Whereas forecasting is the process of predicting the future based on current trend analysis, backcasting approaches the challenge of discussing the future from the opposite direction. Backcasting then is:
a method in which the future desired conditions are envisioned and steps are then defined to attain those conditions, rather than taking steps that are merely a continuation of present methods extrapolated into the future
Typically, several alternative scenarios are examined -- usually representing different normative (or desirable) states. The question is then asked, if we want to arrive at Scenario A, what trends would need to change to get us there. Usually, quantitative analysis provides a feasibility or plausibility assessment. For example, if Scenario A was future in which CO2 emissions were stabilized at Xppm and Scenario B was CO2 stabilization at Yppm -- quantitative analysis could help assess which one was more plausible under any given set of assumptions. This would be backcasting.
Shaping diversity in participatory foresight studies: experiences with interactive backcasting in a stakeholder assessment on long-term climate policy in The Netherlands.
Mar 22, 2002; An alternative approach to traditional forecasting and planning methods is Backcasting. Backcasting is considered...