Climate policy under the Framework Convention demonstrably fails to curb
and reverse growth of GHGs.
[The Covid pandemic dented emissions, but 2022 global emissions are at
a record high level.]
This is the “tragedy of the commons”: as long as fossil fuel pollution can be
dumped in the air free of charge,
agreements such as the 1997 Kyoto Protocol and 2015 Paris Agreement
have little effect on global emissions.
Energy is needed to raise living standards and fossil fuels are still
the most convenient, affordable source of that energy. Thus, growth of
emissions is occurring in emerging economies, while mature economies are
still the larger source of the cumulative emissions that drive climate change.
Thus, exhortations at UN meetings, imploring reduced emissions,
have limited global effect.
Meanwhile, climate science has exposed a crisis that the world is loath to appreciate. IPCC, the
scientific body advising the world on climate, does not bluntly inform the world that the present
“wishful thinking” geopolitical approach will be disastrous for today’s young people and their
children. Political leaders profess ambitions for dubious net-zero emissions while fossil fuel
extraction expands. The only IPCC scenarios that phase down human-made climate change
amount to “a miracle will occur.” The one IPCC scenario that moves rapidly to negative global
emissions has biomass-burning powerplants that capture and sequester CO 2 , a nature-ravaging
proposition without scientific and engineering credibility and without a realistic chance of being
deployed at scale and on time to address the climate threat.
As already noted in the Third Assessment Report 11 ,
‘unequivocal attribution would require controlled experimentation
with the climate system.
Since that is not possible, in practice attribution of anthropogenic
climate change is understood to mean
demonstration that a detected change is
‘consistent with the estimated responses to the given combination of
anthropogenic and natural forcing’ and
’not consistent with alternative, physically plausible explanations of
recent climate change that exclude important
elements of the given combination of forcings.
Therefore attribution analysis is mainly performed through the
application of Global Circulation Models that allow
testing for causal relationships between anthropogenic forcing,
natural variability and temperature evolutions.
Pattern-based fingerprint studies provided strong scientific evidence of a
significant human influence on global atmospheric temperature changes.
Shared Socioeconomic Pathways
The RCPs set pathways for greenhouse gas concentrations and, effectively, the amount of warming that could occur by the end of the century. Whereas the SSPs set the stage on which reductions in emissions will – or will not – be achieved.
The new SSPs offer five pathways that the world could take. Compared to previous scenarios, these offer a broader view of a “business as usual” world without future climate policy, with global warming in 2100 ranging from a low of 3.1C to a high of 5.1C above pre-industrial levels.
While the RCPs were finished in time to be used in the IPCC Fifth Assessment Report, developing the more complex SSPs has been a much longer and more involved process. The SSPs were initially published in 2016, but are only now just starting to be used in the next round of climate modelling – known as the Coupled Model Intercomparison Project version 6, or CMIP6 – in preparation for the IPCC’s sixth assessment report.
The SSPs are based on five narratives describing broad socioeconomic trends that could shape future society. These are intended to span the range of plausible futures.
They include: a world of sustainability-focused growth and equality (SSP1); a “middle of the road” world where trends broadly follow their historical patterns (SSP2); a fragmented world of “resurgent nationalism” (SSP3); a world of ever-increasing inequality (SSP4); and a world of rapid and unconstrained growth in economic output and energy use (SSP5).
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.
The SSPs were designed to reflect worlds in which mitigation and adaptation challenges vary from low to very high. While the baseline SSP scenarios assume an absence of climate policy, researchers also wanted to look at how the underlying socioeconomic conditions would affect the implementation of climate policy.
For example, SSP1 features low challenges to mitigation and adaptation due to its rapid technological development, relative global equality of income and focus on environmental sustainability. SSP4, on the other hand, features similarly low challenges to mitigation due to its rapid technological development, but high challenges to climate adaptation due to persistent inequality and poverty in many parts of the world.
The main differences between SSPs come from their assumptions on global population growth, access to education, urbanisation, economic growth, resources availability, technology developments and drivers of demand, such as lifestyle changes.
All scenarios in the SSP database that keep warming below 2C incorporate some bioenergy with carbon capture and storage (BECCS).
Hausfather (2018) SSP