Recent accelerated warming over the Arctic coincides with sea ice reduction and shifting patterns of land cover. We use a state‐of‐the‐art regional Earth system model, RCAO‐GUESS, which comprises a ...dynamic vegetation model (LPJ‐GUESS), a regional atmosphere model (RCA), and an ocean sea ice model (RCO), to explore the dynamic coupling between vegetation and sea ice during 1989–2011. Our results show that RCAO‐GUESS captures recent trends in observed sea ice concentration and extent, with the inclusion of vegetation dynamics resulting in larger, more realistic variations in summer and autumn than the model that does not account for vegetation dynamics. Vegetation feedbacks induce concomitant changes in downwelling longwave radiation, near‐surface temperature, mean sea level pressure, and sea ice reductions, suggesting a feedback chain linking vegetation change to sea ice dynamics. This study highlights the importance of including interactive vegetation dynamics in modeling the Arctic climate system, particularly when predicting sea ice dynamics.
Plain Language Summary
Recent accelerated warming over the Arctic is associated with dramatic changes in the physical environment, among which unprecedented sea ice decline has received particular attention. In this study, we use a regional Earth system model accounting for interactive coupling between the atmosphere, land vegetation, and sea ice dynamics to explore their potential links. Our model simulates observed spatiotemporal patterns of sea ice thickness and extent reasonably well. Furthermore, the results show that feedbacks of warming‐driven vegetation changes on the near‐surface radiation balance can cause greater variations in sea ice between seasons, which can contribute to an accelerated trend of sea ice reduction. The changes in mean sea level pressure caused by vegetation changes can alter the transport of energy and warm the land, sea, and sea ice surfaces. Downwelling longwave radiation is the dominant factor contributing to the near‐surface warming and increased sea ice melting. Our study highlights the importance of adopting fully coupled Earth system models that account for interactive effects of vegetation dynamics on the physical climate system, in particular when analyzing the reduction of sea ice in the Arctic.
Key Points
Sea ice concentration and extent are simulated by a fully coupled regional Earth system model, including interactive vegetation dynamics
Interactive vegetation dynamics increase the interannual variations of seasonal sea ice cover
Increased downwelling longwave radiation induced by vegetation feedbacks enhances sea ice melting
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Piracy and smuggling are as great a problem today as they were several hundreds of years ago. The studies in Elusive Pirates, Pervasive Smugglers, for the first time, carefully describe and ...critically analyze piracy and smuggling in the Greater China Seas region from the sixteenth century to the present. Because piracy and smuggling involve complex historical processes that are still evolving, to fully understand contemporary problems it is important to place them in larger historical and comparative perspectives. The essays in this book add significantly to the scholarship on East and Southeast Asian history, and in particular to the maritime history of the region we call the Greater China Seas. This is the first book to analyze the whole region from Japan to Southeast Asia as a single, integrated historical and geographical area. This book takes a radical departure from the standard terra-centered histories to place the seas at the center rather than at the margins of our inquiries. By focusing on the water we are better able to stitch together the diverse histories of Japan, China, and Southeast Asia. Although often dismissed as historically unimportant, the contributors to this anthology show that in fact pirates and smugglers have played significant roles in the development of the modern world. Elusive Pirates, Pervasive Smugglers should appeal to undergraduate and graduate students in history and Asian studies, as well as to general readers interested in pirates and maritime history.
Changes in Arctic sea ice have been proposed to affect midlatitude winter atmospheric circulation, often based on observed coincident variability. However, causality of this covariability remains ...unclear. Here, we address this issue using atmospheric model experiments prescribed with observed sea surface temperature variations and either constant or time‐varying sea ice variability. We show that the observed relationship between late‐autumn Barents‐Kara sea ice and the winter North Atlantic Oscillation can be reproduced by simulated atmospheric internal variability but is not simulated as a forced response to sea ice. Observations and models suggest reduced sea ice is linked to a weaker Aleutian Low. We show that simulated Aleutian Low variability is correlated with observed sea ice variability even in simulations with fixed sea ice, implying that this relationship is not incidental. Instead, we suggest that covariability between sea ice and the Aleutian Low originates from tropical sea surface temperature and rainfall variations and their teleconnections to the extratropics.
