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In the 1990s, researchers in the Arctic noticed that floating summer sea ice had begun receding. This was accompanied by shifts in ocean circulation and unexpected changes in weather patterns throughout the world. The Arctic's perennially frozen ground, known as permafrost, was warming, and treeless tundra was being overtaken by shrubs. What was going on? Brave New Arctic is Mark Serreze's riveting firsthand account of how scientists from around the globe came together to find answers. In a sweeping tale of discovery spanning three decades, Serreze describes how puzzlement turned to concern and astonishment as researchers came to understand that the Arctic of old was quickly disappearing--with potentially devastating implications for the entire planet. Serreze is a world-renowned Arctic geographer and climatologist who has conducted fieldwork on ice caps, glaciers, sea ice, and tundra in the Canadian and Alaskan Arctic. In this must-read book, he blends invaluable insights from his own career with those of other pioneering scientists who, together, ushered in an exciting new age of Arctic exploration. Along the way, he accessibly describes the cutting-edge science that led to the alarming conclusion that the Arctic is rapidly thawing due to climate change, that humans are to blame, and that the global consequences are immense. A gripping scientific adventure story, Brave New Arctic shows how the Arctic's extraordinary transformation serves as a harbinger of things to come if we fail to meet the challenge posed by a warming Earth.

Purpose of Review The Arctic has experienced the most rapid change in climate of anywhere on Earth, and these changes are certain to drive changes in the carbon budget of the Arctic as vegetation changes, soils warm, fires become more frequent, and wetlands evolve as permafrost thaws. In this study, we review the extensive evidence for Arctic climate change and effects on the carbon cycle. In addition, we re-evaluate some of the observational evidence for changing Arctic carbon budgets. Recent Findings Observations suggest a more active CO2 cycle in high northern latitude ecosystems. Evidence points to increased uptake by boreal forests and Arctic ecosystems, as well as increasing respiration, especially in autumn. However, there is currently no strong evidence of increased CH4 emissions. Summary Long-term observations using both bottom-up (e.g., flux) and top-down (atmospheric abundance) approaches are essential for understanding changing carbon cycle budgets. Consideration of atmospheric transport is critical for interpretation of top-down observations of atmospheric carbon.

This review article makes six observations about the current body of research on the societal impacts of a changing Arctic. First, climate change and globalisation are the dominant drivers of societal impacts in the Arctic. Second, many contributions focus on the impacts in concrete sectors of society, often from an opportunities-and-risks perspective, which tends to blur the boundary to more policy-oriented work. Third, the mantra of the sustainable development of the Arctic or Arctic sustainability pervades considerations of Arctic societal impacts. Fourth, societal and environment change in the Arctic is increasingly analysed using the image of the Global Arctic , highlighting the inextricable linkages between Arctic and global processes and systems and thus the entangled fate of the North and the entire globe. Fifth, an increasing number of actors is seen as being involved in societal and environmental transformations in the Arctic, often conveyed through the (often ill-defined) stakeholder concept. Sixth, Arctic indigenous peoples are depicted as the group most vulnerable to the societal impacts of a changing Arctic, but are increasingly the subject of research in the form of rights-holders and active participants in governance, law, politics, and research. Challenges for future research include achieving greater clarity and reflexivity around key concepts, and de-essentialising the Arctic via the use of comparative methods on cases both within and beyond the Arctic.

Explores the potential global effects if polar bears were to become extinct.

Purpose of Review The observed substantial loss of Arctic sea ice has raised prospects of a seasonally ice-free Arctic Ocean within the foreseeable future. In this review, we summarize our current understanding of the most likely trajectory of the Arctic sea-ice cover towards this state. Recent Findings The future trajectory of the Arctic sea-ice cover can be described through a deterministic component arising primarily from future greenhouse gas emissions, and a chaotic component arising from internal variability. The deterministic component is expected to cause a largely ice-free Arctic Ocean during summer for less than 2 ∘ C global warming relative to pre-industrial levels. To keep chances below 5 % that the Arctic Ocean will largely be ice free in a given year, total future CO 2 emissions must remain below 500 Gt. Summary The Arctic Ocean will become ice free during summer before mid-century unless greenhouse gas emissions are rapidly reduced.

This paper reviews sea level contributions from land ice across the Arctic, including Greenland. We summarize ice loss measurement methods, ice loss mechanisms, and recent observations and projections, and highlight research advances over the last 3-5 years and remaining scientific challenges.

Under the ongoing and potential risks from anthropogenic warming, net negative carbon dioxide (CO2) emissions are inevitable to stabilize or recover the Earth's climate. It is important not only to understand climate irreversibility in response to CO2 removal but also to understand how fast each component of the climate system will recover to its original state. Based on idealized CO2 ramp‐up and ‐down ensemble simulations, here we show that the initial buoyancy states of the Arctic Ocean, such as upper ocean salinity and density, are vital to determining how fast Arctic and global mean temperatures will recover on a centennial time scale. The denser initial Arctic oceanic condition is linked to faster recovery of the Atlantic meridional overturning circulation (AMOC) in the ramp‐down period, which is further accelerated by strong positive AMOC‐salt‐advection feedback. Faster AMOC recovery can delay Arctic temperature recovery by transporting warmer water into the northern subpolar Atlantic during the ramp‐down period. In addition, denser Arctic water enhances vertical mixing, which also results in delayed Arctic cooling under a strong vertical temperature gradient in the subpolar‐to‐polar Atlantic. Our findings suggest that the Arctic's initial states have a centennial memory for the future Arctic and global climate changes. Plain Language Summary Understanding whether anthropogenic global warming is irreversible, and how fast our climate system will recover to its original state is of great socio‐economic benefit as this is closely related to future climate adaptation and policy decisions. In this study, we investigate what determines the recovery speed of the Arctic temperature. We found that the most uncertain region in response to carbon dioxide (CO2) removal is the Arctic. The Arctic temperature shows a strong inter‐ensemble spread when the CO2 concentration returned to the present level. This different Arctic temperature in each ensemble member can be explained by the density and salinity of the Arctic Ocean about a century ago. For example, a denser Arctic Ocean condition in the early CO2 reduction pathway slows down the recovery of the Atlantic meridional overturning circulation (AMOC) in the presence of positive AMOC‐salt‐advection feedback. Because faster AMOC recovery can transport more warm water into the Atlantic sector of the Arctic, Arctic cooling as a result of CO2 reduction is delayed. Our findings suggest that the Arctic's initial states have a centennial memory for the future Arctic and global climate changes. Key Points The carbon dioxide removal ensemble simulation shows that the Arctic climate changes exhibit the largest ensemble spread, suggesting the most uncertain region The initial buoyancy condition of the Arctic Ocean has a centennial memory for the future recovery of Arctic temperature The denser Arctic Ocean is linked to faster recovery of the Atlantic meridional overturning circulation (AMOC) and Arctic temperature, with strong AMOC‐salt‐advection feedback