nomic, cultural, and other factors that are essential for understanding the potential to reduce emissions and adapt to changed climate conditions. These factors are currently underrepresented in integrated assessment models of emissions and consequences of climate change and mitigation policies.

Scenarios are tools for analyzing situations in which outcomes are uncertain. The goal of working with scenarios is not to predict the future but to better understand uncertainties in order to reach decisions that are robust under a wide range of possible futures. Space constraints do not allow a full review of scenario development, but such reviews exist in the literature.¹⁰²

In climate change research, scenarios describe plausible trajectories of different aspects of the future that are constructed to investigate the potential consequences of anthropogenic climate change. Over time, an increasingly broad array of scenarios has been developed to address different components of the issue. Scenarios currently represent major driving forces, processes, impacts, and potential responses important for informing climate change policy. See Box C.1 for a detailed description of types of scenarios used in climate change research.

A variety of techniques have been used in developing scenarios. For climate scenarios, these approaches include analogues of anticipated future conditions (both temporal and spatial), and model-based scenarios produced with general circulation models (GCMs—both global and regional) “forced” with scenarios of emissions.¹⁰³ Emissions scenarios are developed primarily using integrated assessment models (IAMs), which are comprehensive representations of quantifiable socioeconomic (e.g., demographic, economic, and technological) and environmental (e.g., land use) drivers of emissions and, increasingly, impacts. ¹⁰⁴ A variety of environmental scenarios (e.g., sea level rise, hydrology, land cover, air quality) are produced with specialized hydrological, agricultural, ecological, and other models that incorporate both human and environmental processes—these, along with climate scenarios and socioeconomic assumptions are commonly used in evaluating potential consequences of climate change for a variety of human and natural systems. ¹⁰⁵ Quantitative approaches to scenarios do not adequately account for political, cultural, and institutional influences that are important in understanding innovation, technological change, and the ability of societies to effectively implement policies. These factors are most often represented in qualitative narratives or storylines, which are used by analysts in a variety of ways to coordinate scenarios across scales or subject matters.^{106, 107}

Many different groups have used scenarios at different spatial scales. At a global scale, the IPCC has used emissions and climate scenarios as a central component of its work of assessing climate change research. The IPCC has commissioned several sets of emissions scenarios for use in its reports, convening authors and modelers, providing terms of reference, and approving the scenarios through an intergovernmental process that took several