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Why scenarios?
Scenarios are devices 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 and alternative futures, in order to consider how robust different decisions or options may be under a wide range of possible futures. 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. Scenarios represent many of the major driving forces - including processes, impacts (physical, ecological, and socioeconomic), and potential responses – that are important for informing climate change analysis.

Types of scenarios in climate research and assessment

Emissions scenarios
Emissions scenarios describe future releases to the atmosphere of greenhouse gases, aerosols, and other pollutants and, along with information on land use and land cover, provide inputs to climate models. They are based on assumptions about driving forces such as patterns of economic, population growth, and technology development. In addition to their use as inputs to climate models, emissions scenarios are used in research on mitigation. They do not track “short-term” fluctuations such as business cycles or oil market price volatility but focus on long-term (e.g., decades) trends.

Climate scenarios
Climate scenarios are plausible representations of future climate conditions (temperature, precipitation, and other aspects of climate such as extreme events). They can be produced using a variety of approaches including analysis of observations, models, and other techniques such as extrapolation and expert judgment.

Environmental scenarios
These scenarios focus on changes in environmental conditions other than climate that may occur regardless of climate change. Such factors include water availability and quality at basin levels (including human uses), sea level rise incorporating geological and climate factors, characteristics of land cover and use, and local atmospheric and other conditions affecting air quality.

Vulnerability scenarios
Scenarios of demographic, economic, policy, cultural, and institutional characteristics are needed for evaluating the potential to be impacted by changes in climate as well for examining how future patterns of economic growth and social change affect vulnerability and the capacity to adapt. Many of the same socioeconomic factors that affect emissions also affect vulnerability and adaptive capacity and thus the underlying socioeconomic modeling must be coordinated.

While some socioeconomic factors affecting emissions and vulnerability are modeled quantitatively, others (e.g., political, institutional, and cultural factors) are not effectively quantified. For this reason, qualitative narratives (also referred to in the literature as “storylines”) are used to describe developments in these factors and how they could influence future forcing, vulnerability, and responses. Narratives can be used as the basis for quantitative scenarios. For example, the IPCC SRES scenarios were based on a set of four narratives that described a range of different development pathways for the world. Narratives can also facilitate coordination across spatial scales and substantive domains.

Content last modified: 4 November 2019