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Updated 7 May 2003

US National Assessment of
the Potential Consequences
of Climate Variability and Change
Overview of National Assessment Scenario Strategy




In order to have materials that could be synthesized across regions and sectors, the National Assessment Synthesis Team developed a framework for considering both climate and socieconomic scenarios. Each regional and sectoral team was asked to follow some similar steps in using these scenario frameworks; however, the overall approach was meant to give teams considerable flexibility in pursuing additional models and explorative approaches that would lend information about potential impacts and system thresholds.

This strategy combined historical approaches suited for understanding patterns of natural variability, scenario-driven approaches suited to understanding outcomes based on specific assumptions about future climate and socioeconomic conditions, and parametric approaches, suited to understanding system thresholds given an infinite range of possible future scenarios.

  • Climate Scenario Tools

    There were three primary components of the climate scenario strategy (1-3 below). Each was recommended for use by assessment teams for a range of information about sensitivities and impacts.

    1. Historical Data: A historical climatology of the United States covering the 20th century was used to examine the potential consequences of continuation of past climatic trends and future occurrence of past climate variations.
    2. General Circulation Model (GCM) Runs: General circulation model simulations extending to 2100 of two types were used. The first type were model simulations that were carried out assuming a 1% per year increase in greenhouse gas concentrations, both with and without changes in aerosol concentration. The second type was a set of simulations comparing the climatic response for Business-as-Usual growth in greenhouse gas concentrations with the response assuming stabilization of greenhouse gas concentrations. Within the GCM component, there were several different runs that were made available. However, if a team had time for only one, the Canadian Climate Model was recommended; if two, add Hadley, etc.

      The following runs were made available:

      • Canadian Climate Model (IS92a run)
      • Hadley/UKMO (IS92a run)
      • GISS/GFDL/NCAR (IS92a runs)
      • NCAR Stabilization Run

    3. Search for Qualitative Changes (previously termed "inverse" or "what-if"): Region- or sector-specific scenarios were developed by individual teams to facilitate analysis of the limits of vulnerability of regions and sectors, exploring these in relation to plausible future climate conditions.

  • Socioeconomic Scenario Tools

    The socioeconomic scenario framework that was developed by the Synthesis Team consisted of a set of five principles about evolving socioeconomic changes. Each of these five principles had implications for how a regional or sectoral assessment should approach an assessment (see below). Contextual data and projections were provided to support this framework.

    Socioeconomic Scenarios: Underlying Principles and Implications of Each for the Approach to be Followed
    Underlying Principles Implications for Approach
    Future information about socioeconomic conditions was essential for use in the assessment. Socioeconomic scenarios were developed up to 2025 and 2050; beyond this a parametric approach is recommended.
    This information needed to have some national consistency and some regional diversity. Certain socioeconomic variables were set nationally (i.e. population growth), but others were determined by regional and sectoral teams.
    It was not possible to do excessively detailed predictions The best we could do was to assure that all assessment teams were consistent with some national data.
    One scenario was  not sufficient: there was a need for ranges/bounds. Each assessment team did at least two if/then scenarios (not a single scenario).
    Impacts in any given sector or region depend on that domain and on the general context. Selected key factors so some were local and made assumptions about broader (aggregate) socioeconomic conditions.

    Socioeconomic Forecasts and Contextual Material to be Made Available to National Assessment Teams
    (with DOE support, Oak Ridge National Laboratory is arranging for the development of the following, some through NPA Data Services, Inc.)

    Socioeconomic Forecasts:

    • A copy of the current business-as-usual forecast to 2025
    • Definition of assumptions for high and low scenarios
    • Provision of the high and low scenarios, down to county level, to 2025
    • Provision of all three scenarios (high, low and business-as-usual) to 2050.

    Supporting Contextual Material:

    • Summary of forecasts of technological change in the U.S.
    • Summary of forecasts of institutional change in the U.S.

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