SRES-A1: An "integrated" world with a rapid economic growth, a global population that reaches 9 billion and then gradually declines, quick spread of new and efficient technologies, and convergent incomes and way of life among nations. Subsets of SRES-A1 emphasize the relative balance of fossil intensive and non-fossil energy sources.
SRES-A2: A "divided" world with regionally oriented economic development, continuously increasing population growth, and fragmented technological change (independent, self-reliant nations).
SRES-B1: An "integrated and more ecological friendly" world with a global population that reaches 9 billion and then gradually declines (as in A1), rapid economic growth (as in A1), but with rapid changes in economies towards service and information, reductions in material intensity introduction of clean and resource efficient technologies, and an emphasis on global solutions to economic, social, and environmental stability.
SRES-B2: A "divided but more ecologically friendly" world with continuously increasing population (but at a slower rate than A2), emphasis on local rather than global solutions to economic, social, and environmental stability, intermediate levels of economic development, and less rapid and more fragmented technological change than in A1 and B1.
Three SRES-A1 groups are distinguished by their technological emphasis: fossil fuel energy intensive (A1FI), non-fossil fuel energy intensive (A1T) and balanced across all energy sources (A1B). Here, balanced is defined as not relying too heavily on one particular energy source, on the assumption that similar improvement rates apply to all energy supply and end-use technologies.