Plain Language Summary
Recent dramatic changes in Arctic sea ice due to climate change have been linked to changes in weather patterns across the Northern Hemisphere. Many studies have proposed such links, but correlation does not necessarily imply causality. Here, we explore the causality of this link using atmospheric models run with observed sea surface temperature variations and either constant or time‐varying sea ice. We find that changes in weather patterns over the Atlantic that are correlated with sea ice variations are not caused by changes in sea ice. Instead, the correlation appears to be an incidental occurrence due to internal atmospheric variability. Additionally, we find that changes in weather patterns over the North Pacific, which are also correlated with sea ice variations, are reproduced in model experiments with no knowledge of these sea ice variations. In this case, the correlation appears to arise due to a third factor: rainfall variations over the tropical Pacific Ocean, which can affect midlatitude weather irrespective of sea ice changes.
Key Points
Atmospheric model experiments aid causal interpretation of links between Arctic sea ice and midlatitude winter atmospheric circulation
Observed links between autumn Barents‐Kara sea ice and the winter North Atlantic Oscillation is largely explained by internal variability
Observed links between autumn Barents‐Kara sea ice and the winter Aleutian Low appears to originate from tropical SST and rainfall changes
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Increasing tensions in the South China Sea have propelled the dispute to the top of the Asia-Pacific's security agenda. Fuelled by rising nationalism over ownership of disputed atolls, growing ...competition over natural resources, strident assertions of their maritime rights by China and the Southeast Asian claimants, the rapid modernization of regional armed forces and worsening geopolitical rivalries among the Great Powers, the South China Sea will remain an area of diplomatic wrangling and potential conflict for the foreseeable future.
Featuring some of the world's leading experts on Asian security, this volume explores the central drivers of the dispute and examines the positions and policies of the main actors, including China, Taiwan, the Southeast Asian claimants, America and Japan. The South China Sea Dispute: Navigating Diplomatic and Strategic Tensions provides readers with the key to understanding how this most complex and contentious dispute is shaping the regional security environment.
This book covers topics ranging from a detailed error analysis of SSTs to new applications employed, for example, in the study of the El Niño–La Niña Southern Oscillation, lake temperatures, and ...coral bleaching. New techniques for interpolation and algorithm development are presented, including improvements for cloud detection. Analysis of the pixel-to-pixel uncertainties provides insight to applications for high spatial resolutions. New approaches for the estimation and evaluation of SSTs are presented. In addition, an overview of the Climate Change Initiative, with specific applications to SST, is presented. The book provides an excellent overview of the current technology, while also highlighting new technologies and their applications to new missions.
Increasing coastal inundation risk in a warming climate will require accurate and reliable seasonal forecasts of sea level anomalies at fine spatial scales. In this study, we explore statistical ...downscaling of monthly hindcasts from six current seasonal prediction systems to provide a high‐resolution prediction of sea level anomalies along the North American coast, including at several tide gauge stations. This involves applying a seasonally invariant downscaling operator, constructing by linearly regressing high‐resolution (1/12°) ocean reanalysis data against its coarse‐grained (1°) counterpart, to each hindcast ensemble member for the period 1982–2011. The resulting high‐resolution coastal hindcasts have significantly more deterministic skill than the original hindcasts interpolated onto the high‐resolution grid. Most of this improvement occurs during summer and fall, without impacting the seasonality of skill noted in previous studies. Analysis of the downscaling operator reveals that it boosts skill by amplifying the most predictable patterns while damping the less predictable patterns.
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Currently, the large computer models that form the basis of seasonal climate prediction systems produce coastal sea level forecasts spaced about 100 km apart. This is too coarse to meet the needs of U.S. coastal ocean management and services, which are becoming increasingly important as sea levels rise in a warming climate. In this study, we explored a method to provide such information on much smaller spatial scales, which better correspond to local coastal sea level measurements by tide gauges. We developed an efficient way to generate monthly sea level predictions on distances as small as 10 km apart, by applying the observed statistical relationship between sea level variations on scales of 100–1,000 km and finer‐scale coastal ocean observations to the original coarser model predictions. By testing our approach on past forecasts (“hindcasts”) from existing climate forecast systems, we found that we could improve forecasts for different local regions along both the U.S. West and East Coasts.
