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By better quantifying uncertainties for marine ice-cliff instability, future Antarctic ice loss is predicted to be much lower than previously estimated.

During the Mid-Pleistocene Transition, the Antarctic ice sheet crossed several thresholds that formed a stable West Antarctic Ice Sheet and amplified 100,000-year variability.

Rising sea level in the next century exposes the Ports of Los Angeles and Long Beach to higher hazards from Alaskan tsunamis. By 2100, waves generated by an M8 Alaskan earthquake cause similar impacts in California to waves from an Alaskan M9 today.

The response of the vast West Antarctic Ice Sheet (WAIS) to climate shifts due to changes in Earth's orbit is uncertain, but there is potential for several metres of sea level change. Naish and co-authors extracted a sediment core from beneath the Ross Ice Shelf and found evidence that the WAIS periodically collapsed during the early Pliocene (3-5 million years ago); and the pattern of collapse suggests an influence of ∼40,000-year cycles in the tilt of Earth's rotational axis.

The East Antarctic Ice Sheet is currently surrounded by relatively cool water but changes in ocean dynamics may lead to warmer ocean water on the shelf in the future. This has the potential to dramatically increase its future sea level contribution.

Rapid oceanic and atmospheric circulation shifts led to a transient peak in the mean temperature of the ocean at the start of the Last Interglacial, according to noble gas isotope records from an Antarctic ice core.

Warming of +1.5 °C above pre-industrial levels is too high for the Greenland and Antarctic ice sheets, and even the current climate forcing of +1.2 °C is likely to lead to several meters of sea-level rise, meaning that only a return to +1 °C or lower will avoid extensive loss and damage to coastal populations, according to a synthesis of recent evidence.

Studies of an Antarctic marine sediment core suggest that the East Antarctic Ice Sheet retreated in the vicinity of the Wilkes Subglacial Basin during extended warm periods of the late Pleistocene, when temperatures were similar to those predicted to occur within this century.

If elevated ice-melt rates in the Amundsen Sea Embayment, West Antarctica, can be restored to present levels within 100 years, rates of ice discharge and the sea level contribution from the region can be limited, suggest sensitivity experiments with an ice sheet model.

The sensitivity of the Antarctic ice sheet to obliquity increases when ice-sheet margins are exposed to the ocean, suggests an analysis of sediment core oxygen isotope records.

The Antarctic Ice Sheet’s sea-level contribution in a high-emissions scenario is indistinguishable from that in a low-emissions scenario for the next century, but its long-term contribution depends on warming this century, according to ice sheet simulations and an emulator-based analysis.

The different contributions of long-term and short-term variability to the evolution of ice sheets lead to substantial uncertainties in ice sheet models. This Review describes the response of ice sheets to oceanic, atmospheric and hydrological processes across a range of timescales.

In the Arctic Ocean, a salinity gradient separates a shallow layer of cold, relatively fresh water from the warmer, saltier Atlantic water below. A reconstruction of intermediate water temperatures in the Arctic during the last glacial period shows the presence of relatively warm water that may reflect a deepening of the halocline.

The future of Antarctica and the Southern Ocean by 2070 is described under two scenarios, one in which action is taken to limit greenhouse gas emissions, and one in which no action is taken.

A synthesis of intervals of rapid climatic change evident in the geological record reveals some of the Earth system processes and tipping points that could lead to similar events in the future.

Considerable confusion exists as to the most likely value of climate sensitivity; by proposing a consistent framework for analysing and synthesizing research into the palaeoclimate of the past 65 million years, a value of 2.2–4.8 °C warming in response to atmospheric CO₂ doubling is obtained, in agreement with IPCC estimates.

This Review synthesizes knowledge on projections of the Antarctic and Greenland ice sheets at 1.5 °C and 2 °C of warming, discussing possible nonlinear responses, and outlining the need for more insight into future atmospheric and oceanic forcings.