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Extra‐tropical cyclones are a relevant feature in the climate at middle and high latitudes. Despite their importance, most studies typically focus only on cyclones identified at a single atmospheric level and on events close to the surface. This paper provides a new perspective on the Southern Hemisphere (SH) cyclone events based on the multilevel cyclone tracking algorithm STACKER. The algorithm, using relative vorticity, detects the raw tracks at single levels and objectively combines them to provide the 3D events and their evolutionary timeline. As a result, a 3D cyclone climatology, based on ECMWF Reanalysis ERA‐I data from 12 pressure levels in the troposphere and lowermost stratosphere is presented. To the best of our knowledge, this is the first analysis carried out throughout the troposphere and the lowermost extratropical/subpolar stratosphere in order to give a comprehensive picture of the cyclone events as physical entities throughout their lifetime. Cyclone properties analysed are track densities, translational velocity, vorticity and lifetimes. For the subtropical and extra‐tropical SH, results support many previous ideas about cyclone characteristics, but new insights are also obtained. A total of 58,231 multilevel cyclone events lasting at least 2 days were detected, with vertical structures spanning two or more levels. This means an average of 303 cyclone events of all types per month, between 2001 and 2017, disregarding seasonality. Results show that cyclones are most frequently detected at the lowest levels of 925 and 700 hPa. By considering that cyclonic systems can be grouped into families according to their vertical extent, results per month on average show that shallow systems are the most frequent events with approximately 248 systems detected, followed by 43 intermediary and 11 deep events. Shallow and deep systems have a large percentage of events with genesis at 925 and 700 hPa. Density statistics show that shallow events are present at all latitude ranges mostly poleward of 30°S with high‐ and medium‐intensities, while intermediate ones are mostly restricted to mid‐latitudes and deep events are mostly confined to sub‐polar and polar latitudes. Cyclones over Antarctica seem to be mostly intermediary and deep cyclones, with longer lifetimes and lower velocities. [ABSTRACT FROM AUTHOR]

This paper quantifies the potential benefit of limiting the global warming to 1.5°C above the preindustrial level on the high‐latitude climate of the Southern Hemisphere compared to 2.0°C and above. A set of Coupled Model Intercomparison Project Phase 5 global climate model experiments is used in order to determine the mean projected changes in surface air temperature, sea level pressure, surface winds and sea ice distribution over and around Antarctica. Alongside, changes in selected variables related to extremes (such as the annual number of extremely cold mornings and extremely cold days) are also quantified as a function of the Representative Concentration Pathway (RCP) considered reaching the given warming threshold. Physical mechanisms for the projected variations in sea ice are proposed, including surface air temperature, changes in low‐level air temperature advection and meridional winds. Results show that there would be significant differences in the atmospheric and sea ice variable changes depending on the warming threshold and RCP considered, and that indeed keeping the global warming under 1.5°C could have a noticeable impact particularly on the distribution of sea ice over the Southern Ocean. [ABSTRACT FROM AUTHOR]

This paper suggests that the Polar Regions are excellent places for thinking about historical interactions between climate change, science, and politics from the beginning of the Cold War up to the present. Since the second half of the 1940s, science has played a central role in contesting claims to political authority in both the Arctic and the Antarctic. Research conducted in the Polar Regions has made a major contribution to the science of climate change on a global scale, and research agendas have been closely connected in the two regions. Viewed from a comparative perspective, however, the historical experiences of global warming in the Arctic and Antarctica have been quite different. Climate research has suggested that warming is generally happening faster over much of the Arctic than the Antarctic. In addition, the recent histories of the two regions show that climate change in the Arctic is destabilizing politics there, whereas in Antarctica climate change is helping to reinforce the existing political structures framed by the Antarctic Treaty System (ATS). A comparative approach to the history of climate change in the Polar Regions helps to demonstrate that science, politics, and environmental change have each played important roles without making any single factor deterministic. WIREs Clim Change 2012, 3:145-159. doi: 10.1002/wcc.161 For further resources related to this article, please visit the . [ABSTRACT FROM AUTHOR]

