Climate change is occurring, is caused largely by human activities, and poses significant risks for-and in many cases is already affecting-a broad range of human and natural systems. The compelling case for these conclusions is provided in Advancing the Science of Climate Change, part of a congressionally requested suite of studies known as America's Climate Choices. While noting that there is always more to learn and that the scientific process is never closed, the book shows that hypotheses about climate change are supported by multiple lines of evidence and have stood firm in the face of serious debate and careful evaluation of alternative explanations. As decision makers respond to these risks, the nation's scientific enterprise can contribute through research that improves understanding of the causes and consequences of climate change and also is useful to decision makers at the local, regional, national, and international levels. The book identifies decisions being made in 12 sectors, ranging from agriculture to transportation, to identify decisions being made in response to climate change. Advancing the Science of Climate Change calls for a single federal entity or program to coordinate a national, multidisciplinary research effort aimed at improving both understanding and responses to climate change. Seven cross-cutting research themes are identified to support this scientific enterprise. In addition, leaders of federal climate research should redouble efforts to deploy a comprehensive climate observing system, improve climate models and other analytical tools, invest in human capital, and improve linkages between research and decisions by forming partnerships with action-oriented programs.

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

Climate change poses many challenges that affect society and the natural world. With these challenges, however, come opportunities to respond. By taking steps to adapt to and mitigate climate change, the risks to society and the impacts of continued climate change can be lessened. The National Climate Assessment, coordinated by the U.S. Global Change Research Program, is a mandated report intended to inform response decisions. Required to be developed every four years, these reports provide the most comprehensive and up-to-date evaluation of climate change impacts available for the United States, making them a unique and important climate change document. The draft Fourth National Climate Assessment (NCA4) report reviewed here addresses a wide range of topics of high importance to the United States and society more broadly, extending from human health and community well-being, to the built environment, to businesses and economies, to ecosystems and natural resources. This report evaluates the draft NCA4 to determine if it meets the requirements of the federal mandate, whether it provides accurate information grounded in the scientific literature, and whether it effectively communicates climate science, impacts, and responses for general audiences including the public, decision makers, and other stakeholders.

"Frightening...Firestorm comes alive when Struzik discusses the work of offbeat scientists." —New York Times Book Review "Comprehensive and compelling." —Booklist "A powerful message." —Kirkus "Should be required reading." —Library Journal For two months in the spring of 2016, the world watched as wildfire ravaged the Canadian town of Fort McMurray. Firefighters named the fire “the Beast.” It acted like a mythical animal, alive with destructive energy, and they hoped never to see anything like it again. Yet it’s not a stretch to imagine we will all soon live in a world in which fires like the Beast are commonplace. A glance at international headlines shows a remarkable increase in higher temperatures, stronger winds, and drier lands– a trifecta for igniting wildfires like we’ve rarely seen before. This change is particularly noticeable in the northern forests of the United States and Canada. These forests require fire to maintain healthy ecosystems, but as the human population grows, and as changes in climate, animal and insect species, and disease cause further destabilization, wildfires have turned into a potentially uncontrollable threat to human lives and livelihoods. Our understanding of the role fire plays in healthy forests has come a long way in the past century. Despite this, we are not prepared to deal with an escalation of fire during periods of intense drought and shorter winters, earlier springs, potentially more lightning strikes and hotter summers. There is too much fuel on the ground, too many people and assets to protect, and no plan in place to deal with these challenges. In Firestorm, journalist Edward Struzik visits scorched earth from Alaska to Maine, and introduces the scientists, firefighters, and resource managers making the case for a radically different approach to managing wildfire in the 21st century. Wildfires can no longer be treated as avoidable events because the risk and dangers are becoming too great and costly. Struzik weaves a heart-pumping narrative of science, economics, politics, and human determination and points to the ways that we, and the wilder inhabitants of the forests around our cities and towns, might yet flourish in an age of growing megafires.

