4. National Assessment of the Consequences of Climate Change for the United States

In 1997, the Subcommittee on Global Change Research (SGCR), which coordinates the U.S. Global Change Research Program, initiated a national, scientifically based assessment of the consequences of climate change and climate variability for the people, environment, and economy of the United States. This assessment will provide an opportunity to foster the participation of people who use global change information throughout the country and to enhance their ability to plan for and cope with climate changes and variations.

Goal of the National Assessment

The goal of the National Assessment is to determine the local, regional, and national implications of climate change and climate variability within the United States in the context of other existing and potential future environmental, economic, and social stresses. Of particular importance is understanding the regional mosaic of what has been and will be occurring as a result of global change.

Approach of the Assessment: Regions, Sectors, and National Synthesis

The National Assessment process has been designed to create a continuing dialog among government, business and industry, labor, non-profit organizations, the scientific research and education communities, and the public. A multi-pronged approach will be used to generate the needed information about the implications of climate change and variability for the United States:

  1. Regional assessment activities will focus on the issues of most importance at the regional level across the United States. As an initial step, 20 workshops, encompassing every state and territory, are identifying the distinctive regional characteristics and potential consequences of climate change and variability (see the table in Chapter 1, and Color Plate 8 below).
  2. Sectoral assessment activities will focus on issues that are national in scope and related to the goods and services on which people, society, and the economy depend. Initially, sectors being considered include food availability; water availability; human health; forests; ecosystem services; urban activities and services; and commerce, industry, and trade.
  3. National synthesis activities will identify common themes and core issues concerning the implications of long-term climate change and variability for the United States. These findings will be integrated and consolidated into a synthesis report that will serve as a national summary for decisionmakers.
To promote consistency and coherence across the regions and sectors, a series of guideline scenarios will be prepared that estimate how the Nation is expected to develop economically, demographically, and technologically over the next 25 to 100 years. A series of scenarios also will be developed that define a range of changes in climate, resource use, and ecosystem distribution so that the potential consequences of long-term climate change for the United States can be evaluated.

Color Plate 8. Regional Climate Change Workshops

Regional Climate Change 
Regional Climate Change 
Regional Climate Change Workshops. What are the risks and opportunities for the United States--its people, its environment, and its economy--associated with increased climate variability and climate change? This question is being addressed in a National Assessment of the Consequences of Climate Change for the United States being conducted by the USGCRP. As an initial step, 20 regional workshops, encompassing every state and territory, are identifying the distinctive regional characteristics and potential consequences of climate change and variability. The maps indicate the eight regions in which workshops were held in 1997, and the 12 workshops being held in 1998.

Southeast: Lessons Learned from El Niño Events Should Help Farmers Adjust to Climate Changes Caused by Emissions of Greenhouse Gases

The El Niño-Southern Oscillation (ENSO) signal is quite pronounced in the southeastern United States. Studies of the relationship between El Niño and agricultural production in the region are helping farmers adjust to changing climate conditions, providing an example of how a better understanding of these short- term, interannual climate variations may help those who will be affected in the future by climate change.

Central Great Plains: Turning Problems into Solutions

The agricultural sector in the Great Plains faces a number of challenges. Farmers and ranchers must cope with extreme weather events--floods, droughts, blizzards, hail storms, tornadoes, and others--that might become more severe and frequent in the future. They also are working to reduce runoff of crop and animal wastes into water supplies and to slow the loss of soil to erosion.

But theirs is not a message of despair. Already they are developing and implementing sustainable land practices, both because these practices increase their incomes and because they protect the environment. One example of such a win-win solution occurs when ranchers supplement their incomes by converting animal wastes into marketable biomass fuels, which simultaneously reduces the amount of the greenhouse gas methane released into the atmosphere. Likewise, by increasing the carbon content of the soils and thus pulling carbon dioxide from the atmosphere, farmers are adding to the resilience of their fields to drought, whether natural or enhanced by climate change.

