Climate is changing, forced out of the range of the past million years by levels of carbon dioxide and other greenhouse gases not seen in the Earth's atmosphere for a very, very long time. Lacking action by the world's nations, it is clear that the planet will be warmer, sea level will rise, and patterns of rainfall will change. But the future is also partly uncertain-there is considerable uncertainty about how we will arrive at that different climate. Will the changes be gradual, allowing natural systems and societal infrastructure to adjust in a timely fashion? Or will some of the changes be more abrupt, crossing some threshold or "tipping point" to change so fast that the time between when a problem is recognized and when action is required shrinks to the point where orderly adaptation is not possible? Abrupt Impacts of Climate Change is an updated look at the issue of abrupt climate change and its potential impacts. This study differs from previous treatments of abrupt changes by focusing on abrupt climate changes and also abrupt climate impacts that have the potential to severely affect the physical climate system, natural systems, or human systems, often affecting multiple interconnected areas of concern. The primary timescale of concern is years to decades. A key characteristic of these changes is that they can come faster than expected, planned, or budgeted for, forcing more reactive, rather than proactive, modes of behavior. Abrupt Impacts of Climate Change summarizes the state of our knowledge about potential abrupt changes and abrupt climate impacts and categorizes changes that are already occurring, have a high probability of occurrence, or are unlikely to occur. Because of the substantial risks to society and nature posed by abrupt changes, this report recommends the development of an Abrupt Change Early Warning System that would allow for the prediction and possible mitigation of such changes before their societal impacts are severe. Identifying key vulnerabilities can help guide efforts to increase resiliency and avoid large damages from abrupt change in the climate system, or in abrupt impacts of gradual changes in the climate system, and facilitate more informed decisions on the proper balance between mitigation and adaptation. Although there is still much to learn about abrupt climate change and abrupt climate impacts, to willfully ignore the threat of abrupt change could lead to more costs, loss of life, suffering, and environmental degradation. Abrupt Impacts of Climate Change makes the case that the time is here to be serious about the threat of tipping points so as to better anticipate and prepare ourselves for the inevitable surprises.

The climate record for the past 100,000 years clearly indicates that the climate system has undergone periodic-and often extreme-shifts, sometimes in as little as a decade or less. The causes of abrupt climate changes have not been clearly established, but the triggering of events is likely to be the result of multiple natural processes. Abrupt climate changes of the magnitude seen in the past would have far-reaching implications for human society and ecosystems, including major impacts on energy consumption and water supply demands. Could such a change happen again? Are human activities exacerbating the likelihood of abrupt climate change? What are the potential societal consequences of such a change? Abrupt Climate Change: Inevitable Surprises looks at the current scientific evidence and theoretical understanding to describe what is currently known about abrupt climate change, including patterns and magnitudes, mechanisms, and probability of occurrence. It identifies critical knowledge gaps concerning the potential for future abrupt changes, including those aspects of change most important to society and economies, and outlines a research strategy to close those gaps. Based on the best and most current research available, this book surveys the history of climate change and makes a series of specific recommendations for the future.

Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 193. Abrupt Climate Change: Mechanisms, Patterns, and Impacts brings together a diverse group of paleoproxy records such as ice cores, marine sediments, terrestrial (lakes and speleothems) archives, and coupled ocean-atmosphere climate models to document recent advances in understanding the mechanisms of abrupt climate changes. Since the discovery of the Dansgaard-Oeschger events in Greenland ice cores and the subsequent discovery of their contemporary events in the marine sediments of the North Atlantic, the search for these abrupt, millennial-scale events across the globe has intensified, and as a result, the number of paleoclimatic records chronicling such events has increased. The volume highlights include discussions of records of past climate variability, meridional overturning circulation, land-ocean-atmosphere interactions, feedbacks in the climate system, and global temperature anomalies. Abrupt Climate Change will be of interest to students, researchers, academics, and policy makers who are concerned about abrupt climate change and its potential impact on society.

Climate change can reasonably be expected to increase the frequency and intensity of a variety of potentially disruptive environmental events-slowly at first, but then more quickly. It is prudent to expect to be surprised by the way in which these events may cascade, or have far-reaching effects. During the coming decade, certain climate-related events will produce consequences that exceed the capacity of the affected societies or global systems to manage; these may have global security implications. Although focused on events outside the United States, Climate and Social Stress: Implications for Security Analysis recommends a range of research and policy actions to create a whole-of-government approach to increasing understanding of complex and contingent connections between climate and security, and to inform choices about adapting to and reducing vulnerability to climate change.

The stresses associated with climate change are expected to be felt keenly as human population grows to a projected 9 billion by the middle of this century, increasing the demand for resources and supporting infrastructure. Therefore, information to assess vulnerabilities to climate change is needed to support policies and investments designed to increase resilience in human and Earth systems. There are currently many observing systems that capture elements of how climate is changing, for example, direct measurements of atmospheric and ocean temperature. Although those measurements are essential for understanding the scale and nature of climate change, they do not necessarily provide information about the impacts of climate change on humans that are especially relevant for political and economic planning and decision making. Monitoring Climate Change Impacts tackles the challenge of developing an illustrative suite of indicators, measurements (and the locations around the globe where the measurements can be applied), and metrics that are important for understanding global climate change and providing insight into environmental sustainability. Eight panels provided input on: cryosphere, land-surface and terrestrial ecosystems, hydrology and water resources, atmosphere, human health and other dimensions, oceans (both physical and biological/chemical), and natural disasters. The book also provides an illustrative set of metrics that are likely to be affected by climate change over the next 20-25 years and, when taken together, can potentially give advance warning of climate-related changes to the human and environment systems.

Summarizes the science of climate change and impacts on the United States, for the public and policymakers.

Climate change is occurring. It is very likely caused by the emission of greenhouse gases from human activities, and poses significant risks for a range of human and natural systems. And these emissions continue to increase, which will result in further change and greater risks. America's Climate Choices makes the case that the environmental, economic, and humanitarian risks posed by climate change indicate a pressing need for substantial action now to limit the magnitude of climate change and to prepare for adapting to its impacts. Although there is some uncertainty about future risk, acting now will reduce the risks posed by climate change and the pressure to make larger, more rapid, and potentially more expensive reductions later. Most actions taken to reduce vulnerability to climate change impacts are common sense investments that will offer protection against natural climate variations and extreme events. In addition, crucial investment decisions made now about equipment and infrastructure can "lock in" commitments to greenhouse gas emissions for decades to come. Finally, while it may be possible to scale back or reverse many responses to climate change, it is difficult or impossible to "undo" climate change, once manifested. Current efforts of local, state, and private-sector actors are important, but not likely to yield progress comparable to what could be achieved with the addition of strong federal policies that establish coherent national goals and incentives, and that promote strong U.S. engagement in international-level response efforts. The inherent complexities and uncertainties of climate change are best met by applying an iterative risk management framework and making efforts to significantly reduce greenhouse gas emissions; prepare for adapting to impacts; invest in scientific research, technology development, and information systems; and facilitate engagement between scientific and technical experts and the many types of stakeholders making America's climate choices.