The
A1 scenario family includes different groups of scenarios that explore different specific structures of future energy systems, from carbon - intensive development paths to high rates of decarbonization as captured by the two illustrative scenarios that span most of the emissions range for the A1 family.
As for CO2 emissions related to land use (see Section 5.3.2), at least one scenario from all four
SRES scenario families falls within the 25th and 75th percentiles of the emission range.
What is perhaps more important is that each of the four
scenario families covers a sizable part of this distribution, which implies that a similar quantification of driving forces can lead to a wide range of future emissions.
The A1
scenario family includes four groups designated by A1T, A1C, A1G and A1B (see also note below) that explore alternative structures of future energy systems.
The subsequent sections discuss CH4 emission trajectories for
individual scenario families, with sectoral and regional patterns described on the basis of the output of marker scenarios.
The often - used
A2 scenario family from IPCC SRES («A world of independently operating, self - reliant nations / continuously increasing population.
The B2 storyline and
scenario family describe a world in which the emphasis is on local solutions to economic, social and environmental sustainability.
In the Summary for Policymakers, the A1C and A1G groups have been combined into one «fossil intensive» A1FI scenario group, thus reducing the number of groups constituting the
A1 scenario family to three.
The
SRES scenario families and illustrative cases are summarised in a box at the end of the Summary for Policymakers.
Figure 5 - 5: Standardized global CH4 emissions for SRES scenarios, classified into four
scenario families (each denoted by a different color code - A1, red; A2, brown; B1, green; B2, blue).
At the same time, the uncertainty range for any given
scenario family is also substantial, as indicated by the range of 2100 emissions for the A1, A2, and B1 scenario families in Figure 5 - 5.
As discussed above, global sulfur emissions eventually decline in all SRES
scenario families and associated groups.
In the case of the SRES, the emissions trajectories were the same whether economic activities in the four
scenario families were measured in MER or PPP.
Four illustrative marker scenarios, one for
each scenario family, were used in draft form in the 1998 SRES open process and are included in revised form in this report.
Scenario family A1 is further subdivided into four scenario groups: A1C, A1G, A1B and A1T, (see also note below), resulting in seven scenario groups together with the other three scenario families.
Figure 1 - 6 also shows a range of emissions of the four
scenario families.
The A1
scenario family has explored variations in energy systems most explicitly and hence covers the largest part of the scenario distribution shown in Figure 1 - 6, from the 95th to just above the 10th percentile.
The fact that each of
the scenario families covers a substantial part of the literature range also leads to an overlap in the emissions ranges of the four families.
The 40 SRES scenarios are classified into groups that constitute four
scenario families.
The set of scenarios consists of four
scenario families: A1, A2, B1 and B2.
This leads to six scenario groups that constitute the four
scenario families, three of which are in the A1 family.
The four marker scenarios are characteristic of the four
scenario families and jointly capture most of the ranges of emissions and driving forces spanned by the full set of scenarios.
All the scenarios based on the same storyline constitute
a scenario family.
(See Box 9.1, which briefly describes the main characteristics of the four SRES storylines and
scenario families.)