Southwest: Meeting the Water Needs of a Rapidly Growing Population

Communities in arid and semi-arid environments of the Southwest are especially sensitive to impacts on water resources. They depend on access to adequate supplies for their people and their agriculture, but are at risk to the extremes of flood and drought cycles. Most water in the Southwest comes from melting snow in the Rocky Mountains or underground aquifers. As population in the region increases, overuse is depleting the aquifers and climate change is expected to affect the amount of water from snowmelt. At the same time, rising temperatures over land could intensify the strong convective storms that can occur in the Southwest. Understanding how all of these factors interrelate would provide the information needed by regional decisionmakers to consider options and develop plans for meeting societal needs.

Critical Questions

In conducting the regional workshops leading into the assessment, four fundamental questions are being posed:

  1. What are the current environmental stresses?
  2. How will projected changes in climate and climate variability exacerbate or ameliorate existing stresses, or introduce new stresses (see Figure 6)?
  3. What information is needed to provide better and more certain estimates of the consequences of climate change and variability?
  4. What strategies may help the region or sector cope with the anticipated consequences of changes in climate? What opportunities exist for win-win solutions and approaches?
Figure 6: Potential Climate 
Change Impacts
Figure 6: Potential Climate Change Impacts. Schematic diagram illustrating the types of consequences that can result from changes in the most critical climate parameters.


The Global Change Research Act of 1990 mandates the preparation of scientific assessments of global change. The National Assessment will be a core activity of the USGCRP. The USGCRP's conduct of the assessment will be overseen by the National Science and Technology Council and the Office of Science and Technology Policy.

As the USGCRP conducts the National Assessment, a number of public-private partnerships will be established with the intent of creating a collaborative network of decisionmakers, scientists, and other interested parties. Those partnerships will underlie a continuing process that will produce periodically updated, scientifically based evaluations and summaries of current understanding.

The assessment process will be designed to be comprehensive and integrative, to couple research by scientists with specific policy- relevant needs of stakeholders, to ensure scientific excellence and credibility, to be open to broad participation, and to provide planners, managers, organizations, and the public with information they will need to cope with natural climate fluctuations and projected climate changes.

Northwest: Adjusting Planning for Columbia River Water Management

The Columbia River is the lifeblood of the Northwest. Variations in climate already require management of competing water demands along the river system in order to protect fisheries while providing water for irrigation, hydroelectric power, and communities. Changes in the seasonal timing and amount of precipitation are expected to affect the timing of peak runoff and river discharge, creating a potential mismatch between water supplies and user needs. Understanding these changes would provide opportunities for the various sectors to adjust by improving irrigation efficiency, changing crops, and developing alternative energy sources.

New England: Reducing Emissions Improves Air Quality

Because the upstate New York and New England region is downwind from emissions from industrial, utility, and transportation sources in the rest of the United States and parts of Canada, the quality of life there is threatened by poor air quality. If CO2 emissions were reduced, the region would see benefits far beyond the prevention of climate change. Emission reductions would help abate the region's air pollution and acid rain, while improving visibility during summer months. Improving the gas mileage of automobiles, via new hybrid technologies and other innovative approaches, as well as conversion of midwestern power production facilities to alternative energy sources, would result in lower levels of nitrogen oxides, sulfur dioxide, organic compounds, and tropospheric ozone affecting the region. Human health would benefit immediately from emission reductions; the health of the region's ecosystems also could benefit, and healthier forests would take up more CO2 from the atmosphere.

Alaska: Already Experiencing Warming

Alaska has warmed about 5°F over the past 30 years and this warming is already having a significant influence. Warmer days can bring more personal comfort and longer farming seasons, but they also affect fisheries and cause a thawing of the permafrost layer. This thawing is particularly significant because it results in damage to buildings, roads, railroads, and other infrastructure, while also causing slumping in forests that leads to their transformation into wetlands. Drier summers have reduced forest health, leading to an increase in forest fires and in insect infestation. Alaska is faced with developing the means to cope with what may prove to be the most pronounced climate change in the United States.

