Note: Four qualitative storylines yield four sets of scenarios called ‘families’: A1, A2, B1 and B2. The scenarios specify global annual emissions of the major greenhouse gases, together with sulphate aerosols, from 1990 to 2100. Altogether, 40 SRES scenarios have been developed, all considered equally valid with no assigned probabilities of occurrence. Within the A1 family there are three scenario groups (A1FI, A1T, A1B), characterising alternative developments of energy technology. Within each of the six scenario groups, there is a shared set of so-called ‘harmonised’ assumptions about global population, gross world product and energy use (labelled ‘HS’ for harmonized scenarios). There are other scenarios (labelled ‘OS’) that explore additional uncertainty in these forces that drive future emissions.
Source: Nakicenovic and Swart 2000: figure 1.
Text description of figure
This figure represents the breakdown of IPCC SRES scenarios into four sets known as ‘families’ (A1, A2, B1 and B2). At the next tier down, the A1 family is further split into 3 different groups which depict alternative developments of energy technologies leading to a total of 6 scenario groups (A1F1, A1T, A1B, A2, B1 and B2). Scenario groups can be further divided into ‘harmonised’ or ‘other’ scenarios.