Warm, salty Circumpolar Deep Water (CDW) is recognized as the primary driver for Antarctic glacial melt, but the mechanism by which it reaches the continental shelves remains highly uncertain from an observational standpoint. With the scarcity of eddy flux estimation in the Antarctic margin, we quantify the isopycnal diffusivity of CDW using hydrographic variability and satellite altimetry under the mixing length framework. For comparison, the spiciness and thickness are used as isopycnal tracers, and the two tracers yield qualitatively similar estimates. Over the Antarctic Circumpolar Current (ACC), variation of mixing length is generally aligned with the jet‐induced mixing suppression, including in areas where topography blocks the jet's influence. In contrast, the mixing length does not depend on the mean flow in the subpolar zone, likely reflecting the relatively quiescent flow regime. The estimated isopycnal diffusivity ranges from 100 to 500 m2 s−1 south of the ACC. The eddy diffusivity tends to be enhanced where the gradient of isopycnal thickness becomes small and CDW intrudes onshore. The cross‐slope eddy CDW flux is estimated, and the associated onshore heat flux across is calculated as ∼3.6 TW in the eastern Indian sector. The eddy heat flux and coastal solar heating are generally balanced with cryospheric heat sinks including glacial melting and surface freezing, suggesting that the eddy advection is substantial for the onshore CDW flux. The thickness field is essential for determining mixing length and eddy fluxes in the subpolar zone, however this is not the case in the ACC domain. Plain Language Summary: The deep ocean is a significant source of heat and salt for the Antarctic coasts. Thus, its behavior is relevant for a wide range of climate sciences, such as Antarctic glacial melt, sea ice variability, and global ocean overturning. The warm deep water is presumably transported to the Antarctic coasts by ocean eddies, but observational evidence has not been provided to date. By synthesizing ocean measurements and satellite altimetry, we estimate the eddy‐driven onshore transport of the deep water over the Antarctic margin. It is shown that shoreward heat transport by eddies is generally balanced with heat gain by solar heating and heat loss expected from surface freezing and glacial melt. This result indicates that eddy transport plays a fundamental role in the coastal heat supply. The thickness of the deep water primarily controls the ability to mix along density surfaces that bridge the open ocean to the continental shelves; more homogeneous thickness allows for easier mixing. Our results facilitate the possibility of predicting the diffusion rate of eddies using the thickness of the deep water. This idea is helpful in simulating deep‐water transport in global climate models, where sub‐grid and unresolved effects of eddies need to be prescribed. Key Points: Eddy diffusivity in the subpolar Southern Ocean is estimated to be 100–500 m2 s−1 based on hydrographic variability and satellite altimetryEddy heat flux towards the Wilkes Land is ∼3.6 TW, nearly balancing with surface freezing, glacial melt, and solar heatingThe thickness gradient controls mixing length and eddy diffusivity in the subpolar zone [ABSTRACT FROM AUTHOR]

