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Polar temperatures over the last several million years have, at times, been slightly warmer than today, yet global mean sea level has been 6-9 metres higher as recently as the Last Interglacial (130,000 to 115,000 years ago) and possibly higher during the Pliocene epoch (about three million years ago). In both cases the Antarctic ice sheet has been implicated as the primary contributor, hinting at its future vulnerability. Here we use a model coupling ice sheet and climate dynamics--including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine-terminating ice cliffs--that is calibrated against Pliocene and Last Interglacial sea-level estimates and applied to future greenhouse gas emission scenarios. Antarctica has the potential to contribute more than a metre of sea-level rise by 2100 and more than 15 metres by 2500, if emissions continue unabated. In this case atmospheric warming will soon become the dominant driver of ice loss, but prolonged ocean warming will delay its recovery for thousands of years. Climate and ice-sheet modelling that includes ice fracture dynamics reveals that Antarctica could contribute more than a metre of sea-level rise by 2100 and more than 13 metres by 2500, if greenhouse gas emissions continue unabated. A 500-year model of Antarctica's contribution to future sea-level rise Robert DeConto and David Pollard use a newly improved numerical ice-sheet model calibrated to Pliocene and Last Interglacial sea-level estimates to develop projections of Antarctica's evolution over the next five centuries, driven by a range of greenhouse gas scenarios. The modelling shows that the Antarctic ice sheet has the potential to contribute between almost nothing, to contributing more than a metre of sea-level rise by 2100 and more than 15 metres by 2500. The startling high-end estimate arises from unabated emissions and previously underappreciated mechanisms: ice-fracturing by surface meltwater and collapse of large ice cliffs. The low end shows that a scenario of strong climate mitigation can radically reduce societal exposure to higher sea levels., Author(s): Robert M. DeConto [sup.1] , David Pollard [sup.2] Author Affiliations: (1) Department of Geosciences, University of Massachusetts, Amherst, USA (2) Earth and Environmental Systems Institute, Pennsylvania State University, University [...]

Between about 55.5 and 52 million years ago, Earth experienced a series of sudden and extreme global warming events (hyperthermals) superimposed on a long-term warming trend (1). The first and [...]

The West Antarctic ice sheet (WAIS), with ice volume equivalent to ~5 m of sea level (1), has long been considered capable of past and future catastrophic collapse (2-4). Today, the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams. Grounding lines are several hundred metres below sea level and the bed deepens upstream, raising the prospect of runaway retreat (3,5). Projections of future WAIS behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms (6,7). Its variation since the Last Glacial Maximum is best known, with grounding lines advancing to the continental-shelf edges around ~15 kyr ago before retreating to near-modern locations by ~3 kyr ago (8). Prior collapses during the warmth of the early Pliocene epoch (9) and some Pleistocene interglacials have been suggested indirectly from records of sea level and deep-sea-core isotopes, and by the discovery of open-ocean diatoms in subglacial sediments'. Until now', however, little direct evidence of such behaviour has been available. Here we use a combined ice sheet/ice shelf model (12) capable of high-resolution nesting with a new treatment of grounding-line dynamics and ice-shelf buttressing (5) to simulate Antarctic ice sheet variations over the past five million years. Modelled WAIS variations range from full glacial extents with grounding lines near the continental shelf break, intermediate states similar to modern, and brief but dramatic retreats, leaving only small, isolated ice caps on West Antarctic islands. Transitions between glacial, intermediate and collapsed states are relatively rapid, taking one to several thousand years. Our simulation is in good agreement with a new sediment record (ANDRILL AND-1B) recovered from the western Ross Sea (11), indicating a long-term trend from more frequently collapsed to more glaciated states, dominant 40-kyr cyclicity in the Pliocene, and major retreats at marine isotope stage 31(~1.07 Myr ago) and other super-interglacials., Large-scale modelling of the WAIS requires an ice-sheet model that combines the flow regimes of grounded and floating ice efficiently enough to allow simulations of ~[10.sup.5] yr or more. This [...]

The long-standing view of Earth's Cenozoic glacial history calls for the first continental-scale glaciation of Antarctica in the earliest Oligocene epoch (-33.6 million years ago (1), followed by the onset [...]

Author(s): Robert M. DeConto (corresponding author) [1]; David Pollard [2] The sudden, widespread glaciation of Antarctica and the associated shift towards colder temperatures at the Eocene/Oligocene boundary ([similar]34 million years [...]

Snow reflects sunlight, so when it is melted by higher temperatures, the temperature will tend to rise even higher due to increased absorption of sunlight by the ground. Trees moderate this loop by masking the highly reflective snow. Simulating the removal of all trees north of 45 degrees north latitude, a climatic model predicted a cooling of five to 12 degrees at 60 degrees north latitude, with effects at lower latitudes as well.

In the online-only Methods of our Letter, several erroneous values appear among the parameters used to calculate peatland D, the average thickness of permafrost peatland deposits. Catotelm decay rate (τ) [...]

The sudden, widespread glaciation of Antarctica and the associated shift towards colder temperatures at the Eocene/Oligocene boundary (∼34 million years ago) (refs 1-4) is one of the most fundamental reorganizations of global climate known in the geologic record. The glaciation of Antarctica has hitherto been thought to result from the tectonic opening of Southern Ocean gateways, which enabled the formation of the Antarctic Circumpolar Current and the subsequent thermal isolation of the Antarctic continent[SUP5]. Here we simulate the glacial inception and early growth of the East Antarctic Ice Sheet using a general circulation model with coupled components for atmosphere, ocean, ice sheet and sediment, and which incorporates palaeogeography, greenhouse gas, changing orbital parameters, and varying ocean heat transport. In our model, declining Cenozoic CO[SUB2] first leads to the formation of small, highly dynamic ice caps on high Antarctic plateaux. At a later time, a CO[SUB2] threshold is crossed, initiating ice-sheet height/mass-balance feedbacks that cause the ice caps to expand rapidly with large orbital variations, eventually coalescing into a continental-scale East Antarctic Ice Sheet. According to our simulation the opening of Southern Ocean gateways plays a secondary role in this transition, relative to CO[SUB2] concentration. [ABSTRACT FROM AUTHOR]

The sudden, widespread glaciation of Antarctica and the associated shift towards colder temperatures at the Eocene/Oligocene boundary (∼34 million years ago) (refs 1-4) is one of the most fundamental reorganizations of global climate known in the geologic record. The glaciation of Antarctica has hitherto been thought to result from the tectonic opening of Southern Ocean gateways, which enabled the formation of the Antarctic Circumpolar Current and the subsequent thermal isolation of the Antarctic continent[SUP5]. Here we simulate the glacial inception and early growth of the East Antarctic Ice Sheet using a general circulation model with coupled components for atmosphere, ocean, ice sheet and sediment, and which incorporates palaeogeography, greenhouse gas, changing orbital parameters, and varying ocean heat transport. In our model, declining Cenozoic CO[SUB2] first leads to the formation of small, highly dynamic ice caps on high Antarctic plateaux. At a later time, a CO[SUB2] threshold is crossed, initiating ice-sheet height/mass-balance feedbacks that cause the ice caps to expand rapidly with large orbital variations, eventually coalescing into a continental-scale East Antarctic Ice Sheet. According to our simulation the opening of Southern Ocean gateways plays a secondary role in this transition, relative to CO[SUB2] concentration. [ABSTRACT FROM AUTHOR]