Pervasive ice sheet mass loss reflects competing ocean and atmosphere processes.

Quantifying changes in Earth's ice sheets and identifying the climate drivers are central to improving sea level projections. We provide unified estimates of grounded and floating ice mass change from 2003 to 2019 using NASA's Ice, Cloud and land Elevation Satellite (ICESat) and ICESat-2 satellite laser altimetry. Our data reveal patterns likely linked to competing climate processes: Ice loss from coastal Greenland (increased surface melt), Antarctic ice shelves (increased ocean melting), and Greenland and Antarctic outlet glaciers (dynamic response to ocean melting) was partially compensated by mass gains over ice sheet interiors (increased snow accumulation). Losses outpaced gains, with grounded-ice loss from Greenland (200 billion tonnes per year) and Antarctica (118 billion tonnes per year) contributing 14 millimeters to sea level. Mass lost from West Antarctica's ice shelves accounted for more than 30% of that region's total.

Ice-sheet mass balance and climate change.

Since the 2007 Intergovernmental Panel on Climate Change Fourth Assessment Report, new observations of ice-sheet mass balance and improved computer simulations of ice-sheet response to continuing climate change have been published. Whereas Greenland is losing ice mass at an increasing pace, current Antarctic ice loss is likely to be less than some recently published estimates. It remains unclear whether East Antarctica has been gaining or losing ice mass over the past 20 years, and uncertainties in ice-mass change for West Antarctica and the Antarctic Peninsula remain large. We discuss the past six years of progress and examine the key problems that remain.

A reconciled estimate of ice-sheet mass balance.

We combined an ensemble of satellite altimetry, interferometry, and gravimetry data sets using common geographical regions, time intervals, and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of Earth's polar ice sheets. We find that there is good agreement between different satellite methods--especially in Greenland and West Antarctica--and that combining satellite data sets leads to greater certainty. Between 1992 and 2011, the ice sheets of Greenland, East Antarctica, West Antarctica, and the Antarctic Peninsula changed in mass by -142 ± 49, +14 ± 43, -65 ± 26, and -20 ± 14 gigatonnes year(-1), respectively. Since 1992, the polar ice sheets have contributed, on average, 0.59 ± 0.20 millimeter year(-1) to the rate of global sea-level rise.

Innominosacral dissociation: mechanism of injury as a predictor of resuscitation requirements, morbidity, and mortality.

OBJECTIVES: To assess mechanism of injury as a clinical course predictor in patients with complete anterior and posterior pelvic ring disruptions [innominosacral dissociation (ISD)]. DESIGN: Retrospective review of radiographs and medical data. SETTING: R Adams Cowley Shock Trauma Center, Baltimore, Maryland, statewide trauma center. PATIENTS: Forty-three patients with ISD were admitted to our institution between August 1986 and October 1991. Five patients were excluded because of incomplete medical records or refusal of blood transfusion. INTERVENTION: Injuries were grouped according to the Young classification: 18 anteroposterior compression (APC), 14 vertical shear (VS), and 6 other injuries. MAIN OUTCOME MEASUREMENTS: The mean blood replacement requirements, incidence of multiple organ system failure, mortality rate, and length of hospital stay for each injury classification were compared. RESULTS: The mean ISS was 34, and the mean 24-hour packed red blood cell transfusion requirement was 12.6 units. Thirteen patients (34.4%) developed multisystem organ failure. Eight patients (21%) died. Patients in the APC group were more likely to require > or = 10 units of blood (15/18, p = 0.001, and those in the VS group were more likely to receive <10 units (11/14, p = 0.0014). Multisystem organ failure occurred more frequently (11/18 versus 2/14; p < 0.005), mortality was significantly higher (39 versus 0%, respectively; p = 0.01), and mean hospital stay for survivors was longer (48 versus 27 days; p < 0.025) in the APC than in the VS group, respectively. CONCLUSIONS: These findings suggest that mechanism of injury is an important determinant of clinical behavior in patients with IDS, and that ISD secondary to the APS mechanism is associated with substantially greater resuscitation requirements, morbidity, and mortality than ISD secondary to the VS mechanism.

Surface melt-induced acceleration of Greenland ice-sheet flow.

Ice flow at a location in the equilibrium zone of the west-central Greenland Ice Sheet accelerates above the midwinter average rate during periods of summer melting. The near coincidence of the ice acceleration with the duration of surface melting, followed by deceleration after the melting ceases, indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice-bedrock interface. Interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting, with larger increases accompanying higher amounts of summer melting. The indicated coupling between surface melting and ice-sheet flow provides a mechanism for rapid, large-scale, dynamic responses of ice sheets to climate warming.