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Future sea-level rise is an important issue related to the continuing buildup of atmospheric greenhouse gas concentrations. The Greenland and Antarctic ice sheets, with the potential to raise sea level ~70 meters if completely melted, dominate uncertainties in projected sea-level change. Freshwater fluxes from these ice sheets also may affect oceanic circulation, contributing to climate change. Observational and modeling advances have reduced many uncertainties related to ice-sheet behavior, but recently detected, rapid ice-marginal changes contributing to sea-level rise may indicate greater ice-sheet sensitivity to warming than previously considered., Because a heavy concentration of the population lives along coastlines, even small amounts of sea-level rise would have substantial societal and economic impacts through coastal erosion, increased susceptibility to storm [...]

During the last glacial-interglacial transition, atmospheric [N.sub.2]O values increased front ~190 to 265 parts per billion (ppb) (3-5). Model studies suggest that the lifetime of [N.sub.2]O in the atmosphere has [...], Paleoatmospheric records of trace-gas concentrations recovered from ice cores provide important sources of information on many biogeochemical cycles involving carbon, nitrogen, and oxygen. Here, we present a 106,000-year record of atmospheric nitrous oxide ([N.sub.2])O along with corresponding isotopic records spanning the last 30,000 years, which together suggest minimal changes in the ratio of marine to terrestrial [N.sub.2.]O production. During the last glacial termination, both marine and oceanic [N.sub.2.]O emissions increased by 40 ± 8%. We speculate that our records do not support those hypotheses that invoke enhanced export production to explain low carbon dioxide values during glacial periods.

Analysis of borehole temperature and Greenland Ice Sheet Project II ice-core isotopic composition reveals that the warming from average glacial conditions to the Holocene in central Greenland was large, approximately 15°C. This is at least three times the coincident temperature change in the tropics and mid-latitudes. The coldest periods of the last glacial were probably 21°C colder than at present over the Greenland ice sheet., The Greenland Ice Sheet Project II (GISP2) deep ice core has yielded a remarkable history of the oxygen isotopic composition of central Greenland snowfall [delta.sup.18]O of ice[1]] that extends through [...]

A major West Antarctic ice stream discharges by sudden and brief periods of very rapid motion paced by oceanic tidal oscillations of about 1 meter. Acceleration to speeds greater than 1 meter per hour and deceleration back to a stationary state occur in minutes or less. Slip propagates at approximately 88 meters per second, suggestive of a shear wave traveling within the subglacial till. A model of an episodically slipping friction-locked fault reproduces the observed quasi-periodic event timing, demonstrating an ice stream's ability to change speed rapidly and its extreme sensitivity to subglacial conditions and variations in sea level., Concern that the West Antarctic Ice Sheet did, does, and will contribute to increasing sea level has driven two decades of extensive research on ice-flow dynamics (1, 2). Evidence for [...]

The article informs about polar regions outpacing the global average Antarctic temperatures. Topics discussed include threats to wildlife and traditional human livelihoods, and extreme weather at lower latitudes; mitigation efforts can slow or reduce warming; and international cooperation will be crucial to foreseeing and adapting to changes.

Large ice sheets actively interact with the rest of the climate system by amplifying, pacing, and potentially driving global climate change over several time scales. Direct and indirect influences of ice sheets on climate cause changes in ocean surface temperatures, ocean circulation, continental water balance, vegetation, and land-surface albedo, which in turn cause additional feedbacks in the climate system and help to synchronize global climate change. The effect of the underlying geological substrate on ice-sheet dynamics may be the missing link in understanding the ice sheet--climate interactions that are integral to the middle Pleistocene transition; the 100,000-year climate cycle; high-amplitude, millennial-scale climate variability; and low--aspect ratio ice sheets of the Last Glacial Maximum., Following a long-term global cooling trend through much of the Cenozoic, large ice sheets first developed in the Northern Hemisphere ~2.54 million years ago (Ma) (Fig. 1) (1, 2). Statistical [...]

Humans are changing the amount of carbon dioxide in the atmosphere by burning coal, oil, and gas. The current atmospheric C[O.sub.2] concentration is higher than it has been for at [...]

The big ice sheets in Greenland and Antarctica are key elements of the global climate system. By storing large volumes of water as ice or ice-contact lakes and sometimes releasing [...]

This article discusses the development of advanced weather predicting and environmental forecasting techniques. The authors comment on the social impact of improved weather prediction, including earlier extreme weather warnings. They also examine the efforts of such organizations as the European Centre for Medium-Range Weather Forecasts and the National Oceanic and Atmospheric Administration's National Centers for Environmental Protection.

In the article, the authors discuss issues on climate change, particularly the expected mean sea level rise around the world due to temperature increase. Also cited are how to effectively manage coastal risks due to climate change, a study using a combination of ice-fracture processes and inferences from paleoclimatic data to calculate the Antarctic contribution to global sea level rise by 2100, and the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) on the issue.

Fabrics in Polar Ice Sheets: Development and Prediction THE VISCOSITY OF AN ICE CRYSTAL IS more than an order of magnitude less parallel to its basal plane than perpendicular to [...]

