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Detection and attribution of past changes in cyclone activity are hampered by biased cyclone records due to changes in observational capabilities. Here, we relate a homogeneous record of Atlantic tropical cyclone activity based on storm surge statistics from tide gauges to changes in global temperature patterns. We examine 10 competing hypotheses using nonstationary generalized extreme value analysis with different predictors (North Atlantic Oscillation, Southern Oscillation, Pacific Decadal Oscillation, Sahel rainfall, Quasi-Biennial Oscillation, radiative forcing, Main Development Region temperatures and its anomaly, global temperatures, and gridded temperatures). We find that gridded temperatures, Main Development Region, and global average temperature explain the observations best. The most extreme events are especially sensitive to temperature changes, and we estimate a doubling of Katrina magnitude events associated with the warming over the 20th century. The increased risk depends on the spatial distribution of the temperature rise with highest sensitivity from tropical Atlantic, Central America, and the Indian Ocean. Statistically downscaling 21st century warming patterns from six climate models results in a twofold to sevenfold increase in the frequency of Katrina magnitude events for a 1 °C rise in global temperature (using BNU-ESM, BCC-CSM-1.1, CanESM2, HadGEM2-ES, INM-CM4, and NorESM1-M).

The Systems Ecology Paradigm (SEP) incorporates humans as integral parts of ecosystems and emphasizes issues that have significant societal relevance such as grazing land, forestland, and agricultural ecosystem management, biodiversity and global change impacts. Accomplishing this societally relevant research requires cutting-edge basic and applied research. This book focuses on environmental and natural resource challenges confronting local to global societies for which the SEP methodology must be utilized for resolution. Key elements of SEP are a holistic perspective of ecological/social systems, systems thinking, and the ecosystem approach applied to real world, complex environmental and natural resource problems. The SEP and ecosystem approaches force scientific emphasis to be placed on collaborations with social scientists and behavioral, learning, and marketing professionals. The SEP has given environmental scientists, decision makers, citizen stakeholders, and land and water managers a powerful set of tools to analyse, integrate knowledge, and propose adoption of solutions to important local to global problems.

We conducted a model-based assessment of changes in permafrost area and carbon storage for simulations driven by RCP4.5 and RCP8.5 projections between 2010 and 2299 for the northern permafrost region. All models simulating carbon represented soil with depth, a critical structural feature needed to represent the permafrost carbon–climate feedback, but that is not a universal feature of all climate models. Between 2010 and 2299, simulations indicated losses of permafrost between 3 and 5 million km² for the RCP4.5 climate and between 6 and 16 million km² for the RCP8.5 climate. For the RCP4.5 projection, cumulative change in soil carbon varied between 66-Pg C (1015-g carbon) loss to 70-Pg C gain. For the RCP8.5 projection, losses in soil carbon varied between 74 and 652 Pg C (mean loss, 341 Pg C). For the RCP4.5 projection, gains in vegetation carbon were largely responsible for the overall projected net gains in ecosystem carbon by 2299 (8- to 244-Pg C gains). In contrast, for the RCP8.5 projection, gains in vegetation carbon were not great enough to compensate for the losses of carbon projected by four of the five models; changes in ecosystem carbon ranged from a 641-Pg C loss to a 167-Pg C gain (mean, 208-Pg C loss). The models indicate that substantial net losses of ecosystem carbon would not occur until after 2100. This assessment suggests that effective mitigation efforts during the remainder of this century could attenuate the negative consequences of the permafrost carbon–climate feedback.

The Arctic is warming far faster than the global average, threatening the release of large amounts of carbon presently stored in frozen permafrost soils. Increasing Earth’s albedo by the injection of sulfate aerosols into the stratosphere has been proposed as a way of offsetting some of the adverse effects of climate change. We examine this hypothesis in respect of permafrost carbon-climate feedbacks using the PInc-PanTher process model driven by seven earth system models running the Geoengineering Model Intercomparison Project (GeoMIP) G4 stratospheric aerosol injection scheme to reduce radiative forcing under the Representative Concentration Pathway (RCP) 4.5 scenario. Permafrost carbon released as CO 2 is halved and as CH 4 by 40% under G4 compared with RCP4.5. Economic losses avoided solely by the roughly 14 Pg carbon kept in permafrost soils amount to about US$ 8.4 trillion by 2070 compared with RCP4.5, and indigenous habits and lifestyles would be better conserved. Rising temperatures in the Arctic can lead to the release of vast amounts of carbon stored in permafrost soils. Here the authors show that stratospheric sulfate aerosol injection geoengineering can help to avoid about 14 gigatons of carbon release and US$8.4 trillion in economic losses by 2070 compared to RCP4.5 emissions.

