In order to provide plausible pictures of future emissions of greenhouse gases, the IPCC developed four families of scenarios, based on an extensive assessment of the literature, six alternative modelling approaches and an “open process” that solicited wide participation and feedback from many groups and individuals. The scenarios provide a basis for analysing how drivers may influence future emissions, as well as to assess the associated uncertainties.
The four basic storylines are:
A1. A future world of very rapid economic growth, global population that peaks in the middle of the 2100s and declines thereafter, and rapid introduction of new and more efficient technologies. Major underlying themes are convergence among regions, capacity building and increased cultural and social interactions, with a substantial reduction in regional differences in per capita income.
A2. A very heterogeneous world emerges; the underlying theme is self-reliance and preservation of local identities. Fertility patterns among regions converge very slowly, which results in continuously increasing global population. Economic development is primarily regionally oriented, and per capita economic growth and technological changes are more fragmented and slower than in other story lines.
B1. A convergent world with the same global population trends as the A1 story line, but with rapid changes in economic structure toward a service and information economy, reductions in material intensity, and introduction of clean and resource-efficient technologies. The emphasis is on global solutions for economic, social and environmental sustainability, including improved equity, but without additional climate initiatives.
B2. A world in which the emphasis is on local solutions to economic, social and environmental sustainability. This is a world with continuously increasing global population, although at a rate lower than seen in A2, intermediate levels of economic development, and less rapid, more diverse technological change than in the B1 and A1 story lines.
Box 3: Other long-term scenarios
|Figure 3: IPCC Scenarios
Few other studies have tried to look as far out into the future as IPCC, although the MA (2005b) provided some indication of certain trends to 2100 in its scenarios. Kahn and others (1976) presented a scenario looking 200 years into the future and a small set of 1 000-year scenarios were created as an exercise as part of the United Nations University’s Millennium Project (Glenn and Gordon 2005). Other studies, such as the UN’s World Population to 2300 (UN 2004) represent more narrow projections of specific issues, rather than actual scenarios.
See Exercise 6.4.3