Satellite lidar remote sensing of the atmosphere has been ongoing for more than a decade providing the opportunity to study atmospheric processes in great detail. Here we use 12 years of Cloud‐Aerosol Lidar with Orthogonal Polarization measurements to derive a climatology of blowing snow layer height, optical depth, and frequency over Antarctica for the period 2006–2017. Limited to the vertical resolution of the Cloud‐Aerosol Lidar with Orthogonal Polarization data, our climatology includes all blowing snow layers greater than about 30 m in thickness for clear or optically thin cloud regions. Our results show that blowing snow occurs over 50% of the time over large regions with frequencies often exceeding 70%. The overall pattern of blowing snow frequency is fairly consistent from year to year, but there are regional differences. We examined the data for temporal trends in blowing snow properties and found significant trends only in blowing snow frequency. A small area of East Antarctica with generally low blowing snow frequency shows a statistically significant increase in blowing snow frequency ranging from 10% to 100% per decade. No significant trends in frequency were found in regions of high (>50%) blowing snow frequency, and only isolated small areas exhibited a decrease in frequency through the study period. Plain Language Summary: During the last decade a new satellite remote sensing tool has become available for atmospheric research. The technique, called lidar (light ranging and detection), uses short (laser) pulses of visible light to probe the vertical structure of the atmosphere. The Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations mission launched in 2006 has greatly increased our knowledge of atmospheric structure over the polar region. One of the important discoveries made by this satellite is the ubiquitous nature of blowing snow episodes over Antarctica. Blowing snow occurs when the surface wind exceeds a threshold value (about 5–7 m/s) and snow is carried aloft and transported downwind. Once aloft, the snow particles can be carried great distances and even blown off the continent. In this paper we use Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation data to detect the occurrence of blowing snow over Antarctica and construct a 12‐year climatology of its frequency of occurrence, layer depth, and particle density. We have discovered that many regions of Antarctica experience blowing snow over 70% of the time and that blowing snow storms can last for days, cover areas as large as the state of Texas, and reach heights of 400 m or more. Key Points: A first satellite‐derived climatology of blowing snow over Antarctica is presentedBlowing snow frequency exceeds 70% over large regions of East AntarcticaSome areas of East Antarctic show a statistically significant increasing trend in blowing snow frequency [ABSTRACT FROM AUTHOR]

A suite of chemistry‐climate model simulations, forced by pairs of anthropogenic forcings [comprising greenhouse gases (GHGs), ozone depleting substances (ODSs), or aerosols], were employed to investigate whether the high‐latitude Southern Hemisphere (SH) circulation response to these forcings is linearly additive, a common assumption in attribution studies. We find that the geographical pattern of sea‐level pressure (SLP) response to a combination of GHGs and ODSs is linearly additive. However, we find significant differences in the SLP response when combining GHGs and aerosols compared to the sum of the individual forcings, a non‐additivity that is currently masked by the dominance of the ODSs forcing. This non‐linearity also results in changes to the SH split jet. These results were obtained using a coupled chemistry‐climate model, indicating that the non‐linear response is due to chemical interactions between the forcing agents. As such, future simulations investigating a post‐ozone hole Southern Hemisphere climate should consider this chemical interaction. [ABSTRACT FROM AUTHOR]

Data reported from mid‐2014 to late 2018 by a regional pilot array of Deep Argo floats in the Southwest Pacific Basin are used to estimate regional temperature anomalies from a long‐term climatology as well as regional trends over the 4.4 years of float data as a function of pressure. The data show warm anomalies that increase with increasing pressure from effectively 0 near 2,000 dbar to over 10 (±1) m°C by 4,800 dbar, uncertainties estimated at 5–95%. The 4.4‐year trend estimate shows warming at an average rate of 3 (±1) m°C/year from 5,000 to 5,600 dbar, in the near‐homogeneous layer of cold, dense bottom water of Antarctic origin. These results suggest acceleration of previously reported long‐term warming trends in the abyssal waters in this region. They also demonstrate the ability of Deep Argo to quantify changes in the deep ocean in near real‐time over short periods with high accuracy. Plain Language Summary: The coldest waters that fill much of the deep ocean worldwide originate near Antarctica. Temperature data collected from oceanographic cruises around the world at roughly 10‐year intervals show that these near‐bottom waters have been warming on average since the 1990s, absorbing a substantial amount of heat. Data from an array of robotic profiling Deep Argo floats deployed in the Southwest Pacific Ocean starting in mid‐2014 reveal that near‐bottom waters there have continued to warm over the past 4.4 years. Furthermore, these new data suggest an acceleration of that warming rate. These data show that Deep Argo floats are capable of accurately measuring regional changes in the deep ocean. The ocean is the largest sink of heat on our warming planet. A global array of Deep Argo floats would provide data on how much Earth's climate system is warming and possibly improve predictions of future warming. Key Points: Deep and bottom waters in the Southwest Pacific Basin from 2014 to 2018 are increasingly warmer than climatology with increasing depthThe warm anomaly is statistically different from zero at pressures >2,800 dbar and reaches 11 (±1) m°C by 5,500 dbar (1 m°C = 0.001 °C)Deep Argo floats measure a regional mean warming rate of about 3 (±1) m°C/year from 5,000 to 5,600 dbar and from 2014 to 2018 [ABSTRACT FROM AUTHOR]

