This report critically reviews current knowledge about global distributions and properties of atmospheric aerosols as they relate to aerosol impacts on climate. It assesses possible steps to substantially reduce uncertainties in aerosol radiative forcing estimates.

This report discusses the current state of understanding about the characteristics and implications of uncertainty related to climate change and variability to an audience of policymakers, decision makers, and members of the media and general public with an interest in developing a fundamental understanding of the issue.

This document is part of the Synthesis and Assessment Products described in the U.S. Climate Change Science Program (CCSP) Strategic Plan. The U.S. Government's CCSP is responsible for providing the best science-based knowledge possible to inform management of the risks and opportunities associated with changes in the climate and related environmental systems. To support its mission, the CCSP has commissioned 21 "synthesis and assessment products" (SAPs) to advance decision making on climate change-related issues by providing current evaluations of climate change science and identifying priorities for research, observation, and decision support. This Synthesis and Assessment Product (SAP), developed as part of the U.S. Climate Change Science Program, examines potential effects of sea-level rise from climate change during the twenty-first century, with a focus on the mid-Atlantic coast of the United States. Using scientific literature and policy-related documents, the SAP describes the physical environments; potential changes to coastal environments, wetlands, and vulnerable species; societal impacts and implications of sea-level rise; decisions that may be sensitive to sea-level rise; opportunities for adaptation; and institutional barriers to adaptation.

This Synthesis and Assessment Product focuses on the connection between the scientific ability to predict climate on seasonal scales and the opportunity to incorporate such understanding into water resource management decisions. It directly addresses decision support experiments and evaluations that have used seasonal-to-interannual forecasts and observational data, and is expected to inform (1) decision makers about the relative success of experiences of others who have experimented with these forecasts and data in resource management; (2) climatologists, hydrologists, and social scientists on how to advance the delivery of decision-support resources that use the most recent forecast products, methodologies, and tools; and (3) science and resource managers as they plan for future investments in research related to forecasts and their role in decision support. It is important to note, however, that while the focus of this Product is on the water resources management sector, the findings within this Synthesis and Assessment Product may be directly transferred to other sectors.

This Climate Change Science Program Synthesis and Assessment Product addresses current capabilities to integrate observations of the climate system into a consistent description of past and current conditions through the method of reanalysis. In addition, the Product assesses present capabilities to attribute causes for climate variations and trends over North America during the reanalysis period, which extends from the mid-twentieth century to the present. This Product reviews Past Climate Variability and Change in the Arctic and at High Latitudes. Paleoclimate records play a key role in our understanding of Earth's past and present climate system and in our confidence in predicting future climate changes. Paleoclimate data help to elucidate past and present active mechanisms of climate change by placing the short instrumental record into a longer term context and by permitting models to be tested beyond the limited time that instrumental measurements have been available. Recent observations in the Arctic have identified large ongoing changes and important climate feedback mechanisms that multiply the effects of global-scale climate changes. As discussed in this report, paleoclimate data show that land and sea ice have grown with cooling temperatures and have shrunk with warming ones, amplifying temperature changes while causing and responding to …

This Report (SAP 4.2) focuses on the thresholds of Climate Change in Ecosystems. As defined in this Synthesis and Assessment Report, 'an ecological threshold is the point at which there is an abrupt change in an ecosystem quality, property, or phenomenon, or where small changes in one or more external conditions produce large and persistent responses in an ecosystem'.Ecological thresholds occur when external factors, positive feedbacks, or nonlinear instabilities in a system cause changes to propagate in a domino-like fashion that is potentially irreversible. This report reviews threshold changes in North American ecosystems that are potentially induced by climatic change and addresses the significant challenges these threshold crossings impose on resource and land managers. Sudden changes to ecosystems and the goods and services they provide are not well understood, but they are extremely important if natural resource managers are to succeed in developing adaptation strategies in a changing world. The report provides an overview of what is known about ecological thresholds and where they are likely to occur. It also identifies those areas where research is most needed to improve knowledge and understand the uncertainties regarding them. The report suggests a suite of potential actions that land and resource managers …

This document is part of the Synthesis and Assessment Products (SAP) described in the U.S. Climate Change Science Program (CCSP) Strategic Plan. This report is meant to reduce uncertainty in projections of how the Earth's climate and related systems may change in the future. It provides scientific information for supporting the decision-making audience and the expert scientific and stakeholder community.

