Arctic climate change: observed and modelled temperature and sea-ice variability

Changes apparent in the arctic climate system in recent years require evaluation in a century-scale perspective in order to assess the Arctic's response to increasing anthropogenic greenhouse-gas forcing. Here, a new set of century- and multidecadal-scale observational data of surface air temperature (SAT) and sea ice is used in combination with ECHAM4 and HadCM3 coupled atmosphere-ice-ocean global model simulations in order to better determine and understand arctic climate variability. We show that two pronounced twentieth-century warming events, both amplified in the Arctic, were linked to sea-ice variability. SAT observations and model simulations indicate that the nature of the arctic warming in the last two decades is distinct from the early twentieth-century warm period. It is suggested strongly that the earlier warming was natural internal climate-system variability, whereas the recent SAT changes are a response to anthropogenic forcing. The area of arctic sea ice is furthermore observed to have decreased similar to8 x 10(5) km(2) (7.4%) in the past quarter century, with record-low summer ice coverage in September 2002. A set of model predictions is used to quantify changes in the ice cover through the twenty-first century, with greater reductions expected in summer than winter. In summer, a predominantly sea-ice-free Arctic is predicted for the end of this century

Atmospheric conditions during the Arctic Clouds in Summer Experiment (ACSE): Contrasting open-water and sea-ice surfaces during melt and freeze-up seasons

The Arctic Clouds in Summer Experiment (ACSE) was conducted during summer and early autumn 2014, providing a detailed view of the seasonal transition from ice melt into freeze-up. Measurements were taken over both ice-free and ice-covered surfaces near the ice edge, offering insight into the role of the surface state in shaping the atmospheric conditions. The initiation of the autumn freeze-up was related to a change in air mass, rather than to changes in solar radiation alone; the lower atmosphere cooled abruptly, leading to a surface heat loss. During melt season, strong surface inversions persisted over the ice, while elevated inversions were more frequent over open water. These differences disappeared during autumn freeze-up, when elevated inversions persisted over both ice-free and ice-covered conditions. These results are in contrast to previous studies that found a well-mixed boundary layer persisting in summer and an increased frequency of surface-based inversions in autumn, suggesting that knowledge derived from measurements taken within the pan-Arctic area and on the central ice pack does not necessarily apply closer to the ice edge. This study offers an insight into the atmospheric processes that occur during a crucial period of the year; understanding and accurately modeling these processes is essential for the improvement of ice-extent predictions and future Arctic climate projections

Multilevel genomics of colorectal cancers with microsatellite instability—clinical impact of JAK1 mutations and consensus molecular subtype 1

Background Approximately 15% of primary colorectal cancers have DNA mismatch repair deficiency, causing a complex genome with thousands of small mutations—the microsatellite instability (MSI) phenotype. We investigated molecular heterogeneity and tumor immunogenicity in relation to clinical endpoints within this distinct subtype of colorectal cancers. Methods A total of 333 primary MSI+ colorectal tumors from multiple cohorts were analyzed by multilevel genomics and computational modeling—including mutation profiling, clonality modeling, and neoantigen prediction in a subset of the tumors, as well as gene expression profiling for consensus molecular subtypes (CMS) and immune cell infiltration. Results Novel, frequent frameshift mutations in four cancer-critical genes were identified by deep exome sequencing, including in CRTC1, BCL9, JAK1, and PTCH1. JAK1 loss-of-function mutations were validated with an overall frequency of 20% in Norwegian and British patients, and mutated tumors had up-regulation of transcriptional signatures associated with resistance to anti-PD-1 treatment. Clonality analyses revealed a high level of intra-tumor heterogeneity; however, this was not associated with disease progression. Among the MSI+ tumors, the total mutation load correlated with the number of predicted neoantigens (P = 4 × 10−5), but not with immune cell infiltration—this was dependent on the CMS class; MSI+ tumors in CMS1 were highly immunogenic compared to MSI+ tumors in CMS2-4. Both JAK1 mutations and CMS1 were favorable prognostic factors (hazard ratios 0.2 [0.05–0.9] and 0.4 [0.2–0.9], respectively, P = 0.03 and 0.02). Conclusions Multilevel genomic analyses of MSI+ colorectal cancer revealed molecular heterogeneity with clinical relevance, including tumor immunogenicity and a favorable patient outcome associated with JAK1 mutations and the transcriptomic subgroup CMS1, emphasizing the potential for prognostic stratification of this clinically important subtype. See related research highlight by Samstein and Chan 10.1186/s13073-017-0438-

