4. Developing Pathways to Sustainability: Fulfilling Human Needs and Aspirations while Maintaining Human Life Support Systems

Elisa Lanzi
Shardul Agrawala
Rob Dellink
Wolfgang Lutz
Caroline Zimm
Nebojsa Nakicenovic
Steffen Fritz
Narasimha Rao

In 1987, the “Brundtland Report” of the World Commission on Environment and Development (WCED) began with the following observation:

“Those looking for success and signs of hope can find many: infant mortality is falling; human life expectancy is increasing; the proportion of the world's adults who can read and write is climbing…. But the same processes that have produced these gains have given rise to trends that the planet and its people cannot long bear” (WCED 1987).

A growing body of subsequent research suggests that human activities are already pushing the Earth’s system outside stable planetary boundaries, with damaging and even catastrophic consequences (Rockstrom et al., 2009). Developing pathways that meet the challenge of fulfilling human needs and aspirations while ensuring human life support systems has thus become even more urgent.

Long-term pathways are a useful instrument for governments to identify expectations for the future and as a reference to set up transitional changes to match multiple policy objectives. In this sense, they can be viewed as ‘normative’ backcasting exercises with desirable future goals. For example, pathways have been developed specifically for greenhouse gas (GHG) emission reduction and stabilisation of GHG concentrations. More recently, pathways have been developed to achieve multiple policy objectives that can for instance help achieve different Sustainable Development Goals (SDGs).

Reference pathways are projections used to illustrate the likely future consequences of current trends and policy choices based on specification of underlying drivers. Hence, they are usually referred to as the “business-as-usual” or “baseline” scenarios. Traditionally, reference pathways are based on a stepwise procedure, starting with specific demographic projections that are used as an input to develop economic projections. These are then used to quantify projected environmental consequences.

This chapter reviews developments of pathways analysis in the context of sustainability. First, the Shared Socioeconomic Pathways (SSPs) are introduced. Then integrated population and human capital scenarios for joint analysis of human development, the capacity for coping with environmental changes, and securing human life support systems are considered, before closing the loop on incorporating environmental feedbacks on economic growth. Finally, these scenarios are linked with the SDGs as highlighted by the the World in 2050 initiative (TWI2050, 2018). The chapter concludes with a discussion of how a systems approach could lead to further progress in using pathways to inform policy makers.

Long-term scenarios have been used by the Intergovernmental Panel on Climate Change (IPCC) since the 1990s to analyse possible climate change, its impacts, and mitigation options. Initially the IPCC relied on GHG emission scenarios. However, projecting longer-term climate change impacts and costs is complicated because GHG emissions depend on demographic, economic, technological, and institutional factors, which change over time (Rosenzweig and Wilbanks, 2010). Consequently, scenarios were improved to reflect coherent narrative storylines to describe consistently the relationship between emissions and their driving forces. The resulting product was the set of scenarios described in the Special Report on Emissions Scenarios (SRES) (IPCC, 2000), which included demographic, economic, social, technological, and environmental aspects as part of the storylines.

More recently, a new set of scenarios - the Shared Socioeconomic Pathways (SSPs) - was developed to better describe different climate futures, including the role of both mitigation and adaptation challenges (Field et al., 2014). While the SRES were developed as joint storylines between future emissions and economic development, the SSPs were developed separately from the climate scenarios, or the so-called Representative Concentration Pathways (RCPs).1

The SSPs respond to the need of the Integrated Assessment Modelling (IAM) community to put climate impacts and responses into the context of evolving socioeconomic conditions (see Rosenzweig and Wilbanks, 2010). The SSPs not only focus on pathways to achieve emission reductions and mitigation, but also respond to the rising concerns on vulnerabilities, impacts, and adaptation. These in turn are strongly linked to socioeconomic developments and human well-being.