ABSTRACT The first climatology of strong wind events ( SWEs) at McMurdo station, Antarctica based on the in situ observations and reanalysis fields is presented. SWEs occur throughout the year, but with a minimum during the summer. They are associated with negative mean sea level pressure ( MSLP) and upper height anomalies across the Ross Sea/Ice Shelf, as well as positive temperature anomalies at the station. Wind directions during SWEs exhibit a bimodal distribution of 135-180° and 45-90°. This distribution occurs because of the interaction of the predominantly southerly flow with the orography of Black and White Island and Minna Bluff. The east-northeast flow is associated with winds that are deflected around the orography, while the more southerly events have sufficient energy to override the barriers. The bimodal wind distribution is most common during the winter season since the southerly flow is stronger as a result of deeper cyclonic systems. SWEs also occur when there are large, positive MSLP anomalies at McMurdo station as ridges of high pressure build from the interior and enhance the pressure gradient between the continental high and offshore lows. The interannual variability in the number of winter SWEs is large. Years with many SWEs are associated with a deep climatological low centred over the north eastern Ross Ice Shelf. Years with few winter SWEs have a weakened mid-tropospheric vortex over the Ross Ice Shelf. There are periods when the index of the El Niño-Southern Oscillation ( ENSO) correlates with the number of SWEs. However, the links are not statistically significant in the longer term. A similar link was also observed between the Southern Annular Mode ( SAM) and the interannual variability in the number of SWEs. The relationship was found to be stronger when the phase of ENSO and the SAM were the same. [ABSTRACT FROM AUTHOR]

Aim Variation in species richness has been related to (1) environmental conditions (water, energy and habitat characteristics) and (2) regional differences (contingent historical events and regional particularities that result in differences between regional faunas acting at broad extents). Whereas climatic factors have been widely studied, the effects of regional differences are less often quantified. This work aims to characterize global trends in the species richness of mammal assemblages with respect to both current and historical influences. Location All terrestrial biogeographical realms except Antarctica. Methods Species richness in checklists from 224 sites distributed worldwide were investigated by partitioning the variation between a general set of habitat/climate factors, biogeographical regions, and their overlaps. Additional analyses studied the specific overlaps of region, water and energy. Data were also divided according to area to determine if the strength of these effects varies according to the size of sites. Results Environmental effects explained 38% of richness variation across all sites, whereas environmentally independent regional effects explained 11% and the overlap between region and environment explained 13%. Results were similar when only larger sites (between 1000 km2 and 10,000 km2) were considered. However, the importance of the overlap between region and all environmental variables was greater in smaller sites (between 100 km2 and 1000 km2). In contrast, the specific importance of water and energy variables and their overlap with region was greater in larger sites. The strength of the independent effect of region remained almost invariant regardless of the size of the sites studied. Main conclusions The relationship between species richness and climate varies with scale and among regions. Although environmental variables are the strongest correlates of richness, the unique history and physiographic characteristics of a region produce differences between the richness of mammal assemblages and their response to environmental gradients. The importance of environmental variables varies with scale: climatic gradients are more important at coarse grain (larger sites), possibly as a result of their effects on species ranges, whereas habitat type is more important at the smaller sites, where the importance of ecological interactions increases. Therefore, regional differences and the scale at which richness is measured should be taken into account when evaluating species richness–energy hypotheses. [ABSTRACT FROM AUTHOR]

The article offers information on half-century seasonal relationships between the Southern Hemisphere Annular Mode (SAM) and Antarctic temperatures. It is posed that a general pattern of positive correlations between the strength of the SAM and temperatures in the northern Antarctic Peninsula (East Antarctica) is manifested to be valid for the last half-century, but differences are noted between the seasons. Moreover, SAM-temperature correlations are stronger across Antarctica in austral summer and autumn.

