All of the SRES storylines assume a future world that is more prosperous and technologically advanced than present day. The levels of greenhouse gas emissions are generally less than the previous IPCC IS92 scenarios, especially towards the end of the 21st century. The emissions of sulphur dioxide, which produce sulphate aerosols that have a cooling effect on climate, are substantially less than in the IS92 scenarios. The SRES scenarios are based on more-recent projections of global population and span a greater range of potential economic futures than the IPCC IS92 scenarios, including some with a significant closing of the gap between developing and developed countries.
Global population rises during the first half of the century, peaks mid-century, then declines.
New and efficient technology is rapidly introduced. The A1FI scenario sees the continuation of fossil fuels as the main energy source. The B1 family describes a world with the same population growth as the A1 family. There are rapid changes in economic activity away from production towards a service economy. Clean and efficient technologies are introduced.