Decreasing Arctic Sea Ice Mirrors Increasing CO2 on Decadal Time Scale

Arctic sea ice is a keystone indicator of greenhouse-gas induced global climate change, which is expected to be amplified in the Arctic. Here we directly compare observed variations in arctic sea-ice extent and CO2 since the beginning of the 20th century, identifying a strengthening linkage, such that in recent decades the rate of sea-ice decrease mirrors the increase in CO2, with r ~ –0.95 over the last four decades, thereby indicating that 90 % (r2 ~ 0.90) of the decreasing sea-ice extent is em-pirically “accounted for” by the increasing CO2 in the atmosphere. The author presents an empirical relation between annual sea-ice extent and global atmospheric CO2 concentrations, in which sea-ice reductions are line-arly, inversely proportional to the magnitude of increase of CO2 over the last few decades. This approximates sea-ice changes during the most recent four decades, with a proportionality constant of 0.030 million km2 per ppmv CO2. When applied to future emission scenarios of the Intergovernmental Panel on Climate Change (IPCC), this relationship results in substantially faster ice decreases up to 2050 than predicted by IPCC models. However, depar-tures from this projection may arise from non-linear feedback effects and/or temporary natural variations on interannual timescales, such as the record minimum of sea-ice extent observed in September 2007

Climate change in the North – past, present and future

The Nordic countries have produced famous polar explorers and researchers who have generated climate research schools at a variety of locations. The dependence of these countries with respect to the lifelihood of their societies, of their use of lands and seas, the exploitation of marine living and non-living resources have made climate research an eminent topic, and many outstanding discoveries of long- and short-term climate change have been made for the first time in Scandinavia. These include early contributions to our understanding of the geological effects of continent-wide glaciations during the ice ages, the complex postglacial history of the Baltic Sea and the varved sediment sequences preserved from lakes with an extraordinary seasonality in their sediment input, as well as the detailed records of temperature, ice texture and impurities and greenhouse gas variations of the last Glacial and of the Holocene preserved in the ice cores from Greenland. Iceland with its volcanic sequences and intercalated sediment layers not only preserved the history of this subaerial segment of the mid-Atlantic Ridge, but also easily datable paleoclimate records. The fate of the Vikings, who settled during the Medieval climate optimum on Iceland and later on Greenland and who lost their habitat on Greenland at the beginning of the Little Ice Age, illustrates vividly the climate-dependent subsistence of the indigenous and non-indigenous Scandinavian populations. Modern Scandinavian climate research institutions also include sophisticated modelling groups

Critical vulnerabilities of marine and sea ice–based ecosystems in the high Arctic

The objectives of this paper are to summarise: (1) observed 20th-century and projected 21st-century changes in key components of the Arctic climate system and (2) probable impacts on the Arctic marine environment, with emphasis on the vulnerabilities of marine and sea ice–based ecosystems. Multi-decadal to century-scale observational data sets of surface air temperature (SAT) and sea ice indicate that the two pronounced 20th-century warming events, both amplified in the Arctic, were linked to sea-ice variability. Arctic sea-ice coverage has decreased *8% in the past quarter century, with record- and nearrecord low summer ice in observed recent years. A set of coupled atmosphere–ice–ocean global model simulations quantifies the expected changes in Arctic temperature and sea ice through the twenty-first century. Projected are polar-amplified increases in SAT and reductions in sea ice, with a predominantly ice-free Arctic Ocean in summer projected before the end of this century. A range of potential consequences of Arctic warming and a shrinking ice cover are foreseen. First, exposure of vast areas of the Arctic Ocean would greatly alter the coastal and shelf marine environment. Second, broad changes in the marine and sea ice–based ecosystem—e.g. changes in plankton due to less ice and greater inflow of melt water—could negatively impact Arctic and sub-Arctic marine biodiversity, not least the vulnerable ice-based mammals such as polar bears. Third, there would be a larger open area for potential Arctic fisheries, as well as increased offshore activities and marine transportation, including the Northern Sea Route north of Siberia. Changes in the physical environment of the Arctic Ocean are thus expected to be dramatic, and although projecting ecosystem changes several decades into twenty-first century is challenging, the impact of diminishing sea ice on Arctic marine and sea ice–based ecosystems will certainly be transformative

Seasonal variations of the oceanographic conditions off the southwest coast of India during 1971-1975

As part of a survey of the coastal fish resources off the southwest coast of India, the UNDP/ FAO (United Nations Development Programme/Food and Agriculture Organization) Pelagic Fishery Project, Cochin, collected environmental data from June 1971 through October 1975. Based on these data, the oceanographic conditions during the 4-year period are discussed. The seasonal variations are highly repetitive from year to year. An uplift of water onto the shelf begins in March or April. Associated with a south-flowing current, this type of upwelling lasts throughout the SW monsoon period until September-October. A northflowing coastal current from November-December through January-February is associated with an influx of low-salinity water from the south. The environmental variations on the shelf are reflected in seasonal biological events