What are the Shared Socioeconomic Pathways (SSPs)?

The Shared Socioeconomic Pathways are a set of scenarios which are central to the work of the UN climate reports produced by the Intergovernmental Panel on Climate Change (IPCC).

Why are these scenarios so important for the IPCC report?

How much greenhouse gas emissions the world emits in the coming decades is unknown. It is up to us. It will depend on what people around the world will do now and in the future.

In this situation, it’s helpful to create scenarios that cover a range of possible futures. This is what the ‘Shared Socioeconomic Pathways’ (SSPs) are. SSPs are the possible futures that climate researchers in the IPCC consider in their models.

SSPs do not tell us what the world will look like. Instead, they tell us what the world could look like.

The key aspect of these scenarios is the emissions of greenhouse gases that result. This is the key aspect because that what will determine the future of the climate.

To understand how our emissions might evolve we need to know how the world might change from a socioeconomic and technological perspective. These scenarios therefore differ in their assumptions about socioeconomic and technological development in the coming decades.

The socioeconomic and technological factors that the SSPs include are: population growth, economic growth, urbanization, trade, energy, and agricultural systems. You find all them in the Data Explorer above.

For more details on how SSPs are constructed, Zeke Hausfather has written an excellent explainer for Carbon Brief on this topic.

Summaries of the five Shared Socioeconomic Pathways

There are five key SSPs that are used in the research, and adopted by the IPCC. 

Below we provide the full description – as given by the IPCC – of these futures.

In summary, SSP1 provides the most positive scenario for both human development and environmental action. We continue to see improvements in education and health across the world; large reductions in poverty; and a shrinking in global inequalities. This is a scenario in which the researchers at the same time envision that the world is moving into a much more sustainable direction. 

SSP5 is similarly optimistic in terms of human development, but achieves this through a large growth in fossil fuels. This is therefore leading to continued large negative effects on the environment.

SSP3 and SSP4 are pessimistic about development: they envision a divided future with high levels of nationalism and large persistent global inequalities as a result. SSP2 sits in the middle of these scenarios: development is not as slow or divided as in SSP3 and SSP4, but progress is slow and unequal.

Complete descriptions of the five Shared Socioeconomic Pathways

These are the full descriptions of the SSP narratives, as described by the IPCC:

SSP1: Sustainability – Taking the Green Road (Low challenges to mitigation and adaptation)

“The world shifts gradually, but pervasively, toward a more sustainable path, emphasizing more inclusive development that respects perceived environmental boundaries. Management of the global commons slowly improves, educational and health investments accelerate the demographic transition, and the emphasis on economic growth shifts toward a broader emphasis on human well-being. Driven by an increasing commitment to achieving development goals, inequality is reduced both across and within countries. Consumption is oriented toward low material growth and lower resource and energy intensity.”

SSP2: Middle of the Road (Medium challenges to mitigation and adaptation)

“The world follows a path in which social, economic, and technological trends do not shift markedly from historical patterns. Development and income growth proceeds unevenly, with some countries making relatively good progress while others fall short of expectations. Global and national institutions work toward but make slow progress in achieving sustainable development goals. Environmental systems experience degradation, although there are some improvements and overall the intensity of resource and energy use declines. Global population growth is moderate and levels off in the second half of the century. Income inequality persists or improves only slowly and challenges to reducing vulnerability to societal and environmental changes remain.”

SSP3: Regional Rivalry – A Rocky Road (High challenges to mitigation and adaptation)

“A resurgent nationalism, concerns about competitiveness and security, and regional conflicts push countries to increasingly focus on domestic or, at most, regional issues. Policies shift over time to become increasingly oriented toward national and regional security issues. Countries focus on achieving energy and food security goals within their own regions at the expense of broader-based development. Investments in education and technological development decline. Economic development is slow, consumption is material-intensive, and inequalities persist or worsen over time. Population growth is low in industrialized and high in developing countries. A low international priority for addressing environmental concerns leads to strong environmental degradation in some regions.”