Multicellular aggregates of circulating tumor cells (CTC clusters) are potent initiators of distant organ metastasis. However, it is currently assumed that CTC clusters are too large to pass through narrow vessels to reach these organs. Here, we present evidence that challenges this assumption through the use of microfluidic devices designed to mimic human capillary constrictions and CTC clusters obtained from patient and cancer cell origins. Over 90% of clusters containing up to 20 cells successfully traversed 5- to 10-μm constrictions even in whole blood. Clusters rapidly and reversibly reorganized into single-file chain-like geometries that substantially reduced their hydrodynamic resistances. Xenotransplantation of human CTC clusters into zebrafish showed similar reorganization and transit through capillary-sized vessels in vivo. Preliminary experiments demonstrated that clusters could be disrupted during transit using drugs that affected cellular interaction energies. These findings suggest that CTC clusters may contribute a greater role to tumor dissemination than previously believed and may point to strategies for combating CTC cluster-initiated metastasis.

Iceberg calving from all Antarctic ice shelves has never been directly measured, despite playing a crucial role in ice sheet mass balance. Rapid changes to iceberg calving naturally arise from the sporadic detachment of large tabular bergs but can also be triggered by climate forcing. Here we provide a direct empirical estimate of mass loss due to iceberg calving and melting from Antarctic ice shelves. We find that between 2005 and 2011, the total mass loss due to iceberg calving of 755 ± 24 gigatonnes per year (Gt/y) is only half the total loss due to basal melt of 1516 ± 106 Gt/y. However, we observe widespread retreat of ice shelves that are currently thinning. Net mass loss due to iceberg calving for these ice shelves (302 ± 27 Gt/y) is comparable in magnitude to net mass loss due to basal melt (312 ± 14 Gt/y). Moreover, we find that iceberg calving from these decaying ice shelves is dominated by frequent calving events, which are distinct from the less frequent detachment of isolated tabular icebergs associated with ice shelves in neutral or positive mass balance regimes. Our results suggest that thinning associated with ocean-driven increased basal melt can trigger increased iceberg calving, implying that iceberg calving may play an overlooked role in the demise of shrinking ice shelves, and is more sensitive to ocean forcing than expected from steady state calving estimates. Significance The floating parts of the Antarctic ice sheet (“ice shelves”) help to hold back the flow of the grounded parts, determining the contribution to global sea level rise. Using satellite images, we measured, for the first time, all icebergs larger than 1 km ² calving from the entire Antarctic coastline, and the state of health of all the ice shelves. Some large ice shelves are growing while many smaller ice shelves are shrinking. We find high rates of iceberg calving from Antarctic ice shelves that are undergoing basal melt-induced thinning, which suggests the fate of ice shelves may be more sensitive to ocean forcing than previously thought.

Two decades of summer warming in an Alaskan tundra ecosystem increased plant biomass and woody dominance, indirectly increased winter soil temperature, homogenized the soil trophic structure and suppressed surface-soil-decomposer activity, but did not change net soil carbon or nitrogen storage. Arctic tundra response to warming Nearly half of the global soil carbon is stored at high latitudes, so it is vital to understand how these regions will respond to climate change. Warming initially accelerates decomposition and raises productivity, but longer-term effects depend on how soil ecology develops with time. This study reports findings from a two-decade warming experiment in an Alaskan tundra ecosystem. Overall the tundra soil system proved resistant to carbon loss. There was an increase in shrub dominance and, although decomposer activity at the surface decreased, it increased in the deep mineral soil following a 'biotic awakening'. The authors conclude that identifying the mechanisms under which warming stimulates and regulates tundra decomposer activity at depth — where much of the permafrost soil carbon is stored — should be a priority. High latitudes contain nearly half of global soil carbon, prompting interest in understanding how the Arctic terrestrial carbon balance will respond to rising temperatures 1 , 2 . Low temperatures suppress the activity of soil biota, retarding decomposition and nitrogen release, which limits plant and microbial growth 3 . Warming initially accelerates decomposition 4 , 5 , 6 , increasing nitrogen availability, productivity and woody-plant dominance 3 , 7 . However, these responses may be transitory, because coupled abiotic–biotic feedback loops that alter soil-temperature dynamics and change the structure and activity of soil communities, can develop 8 , 9 . Here we report the results of a two-decade summer warming experiment in an Alaskan tundra ecosystem. Warming increased plant biomass and woody dominance, indirectly increased winter soil temperature, homogenized the soil trophic structure across horizons and suppressed surface-soil-decomposer activity, but did not change total soil carbon or nitrogen stocks, thereby increasing net ecosystem carbon storage. Notably, the strongest effects were in the mineral horizon, where warming increased decomposer activity and carbon stock: a ‘biotic awakening’ at depth.

