Workshop Report - IPCC

Annex I: Paper
Socio‐economic reference pathway
SSP1 SSP2 SSP3 …
Forcing level (W/m 2 )
8.5
6.0
4.5
2.6
Figure 1.1: The scenario matrix architecture: confronting different future levels of climate forcing with different
socio-economic reference assumptions described by SSPs. See Section 2 for details.
1.2. Scenarios in previous assessments
Global change scenarios widely used include those of the Special Report on Emissions Scenarios (SRES), the
scenarios developed for the Millennium Ecosystem Assessment, and the GEO-4 scenarios.
The SRES set of scenarios was developed to represent the range of driving forces and emissions in the scenario
literature, to reflect current understanding about underlying uncertainties (Nakicenovic, 2000). The scenarios
were based on an extensive assessment of driving forces and emissions in the scenario literature, alternative
modelling approaches, and a process that solicited wide participation and feedback. Four narrative storylines
were developed to consistently describe the relationships between emission driving forces and their evolution,
with each storyline representing different demographic, social, economic, technological, and environmental
development pathways. The scenarios cover a wide range of the main demographic, economic, and
technological driving forces of GHG and sulfur emissions. For each storyline, several different scenarios were
developed using different modelling approaches to examine the range of outcomes arising from models that use
similar assumptions about driving forces. Contrary to the new scenarios described here, the SRES scenarios
assumed no specifically targeted climate mitigation and adaptation policies and measures. In subsequent studies
and assessments, such extensions to the original SRES set were explored extensively.
The Millennium Ecosystem Assessment (MEA) was a large assessment of the current status, present trends, and
longer-term challenges to the world’s ecosystems, including climate change and other sources of stress. The
MEA sought to assess changes in ecosystems in terms of the services they provide to people and the effects of
ecosystem change on human well-being; and to identify and assess methods to mitigate and respond to
ecosystem change. Scenarios to 2050, with more limited projections to 2100, were developed in an iterative
process, including consultations with potential scenario users and experts (Carpenter, 2005). Two basic
dimensions of uncertainty in long-term ecosystem stresses were identified: globalization (continuation and
acceleration of present global integration trends, versus reversal of these trends to increasing separation and
isolation of nations and regions) and whether responses to increasing ecosystem stresses are predominantly
reactive – waiting until evidence of deterioration and loss of services is clear – or predominantly proactive,
taking protective measures in advance of their clear need. The extreme values of each of these dimensions
yielded four scenarios, summarized in table 1.2.
Workshop on Socio-Economic Scenarios - 8