This Synthesis and Assessment Product (SAP 2.4) focuses on the Climate models. Depletion of the stratospheric ozone layer by human-produced ozone-depleting substances has been recognized as a global environmental issue for more than three decades, and the international effort to address the issue via the United Nations Montreal Protocol marked its 20-year anniversary in 2007. Scientific understanding underpinned the Protocol at its inception and ever since. As scientific knowledge advanced and evolved, the Protocol evolved through amendment and adjustment. Policy-relevant science has documented the rise, and now the beginning decline, of the atmospheric abundances of many ozone-depleting substances in response to actions taken by the nations of the world. Projections are for a return of ozone-depleting chemicals (compounds containing chlorine and bromine) to their "pre-ozone-depletion" (pre-1980) levels by the middle of this century for the midlatitudes; the polar regions are expected to follow suit within 20 years after that. Since the 1980s, global ozone sustained a depletion of about 5 percent in the midlatitudes of both the Northern Hemisphere and Southern Hemisphere, where most of the Earth's population resides; it is now showing signs of turning the corner towards increasing ozone. The large seasonal depletions in the polar regions are …

This document is part of the Synthesis and Assessment Products (SAP) described in the U.S. Climate Change Science Program (CCSP) Strategic Plan. This report is meant to synthesize and communicate the current state of understanding about the characteristics and implications of uncertainty related to climate change and variability to an audience of policymakers, decision makers, and members of the media and general public with an interest in developing a fundamental understanding of the issue.

This report focuses on the Climate Projections Based on Emissions Scenarios. The influence of greenhouse gases and particle pollution on our present and future climate has been widely examined. While both long-lived (e.g., carbon dioxide) and short-lived (e.g., soot) gases and particles affect the climate, other projections of future climate, such as the IPCC reports focus largely on the long-lived gases. This U.S. Climate Change Science Program Synthesis and Assessment Product provides a different emphasis. The authors examine the effect of long-lived greenhouse gases on the global climate based on updated emissions scenarios produced by another CCSP Synthesis and Assessment Product (SAP 2.1a). In these scenarios, atmospheric concentrations of the long-lived greenhouse gases leveled off, or stabilized, at predetermined levels by the end of the twenty-first century (unlike in the IPCC scenarios). However, the projected future temperature changes fall within the same range as those projected for the latest IPCC report. The authors confirm the robust future warming signature and other associated changes in the climate.

This Synthesis and Assessment Product (SAP), Uses and Limitations of Observations, Data, Forecasts, and Other Projections in Decision Support for Selected Sectors and Regions. This is part of a series of 21 SAPs produced by the CCSP aimed at providing current assessments of climate change science to inform public debate, policy, and operational decisions. This SAP focuses on the use of climate observations, data, forecasts, and other projections in decision support.

This Synthesis and Assessment Product (SAP 3.1) focuses on the Climate models. Scientists extensively use mathematical models of Earth's climate, executed on the most powerful computers available, to examine hypotheses about past and present-day climates. Development of climate models is fully consistent with approaches being taken in many other fields of science dealing with very complex systems. These climate simulations provide a framework within which enhanced understanding of climate-relevant processes, along with improved observations, are merged into coherent projections of future climate change. This report describes the models and their ability to simulate current climate.

The U.S. Government's Climate Change Science Program (CCSP) is responsible for providing the best science-based knowledge possible to inform management of the risks and opportunities associated with changes in the climate and related environmental systems. To support its mission, the CCSP has commissioned 21 "synthesis and assessment products" (SAPs) to advance decision making on climate change-related issues by providing current evaluations of climate change science and identifying priorities for research, observation, and decision support. This Report-SAP 4.4-focuses on federally managed lands and waters to provide a "Preliminary Review of Adaptation Options for Climate-Sensitive Ecosystems and Resources." It is one of seven reports that support Goal 4 of the CCSP Strategic Plan to understand the sensitivity and adaptability of different natural and managed ecosystems and human systems to climate and related global changes. The purpose of SAP 4.4 is to provide useful information on the state of knowledge regarding adaptation options for key, representative ecosystems and resources that may be sensitive to climate variability and change. As its title suggests, this report is a preliminary review, defined as "the process of collecting and reviewing available information about known or potential adaptation options."

