Intergovernmental Panel on Climate Change SSP-RCP scenarios

The IPCC began its sixth assessment reporting cycle (AR6) in 2021. The AR6 assessment reports use SSP-RCP (‘SSPX-Y’) scenarios based on the Shared Socio-economic Pathways (SSPs), and partly informed by the Representative Concentration Pathways (RCPs) scenarios of AR5.

Read the IPCC’s sixth assessment (AR6) reports, including the summary for policymakers

The set of SSPs is described in Chapter 1 of the IPCC’s AR6 Working Group I report, Climate Change 2021: The Physical Science Basis. Chapter 4 describes the assumptions associated with each of the SSP-RCP scenarios.

The chapter includes figures comparing the differences between each scenario, such as:

• global temperature change
• global land precipitation changes
• arctic sea ice area for selected months
• global mean sea level change
• annual mean surface air temperature.

The IPCC’s working group I (WGI) Interactive atlas is an online tool that allows users to explore projected climate change information underpinning each of the SSP-RCP scenarios.

The AR6 scenario explorer and database presents the dataset of quantitative, model-based pathways related to the mitigation of climate change which underpin the Sixth Assessment Report (AR6) of IPCC Working Group III.

The Intergovernmental Panel on Climate Change (IPCC) is the international body tasked with assessing the science of climate change.

Since 1988, the IPCC has informed policy makers on:

• the physical science of climate change
• its impacts and future risks
• options for adaptation and mitigation.

The IPCC Assessment Reports

The IPCC released its Fifth Assessment Report (AR5) [Ipcc website] in 2014. The Fifth Assessment Report explores five different Representative Concentration Pathways (RCPs). Each RCP corresponds with a level of radiative forcing (and degree of global warming) by 2100.

The IPCC released its latest Sixth Assessment Report (AR6) [Ipcc website] in 2021. The Sixth Assessment Report explores five different Shared Socio-economic Pathways (SSPs) combined with Representative Concentration Pathways (RCPs). These AR6 scenarios are referred to as the ‘SSP-RCP’ scenarios (or the ‘SSPX-Y’ scenarios).

Read more about the history of the IPCC scenarios [Ipcc website] – including the SSPs and RCPs – in Chapter 1 of the Working Group I (WGI) Sixth Assessment Report (AR6).

The IPCC’s Sixth Assessment Report (AR6) explores the projected climate response to five emissions scenarios based on Shared Socio-economic Pathways (SSPs).

The SSPs are baseline narrative scenarios that identify:

• socio-economic assumptions
• geopolitical assumptions
• economic and technological trends.

See Summary of the Shared Socio-economic Pathways (SSP) scenarios

The SSP narratives form part of the basis for modelling the combined SSP-RCP scenarios. The SSP narratives alone do not impose emissions mitigation targets or mitigation policy assumptions.

The SSP-RCP scenarios (sometimes referred to as the ‘SSPX-Y scenarios’) combine the baseline SSPs with Representative Concentration Pathways (RCP) scenarios from the IPCC’s fifth assessment reporting period (AR5).

The SSP-RCP scenarios impose global warming targets on the baseline SSP scenarios using the radiative forcing levels of the RCP scenarios.

There are five SSP-RCP (‘SSPX-Y’) scenarios:

• SSP1-1.9
• SSP1-2.6
• SSP2-4.5
• SSP3-7.0
• SSP5-8.5

The first number ‘X’ in the SSPX-Y acronym refers to the baseline SSP scenario. The second number ‘Y’ refers to the RCP radiative forcing levels. For example, ‘SSP1-1.9’ is a scenario that combines SSP1 with 1.9 W m-2 radiative forcing in 2100 (RCP1.9).

The SSP-RCP (‘SSPX-Y’) scenarios are among the most commonly used global climate scenarios. The SSP-RCP scenarios combine baseline socio-economic narratives (the SSPs) with different emissions trajectories (based on the RCPs).

The SSP-RCP scenarios are useful building blocks (or scenarios ‘archetypes’) for creating scenarios, since they provide a global narrative, global emissions trajectory, and level of global warming upon which to build.

If you are developing scenarios with a broad focus, you may find it useful to align some, or all, of your scenarios with an equivalent IPCC SSP-RCP scenario. This will help create the structure of your scenarios by painting a picture of what is happening at a global scale.

