7 research outputs found
The 800 year long ion record from the Lomonosovfonna (Svalbard) ice core
No full textWe present a high-resolution record of water-soluble ion chemistry from a 121 m ice core spanning about 800 years. The core is well dated to 2/3 depth using cycle counting and reference horizons and a simple but close fitting model for the lower 1/3 of the core. This core suffers from modest seasonal melt, and so we present concentration data in decadal running means to minimize percolation effects. Sea-salt ions (Na+, Cl−, Mg2+, and K+) account for more than 70% of all ions. In general, sea-salt ion concentrations are rather variable and have no clear association with climatic variations. Sulfate, with 74% being from non-sea-salt sources, has higher concentrations than seen on Vestfonna ice cap but lower than in Ny-Ålesund aerosols, suggesting central Spitsbergen receives more marine (westerly) air masses than Ny-Ålesund but more sulfate enriched (easterly) air masses than Nordaustlandet. Clear anthropogenic impacts are found for sulfate, nitrate, and ammonium (and probably excess chloride) after the mid twentieth century, with sulfate showing a significant rise by the end of the nineteenth century. Sulfate and methanesulfonate concentrations correlate well during the twentieth century, and it is clear that most of the preindustrial sulfate is of biogenic origin. Terrestrial component (Ca2+) has the highest concentrations in the coldest part of the Little Ice Age, suggesting more windy conditions, transporting local terrestrial dust to the ice cap. All ion concentrations decrease at the end of the twentieth century, which reflects loss of ions by runoff, with non-sea-salt magnesium being particularly sensitive to melting
Thousand years of winter surface air temperature variations in Svalbard and northern Norway reconstructed from ice-core data
No full textTwo isotopic ice core records from western Svalbard are calibrated to reconstruct more than 1000 years of past winter surface air temperature variations in Longyearbyen, Svalbard, and Vardø, northern Norway. Analysis of the derived reconstructions suggests that the climate evolution of the last millennium in these study areas comprises three major sub-periods. The cooling stage in Svalbard (ca. 800-1800) is characterized by a progressive winter cooling of approximately 0.9 °C century-1 (0.3 °C century-1 for Vardø) and a lack of distinct signs of abrupt climate transitions. This makes it difficult to associate the onset of the Little Ice Age in Svalbard with any particular time period. During the 1800s, which according to our results was the coldest century in Svalbard, the winter cooling associated with the Little Ice Age was on the order of 4 °C (1.3 °C for Vardø) compared to the 1900s. The rapid warming that commenced at the beginning of the 20th century was accompanied by a parallel decline in sea-ice extent in the study area. However, both the reconstructed winter temperatures as well as indirect indicators of summer temperatures suggest the Medieval period before the 1200s was at least as warm as at the end of the 1990s in Svalbard.
Experimental protocol for sea level projections from ISMIP6 stand-alone ice sheet models
No full textAbstract. Projection of the contribution of ice sheets to sea level change as part of
the Coupled Model Intercomparison Project Phase 6 (CMIP6) takes the form
of simulations from coupled ice sheet–climate models and stand-alone ice
sheet models, overseen by the Ice Sheet Model Intercomparison Project for
CMIP6 (ISMIP6). This paper describes the experimental setup for
process-based sea level change projections to be performed with stand-alone
Greenland and Antarctic ice sheet models in the context of ISMIP6. The
ISMIP6 protocol relies on a suite of polar atmospheric and oceanic
CMIP-based forcing for ice sheet models, in order to explore the uncertainty
in projected sea level change due to future emissions scenarios, CMIP
models, ice sheet models, and parameterizations for ice–ocean interactions.
We describe here the approach taken for defining the suite of ISMIP6
stand-alone ice sheet simulations, document the experimental framework and
implementation, and present an overview of the ISMIP6 forcing to be
used by participating ice sheet modeling groups.
