The generation of greenhouse gas (GHG) emissions is one source of uncertainty in climate decision making. We do not know how emissions will change over time and making predictions is difficult, partly because it is dependent on human behaviour. Technological innovation, economic change, and social patterns all influence emissions and are inherently uncertain, which in turn limits our ability to predict emissions levels.
A GHG emission scenario is an image of a possible pattern of emission generation. The Intergovernmental Panel on Climate Change (IPCC) has developed an extensive range of possible emission scenarios based on assumptions that differ along several dimensions including population, technological development, and expectations about economic growth. Each of these scenarios presents an image of possible GHG emissions levels based on its assumptions about what the world is likely to look like over time.
The suite of scenarios developed by the IPCC has been broadly used as the basis for GCM modelling. For example, the Pacific Climate Impacts Consortium (PCIC) Regional Analysis Tool and the Canadian Climate Change Scenarios Network both work from these scenarios. The utility of scenarios in decision making is further explained the Scenarios section.
For additional information, please see the materials under "Greenhouse Gas Emission Scenarios" in the Recommended Links section.