This document is part of the Synthesis and Assessment Products described in the U.S. Climate Change Science Program (CCSP) Strategic Plan. Changes in extreme weather and climate events have significant impacts and are among the most serious challenges to society in coping with a changing climate. This Synthesis and Assessment Product (SAP 3.3) focuses on weather and climate extremes in a changing climate. Many extremes and their associated impacts are now changing. For example, in recent decades most of North America has been experiencing more unusually hot days and nights, fewer unusually cold days and nights, and fewer frost days. Heavy downpours have become more frequent and intense. Droughts are becoming more severe in some regions, though there are no clear trends for North America as a whole. The power and frequency of Atlantic hurricanes have increased substantially in recent decades, though North American mainland land-falling hurricanes do not appear to have increased over the past century. Outside the tropics, storm tracks are shifting northward and the strongest storms are becoming even stronger. It is well established through formal attribution studies that the global warming of the past 50 years is due primarily to human-induced increases in heat-trapping gases. Such …

This document is a part of the Synthesis and Assessment Products described in the U.S. Climate Change Science Program Strategic Plan. The report describes how climate affects the design, construction, safety, operations, and maintenance of transportation infrastructure and systems. The prospect of a changing climate raises critical questions regarding how alterations in temperature, precipitation, storm events, and other aspects of the climate could affect the nation's roads, airports, rail, transit systems, pipelines, ports, and waterways. Phase I of this regional assessment of climate change and its potential impacts on transportation systems addresses these questions for the region of the U.S. central Gulf Coast between Galveston, Texas and Mobile, Alabama.

This document, part of the Synthesis and Assessment Products described in the U.S. Climate Change Science Program (CCSP) Strategic Plan. Climate affects the design, construction, safety, operations, and maintenance of transportation infrastructure and systems. The prospect of a changing climate raises critical questions regarding how alterations in temperature, precipitation, storm events, and other aspects of the climate could affect the nation's roads, airports, rail, transit systems, pipelines, ports, and waterways. Phase I of this regional assessment of climate change and its potential impacts on transportation systems addresses these questions for the region of the U.S. central Gulf Coast between Galveston, Texas and Mobile, Alabama. This region contains multimodal transportation infrastructure that is critical to regional and national transportation services. The significance of various climate factors for transportation systems was assessed.

This document, part of the Synthesis and Assessment Products described in the U.S. Climate Change Science Program (CCSP) Strategic Plan. Climate affects the design, construction, safety, operations, and maintenance of transportation infrastructure and systems. The prospect of a changing climate raises critical questions regarding how alterations in temperature, precipitation, storm events, and other aspects of the climate could affect the nation's roads, airports, rail, transit systems, pipelines, ports, and waterways. Phase I of this regional assessment of climate change and its potential impacts on transportation systems addresses these questions for the region of the U.S. central Gulf Coast between Galveston, Texas and Mobile, Alabama. This region contains multimodal transportation infrastructure that is critical to regional and national transportation services. Historical trends and future climate scenarios were used to establish a context for examining the potential effects of climate change on all major transportation modes within the region. Climate changes anticipated during the next 50 to 100 years for the central Gulf Coast include warming temperatures, changes in precipitation patterns, and increased storm intensity. The warming of the oceans and decline of polar ice sheets is expected to accelerate the rate of sea level rise globally. The effects of sea level …

This brochure provides an overview of how air pollutants have an impact on climate change.

This brochure describes methods and technologies for assessing and predicting climate change.

This brochure summarizes a report of the same title. It describes the likely impacts of climate change on human health, and potential adaptation strategies to limit the risks and damages.

This brochure describes the role of ozone in the stratosphere, and the effect it has on ultraviolet light, as well as how the Montreal Protocol and subsequent laws have affected ozone-depleting pollutants in the atmosphere.

This brochure discusses climate change, and scientific methods of making climate observations.

This Climate Change Science Program Synthesis and Assessment Product addresses current capabilities to integrate observations of the climate system into a consistent description of past and current conditions through the method of reanalysis. In addition, the Product assesses present capabilities to attribute causes for climate variations and trends over North America during the reanalysis period, which extends from the mid-twentieth century to the present. This Product reviews the strengths and limitations of current atmospheric reanalysis products. It finds that reanalysis data play a crucial role in helping to identify, describe, and understand atmospheric features associated with weather and climate variability, including high-impact events such as major droughts and floods. Reanalysis data play an important role in assessing the ability of climate models to simulate the average climate and its variations. The data also help in identifying deficiencies in representations of physical processes that produce climate model errors.

This brochure summarizes research that focuses on the scientific ability to predict climate on seasonal and year-to-year timescales and the opportunity to incorporate such information into water resource management decisions.