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This Overview section

More detailed chapter from  "Foundation" report.

The National Assessment Overview and Foundation Reports were produced  by the National Assessment Synthesis Team, an advisory committee chartered under the Federal Advisory Committee Act, and were not subjected to OSTP's Information Quality Act Guidelines. The National Assessment was forwarded to the President and Congress in November 2000 for their consideration.

Positive impacts will possibly be associated with climate changes such as warmer winters in the North, more precipitation in the Southwest, and longer growing seasons in parts of the nation where agriculture and forestry are important.

The warmer conditions associated with longer growing seasons in many parts of the country are likely to lead to increased  pest and disease problems for agriculture and forestry.

This national discourse involved thousands of Americans: farmers, ranchers, engineers, scientists, business people, local government officials, and a wide variety of others. This unique level of stakeholder involvement has been essential to this process, and will be a vital aspect of its continuation. The value of such involvement includes helping scientists understand what information stakeholders want and need.

Large Impacts in Some Places

The impacts of climate change will be significant for Americans. The nature and intensity of impacts will depend on the location, activity, time period, and geographic scale considered. For the nation as a whole, direct economic impacts are likely to be modest. However, the range of both beneficial and harmful impacts grows wider as the focus shifts to smaller regions, individual communities, and specific activities or resources. For example, while wheat yields are likely to increase at the national level, yields in western Kansas, a key US breadbasket region, are projected to decrease substantially under the Canadian climate model scenario. For resources and activities that are not generally assigned an economic value (such as natural ecosystems), substantial disruptions are likely.

Multiple-stresses Context

While Americans are concerned about climate change and its impacts, they do not think about these issues in isolation. Rather they consider climate change impacts in the context of many other stresses, including land-use change, consumption of resources, fire, and air and water pollution. This finding has profound implications for the design of research programs and information systems at the national, regional, and local levels. A true partnership must be forged between the natural and social sciences to more adequately conduct assessments and seek solutions that address multiple stresses.

Urban Areas

Urban areas provide a good example of the need to address climate change impacts in the context of other stresses. Although large urban areas were not formally addressed as a sector, they did emerge as an issue in most regions. This is clearly important because a large fraction of the US population lives in urban areas, and an even larger fraction will live in them in the future. The compounding influence of future rises in temperature due to global warming, along with increases in temperature due to local urban heat island effects, makes cities more vulnerable to higher temperatures than would be expected due to global warming alone. Existing stresses in urban areas include crime, traffic congestion, compromised air and water quality, and disruptions of personal and business life due to decaying infrastructure. Climate change is likely to amplify some of these stresses, although all the interactions are not well understood.

Impact, Adaptation, and Vulnerability

As the Assessment teams considered the negative impacts of climate change for regions, sectors, and other issues of concern, they also considered potential adaptation strategies. When considered together, negative impacts along with possible adaptations to these impacts define vulnerability. As a formula, this can be expressed as vulnerability equals negative impact minus adaptation. Thus, in cases where teams identified a negative impact of climate change, but could not identify adaptations that would reduce or neutralize the impact, vulnerability was considered to be high. A general sense emerged that American society would likely be able to adapt to most of the impacts of climate change on human systems but that the particular strategies and costs were not known.

Widespread Water Concerns

A prime example of the need for and importance of adaptive responses is in the area of water resources. Water is an issue in every region, but the nature of the vulnerabilities varies, with different nuances in each. Drought is an important concern in every region. Snowpack changes are especially important in the West, Pacific Northwest, and Alaska. Reasons for the concerns about water include increased threats to personal safety, further reduction in potable water supplies, more frequent disruptions to transportation, greater damage to infrastructure, further degradation of animal habitat, and increased competition for water currently allocated to agriculture. The table below illustrates some of the key concerns related to water in each region.

Health, an Area of Uncertainty

Health outcomes in response to climate change are highly uncertain. Currently available information suggests that a range of health impacts is possible. At present, much of the US population is protected against adverse health outcomes associated with weather and/or climate, although certain demographic and geographic populations are at greater risk. Adaptation, primarily through the maintenance and improvement of public health systems and their responsiveness to changing climate conditions and to identified vulnerable subpopulations should help to protect the US population from adverse health outcomes of projected climate change. The costs, benefits, and availability of resources for such adaptation need to be considered, and further research into key knowledge gaps on the relationships between climate/weather and health is needed.

Vulnerable Ecosystems

Many US ecosystems, including wetlands, forests, grasslands, rivers, and lakes, face possibly disruptive climate changes. Of everything examined in this Assessment, ecosystems appear to be the most vulnerable to the projected rate and magnitude of climate change, in part because the available adaptation options are very limited. This is important because, in addition to their inherent value, they also supply Americans with vital goods and services, including food, wood, air and water purification, and protection of coastal lands. Ecosystems around the nation are likely to be affected, from the forests of the Northeast to the coral reefs of the islands in the Caribbean and the Pacific.

Agriculture and Forestry Likely to Benefit in the Near Term

In agriculture and forestry, there are likely to be benefits due to climate change and rising CO2 levels at the national scale and in the short term under the scenarios analyzed here. At the regional scale and in the longer term, there is much more uncertainty. It must be emphasized that the projected increases in agricultural and forest productivity depend on the particular climate scenarios and assumed CO2 fertilization effects analyzed in this Assessment. If, for example, climate change resulted in hotter and drier conditions than projected by these scenarios, both agricultural and forest productivity could possibly decline.

Potential for Surprises

Some of the greatest concerns emerge not from the most likely future outcomes but rather from possible "surprises." Due to the complexity of Earth systems, it is possible that climate change will evolve quite differently from what we expect. Abrupt or unexpected changes pose great challenges to our ability to adapt and can thus increase our vulnerability to significant impacts.

A Vision for the Future

Much more information is needed about all of these issues in order to determine appropriate national and local response strategies. The regional and national discussion on climate change that provided a foundation for this first Assessment should continue and be enhanced. This national discourse involved thousands of Americans: farmers, ranchers, engineers, scientists, business people, local government officials, and a wide variety of others. This unique level of stakeholder involvement has been essential to this process, and will be a vital aspect of its continuation. The value of such involvement includes helping scientists understand what information stakeholders want and need. In addition, the problem-solving abilities of stakeholders have been key to identifying potential adaptation strategies and will be important to analyzing such strategies in future phases of the assessment.

The next phase of the assessment should begin immediately and include additional issues of regional and national importance including urban areas, transportation, and energy. The process should be supported through a public-private partnership. Scenarios that explicitly include an international context should guide future assessments. An integrated approach that assesses climate impacts in the context of other stresses is also important. Finally, the next assessment should undertake a more complete analysis of adaptation. In the current Assessment, the adaptation analysis was done in a very preliminary way, and it did not consider feasibility, effectiveness, costs, and side effects. Future assessments should provide ongoing insights and information that can be of direct use to the American public in preparing for and adapting to climate change.

The following section offers suggestions about new approaches, new knowledge, and new capabilities that would improve future assessments and thus provide more effective guidance for responding to the challenges posed by climate change.