Downscaled climate data for Aotearoa New Zealand

NIWA is a crown research entity that has previously conducted modelling to downscale the IPCC AR5 data (2014) to the New Zealand scale.

NIWA will also be downscaling the IPCC’s AR6 data (2021) to the New Zealand scale. ‘Downscaling’ involves deriving local climate information from a larger scale model. The downscaled AR6 data for New Zealand is due for publication in 2024.

Read more about Climate data for Aoteaora New Zealand (based on the IPCC Fifth and Sixth Assessment Report scenarios).

The SSP-RCP scenarios incorporate assumptions about future socioeconomic developments, such as population growth, economic trends, and technological advancements.

The SSP-RCP scenarios assume a certain level of global cooperation and implementation of climate policies. Real-world political and societal dynamics may deviate from these assumptions, affecting the feasibility of mitigation and adaptation measures.

Other limitations of the SSP-RCP scenarios include:

• While the IPCC considers the role of oceans in the climate system, the representation of ocean processes in climate models may have limitations, affecting the accuracy of sea-level rise projections and other ocean-related impacts.
• The IPCC notes that one limitation of the SSP-RCPs is that they reduce emissions from all the major ozone-depleting substances controlled under the Montreal Protocol uniformly, rather than presenting a fuller range of possible high- and low-emissions futures.
• While the SSP-RCP scenarios primarily focus on CO₂ emissions, other factors like non-CO₂ GHG, aerosols, and land-use changes also influence climate.

Tipping points

The treatment of potential tipping points [Global Tipping Points website] and abrupt climate changes within the SSP-RCP scenarios is an area of ongoing research and uncertainty. Some critics argue that these scenarios may not fully account for the risks associated with tipping points.

Read more about climate tipping points in the What Planet Are We On? article pages 27-30 [Institute and Faculty of Actuaries website]

More on limitations

For more on the limitations of existing climate scenarios, including the IPCC scenarios, see the University of Exeter report Emperor’s New Climate Scenarios – a warning for financial services [Institute and Faculty of Actuaries website]

There are five SSP-RCP (‘SSPX-Y’) scenarios, each with a different set of narrative assumptions and emissions trajectories.

The baseline SSP scenarios provide descriptions of how the future may develop, based on a coherent and internally consistent set of assumptions about key driving forces (e.g., rate of technological change) and relationships. The RCP scenario components correspond to the level of radiative forcing at 2100.

The SSP-RCP scenarios drive climate model projections of changes in the climate system. Projections account for solar activity and background forcing from volcanoes.

Results over the 21^st century are provided for the near term (2021–2040), mid-term (2041–2060), and long term (2081–2100) relative to 1850–1900 (unless otherwise stated).

Changes in global surface temperature, for selected 20-year time periods and the five SSP-RCP emissions scenarios

*Temperature differences relative to the average global surface temperature of the period 1850-1900 are reported in ºC.

The Socio-economic Pathways (SSPs) provide baseline narratives. The SSPs form part of the basis for modelling the combined SSP-RCP scenarios. 

SSP1 Sustainability – Taking the Green Road

The world shifts gradually, but pervasively, toward a more sustainable path, emphasising more inclusive development that respects perceived environmental boundaries.

• Management of the global commons slowly improves.
• Educational and health investments accelerate the demographic transition.
• 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

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 the Sustainable Development Goals.
• Environmental systems experience degradation, although there are some improvements and the overall 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

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 industrialised countries and high in developing ones.
• A low international priority for addressing environmental concerns leads to strong environmental degradation in some regions.

SSP4 Inequality – A Road Divided

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 labour-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.
• Environmental policies focus on local issues around middle- and high-income areas.

SSP5 Fossil-fueled Development

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.
• 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.
• Rapid growth of the global economy, while global population peaks and declines in the 21^st
• 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.

These summaries for the SSP baseline narratives are adapted from a Riahi et al. 2017 article in Global Environmental Change [ScienceDirect website].

Read more about the SSPs in the IPCC’s Sixth Assessment Report (AR6) [Ipcc website].

The RCP components of the SSP-RCP scenarios impose a level of radiative forcing in 2100, which corresponds with a related level of global warming.

Read more about the RCPs in the IPCC’s Fifth Assessment Report (AR5) [Ipcc website]