In 1997, the U. S. Global Change Research Program initiated the
"National Assessment of the Potential Consequences of Climate
Variability and Change for the United States." This national level
assessment included analyses of the importance of climate
variability and change in twenty regions around the US, in five
cross-cutting sectors focused around natural resources and public
health, and for the US as a whole.
Climatically, the hundred-year projections that were used indicated
that the climatic conditions of the northern US would become like the
central US, the conditions of the central US like those across the
southern US, and conditions across the southern US like tropical and
subtropical regions. The results of the analyses indicated that there will
be significant regional variability in both climate change and resultant
consequences across the US. Although overall forest productivity was
projected to increase for the next several decades as a result of the
carbon dioxide fertilization effect, specific natural ecosystems were
projected to be at significant risk because of the very limited potential
for their movement and reestablishment.
Although the US has abundant water resources, widespread concerns about
water resources arose in every region. As a whole, US agricultural
production was projected to increase, although those farming marginal
lands are likely to be impacted by further reductions in their economic
competitiveness. The extensive coastal regions in the US were projected to
be exposed to rising sea levels, increasing the risk to extensive coastal
infrastructure, barrier islands, and coastal wetlands. Rising temperatures
and the accompanying rise in the absolute humidity, were projected to lead
to much more uncomfortable summer weather conditions across the southern
and eastern US; analyses indicated in general that health consequences
could be minimized by taking a wide array of public health measures.
As the issue of climate change gained attention in the 1980s as a result
of scientific advances and early international conferences, the US Congress
passed the Global Change Research Act of 1990. This public
law recognized the early scientific findings that human activities were
starting to change the global climate, asserting that: "(1) Industrial,
agricultural, and other human activities, coupled with an expanding world
population, are contributing to processes of global change that may significantly
alter the Earth habitat within a few generations; (2) Such human-induced
changes, in conjunction with natural fluctuations, may lead to significant
global warming and thus alter world climate patterns and increase global
sea levels. Over the next century, these consequences could adversely
affect world agricultural and marine production, coastal habitability,
biological diversity, human health, and global economic and social well-being."
To address these issues, the US Congress established the U.S. Global
Change Research Program (USGCRP) and instructed US federal research agencies
to cooperate in developing and coordinating a "comprehensive and
integrated United States research program which will assist the Nation
and the world to understand, assess, predict, and respond to human-induced
and natural process of global change." The USGCRP has led to coordination
of the global-change related research efforts of ten federal agencies,
including the departments of Agriculture, Commerce (specifically the National
Oceanic and Atmospheric Administration-NOAA), Defense, Energy, Health
and Human Services, and the Interior along with the agency-based research
programs in the Environmental Protection Agency (EPA), National Aeronautics
and Space Administration (NASA), the National Science Foundation (NSF),
and the Smithsonian Institution. While interagency coordination has led
to a number of organizational challenges, each agency contributes particular
strengths needed to address the very broad issues raised by concerns about
One section of the Congressionally approved Act indicated that the USGCRP:
"shall prepare and submit to the President
and the Congress an assessment which
1) integrates, evaluates, and interprets the findings of the Program
and discusses the scientific uncertainties associated with such findings;
2) analyzes the effects of global change on the natural environment,
agriculture, energy production and use, land and water resources,
transportation, human health and welfare, human social systems, and
biological diversity; and
3) analyzes current trends in global change, both human-induced and
natural, and projects major trends for the subsequent 25 to 100 years."
Fulfilling this mandate for the issue of potential climate change has
taken several forms. At the international level, the USGCRP coordinates
US participation in the assessments of the Intergovernmental Panel on
Climate Change (IPCC). The IPCC assessments in 1990, 1995, and 2000 have,
at the global and continental scales, carefully reviewed the scientific
literature concerning climate change, its potential consequences, and
options for mitigation. With the IPCC finding in 1995 that human activities
were having a "discernible influence" on the global climate,
the USGCRP undertook a national-level assessment intended to provide detail
about potential consequences within the US.
Given this charge, the overall goal of the National Assessment was to
analyze and evaluate what is known about the potential consequences of
climate variability and change for the US in the context of other pressures
on the public, the environment, and the nation's resources. At the same
time, the assessment was to be designed to initiate an active dialogue
with those who would be affected by the potential consequences in order
to help prepare them to more effectively deal with climate variability
and change and to sharpen the research focus concerning coping options.
Thus was born the National Assessment of the Potential Consequences
of Climate Variability and Change for the United States, commonly
called simply the National Assessment.
The US National Assessment had three major components:
1. Regional analyses: Regional workshops and assessments were used
to characterize the potential consequences of climate variability and
change in regions spanning the US. A total of 20 workshops were held
around the country during 1997 and 1998. Regions holding workshops included:
New England and upstate New York; Metropolitan New York; Mid-Atlantic;
Central and Southern Appalachians; Southeast; South Atlantic Coast and
Caribbean; Gulf Coast; Great Lakes; Eastern Midwest; Northern Great
Plains; Central Great Plains; Southern Great Plains; Rocky Mountain/Great
Basin; Southwest-Rio Grande basin; Southwest-Colorado River basin; California;
Pacific Northwest; Alaska; Pacific islands; and Native peoples and homelands.
Based on the issues identified, most of the regions went on to prepare
assessment reports that would address the issues identified in the workshops;
remaining regions are likely to be the subject of subsequent studies.