The SSPs consist of five scenarios, based on narratives describing alternative socioeconomic developments and the corresponding challenges for mitigation and adaptation (O’Neill et al., 2017), as illustrated in Figure 4.1. The SSP narratives were associated with quantitative descriptions for key scenario drivers, such as population (KC and Lutz, 2017), economic growth (Crespo Cuaresma, 2017, Dellink et al., 2017, Leimbach et al., 2017), and urbanisation (Jiang and O’Neill, 2016). The narratives were further developped to describe the implications for energy and land use (Riahi et al, 2017). For each SSP, there exists a single population and urbanisation scenario (by IIASA and NCAR). Meanwhile, three different GDP scenarios have been developed, with the OECD’s used as an illustrative case. The methodology behind the creation of the SSPs ensures the two-way causality between demographics and economic projections is accounted for.

The SSPs were an important achievement but they have also been the starting point to explore further pathways for the study of future human development. Unlike the previous generation of scenarios that only considered total population size, this new set of scenarios provides population projections by age, sex, and six levels of education for all countries.

Beyond economic growth, education is a basic force for empowering people. Providing access to information has been shown to matter to a large range of important aspects in the context of sustainable development. There is overwhelming evidence that education is a key determinant of infant mortality (Pamuk et al., 2011) as well as adult health and mortality (KC, S. and H. Lentzner, 2010). Beyond individual benefits, improving education for different age groups and sex has also been shown to matter for countries in transition towards modern democracies and the rule of law (Abbasi-Shavazi et al., 2008: Lutz, 2009; Lutz et al., 2010). Furthermore, it has been demonstrated that basic education of the agricultural labour force is a key factor in agricultural production, therefore facilitating food security (Hayami and Ruttan, 1971). Finally, in the context of adaptation to climate change, a series of empirical studies on differential vulnerability to natural disasters in different parts of the world have confirmed the importance of education (Frankenberg et al., 2013; Hegelson et al., 2013; KC, S. and H. Lentzner, 2013; Sharma et al., 2013; Striessnig et al., 2013; Wamsler et al., 2012). Education is shown to be an empowering factor that reduces vulnerability and enhances the adaptive capacity to the negative consequences of climate change. These effects show the interlinkages of education into the wider economic, political, and climate systems, and thus should be accounted for as such.

The integrated population and human capital scenarios shown in Figure 4.2 also show alternative trajectories of world population growth. They are based on the most extensive summary of expert arguments on future fertility, mortality, migration and education trends as published in Lutz et al. (2014) and updated by the European Commission (2018). Population trends matter greatly for assessing the number of people potentially at risk of suffering from environmental changes. SSP1 demonstrates a scenario of rapid education expansion that will be associated with both lower fertility and mortality. This leads to world population peaking around 2050 below 9 billion followed by a decline, which in 2100 may mean a global population size comparable to today. The medium scenario SSP2 will peak around 2070 at around 9.6 billion and only shows modest declines by the end of the century. The stalled development scenario SSP3 sees little to no progress in education. This is associated with a much slower fertility decline, which will result in a world population of over 13 billion in 2100. The Sustainable Development Scenario SSP1 will not only have lower population growth but also a significantly better-educated population. Both aspects together will make it more likely that under such a pathway human needs and aspirations will be better ensured than under the other two scenarios. SSP3 could be disastrous for future human well-being.

One important development in recent literature is the movement from a single to multiple policy targets. The recognition of the need to consider multiple policy goals has been highlighted by the SDGs. Indeed, it is not just important to achieve a climate goal but also that the goal is met for instance in an inclusive way, without affecting the most vulnerable parts of the population.

This new approach is key to TWI20502. TWI2050 aims to provide fact-based knowledge to support the policy process and implementation of the SDGs. It is a first attempt to explore transformational pathways that take a comprehensive people and planet approach to attaining the SDGs to ensure a prosperous and healthy future for all on a resilient and healthy planet in the long run.

Using an integrated and systemic approach, TWI2050 addresses the full spectrum of transformational challenges related to achieving the 17 SDGs, to avoid potential conflicts among them, reap the benefits of potential synergies, and reach the desired just and safe space for people and planet by 2050. This approach is the first goal-based, multi-model quantitative and qualitative integrated analysis that encompasses the full set of SDGs. The successful identification of sustainable development pathways (SDPs), which are rooted in the SSPs, requires a comprehensive, robust approach that spans disciplines and methodologies, and that can deal with nonlinearity.