The carbon-rich northern high-latitude permafrost is a potential climate tipping point. Once triggered, its thawing and release of carbon dioxide and methane might unleash irreversible changes in the Earth’s climate system. We investigate the response of permafrost under three Shared Socioeconomic Pathways (SSPs) with no mitigation (SSP5-8.5), moderate mitigation (SSP2-4.5) and delayed mitigation (SSP5-3.4-OS), and three solar geoengineering scenarios applied to each experiment to prevent global warming from exceeding 2 °C above pre-industrial. The long-term negative emissions in SSP5-3.4-OS preserves much more frozen soil than SSP5-8.5, but shows nearly as much permafrost carbon loss this century as SSP2-4.5 due to its mid-century temperature overshoot. Solar geoengineering to meet the 2 °C target above pre-industrial effectively suppresses permafrost thawing and reduces subsequent carbon release from the soil. However, the carbon emission from permafrost still continues after the temperature is stabilized, due to the decomposition of thawed permafrost carbon. More solar insolation reduction is required to compensate the positive permafrost carbon feedback, which exerts greater impacts on the efficiency of solar geoengineering under a scenario with strong climate policy and lower carbon emissions.

Untangling the influence of human activities on food-web stability and persistence is complex given the large numbers of species and overwhelming number of interactions within ecosystems. Although biodiversity has been associated with stability, the actual structures and processes that confer stability to diverse food webs remain largely unknown. Here we show that real food webs are structured such that top predators act as couplers of distinct energy channels that differ in both productivity and turnover rate. Our theoretical analysis shows that coupled fast and slow channels convey both local and non-local stability to food webs. Alarmingly, the same human actions that have been implicated in the loss of biodiversity also directly erode the very structures and processes that we show to confer stability on food webs. Ecological complexity untangled Food webs map which organisms eat which other organisms, and help to visualize community organization. They are complex, as Darwin recognized in his metaphor of a “tangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth”. The cover (by Sergi Valverde using Netlab software) illustrates complexity in an empirical food web — here it's species associated with Scotch broom at Silwood Park, UK. Montoya et al . review recent work on ecological networks and consider a paradox: theory predicts that complex networks will be fragile, yet complexity evolves and persists. Yes, these networks are complex, they conclude, but not so complex that we can't understand them. There are simplifying patterns in maps of feeding relationships, and parts of the 'tangled bank' are less tangled than others. As simulations grow more realistic, factors influencing ecological fragility should become clearer, with benefits for work on ecological impact and conservation. Ecology features elsewhere this week. In a contribution to the debate on ecosystem biodiversity, Rooney et al . identify a recurring pattern in real food webs: the top predators couple distinct 'fast' and 'slow' energy channels that differ in both productivity and turnover rate. Theory suggests that such coupling is critical to food-web stability. Alarmingly, human actions that reduce biodiversity also erode structures that provide that stability. So it may be time to stop focusing exclusively on ecosystem biodiversity, and to look more closely at the factors that create food-web stability. All agree: matters ecological are complex. But policymakers do not have a recognized international body of experts to turn to. Climate change has the IPCC. Now ecologists present the case for IMoSEB, the International Mechanism of Scientific Expertise on Biodiversity. Real food webs are structured so that top predators couple distinct energy channels that differ in both productivity and turnover rate. Theory suggests that such coupling is critical to the maintenance of food web stability, with important implications for conservation and ecosystem management.