Emissions Scenarios - IPCC

An Overview of Scenarios 179
Figure 4-3: Schematic illustration of the multidimensional classification space of SRES scenarios. The set of scenarios
consists of four scenario families (Al, A2, Bl, and B2), each of which consists of a number of scenarios. Some of these have
"hannonized" inputs - they share similar pre-specified global population and GDP trajectories. They are marked as "HS" for
(globally) harmonized scenarios. All other scenarios of the same family based on the quantification of the storyline chosen by
the modeling team are marked as "OS." The Al family is divided into four scenario groups that explore altemative
developments in the future energy sector. These were merged into three groups in the SPM (see also footnote 1). Finally, one
of the harmonized scenarios is designated as the characteristic representative of each family and is the marker scenario.
judgments have been made by the SRES team as to their
desirability or probability. Storylines in the literature, however,
are often explicitly intended by their authors to have a positive
or negative connotation, and sometimes explicitly include
assumed dominant or preferred types of governance. Thus, the
four SRES storylines are fundamentally different in this
respect compared to many narrative scenarios in the underlying
literature.
Two arguments are pertinent to the linkage between the
scenario storylines and the underlying literature. First, a
future regarded as negative by some people may be perceived
as positive by others. Second, the storylines represent families
of scenarios that can include both success and failure,
depending on the perspective of the beholder. To quote
Wilkerson (1995): "Like the real life from which they are
drawn, the scenarios are mixed bags, at once wonderfully
dreadful and dreadfully wonderful." Importantly, the
"neutral" or "agnostic" character of SRES scenarios is an
explicit departure from most of the underlying literature about
storylines and narrative scenarios.
Another important departure and an innovation unique to the
SRES approach is the use of the storylines in conjunction with
multiple (six) modeling approaches to develop and formulate a
set of quantifications or scenarios that are overall consistent
with the underlying storylines. This approach provides a
rigorous modeling test of the underlying logic and structure of
the storyline, while the naffative aspect of the storyline
provides a broader, descriptive context for better understanding
and interpretation of the scenarios.
4.3.1. Al Storyline and Scenario Family
The Al storyline is a case of rapid and successful economic
development, in which regional average income per capita
converge - current distinctions between "poor" and "rich"
countries eventually dissolve. The primary dynamics are:
• Strong commitment to market-based solutions.
• High savings and commitment to education at the
household level.
• High rates of investment and innovation in education,
technology, and institutions at the national and
intemational levels.
• Intemational mobility of people, ideas, and technology.