Glaciers flow under gravitationally induced stresses. The weight of the ice causes the glacier to spread and thin in a manner dictated by surface conditions, basal conditions, and the ice [...]

The article discusses research investigating the effect of oceanic forcing on the ice sheets in Greenland and Antarctica. The authors note that much of the ice loss in Greenland and Antarctica's ice sheets is in response to oceanic forcing, particularly the floating ice shelves. Topics include observations establishing a clear correspondence between the increased delivery of oceanic heat to the ice-sheet margin and increased ice loss, scientists' lack of understanding of the processes by which warmer ocean temperatures drive the observed retreat in Greenland, and the difficulties of conducting experiments in Greenland and Antarctica which are designed to identify the relevant processes.

Paleoatmospheric records of trace-gas concentrations recovered from ice cores provide important sources of information on many biogeochemical cycles involving carbon, nitrogen, and oxygen. Here, we present a 106,000-year record of atmospheric nitrous oxide (N[sub2]O) along with corresponding isotopic records spanning the last 30,000 years, which together suggest minimal changes in the ratio of marine to terrestrial N[sub2]O production. During the last glacial termination, both marine and oceanic N[sub2]O emissions increased by 40 ± 8%. We speculate that our records do not support those hypotheses that invoke enhanced export production to explain low carbon dioxide values during glacial periods. [ABSTRACT FROM AUTHOR]

In this article, the author discusses the climatic changes occurred during the Paleocene- Eocene Thermal Maximum (PETM). Topics include increase in the major biological and physical impacts, effects of carbon dioxide (CO2) release, increase in the concentration of CO2, impact of climate sensitivity, disruption of established ecological balances, decrease in the impacts of acidification on creatures, increase in the atmospheric CO2 concentration, and shifting in carbon isotopic compositions.

The article discusses the use of full-stress flow models for modeling ice sheet flow in Greenland and Antarctica. The authors note that the Greenland and Antarctic ice sheets have been represented as static entities in atmosphere-ocean models, arguing that observations have shown them to be capable of rapid change. Topics include the computationally difficulties in ice-sheet modeling, such as variations in the orders-of-magnitude of frictional drag at the ice bed and margins, the limitations of full-stress models, and the use of ice-flow models to simulate the stress states that create crevasse patterns and their effect on the ice.

The article discusses the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment, which admitted that poorly characterized uncertainties have prevented a best estimate or upper bound on sea-level rise that has been catalyzed by accelerations in outland glaciers of the Greenland and Antarctic ice sheets. Research on the topic is presented chronologically, beginning with the discovery that surface meltwater can facilitate summer ice flow. The difficulty associated with accruing quantitative research is examined, and the ambiguity of the relationship between ice sheets and their underlying beds is highlighted.

A personal narrative is presented which explores the author's perspective on the new ice-core measurement, as of September 2007.

Focuses on the climatic changes in the West Antarctic Ice Sheet. Persistence of the ice sheet during interglacial periods; Similarities between surface and bed velocities; Measurement of mass balance.

The article discusses the need for a physically based law that explains the calving process in ice-shelves. The authors state that a complete calving law would include forcing from waves, tides, and colliding icebergs, geometry, and material properties such as thickness, temperature and density. The testing of a hypothesis and the analysis of data associated with this law are presented.

A major West Antarctic ice stream discharges by sudden and brief periods of very rapid motion paced by oceanic tidal oscillations of about 1 meter. Acceleration to speeds greater than 1 meter per hour and deceleration back to a stationary state occur in minutes or less. Slip propagates at approximately 88 meters per second, suggestive of a shear wave traveling within the subglacial till. A model of an episodically slipping friction-locked fault reproduces the observed quasi-periodic event timing, demonstrating an ice stream's ability to change speed rapidly and its extreme sensitivity to subglacial conditions and variations in sea level. [ABSTRACT FROM AUTHOR]

A response by the authors to a letter about their articles on the stability of the Antarctic and Greenland Ice Sheets in the March 24, 2006 issue is presented.

Water-stable isotopes in polar ice cores are a widely used temperature proxy in paleoclimate reconstruction, yet calibration remains challenging in East Antarctica. Here, we reconstruct the magnitude and spatial pattern of Last Glacial Maximum surface cooling in Antarctica using borehole thermometry and firn properties in seven ice cores. West Antarctic sites cooled ~10°C relative to the preindustrial period. East Antarctic sites show a range from ~4° to ~7°C cooling, which is consistent with the results of global climate models when the effects of topographic changes indicated with ice core air-content data are included, but less than those indicated with the use of water-stable isotopes calibrated against modern spatial gradients. An altered Antarctic temperature inversion during the glacial reconciles our estimates with water-isotope observations., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Barrows et al. (Reports, 5 October 2007, p. 86) presented cosmogenic exposure dates and data from an ocean sediment core that challenge evidence for glacier advance in New Zealand during the Younger Dryas event. We use modeling of geomorphic processes to argue that their cosmogenic exposure dates are inconclusive.