Verification of model simulated mass balance, flow fields and tabular calving events of the Antarctic ice sheet against remotely sensed observations

The Antarctic ice sheet (AIS) has the greatestpotential for global sea level rise. This study simulates AISice creeping, sliding, tabular calving, and estimates the totalmass balances, using a recently developed, advanced icedynamics model, known as SEGMENT-Ice. SEGMENTIceis written in a spherical Earth coordinate system.Because the AIS contains the South Pole, a projectiontransfer is performed to displace the pole outside of thesimulation domain. The AIS also has complex ice-watergranularmaterial-bedrock configurations, requiringsophisticated lateral and basal boundary conditions.Because of the prevalence of ice shelves, a ‘girder yield’type calving scheme is activated. The simulations of presentsurface ice flow velocities compare favorably with InSARmeasurements, for various ice-water-bedrock configurations.The estimated ice mass loss rate during 2003–2009agrees with GRACE measurements and provides morespatial details not represented by the latter. The modelestimated calving frequencies of the peripheral ice shelvesfrom 1996 (roughly when the 5-km digital elevation andthickness data for the shelves were collected) to 2009compare well with archived scatterometer images. SEGMENT-Ice’s unique, non-local systematic calving schemeis found to be relevant for tabular calving. However, theexact timing of calving and of iceberg sizes cannot besimulated accurately at present. A projection of the futuremass change of the AIS is made, with SEGMENT-Iceforced by atmospheric conditions from three differentcoupled general circulation models. The entire AIS is estimatedto be losing mass steadily at a rate of*120 km3/a atpresent and this rate possibly may double by year 2100

Impacts of climate warming on maximum aviation payloads

© 2018, The Author(s). The increasing importance of aviation activities in modern life coincides with a steady warming climate. However, the effect of climate warming on maximum aircraft carrying capacity or payload has been unclear. Here we clarify this issue using primary atmospheric parameters from 27 fully coupled climate models from the Coupled Model Inter-comparison Project 5 (CMIP5) archive, utilizing the direct proportionality of near-surface air density (NSAD) to maximum take-off total weight (MTOW). Historical (twentieth century) runs of these climate models showed high credibility in reproducing the reanalysis period (1950–2015) of NSAD. In particular, the model simulated trends in NSAD are highly aligned with the reanalysis values. This reduction in NSAD is a first order global signal, just as is the warming itself, that continues into the future. To examine the statistical significance of the density reduction, a t-test was performed for two 20-year periods 75 years apart (2080–2100 vs. 2005–2025), using the Representative Concentration Pathways (RCP) 8.5 emission scenario of the Intergovernmental Panel on Climate Change (IPCC). Most continental areas easily passed the test at a P-value of 0.05. These future changes of NSAD will likely have significant economic impacts on the aviation industry. For these two 20-year periods that we examined, the most extreme changes are in the Northern hemisphere in high latitudes, i.e., a 5% decrease in MTOW, or ~ 8.5–19% (aircraft-dependent) reduction in payload. The global average change is about 1%. For the busy North Atlantic Corridor (NAC), the reduction in MTOW is generally greater than 1% and that of payload several times larger

Ice-sheet model sensitivities to environmental forcing and their use in projecting future sea level (the SeaRISE project)

Ten ice-sheet models are used to study sensitivity of the Greenland and Antarctic ice sheets to prescribed changes of surface mass balance, sub-ice-shelf melting and basal sliding. Results exhibit a large range in projected contributions to sea-level change. In most cases, the ice volume above flotation lost is linearly dependent on the strength of the forcing. Combinations of forcings can be closely approximated by linearly summing the contributions from single forcing experiments, suggesting that nonlinear feedbacks are modest. Our models indicate that Greenland is more sensitive than Antarctica to likely atmospheric changes in temperature and precipitation, while Antarctica is more sensitive to increased ice-shelf basal melting. An experiment approximating the Intergovernmental Panel on Climate Change’s RCP8.5 scenario produces additional first-century contributions to sea level of 22.3 and 8.1cm from Greenland and Antarctica, respectively, with a range among models of 62 and 14 cm, respectively. By 200 years, projections increase to 53.2 and 26.7 cm, respectively, with ranges of 79 and 43 cm. Linear interpolation of the sensitivity results closely approximates these projections, revealing the relative contributions of the individual forcings on the combined volume change and suggesting that total ice-sheet response to complicated forcings over 200 years can be linearized