Key Points
Sea level prediction from relatively coarse operational forecasts can be enhanced to finer coastal scales using statistical downscaling
Downscaling can be determined by multivariate linear regression trained from high‐resolution reanalysis and its coarse‐grained counterpart
This downscaling method significantly improves skill compared to bilinearly interpolated hindcasts at several U.S. tide gauge locations
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The low‐amplitude, large‐scale, interannual, and longer‐term sea level changes are linked to the variations of ocean heat and freshwater content and strongly controlled by ocean dynamics. Near the ...coast, especially in low‐lying and flood‐vulnerable regions, these changes can provide background conditions favorable for the occurrence of extreme sea levels that represent a threat for coastal communities and ecosystems. In this study, we identify a tripole mode of the ocean gyre‐scale sea surface height variability in the North Atlantic and show that this mode is responsible for most of the interannual‐to‐decadal sea surface height changes along the southeast coast of the United States, including the Gulf of Mexico. We also show that these changes are largely driven by the large‐scale heat divergence related to the Atlantic Meridional Overturning Circulation and linked to the low‐frequency North Atlantic Oscillation.
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The global mean sea level rise caused by ocean warming and terrestrial glacier melting is one of the most alarming aspects of climate change. However, ocean and atmosphere dynamics make sea level change spatially and temporally nonuniform. In fact, the ocean exhibits certain patterns of sea level change with alternating signs over different time periods. These patterns provide background conditions, on top of which shorter‐period and often stronger weather‐driven sea level fluctuations are superimposed. In order to improve our capacity to predict regional sea level variability, it is important to identify these patterns and to explore the mechanisms responsible for their evolution. In this study, we identify such a pattern in the North Atlantic Ocean and show that it is largely responsible for year‐to‐year changes of coastal sea level south of Cape Hatteras and in the Gulf of Mexico. These coastal regions of the United States are particularly vulnerable to extreme weather conditions, such as tropical storms and hurricanes, that can cause catastrophic flooding. We show that the temporal evolution of the identified pattern is due to the basin‐scale ocean heat content changes in the North Atlantic, driven by changes in the large‐scale ocean and atmosphere circulations.
Key Points
Interannual sea surface height variability in the North Atlantic exhibits a tripole pattern
The sea surface height tripole explains up to 60–80% of interannual sea level variance along the southeast U.S. coast and in the Gulf of Mexico
The tripole is associated with gyre‐scale heat divergence in response to low‐frequency North Atlantic Oscillation
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Earth is heading towards a climate that last existed more than three million years ago (Ma) during the 'mid-Pliocene warm period'
, when atmospheric carbon dioxide concentrations were about 400 parts ...per million, global sea level oscillated in response to orbital forcing
and peak global-mean sea level (GMSL) may have reached about 20 metres above the present-day value
. For sea-level rise of this magnitude, extensive retreat or collapse of the Greenland, West Antarctic and marine-based sectors of the East Antarctic ice sheets is required. Yet the relative amplitude of sea-level variations within glacial-interglacial cycles remains poorly constrained. To address this, we calibrate a theoretical relationship between modern sediment transport by waves and water depth, and then apply the technique to grain size in a continuous 800-metre-thick Pliocene sequence of shallow-marine sediments from Whanganui Basin, New Zealand. Water-depth variations obtained in this way, after corrections for tectonic subsidence, yield cyclic relative sea-level (RSL) variations. Here we show that sea level varied on average by 13 ± 5 metres over glacial-interglacial cycles during the middle-to-late Pliocene (about 3.3-2.5 Ma). The resulting record is independent of the global ice volume proxy
(as derived from the deep-ocean oxygen isotope record) and sea-level cycles are in phase with 20-thousand-year (kyr) periodic changes in insolation over Antarctica, paced by eccentricity-modulated orbital precession
between 3.3 and 2.7 Ma. Thereafter, sea-level fluctuations are paced by the 41-kyr period of cycles in Earth's axial tilt as ice sheets stabilize on Antarctica and intensify in the Northern Hemisphere
. Strictly, we provide the amplitude of RSL change, rather than absolute GMSL change. However, simulations of RSL change based on glacio-isostatic adjustment show that our record approximates eustatic sea level, defined here as GMSL unregistered to the centre of the Earth. Nonetheless, under conservative assumptions, our estimates limit maximum Pliocene sea-level rise to less than 25 metres and provide new constraints on polar ice-volume variability under the climate conditions predicted for this century.
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