Climate change is one of the most complex and challenging issues facing the world today. A changing climate will affect humankind in many ways and alter our physical environment, presenting ethical challenges in how we respond. The impact of climate change will likely be exacerbated in heavily populated regions of the planet, such as the Northeastern United States (NEUS). The NEUS is comprised of complex, sprawling urban centers and rural regions, both of which are vital to the economic and cultural character of the region. Furthermore, both urban and rural areas in the NEUS contain communities that have been historically susceptible to climate change (Horton et al. 2014). Over the past 120 years, average temperatures have increased by 2°F, precipitation has increased by 10%, and sea levels have also risen (Kunkel 2013). One poorly understood consequence of climate change is its effects on extreme events such as wildfires. Robust associations between wildfire frequency and climatic variability have been shown to exist (Scholze et al. 2006; Westerling et al. 2006), indicating that future climate change may continue to have a significant effect on wildfire activity. The NEUS has been home to some of the most infamous and largest historic "megafires" in North America, such as the Miramichi Fire of 1825 and the fires of 1947 (Irland 2013). Although return intervals in most areas of the NEUS are high (hundreds of years), wildfires have played a critical role in ecosystem development and forest structure in the region (Carlson 2013). Therefore, predicting fire occurrence and vulnerability to large wildfires in the NEUS is economically and culturally relevant. However, predicting fire occurrence is not a simple task due to the nature of wildfire activity in the NEUS. While in most regions of the world, natural factors such as lightning are the driving cause of wildfires, it has been estimated that the vast majority (>99%) of wildfires in the NEUS are caused by anthropogenic activity and not natural causes (Pyne 1982). Consequently, only studying data associated with fire occurrence (i.e. area burned, number of fires) is likely inadequate for the investigation the region's fire risk over time. Furthermore, little is known about how the direct (temperature and precipitation trends) and indirect (ecosystem-wide species distribution) effects of climate change will impact fire risk in the NEUS under future climate scenarios. Fully understanding the natural mechanisms that control fire risk and occurrence requires continuous records of past fires and climatic variability on centennial to millennial timescales. However, historical fire records in the NEUS are temporally limited, and do not provide an adequate analysis of the impacts of regional wildfire regimes, prior to human disturbance and anthropogenic climate change. We find that regional climatic fire risk for the NEUS can be estimated most accurately using the Keetch Byram Drought Index (KBDI) from 20th century historical meteorological records from various stations located throughout the region. Regional fire risk is then estimated through 2100 AD, using the KBDI and dynamically downscaled regional climate models from CMIP5 climate models. Under RCP 8.5, average KBDI and max yearly KBDI is shown to increase by 300% and 500%, respectively, in an exponential trend. Under RCP 4.5, KBDI is also expected to increase through 2100 AD to a lesser extent. Interestingly, these increases in regional fire risk are present regardless of increases in precipitation, indicating that future fire risk in the NEUS is driven largely by changes in temperature as opposed to precipitation. In order to investigate long-term regional wildfire activity over the past millennium, we examine PAHs and macrocharcoal from a varved sedimentary record from Basin Pond, Fayette, Maine (USA). We find elevated concentrations of the PAH retene were found to be highly correlated with known large-scale regional wildfire events that occurred in 1761-1762, 1825, and 1947 (A.D.). To distinguish between biomass burning and anthropogenic combustion, we examined the ratio of the PAHs retene and chrysene. The new Basin Pond PAH records, along with a local signal of fire occurrence from charcoal analysis, offers the prospect of using this multi-proxy approach as a method for examining wildfire frequency at the local and regional scale in the NEUS. Finally, we report seasonally resolved measurements of brGDGT production in the water column, in catchment soils, and in a sediment core from Basin Pond. We utilize these observations to help interpret a Basin Pond brGDGT-based temperature reconstruction spanning the past 900 years. This record exbibits similar trends to a pollen record from the same site and also to regional and global syntheses of terrestrial temperatures over the last millennium. However, the Basin Pond temperature record shows higher-frequency variability than has previously been captured by such an archive in the NEUS, potentially attributed to large scale atmospheric patterns. These new records of temperature variability and wildfire activity, when compared to regional hydroclimate records, shed insight into pre-historic wildfire risk in the NEUS.

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.