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Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2)
No full textThe sea level contribution of the Antarctic ice sheet constitutes a large uncertainty in future sea level projections. Here we apply a linear response theory approach to 16 state-of-the-art ice sheet models to estimate the Antarctic ice sheet contribution from basal ice shelf melting within the 21st century. The purpose of this computation is to estimate the uncertainty of Antarctica's future contribution to global sea level rise that arises from large uncertainty in the oceanic forcing and the associated ice shelf melting. Ice shelf melting is considered to be a major if not the largest perturbation of the ice sheet's flow into the ocean. However, by computing only the sea level contribution in response to ice shelf melting, our study is neglecting a number of processes such as surface-mass-balance-related contributions. In assuming linear response theory, we are able to capture complex temporal responses of the ice sheets, but we neglect any self-dampening or self-amplifying processes. This is particularly relevant in situations in which an instability is dominating the ice loss. The results obtained here are thus relevant, in particular wherever the ice loss is dominated by the forcing as opposed to an internal instability, for example in strong ocean warming scenarios. In order to allow for comparison the methodology was chosen to be exactly the same as in an earlier study (Levermann et al., 2014) but with 16 instead of 5 ice sheet models. We include uncertainty in the atmospheric warming response to carbon emissions (full range of CMIP5 climate model sensitivities), uncertainty in the oceanic transport to the Southern Ocean (obtained from the time-delayed and scaled oceanic subsurface warming in CMIP5 models in relation to the global mean surface warming), and the observed range of responses of basal ice shelf melting to oceanic warming outside the ice shelf cavity. This uncertainty in basal ice shelf melting is then convoluted with the linear response functions of each of the 16 ice sheet models to obtain the ice flow response to the individual global warming path. The model median for the observational period from 1992 to 2017 of the ice loss due to basal ice shelf melting is 10.2 mm, with a likely range between 5.2 and 21.3 mm. For the same period the Antarctic ice sheet lost mass equivalent to 7.4 mm of global sea level rise, with a standard deviation of 3.7 mm (Shepherd et al., 2018) including all processes, especially surface-mass-balance changes. For the unabated warming path, Representative Concentration Pathway 8.5 (RCP8.5), we obtain a median contribution of the Antarctic ice sheet to global mean sea level rise from basal ice shelf melting within the 21st century of 17 cm, with a likely range (66th percentile around the mean) between 9 and 36 cm and a very likely range (90th percentile around the mean) between 6 and 58 cm. For the RCP2.6 warming path, which will keep the global mean temperature below 2 ∘C of global warming and is thus consistent with the Paris Climate Agreement, the procedure yields a median of 13 cm of global mean sea level contribution. The likely range for the RCP2.6 scenario is between 7 and 24 cm, and the very likely range is between 4 and 37 cm. The structural uncertainties in the method do not allow for an interpretation of any higher uncertainty percentiles. We provide projections for the five Antarctic regions and for each model and each scenario separately. The rate of sea level contribution is highest under the RCP8.5 scenario. The maximum within the 21st century of the median value is 4 cm per decade, with a likely range between 2 and 9 cm per decade and a very likely range between 1 and 14 cm per decade
Cancer patients' care at the end of life in a critical care environment: perspectives of families, patients and practitioners
No full textInnovations in cancer care requiring intensive support, and improved cancer patient survival in and out of critical care, have led to greater numbers of cancer patients than ever accessing critical care. Of these, however, a fair proportion will die. Current research points to around one in six patients dying in general critical care units and even higher numbers for cancer patients. End-of-life care (EOLC) for critically ill patients is problematic and rarely addressed beyond satisfaction or chart review studies, while palliative care is an established domain in cancer. It is not known whether dying, critically ill cancer patients experience good EOLC. In the context of a cancer critical care unit, this thesis explores the provision of EOLC for cancer patients in a critical care unit. Exploring measures for comfort care and palliative principles of care helped identify what is important for patients and families, and what those measures meant for all participants. The diagnosis of cancer and how it impacts on EOLC provision for critically ill cancer patients was also explored from the perspective of patients, families, doctors and nurses. A Heideggerian phenomenological interview approach was undertaken, in order to gain personal experiences. Families of those patients who died after decisions to forgo life-sustaining treatment (DFLSTs) were interviewed. Patients who have experienced critical care were also interviewed, since patients‘ views about EOL care provision are very rarely explored. Doctors and nurses also contribute their vision for, and experiences of, EOL care in a cancer critical care unit. Thirty one interviews with 37 participants were carried out. Cancer prognosis together with critical illness prognosis contributed to difficulties in deciding to move to, and enact EOLC. The nursing voice in DFLSTs was minimal and their role in EOLC depended on experience and confidence. Achieving a good death was possible through caring activities that made best use of technology to prevent prolonged dying. EOLC was an emotive experience. Decision-making and EOLC could be difficult to separate out which, in turn, affects prospects for EOLC. A continuum of dying in cancer critical illness is presented with different participants‘ experiences along that continuum. Three main themes included: Dual Prognostication; The Meaning of Decision-Making; and Care Practices at EOL: Choreographing a Good Death with two organising themes: Thinking the Unthinkable and Involvement in Care. These themes outlined the essence of moving along a continuum toward patients‘ deaths and the impact that had on opportunities for care and a good death. Nurses could use the care of patients dying in critical care as an opportunity to develop specialist knowledge and lead in care, but this requires mastery and reconciliation of both technology and EOLC. This work builds on Seymour‘s (2001) theory of a negotiated and natural death related to achieving a good death in critical care. Trajectories of dying, part of Seymour‘s (2001) theory, are extrapolated on with reference to Glaser and Strauss (1965) and Lofland (1978)‘s theories on dying trajectories. Nursing theory is developed through examination of Falk Rafael‘s (1996) and Locsin‘s (1998) theories of empowered caring. Implications and propositions are presented for nursing and wider practice around EOL care for critically ill cancer patients
Turn down the heat
No full textThis report provides a snapshot of recent scientific literature and new analyses of likely impacts and risks that would be associated with a 4° Celsius warming within this century. It is a rigorous attempt to outline a range of risks, focusing on developing countries and especially the poor. A 4°C world would be one of unprecedented heat waves, severe drought, and major floods in many regions, with serious impacts on ecosystems and associated services. But with action, a 4°C world can be avoided and we can likely hold warming below 2°C.
Without further commitments and action to reduce greenhouse gas emissions, the world is likely to warm by more than 3°C above the preindustrial climate. Even with the current mitigation commitments and pledges fully implemented, there is roughly a 20 percent likelihood of exceeding 4°C by 2100.
If they are not met, a warming of 4°C could occur as early as the 2060s. Such a warming level and associated sea-level rise of 0.5 to 1 meter, or more, by 2100 would not be the end point: a further warming to levels over 6°C, with several meters of sea-level rise, would likely occur over the following centuries
Projected land ice contributions to twenty-first-century sea level rise
No full textThe land ice contribution to global mean sea level rise has not yet been predicted1 using ice sheet and glacier models for the latest set of socio-economic scenarios, nor using coordinated exploration of uncertainties arising from the various computer models involved. Two recent international projects generated a large suite of projections using multiple models2,3,4,5,6,7,8, but primarily used previous-generation scenarios9 and climate models10, and could not fully explore known uncertainties. Here we estimate probability distributions for these projections under the new scenarios11,12 using statistical emulation of the ice sheet and glacier models. We find that limiting global warming to 1.5 degrees Celsius would halve the land ice contribution to twenty-first-century sea level rise, relative to current emissions pledges. The median decreases from 25 to 13 centimetres sea level equivalent (SLE) by 2100, with glaciers responsible for half the sea level contribution. The projected Antarctic contribution does not show a clear response to the emissions scenario, owing to uncertainties in the competing processes of increasing ice loss and snowfall accumulation in a warming climate. However, under risk-averse (pessimistic) assumptions, Antarctic ice loss could be five times higher, increasing the median land ice contribution to 42 centimetres SLE under current policies and pledges, with the 95th percentile projection exceeding half a metre even under 1.5 degrees Celsius warming. This would severely limit the possibility of mitigating future coastal flooding. Given this large range (between 13 centimetres SLE using the main projections under 1.5 degrees Celsius warming and 42 centimetres SLE using risk-averse projections under current pledges), adaptation planning for twenty-first-century sea level rise must account for a factor-of-three uncertainty in the land ice contribution until climate policies and the Antarctic response are further constrained