The TWI2050 framework (Figure 4.3) includes qualitative and quantitative elements and consists of a broad transformational narrative; targets and indicators for 2030, 2050, and beyond; and specific SDPs, which include quantitative elements based on modelling approaches and complementary narratives.

In its 2018 report, TWI2050 identified six exemplary transformations needed to achieve the SDGs: (1) Human Capacity and Demography; (2) Consumption and Production; (3) Decarbonisation and Energy; (4) Food, Biosphere and Water; (5) Smart Cities; and (6) Digital Revolution (Figure 4.4).

While the TWI2050 2018 report is only the beginning of a long-term effort to understand sustainability pathways, it provides interesting key policy messages and research gaps. These include the need for early ambitious policy action to achieve the SDGs. The integrated framework highlighted the need for a holistic perspective, with effective and inclusive governance, combining action at local and global level.

The new approaches outlined in Section 4.2 highlight the movement from disciplinary, central baselines to tackle one specific policy objective towards more holistic approaches that acknowledge that different elements in a system are interlinked, and that robust policy advice hinges on a full systems approach. To obtain more-integrated sustainability pathways, a number of major developments are needed. Joint activities by OECD and IIASA can help bridge these remaining gaps.

One new direction would be to integrate feedbacks from environmental damages into demographic and education projections. As the OECD’s Costs of Inaction and Resource scarcity: Consequences for Long-term Economic growth (CIRCLE) project has shown, environmental feedbacks could be significant already in the coming decades. Pathways that ignore the mortality and morbidity effects (including e.g. learning and cognitive capabilities) of pollution and climate change lead to biased results. The OECD and IIASA could collaborate in preparing impact assessments of pollution feedbacks on specific demographic groups, differentiating between mortality and morbidity effects. These could then be used in IIASA’s demographic projections to provide integrated pathways that encompass environmental feedbacks.

Another new direction could consist of further integrating demographic, education, and income projections. Identifying how demographic, education, and income projections can be constructed in a mutually consistent and highly granular manner, as pioneered in the SSPs, will enhance the insights on how policy interventions affect the various parts of these linked systems. A gender aspect could also be considered to contribute to the understanding of the crucial role of gender-balance in education for economic development. The OECD and IIASA could work together on enhancing policy scenarios for education systems that are consistent with economic projections of government budgets.

There is also a clear need to link education levels to occupational skill categories. While (re)training programmes can alter occupational skillsets of employees, the main driver of occupational skills is the education received by employees when they grow up. However, the links between investing in education systems and the resulting changes in occupational skills is relatively weak, leaving governments with imperfect information on how to best prepare the workforce for changes in skillsets demanded by economic sectors that transition towards sustainability. OECD and IIASA could first work on better mapping educational and occupational skills, potentially in collaboration with the International Labour Organisation (ILO), and then improve and integrate the tools used for making education pathways at IIASA and for pathways of labour supply and productivity at OECD.

Modelling assessments of sustainability pathways can be further enhanced. Quantitative scenarios for SDGs related to human development are still scarce and can be improved and better integrated with indicators for other SDGs. This would help to achieve a more integrative approach and to obtain a full overview of the consequences of different scenarios and policies on a wider range of SDGs. Similarly, societal changes, the evolution of human needs, and possible changes in governance could be better integrated into modelling work. For instance, changes in consumption patterns towards a more service-based economy could contribute to achieving sustainability while limiting the impacts on resources and the environment. Further integrating the available modelling tools at IIASA and the OECD could help to mainstream sustainability considerations into the long-term projections.


