Introduction to the Unified Synthesis Product (USP), Global Climate Change Impacts in the United States
The USP provides in plain language a synthesis of our current understanding of global climate change impacts in the United States. It does this by addressing special issues facing a variety of sectors and regions across the United States. In the process of synthesizing this information across a large number of recently completed assessments and new research since, the USP provides some new insights about climate change impacts in the United States. Highlights include: 1. Climate-related changes already have been observed globally and in the United States. These include increases in air and water temperatures, reduced frost days, increased frequency and intensity of heavy downpours, a rise in sea level, and reduced snow cover, glaciers, and sea ice. A longer ice-free period on lakes and rivers, lengthening of the growing season, and increased water vapor in the atmosphere has also been observed. 2. These changes are expected to increase and will impact human health, water supply, agriculture, coastal areas, and many other aspects of society and the natural environment. Some changes are likely for the United States and surrounding coastal waters including more intense hurricanes and related increases in wind, rain, and storm surges (but not necessarily an increase in the number of storms that make landfall), as well as drier conditions in the Southwest and Caribbean. 3. Society and ecosystems are generally adapted to a stable climate. For this reason, the projected rapid rate and large amount of climate change over this century will challenge the ability of society and natural systems to adjust. 4. In projecting future conditions, there is always some level of uncertainty. For example, there is a high degree of confidence in projections of future temperature increases that are greatest nearer the poles and in the middle of continents. For precipitation, there is high confidence in continued increases in the Arctic and sub-Arctic (including Alaska) and decreases in the tropical regions, but the precise location of the transition zone between these is less certain. On smaller time and space scales, natural climate variations can be relatively large and can temporarily mask the progressive nature of global climate change. 5. Unanticipated impacts of climate change have already occurred and more are likely in the future. These future impacts might stem from unforeseen changes in the climate system such as major alterations in oceans, ice, or storms; and unpredicted consequences of ecological changes, such as massive dislocations of species or pest outbreaks.
Climate-Change Impacts on Major Societal and Environmental Sectors: a National View
The U.S. Climate Change Science Program's Unified Synthesis Product reports on extant and possible future impacts of climate change for seven sectors at the national level - water resources, energy supply and use, transportation, agriculture, ecosystems, human health and society. The sectoral analyses provide an integrated national picture of the climate-change consequences, now and in the future, for society and the environment, albeit a picture with regional texture. Major report findings for each sector will be presented. In addition to the specific sectoral findings, several overarching messages emerge from this component of the synthesis activity. First, it is important to think about interactions between and among sectors with regard to climate impacts. For example, the projected changes in the timing and amount of precipitation, and hence water supply, will very likely have significant implications for other sectors considered in the report. Changes in water supply have the potential to affect hydropower generation, river transportation, crop timing and management, in-stream ecosystem services including fish habitat, and human health issues related to links between heavy rains ad water-borne diseases. Second, the report concludes that climate-change impacts on the sectors must be considered in the context of a range of environmental and social factors including pollution, population growth, over use of resources, and urbanization. The multi-factor analysis provides insight into our understanding of where, when and how climate change combines with other environmental and social changes to affect the sectors. It also provides some understanding of how these interactions can either amplify or dampen climate-change impacts. This message has profound implications for the design of research programs and information systems at the national, regional and local levels. Furthermore, it demands that a true partnership be forged between the natural and social sciences to more adequately conduct assessments and seek solutions that address the complex challenges that multiple stresses pose. Third, the report notes that the United States is connected to a world that is unevenly vulnerable to climate change and thus will be affected by impacts globally. One example is agriculture. The degree to which climate change affects food production across the globe will affect the demand for our agricultural products and so the profitability of this sector. Fourth, the report highlights the importance of considering the unintended consequences of adaptation measures designed to avert or minimize negative impacts of climate change on various sectors. For example, the "hardening" of coastlines with sea walls and other structures to protect transportation infrastructure against storm surge and sea-level rise eliminates the ability of coastal ecosystems to adapt to these aspects of climate change by inward migration. While this "tradeoff" may be essential, it must be understood that with the loss of coastal ecosystems such as marshlands, comes the loss of the services they provide to society such as their function as nurseries for juvenile fish stocks that are essential for the sustainability of coastal fisheries. The general message about unintended consequences is that system-level analyses must be part of developing intelligent adaptation strategies to meet the challenges of climate change.
