also limited: it can only assess the status quo and the attached goals and perspectives, and promote actions-but not anticipate future needs.

Conclusions
The terms sustainability and justice are utilized more and more in political debate (Quental et al. 2011;, particularly in the context of the SDGs (Keitsch 2018). However, to date, it is not clear what sustainability means in the context of migration. It is, therefore, meaningful to initiate that conversation, to avoid neglecting important issues in international and national political debates, due to the complexity of migration processes. Responding to this issue, our conceptual framework represents one of the first attempts to grasp sustainability issues for migration processes, and to analyse different types of migration systematically-through the analytical lens of inter/intragenerational justice. It utilizes a justice approach because this approach is well-recognized in the sustainability literature, and because it can be applied to various scales of a nested migration system. Also, justice represents a normative concept that can be grasped and, in the future, be used to negotiate the respective societal conditions in origin and destination locations (Janker 2020). Opportunities for justice, injustices, and the problematic of trade-offs between them can be detected analytically, and can point at important sustainability issues in migration processes. The research is novel as it addresses sustainability and migration, offering a framework that additionally overcomes issues of scale and thus, has the potential to address questions of power.
An empirical migration case study was chosen to test the framework on potential shortcomings and benefits of low skilled labour migration in Kyrgyzstan. The primary potential aspects of justice for this case are the promise of better living and working conditions and resulting livelihood and economic benefits at household and national scales. Injustices consist of unequal access to information and resources. Also relevant are low availability and low usefulness of social networks, disadvantages for the national realities of sending countries, as well as the emotional hardship of people who are separated through migration. Remittances and other effects of migration, such as increased labour availability, vary strongly for the places of origin and destinations; different benefits and challenges arise for countries, regions, and households. Further, intergenerational justice is difficult to anticipate, and in some cases can only be discussed in highly theoretical terms. A discussion centred at multiple scales on the desired effects of migration for the future could offer an interesting complementary pathway.
Our analytical framework provides a way to make visible conflicts of interests and injustices, and the potential for increasing justice across generations, between people living in different countries, and between individuals, households, regions and nations. This is particularly important because current academic debates mainly analyse problems related to migration on the individual or household scale, often limited to a small number of empirical cases, while political debates take place nationally and internationally, often neglecting individuals' or minorities' needs. The conceptual framework presented here further reveals conflicts between these aspects of justice. These trade-offs need to be addressed by national and international political frameworks (Hackl 2018). The fairness principle, according to Rawls (1999) and recent justice scholars (e.g., Sheller 2019), confirms the responsibility of national governments and international governmental institutions-to define what justice means in migration cases, and to implement adjustments in cases of injustice. While we see free mobility and equal rights to mobility as a desirable goal, the reality lags far behind this ideal. International frameworks that grasp the complexity of nested actor scales are necessary to implement these rights. Last but not least, Rawlsian fairness means that everyone should contribute to achieving these goals. We intend to do our part by opening up the debate on sustainability, justice and migration.
Author contributions Both authors contributed equally to the conceptual and analytical chapters of the paper. While the theory section was mainly the responsibility of J. Janker and the case studies were part of S. Thieme's research, the conceptual framework and the writing process were developed collaboratively.
Funding Open Access funding enabled and organized by Projekt DEAL. This study was funded by no specific institution.

Conflict of interest
The authors declare that they have no conflict of interest.
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