Abbasi-Shavazi, M.J. et al. (2008), “Education and the World’s Most Rapid Fertility Decline in Iran”, Laxenburg, Austria: International Institute for Applied Systems Analysis

Arnell, N. et al. (2011), “A framework for a new generation of socio-economic scenarios for climate change impact, adaptation, vulnerability, and mitigation research”. Working paper

Cuaresma, JC. (2016), “Income projections for climate change research: a framework based on human capital dynamics”, Global Environ. Change, Vol. 42, pp. 226-236

Dellink, R., J. Chateau, E. Lanzi, B. Magné (2017), “Long-term economic growth projections in the Shared Socioeconomic Pathways”, Global Environ. Change, Vol. 42, January 2017, pp. 200-214

Field, C.B. et al. (2014), “Summary for policymakers. Climate change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects”, Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, pp. 1–32

Frankenberg, E. et al. (2013), “Education, Vulnerability, and Resilience after a Natural Disaster”, Ecology and Society, Vol. 18/2: 16

Hayami, Y. and V.W. Ruttan (1971), “Agricultural Development: An International Perspective”, Johns Hopkins University Press, Baltimore, Maryland

Helgeson, J.F., S. Dietz, and S. Hochrainer-Stigler (2013), “Vulnerability to weather disasters: The choice of coping strategies in rural Uganda”, Ecology and Society. Vol. 18/2

KC, S. and H. Lentzner (2013),” Community vulnerability to floods and landslides in Nepal”, Ecology and Society, Vol. 18/1

KC, S. and H. Lentzner (2010), “The effect of education on adult mortality and disability: A global perspective”, Vienna Yearbook of Population Research, Vol. 8, pp. 201–235

KC, S. and W. Lutz (2017), “The human core of the Shared Socioeconomic Pathways: population scenarios by age, sex and level of education for all countries to 2100”, Global Environ. Change, Vol. 42, pp. 181-192

IPCC (2000), Nebojsa Nakicenovic and Rob Swart (Eds.), “Emission Scenarios”, Cambridge University Press, UK

Jiang, B.C. O’Neill (2017), “Global urbanisation projections for the Shared Socioeconomic Pathways”, Global Environ. Change, Vol. 42, pp. 193-199

Leimbach, M., et al. (2017), “Future growth patterns of world regions—a GDP scenario approach”, Global Environ. Change (2016), Vol. 42, pp. 215-225, 10.1016/j.gloenvcha.2015.02.005

Lutz, W., W. Sanderson, S. Scherbov (1997), “Doubling of world population unlikely”, Nature, Vol. 387, pp. 803-805

Lutz, W., W. Sanderson, S. Scherbov (2001), “The end of world population growth”, Nature, Vol. 412, pp.  543-545

Lutz, W., W. Sanderson, S. Scherbov (2008), “The coming acceleration of global population ageing”, Nature, Vol. 451, pp. 716-719

Lutz, W. (2009), “Sola schola et sanitate: Human capital as the root cause and priority for international development?” Philosophical Transactions of the Royal Society B: Biological Sciences, Vol. 364/1532, pp. 3031–3047

Lutz, W., J. Crespo Cuaresma, and M.J. Abbasi-Shavazi (2010), “Demography, education, and democracy: Global trends and the case of Iran”, Population and Development Review Vol. 36/2, pp. 253–281

Lutz, W., W.P. Butz, and S. KC (eds.) (2014), “World Population and Human Capital in the Twenty-First Century”, Oxford, UK: Oxford University Press

Lutz, W. and R. Muttarak (2017), “Forecasting societies’ adaptive capacities through a demographic metabolism model”, Nature Climate Change, Vol. 7/3, pp. 177–184

Lutz, W. et al. (2018), “Demographic and Human Capital Scenarios for the 21st Century: 2018 Assessment for 201 Countries”, Luxembourg: Publications Office of the European Union

Nakicenovic, N. et al. (2000), “Special Report on Emissions Scenarios (SRES), A Special Report of Working Group III of the Intergovernmental Panel on Climate Change, IPCC Special Reports on Climate Change”, Cambridge University Press, Cambridge, UK (2000)

Nordhaus W.D. (1994). “Managing the Global Commons: The Economics of the Greenhouse Effect”, MIT Press, Cambridge, MA

Nordhaus W.D. and J. Boyer (2000). “Warming the World. Economic Models of Global Warming”, The MIT Press, Cambridge, MA

Nordhaus W.D. and Z. Yang (1996). “A Regional Dynamic General-Equilibrium Model of Alternative Climate Change Strategies,” American Economic Review, Vol. 4, pp. 741-765

