Potential Consequences of and Adaptation to Climate Change

Introduction

Since the late 1980s, an increasing number of studies have been undertaken to investigate the potential impacts of climate change on U.S. society and the environment (e.g., U.S. EPA 1989, U.S. Congress 1993) and as components of international assessments (e.g., IPCC 1996a, 1998). While these studies have generally indicated that many aspects of the U.S. environment and society are likely to be sensitive to changes in climate, they were unable to provide in-depth perspectives of how various types of impacts might evolve and interact. In 1997, the interagency U.S. Global Change Research Program (USGCRP) initiated a National Assessment process to evaluate and synthesize available information about the potential impacts of climate change for the United States, to identify options for adapting to climate change, and to summarize research needs for improving knowledge about vulnerability, impacts, and adaptation (see Chapter 8). The findings were also undertaken to provide a more in-depth analysis of the potential time-varying consequences of climate change for consideration in scheduled international assessments (IPCC 2001a) and to contribute to fulfilling obligations under sections 4.1(b) and (e) of the United Nations Framework Convention on Climate Change.

The U.S. National Assessment was carried out recognizing that climate change is only one among many potential stresses that society and the environment face, and that, in many cases, adaptation to climate change can be accomplished in concert with efforts to adapt to other stresses. For example, climate variability and change will interact with such issues as air and water pollution, habitat fragmentation, wetland loss, coastal erosion, and reductions in fisheries in ways that are likely to compound these stresses. In addition, an aging national populace and rapidly growing populations in cities, coastal areas, and across the South and West are social factors that interact with and in some ways can increase the sensitivity of society to climate variability and change. In both evaluating potential impacts and developing effective responses, it is therefore important to consider interactions among the various stresses.

In considering the potential impacts of climate change, however, it is also important to recognize that U.S. climate conditions vary from the cold of an Alaskan winter to the heat of a Texas summer, and from the year-round near-constancy of temperatures in Hawaii to the strong variations in North Dakota. Across this very wide range of climate conditions and seasonal variation, American ingenuity and resources have enabled communities and businesses to develop, although particular economic sectors in particular regions can experience losses and disruptions from extreme conditions of various types. For example, the amount of property damage from hurricanes has been rising, although this seems to be mainly due to increasing development and population in vulnerable coastal areas. On the other hand, the number of deaths each year from weather extremes and from climatically dependent infectious diseases has been reduced sharply compared to a century ago, and total deaths relating to the environment are currently very small in the context of total deaths in the United States, even though the U.S. population has been rising. In addition, in spite of climate change, the productivity of the agriculture and forest sectors has never been higher and continues to rise, with excess production helping to meet global demand.

This adaptation to environmental variations and extremes has been accomplished because the public and private sectors have applied technological change and knowledge about fluctuating climate to implement a broad series of steps that have enhanced resilience and reduced vulnerability. For example, these steps have ranged from better design and construction of buildings and communities to greater availability of heating in winter and cooling in summer, and from better warnings about extreme events to advances in public health care. Because of this increasing resilience to climate variations and relative success in adapting to the modest changes in climate that were observed during the 20th century, information about likely future climate changes and continuing efforts to plan for and adapt to these changes are likely to prove useful in minimizing future impacts and preparing to take advantage of the changing conditions.

With these objectives in mind, the U.S. National Assessment process, which is described more completely in Chapter 8, initiated a set of regional, sectoral, and national activities. The box, Key National Findings Adapted from the US National Assessment,  presents an overview of key national findings, and the following subsections elaborate on these findings, covering both potential consequences and the types of adaptive steps that are underway or could be pursued to moderate or deal with adverse outcomes. The subsections summarize the types of impacts that are projected, covering initially the potential impacts on land cover; then the potential impacts on agriculture, forest, and water resources, which are key natural resource sectors on which society depends; then potential impacts associated with coastal regions and human health that define the environment in which people live; and finally summarization of the primary issues that are specific to particular U.S. regions. A full list of regional, sectoral, and national reports prepared under the auspices of the U.S. National Assessment process is available.  Additional materials relating to research and assessment activities also may be accessed via the US Global Change Research Program web site.