Regional Climate Change Impacts in the United States
Climate change will affect one region differently from another. For that reason, the U.S. Unified Synthesis Product "Global Climate Change Impacts in the United States" broke down its assessment of climate change impacts on the country into 8 regions. Key highlights include: In the Northeast, agricultural production, including dairy, fruit, and maple syrup, will be increasingly affected as favorable climates shift northward. In the Southeast, accelerated sea-level rise and increased hurricane intensity will have serious impacts. In the Midwest, under higher emissions scenarios, significant reductions in Great Lakes water levels will impact shipping, infrastructure, beaches, and ecosystems. In the Great Plains, projected increases in temperature, evaporation, and drought frequency exacerbate concerns regarding the region's declining water resources. In the Southwest, water supplies will become increasingly scarce, calling for trade-offs among competing uses, and potentially leading to conflict. In the Northwest, salmon and other cold-water species will experience additional stresses as a result of rising water temperatures and declining summer streamflows. In Alaska, thawing permafrost damages roads, runways, water and sewer systems, and other infrastructure. And in the U.S. islands in the Caribbean and Pacific, climate changes affecting coastal and marine ecosystems will have major implications for tourism and fisheries. In addition, significant sea-level rise and storm surge will affect coastal cities and ecosystems around the nation; low-lying and subsiding areas are most vulnerable.
Unified Synthesis Product (USP) Recommendations
The USP identifies a number of areas in which inadequate information or understanding hampers our ability to estimate likely future climate change and its impacts. For example, our knowledge of changes in tornadoes, hail, and ice storms is quite limited, making it difficult to know if and how such events have changed as climate has warmed, and how they might change in the future. Research on ecological responses to climate change also is limited, as is our understanding of social responses. The Report identifies the five most important gaps in knowledge and offers some thoughts on how to address those gaps: 1. Expand our understanding of climate change impacts. There is a clear need to increase understanding of how ecosystems, social and economic systems, human health, and the built environment will be affected by climate change in the context of other stresses. This includes ecosystems as well as economic systems, human health, and the built environment. 2. Refine ability to project climate change at local scales. One of the main messages to emerge from the past decade of synthesis and assessments is that while climate change is a global issue, it has a great deal of regional variability. There is an indisputable need to improve understanding of climate system effects at these smaller scales, because these are often the scales of decision-making in society. 3. Expand capacity to provide decision makers and the public with relevant information on climate change and its impacts. The United States has tremendous potential to create more comprehensive measurement, archive, and data-access systems that could provide great benefit to society. 4. Improve understanding of and ability to identify thresholds likely to lead to abrupt changes in the climate system. Paleoclimatic data shows that climate can and has changed quite abruptly when certain thresholds are crossed. Similarly, there is evidence that ecological and human systems can undergo abrupt change when tipping points are reached. 5. Enhance understanding of how society can adapt to climate change in the context of multiple stresses. There is currently limited knowledge about the ability of communities, regions, and sectors to adapt to future climate change. It is essential to improve understanding of how the capacity to adapt to a changing climate might be exercised, and the vulnerabilities to climate change and other environmental stresses that might remain. Results from these efforts would inform future assessments that continue building our understanding of humanity's impacts on climate, and climate's impacts on us. Such assessments will continue to play a role in helping the U.S. respond to changing conditions. A vision for future climate change assessments includes both sustained extensive practitioner and stakeholder involvement, and periodic, targeted, scientifically rigorous reports similar to the CCSP Synthesis and Assessment Products.