OECD (2015), “The Economic Consequences of Climate Change”, OECD Publishing, Paris, https://doi.org/10.1787/9789264235410-en

OECD (2016), “The Economic Consequences of Outdoor Air Pollution”, OECD Publishing, Paris, https://doi.org/10.1787/9789264257474-en

OECD (2017), “The Land-Water-Energy Nexus: Biophysical and Economic Consequences”, OECD Publishing, Paris, https://doi.org/10.1787/9789264279360-en

OECD (2019), “Global Material Resources Outlook to 2060: Economic Drivers and Environmental Consequences”, OECD Publishing, Paris, https://doi.org/10.1787/9789264307452-en

O’Neill, B.C. et al. (2016), “The roads ahead: narratives for Shared Socioeconomic Pathways describing world futures in the 21st century”, Global Environ. Change, Vol. 42, pp. 169-180

Pamuk, E.R., R. Fuchs, and W. Lutz (2011), “Comparing relative effects of education and economic resources on infant mortality in developing countries”, Population and Development Review, Vol. 37/4, pp. 637–664

Riahi, K., et al. (2017), “The Shared Socioeconomic Pathways and their energy, land use, and greenhouse gas emissions implications: an overview”, Glob. Environ. Chang., Vol. 42 (2017), pp. 153-168

Rockström, J., et al. (2009). “Planetary boundaries: exploring the safe operating space for humanity”, Ecology and Society Vol. 14/2

Rosenzweig, C., and T.J. Wilbanks, (2010): “The state of climate change vulnerability, impacts, and adaptation research: Strengthening knowledge base and community”, Climatic Change, Vol. 100, pp. 103-106, https://doi.org/10.1007/s10584-010-9826-5

Sharma, U., A. Patwardhan, and A.G. Patt (2013), “Education as a determinant of response to cyclone warnings: Evidence from coastal zones in India”, Ecology and Society Vol. 18/2

Striessnig, E., W. Lutz, and A.G. Patt (2013), “Effects of Educational Attainment on Climate Risk Vulnerability”, Ecology and Society, Vol. 18/1

Sue Wing, I. and E. Lanzi (2014), “Integrated Assessment of Climate Change Impacts: Conceptual Frameworks, Modelling Approaches and Research Needs”, OECD Environment Working Papers, No. 66, OECD Publishing, Paris. https://doi.org/10.1787/19970900

TWI2050 - The World in 2050 (2018). “Transformations to Achieve the Sustainable Development Goals”, Report prepared by the World in 2050 initiative. International Institute for Applied Systems Analysis (IIASA), Laxenburg, Austria. http://www.twi2050.org

van Vuuren, Detlef P., et al. (2011), “The representative concentration pathways: an overview”, Climatic Change, Vol.109/5 :https://doi.org/10.1007/s10584-011-0148-z

van Vuuren, D.P. , et al. (2014), “A new scenario framework for climate change research: scenario matrix architecture”, Climate Change, Vol. 122, pp. 373-386, https://doi.org/10.1007/s10584-013-0906-1

Wamsler, C., E. Brink, and O. Rantala (2012), “Climate change, adaptation, and formal education: The role of schooling for increasing societies adaptive capacities in El Salvador and Brazil”, Ecology and Society, Vol. 17/2

WCED (1987) Our Common Future, World Commission on Environment and Development (Brundtland Report) United Nations, Oxford University Press, UK


← 1. As a parallel process to the development of the SSPs, the RCPs were developed to describe a range of possible climate scenarios (Van Vuuren et al., 2011). Four RCP scenarios - RCP2.6, RCP4.5, RCP6, and RCP8.5 - are labelled after a possible range of radiative forcing values in the year 2100 relative to pre-industrial values (+2.6, +4.5, +6.0, and +8.5 W/m2, respectively). The two extremes of the RCPs (RCP2.6 and RCP8.5) would therefore lead to very different changes in climate, with RCP8.5 leading to much higher temperature increases and changes in precipitations. A matrix has been developed to map SSPs and RCPs (van Vuuren et al., 2014).

← 2. See: http://www.twi2050.org.

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