Products of the National Assessment Process

A series of summary reports will describe the consequences of climate change and variability for regions and sectors. These will be based on more detailed findings and documentation published by each regional or sectoral assessment activity. The set of summary reports will be accompanied by a synthesis report that provides an overview and integration of the regional and sectoral reports. The first series of assessment reports will be completed in late 1999. These reports will point to many issues requiring elaboration as part of the continuing research and assessment process.

Integration with USGCRP Research Activities

To support the various assessment activities, a significant USGCRP priority will be an assessment-oriented research agenda as well as a strong, broadly based research program aimed at improving fundamental understanding of the Earth system. A number of agencies already have regional research and assessment programs underway, and additional activities are being planned by a broader set of USGCRP agencies.

Ensuring Scientific Credibility and Relevance

An open and inclusive process that encourages the participation of the most qualified scientific, technical, and socioeconomic experts will ensure the credibility of the National Assessment reports. Draft assessment reports will be subject to an open and wide-reaching review process, and well-documented and reviewed alternative interpretations will be accommodated. Continuing and close involvement of stakeholders and decisionmakers will ensure relevance to policymakers. Internal and external evaluation processes will ensure that the continuing series of assessment activities and reports present a clear and fair depiction of scientific understanding and stakeholder interests and needs.

Outreach and Communication

The value of the assessment process will depend on communicating the findings and lessons emerging from the dialog among the many and diverse stakeholders and scientific communities. The U.S. Climate Forum, held at the Department of Commerce on November 1213, 1997, was the first major step to encourage nationwide participation in the assessment process. Assessment activities, workshop reports, and analytic findings will be communicated broadly through the media, the World Wide Web, and other channels. Reports will be made widely and inexpensively available. Outreach also will occur through programs that target both the formal (i.e., school-based) and informal (i.e., museum, park, and community-based) educational communities.

Mid-Atlantic Region: Protecting the Coastal Zones

In the Mid-Atlantic region, climate change could have profound effects on human health, ecosystems, and outdoor recreation because of the region's unique combination of geography, aging infrastructure, economic structure, population density, and mixed land use. One of the prime issues for the Chesapeake Bay is sea-level rise. Past rises have caused coasts to erode, threatened homes, narrowed recreational beaches, and eroded wetlands and bay beaches that are important habitat for birds and fish. Information is needed to evaluate new construction or re-building within areas of high risk from natural hazards (e.g., zones prone to flooding, coastal storms, or tidal surges), and to determine the best means of protecting ecosystems and infrastructure. One of the most important elements of a response strategy would be the communication of climate change projections to improve land-use and drought planning efforts and strategies for managing water across regional or local districts.

Northern Great Plains: Rebuilding after Flood

The April 1997 flood of the Red River washed out homes and businesses that had been in Grand Forks, North Dakota, and East Grand Forks, Minnesota, for generations. The disaster was expected to occur, at least on the average, only once every 500 years. But now Mayors Pat Owens of Grand Forks and Lynn Stauss of East Grand Forks face a new uncertainty as they rebuild their cities. Will floods of this magnitude occur more frequently in the future? If so, what level of protection must be provided? Can dikes or diversion channels be built to withstand even greater floods? No one is quite certain how severe or how frequent future floods--or their opposites, droughts--will be. But the climate change that is already underway is likely to change the pattern of storms and spring melts in this region. The historical pattern of seasonal river flows might change as well.

For Mayors Owens and Stauss, climate change is a current issue. Displaced people and businesses need decisions now on how close to the river they can build and what level of protection will need to be provided. These decisions affect future generations as well. To protect lives, property, and livelihoods for residents both today and tomorrow, the two mayors need the best possible information about future climates.

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