2. Sectoral analyses: Workshops and assessments were also organized
to characterize the potential consequences of climate variability and
change for five major sectors that cut across environmental, economic,
and societal interests. The sectors included agriculture, forests, human
health, water, and coastal areas and marine resources. As US assessment
activities continue, the expectation is that examination of additional
sectors such as transportation, energy, business and trade, wildlife,
urban communities, international couplings, and many other sectoral
perspectives will be needed to provide a more comprehensive perspective
on US vulnerability.
3. National overview: A thirteen-member National Assessment Synthesis
Team (NAST) was appointed as a federal advisory committee to provide
the national overview. The NAST co-chairs were Dr. Jerry Melillo of
the Marine Biological Laboratory in Woods Hole MA, Dr. Tony Janetos
of the World Resources Institute in Washington DC, and Dr. Tom Karl
of NOAA's National Climatic Data Center in Asheville NC. The NAST was
given responsibility for providing a national perspective that summarized
and integrated the findings of the regional and sectoral studies and
that then drew conclusions about the importance of the consequences
of climate change and variability for the US. Both an Overview report
intended for decision makers and the public and a Foundation report
intended for experts were prepared (NAST, 2000). Among the innovations
in the NAST report was use of a well-defined lexicon for conveying the
relative level of likelihood and certainty of particular consequences.
Thus, consequences were described as being either "very likely,"
"likely," "possible," "unlikely," or "very
unlikely" in a consistent manner, based on the expert judgment
of the NAST in evaluating the available literature and commissioned
There were a number of unique organizational approaches used in the conduct
of the Assessment. First, responsibility for the National Assessment process
was widely distributed and broadly inclusive, with each of the regional,
sectoral, and synthesis activities being comprised of experts from universities,
government agencies, public and private sector organizations, and from
other stakeholder communities. Second, the assessment process was financially
supported in a shared manner by the set of USGCRP agencies, with each
agency assuming responsibilities for which they had particular interests.
Third, the assessment is viewed by the agencies as the start of a long-term
engagement bringing together the scientific community and those affected
by climate change. Together, these steps have been designed to promote
broad understanding of the issue and its importance and to encourage early
recognition of the need to start adapting to climate change.
Conduct of the Assessment focused on addressing issues of importance
to people in particular places (the regions) and with particular interests
(the sectors). Starting with the broad array of public concerns about
the environment, the Assessment explored the degree to which existing
and future variations and changes in climate might affect issues that
people really care about. A short list of questions guided the process
- What are the current environmental stresses and issues that form
the backdrop for potential additional impacts of climate change?
- How might climate variability and change exacerbate or ameliorate
existing problems? What new problems and issues might arise?
- What are the priority research and information needs that can better
prepare the public and policy makers for reaching informed decisions
related to climate variability and change?
- What coping options exist that can build resilience to current environmental
stresses, and also possibly lessen the impacts of climate change?
In analyzing the potential consequences, the National Assessment teams
utilized three approaches to generate plausible future climatic conditions.
Historic data sets were assembled and used to evaluate the potential consequences
of a reoccurrence of past variations in the climate, recognizing that
there would also be an underlying warming trend. Computer-generated scenarios
from the Canadian and Hadley (U.K.) climate modeling centers were used
to provide a self-consistent set of plausible future conditions. These
model scenarios spanned the range from warm/moist to hot/dry conditions
that are typical of the wider set of climate models. Should these conditions
occur, the US would experience about a 5 to 10F (about 3 to
6C) warming and modest to strong precipitation increases across
Such changes would be equivalent to shifting warm climatic zones
northward such that, over the 21st century, the future climate
of the central US would become like the current climate of the southern
US. The third approach, only used in a few instances in this initial assessment
phase, was to consider the amount of change that would significantly increase
existing vulnerability by, for example, crossing a threshold or triggering
a non-linearity. In addition to the various approaches to treating prospective
climate variability and change, ecosystem models were used to generate
prospective changes in vegetation cover, and socio-economic scenarios
were generated to consider possible changes in population and economic
The various regional and sectoral studies provided a diverse picture
of potential consequences, with a mixture of beneficial and detrimental
consequences. While potential adaptation measures were identified that
could moderate adverse consequences for many societal activities, disruptions
were found to be likely to affect the complex distribution of ecosystems
across the US, with some types of rare ecosystems (e.g., alpine meadows,
coral reefs) being particularly impacted because there was little potential
for natural or assisted adaptation. Because of the likelihood of intensified
evaporation and changes in the amounts and duration of mountain snowpack,
water resources arose as an issue in regions across the US, from the dry
regions of the southwest to the more abundant regions of the Pacific Northwest.
Timber and agricultural production were found to be likely to increase
due to CO2 fertilization, but, should warming occur near the
upper bounds of estimates, increased water stress and potential disruptive
threats (e.g., fires for forests, pests for agriculture) could create
significant vulnerability. Coastal and permafrost regions were found to
be likely to suffer increasing stress, creating problems for buildings
and other infrastructure. While the warmer, moister conditions would raise
the heat index, reducing the quality of life, the health threat from such
conditions is currently being reduced through increased reliance on air-conditioning.
More generally, sustaining the health of the US population was found to
require intensified attention to public health practices and community
structure (e.g., building codes).
Quite clearly, many important questions and issues remain to be addressed.
Given the initial nature and limited scope of the assessment, it was also
recognized that uncertainties, including possible surprises, are also
likely. For this reason, it is expected that assessment activities will
become an ongoing part of the USGCRP.