Workshop Report - IPCC

Annex I: Paper
2.4.2. Use of marker scenarios
The scenario framework can also be explicitly used to develop new scenarios. For this purpose, one would need
to define elements for each SSP/radiative forcing combination that would guide new development. There is a
trade-off between harmonization and providing flexibility. Any new scenario framework should provide flexibility
and not over-specify scenarios. Reasons for this include the need to communicate existing uncertainties, to allow
for different approaches, to avoid constraints on research directions, and to provide an opportunity for a wide
research community to participate in scenario analysis. At the same time, however, the scenarios also have a
function to organize information (acts as a thread to the communities), which benefits from some form of
standardization.
In this context, we propose the following steps.
The basic SSPs include a minimum set of qualitative and semi-quantitative descriptions (see Section 3)
allowing for a great flexibility in interpretation of the underlying narratives, including a preferred range
for basic quantitative indicators and key model input assumptions such as population and income.
The scientific community should be encouraged to submit scenarios to populate the different cells
within the framework based on simple criteria that define the columns/cells.
Define specific “marker” scenarios that are considered illustrative of the type of scenarios within the
framework (similar to what was done for SRES). These markers or illustrative scenarios are not the only
possible quantification of a SSP (or SPA), but will preferably be used in most analyses as a basis for
comparison, in addition to using other scenarios from a specific element in the framework. In the
definition of the markers, it can be decided the degree to which parameters are specified – and how
much is left as choice for individual analysts.
2.4.3 Uncertainty in climate policy and climate impact
A similar discussion exists regarding the specification of the climate projections along the RCP axis. At the very
least, there is a need to indicate clearly how future climate and its uncertainties have been characterized using
different climate models, as the use of different climate models may lead to very different results. The methods
by which climate uncertainties associated with similar levels of radiative forcing are to be addressed by IAV and
other analysts remain to be determined, and it is important that further guidance be provided on how to handle
these important choices (e.g. by clearly identifying the characteristics of different CM model runs).
3. Defining the Shared Socioeconomic Pathways (SSPs)
3.1 Introduction
As discussed in Section 2, the intent of this process is the development of scenarios based on combinations of
climate model projections, socioeconomic conditions, and assumptions about climate policies (including a no
policy reference). Narratives and qualitative and quantitative assumptions about broad development patterns for
major world regions, relevant to impacts, adaptation, and mitigation, define the SSPs. These assumptions
include common inputs required by integrated assessment and impact models, but not typical model outputs
such as greenhouse gas emissions. It is desirable to develop a set of scenarios that present a broad range of
possible development pathways; with reference scenarios based on SSPs and assumptions of no (new) climate
policy, and policy scenarios based on SSPs combined with assumptions about climate policies for reaching a
given RCP level.
This section discusses the framework for defining the content of SSPs. We first discuss the logic used to define
the space of possible futures that the set of SSPs is intended to span, and the relation of this space to the
scenario matrix architecture. We then discuss the dimensions of socioeconomic systems that might be used to
specify particular SSPs, including demographic, economic, institutional, and other dimensions. We distinguish
two variants of SSPs – basic vs. extended – that provide different levels of detail about future development
Workshop on Socio-Economic Scenarios - 19