What are the SSPs?
The Intergovernmental Panel on Climate Change is a group of scientists that studies global warming. In their recent report, the IPCC studied the possibilities of different pathways for our future. They did this by analyzing various possible futures, and then coming up with a range of projected climate changes based on these different pathways.
The IPCC chose the name Shared Socioeconomic Pathways (SSPs) because it refers to how these pathways are projected to vary according to population, economic growth, and other factors that are impacted by socioeconomic conditions.
The different SSPs are also related to and correlated to different levels of global temperature warming by the year 2100. For example, the baseline ("business-as-usual") warming scenario is called RCP 8.5. RCP stands for "Representative Concentration Pathways". Each pathway is listed with a number, and the number after the dash is the amount of global warming above pre-industrial levels by the year 2100. So in this case, RCP 8.5 means that average global temperatures will rise about 8 degrees celsius.
The interaction between the SSPs and the RCPs is a technical-jargon shorthand for explaining scenarios about what kind of world we are likely to see by 2100. What this is all really trying to say is that our politics will determine our emissions level, and that the IPCC's assessment scenario framework has to look at the wide range of political possibilities facing the future of the human race.
Here is what they mean when they talk about “shared socio-ecological systems”:
Social development - How societies adapt socially within an ecological context. For example, do countries become more equal or less? Do populations continue growing or shrink? What happens to gender equality?
Ecological development - How ecosystems change as human activities impact them. Does nature recover from past damage? Will species go extinct? Are forests being replaced by cities? Is soil becoming degraded?
Equity - How resources are distributed among social groups such as rich/poor, men/women, old/young etc.
Common but differentiated responsibilities – Who bears responsibility for dealing with environmental problems? Should everyone be responsible for protecting the environment? Or should some sectors take greater responsibility than others? What do climate policy assumptions look like in terms of current conditions and an integrated assessment of the adaptive capacity of countries and populations as diverse as the Republic of Korea and the Central African Republic? Will the US take a responsibility for global climate stabilization because of its responsibility for cumulative carbon emissions? Or do we focus on the countries with increasing population size, high combinations of challenges historically, threatened boundary conditions, and questionable mitigative and response capacity?
These questions aren't just theoretical; they're important ones that need answers if we want to avoid dangerous levels of greenhouse gas emissions. So far, most research has focused on understanding the effects of individual pathways rather than looking at all of them together. But as the Sixth Assessment Report gets closer to publication, the IPCC wants us to think about the consequences of living under any of those paths. It also wants us to consider the implications of not taking action against climate change.
Narratives for an uncertain future
Narratives for each Shared Socioeconomic Pathway, from Riahi et al 2017
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.
Avoiding Business as Usual
So in conclusion, the IPCC has identified a number of "roadmaps" of where we may be going in the future, based on a number of factors. It is important to remember that they are not making predictions. Rather, they are describing possible pathways that we may head down in the future. They will have massively different effects on environmental conditions like sea level rise, population size, and annual CO2 emissions. They will also have a high range of socioeconomic challenges - in the absence of climate policies, many nations are facing quantitative projections of aspects of society like resurgent nationalism, educational attainment, and the socioeconomic futures of billions of people.
In future work, we will continue to look under the hood of these models - but also explain in more human and qualitative language what these things are likely to mean in the real world for normal people. The fact of the matter is, if we continue to do nothing, billions of people will die.