Abstract
In every Intergovernmental Panel on Climate
Change (IPCC) Assessment cycle, a multitude of scenarios
are assessed, with different scope and emphasis throughout
the various Working Group reports and special reports, as
well as their respective chapters. Within the reports, the am-
bition is to integrate knowledge on possible climate futures
across the Working Groups and scientific research domains
based on a small set of “framing pathways” such as the so-
called representative concentration pathways (RCPs) in the
Fifth IPCC Assessment Report (AR5) and the shared socioe-
conomic pathway (SSP) scenarios in the Sixth Assessment
Report (AR6). This perspective, initiated by discussions at
the IPCC Bangkok workshop in April 2023 on the “Use of
Scenarios in AR6 and Subsequent Assessments”, is intended
to serve as one of the community contributions to highlight
the needs for the next generation of framing pathways that is
being advanced under the Coupled Model Intercomparison
Project (CMIP) umbrella, which will influence or even pred-
icate the IPCC AR7 consideration of framing pathways. Here
we suggest several policy research objectives that such a set
of framing pathways should ideally fulfil, including mitiga-
tion needs for meeting the Paris Agreement objectives, the
risks associated with carbon removal strategies, the conse-
quences of delay in enacting that mitigation, guidance for
adaptation needs, loss and damage, and for achieving mit-
igation in the wider context of societal development goals.
Based on this context, we suggest that the next generation of
climate scenarios for Earth system models should evolve to-
wards representative emission pathways (REPs) and suggest
key categories for such pathways. These framing pathways
should address the most critical mitigation policy and adapta-
tion plans that need to be implemented over the next 10 years.
In our view, the most important categories are those relevant
in the context of the Paris Agreement long-term goal, specif-
ically an immediate action (low overshoot) 1.5 °C pathway
and a delayed action (high overshoot) 1.5 °C pathway. Two
other key categories are a pathway category approximately
in line with current (as expressed by 2023) near- and long-
term policy objectives, as well as a higher-emission category
that is approximately in line with “current policies” (as ex-
pressed by 2023). We also argue for the scientific and policy
relevance in exploring two “worlds that could have been”.
One of these categories has high-emission trajectories well
above what is implied by current policies and the other has
very-low-emission trajectories which assume that global mit-
igation action in line with limiting warming to 1.5 °C with-
out overshoot had begun in 2015. Finally, we note that the
timely provision of new scientific information on pathways
is critical to inform the development and implementation of
climate policy. Under the Paris Agreement, for the second
global stocktake, which will occur in 2028, and to inform
subsequent development of nationally determined contribu-
tions (NDCs) up to 2040, scientific inputs are required by
2027. These needs should be carefully considered in the de-
velopment timeline of community modelling activities, in-
cluding those under CMIP7.