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
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.
- 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.
- 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
- 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
- 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
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
consistent with some national data.
One scenario was not sufficient: there was a need for
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
- 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.