This article reports on the environmental and climatic changes and their causes in the Antarctic and Arctic. It discusses that there are continuing increases in surface temperatures, losses of sea ice and tundra, as well as warming of permafrost over areas of the Arctic, while most of the major increase in Antarctic temperatures is on the Antarctic Peninsula linked with sea ice loss in the Bellingshausen-Amundsen Seas sector. The synthesis of observational evidence leads to the conclusion that the Arctic changes of the past several decades are attributable to circulation-driven changes.

The article investigates the surface temperature changes over different land surface vegetation classes by the dividing the globe into seven regions using a global land cover classification data set. The authors also examine the detection and attribution of surface temperature trends over various vegetation classes for the last 50 years using outputs from three coupled climate models. Findings of the study indicate significant warming in all regions from the year 1900 and antropogenic warming trend in six out of seven regions.

Aim To investigate the major paradigms of intense isolation and little anthropogenic influence around Antarctica and to examine the timings and scales of the modification of the southern polar biota. Location Antarctica and surrounding regions. Methods First, mechanisms of and evidence for long-term isolation are reviewed. These include continental drift, the development of a surrounding deep-water channel and the Antarctic Circumpolar Current (ACC). They also include levels of endemism, richness and distinctiveness of assemblages. Secondly, evidence for past and modern opportunities for species transport are investigated. Comparative levels of alien establishments are also examined around the Southern Ocean. Discussion On a Cenozoic time-scale, it is clear that Gondwana's fragmentation led to increasing geographical isolation of Antarctica and the initiation of the ACC, which restricted biota exchange to low levels while still permitting some movement of biota. On a shorter Quaternary time-scale, the continental ice-sheet, influenced by solar (Milankovitch) cycles, has expanded and contracted periodically, covering and exposing terrestrial and continental shelf habitats. There were probably refugia for organisms during each glacial maxima. It is also likely that new taxa were introduced into Antarctica during cycles of ice sheet and oceanic front movement. The current situation (a glacial minimum) is not ‘normal’; full interglacials represent only 10% of the last 430 ka. On short (ecological) time-scales, many natural dispersal processes (airborne, oceanic eddy, rafting and hitch-hiking on migrants) enable the passage of biota to and from Antarctica. In recent years, humans have become influential both directly by transporting organisms and indirectly by increasing survival and establishment prospects via climate change. Main conclusions Patterns of endemism and alien establishment are very different across taxa, land and sea, and north vs. south of the Polar Frontal Zone. Establishment conditions, as much as transport, are important in limiting alien establishment. Three time-scales emerge as important in the modification of Antarctica's biota. The natural ‘interglacial’ process of reinvasion of Antarctica is being influenced strongly by humans. [ABSTRACT FROM AUTHOR]

During the middle of the 1992 austral winter in the northern Windmill Islands, continental Antarctica, a highly unusual climate event occurred in which the air temperature exceeded 0 °C for some 60 h, at the end of which there was a significant rain shower before the ambient temperature returned to subzero conditions. This event caused most of the snow cover to melt and refreeze as clear ice. Lichens were thus rehydrated in the dark, in some places completely inundated, then frozen in ice. The effect that these conditions had on the distribution of K, Na, Mg, and Ca within the thallus was estimated for two of the dominant macrolichen species, Umbilicaria decussata (Vill.) Zahlbr. and Usnea sphacelata R.Br. from three sites on a knoll on Clark Peninsula. One site acted as a natural control, owing to the very deep snow cover at the sites, there was no overall effect of the climate event on the membrane integrity of either lichen species. Only Usnea sphacelata from the most exposed site showed a significant leakage of K across the cell membrane, which indicated a loss of membrane integrity. Overall, both species were tolerant of the extreme conditions, although Umbilicaria decussata was the more tolerant. [ABSTRACT FROM AUTHOR]