SSP4 Inequality – A Road Divided (Low challenges to mitigation, high challenges to adaptation)

“Highly unequal investments in human capital, combined with increasing disparities in economic opportunity and political power, lead to increasing inequalities and stratification both across and within countries. Over time, a gap widens between an internationally-connected society that contributes to knowledge- and capital-intensive sectors of the global economy, and a fragmented collection of lower-income, poorly educated societies that work in a labor-intensive, low-tech economy. Social cohesion degrades and conflict and unrest become increasingly common. Technology development is high in the high-tech economy and sectors. The globally connected energy sector diversifies, with investments in both carbon-intensive fuels like coal and unconventional oil, but also low-carbon energy sources. Environmental policies focus on local issues around middle and high-income areas.”

SSP5 Fossil-fueled Development – Taking the Highway (High challenges to mitigation, low challenges to adaptation)

“This world places increasing faith in competitive markets, innovation and participatory societies to produce rapid technological progress and development of human capital as the path to sustainable development. Global markets are increasingly integrated. There are also strong investments in health, education, and institutions to enhance human and social capital. At the same time, the push for economic and social development is coupled with the exploitation of abundant fossil fuel resources and the adoption of resource and energy-intensive lifestyles around the world. All these factors lead to rapid growth of the global economy, while global population peaks and declines in the 21st century. Local environmental problems like air pollution are successfully managed. There is faith in the ability to effectively manage social and ecological systems, including by geo-engineering if necessary.”

How are SSPs modeled to fit specific climate scenario outcomes?

Each of the five SSPs also have variations of each scenario that would deliver a particular climate target. These variations correspond to the level of radiative forcing that they would lead to. 

Let’s take ‘SSP1 – 2.6’ as an example.  You can do this for yourself by selecting ‘SSP1 – 2.6’ in our explorer, and changing the metrics.

It is a scenario with the socioeconomic development pathway of SSP1 (the same scenario in terms of population and economic growth) that would lead to a forcing of 2.6 watts per meter squared. 

To achieve that under these socioeconomic conditions would mean that something else would have to change to reduce emissions. For example, it lays out a future in which the world implements a carbon price globally; or total energy consumption is lower because we improve efficiency; or we have more nuclear energy; or we have much more carbon capture and storage.

For some SSPs, the changes would have to be extreme to meet these climate pathways. For example, in SSP5 – the fossil-fuel-heavy development path – we would need a very high carbon price, and lots of carbon capture and storage.

What is the source of this data?

The data presented is sourced from the work of  Keywan Riahi et a. (2017), which brings together the results of independent researchers that have mapped out a range of socioeconomic scenarios for how the world could change in the coming decades.{ref}Riahi, K., Van Vuuren, D. P., Kriegler, E., Edmonds, J., O’neill, B. C., Fujimori, S., … & Tavoni, M. (2017). The shared socioeconomic pathways and their energy, land use, and greenhouse gas emissions implications: an overview . Global environmental change, 42, 153-168.{/ref}

The underlying data from these scenarios – that we presented in our Explorer – is accessible from the SSP Database , published and maintained by the International Institute for Applied Systems Analysis (IIASA).

Full citation: Keywan Riahi, Detlef P. van Vuuren, Elmar Kriegler, Jae Edmonds, Brian C. O’Neill, Shinichiro Fujimori, Nico Bauer, Katherine Calvin, Rob Dellink, Oliver Fricko, Wolfgang Lutz, Alexander Popp, Jesus Crespo Cuaresma, Samir KC, Marian Leimbach, Leiwen Jiang, Tom Kram, Shilpa Rao, Johannes Emmerling, Kristie Ebi, Tomoko Hasegawa, Petr Havlík, Florian Humpenöder, Lara Aleluia Da Silva, Steve Smith, Elke Stehfest, Valentina Bosetti, Jiyong Eom, David Gernaat, Toshihiko Masui, Joeri Rogelj, Jessica Strefler, Laurent Drouet, Volker Krey, Gunnar Luderer, Mathijs Harmsen, Kiyoshi Takahashi, Lavinia Baumstark, Jonathan C. Doelman, Mikiko Kainuma, Zbigniew Klimont, Giacomo Marangoni, Hermann Lotze-Campen, Michael Obersteiner, Andrzej Tabeau, Massimo Tavoni. The Shared Socioeconomic Pathways and their energy, land use, and greenhouse gas emissions implications: An overview , Global Environmental Change , Volume 42, Pages 153-168 (2017).