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During glacial climates, the strength of the Atlantic overturning circulation has changed abruptly. Climate model simulations show that gradual changes in atmospheric CO₂ levels can trigger such events via atmospheric moisture transport.

During the expansion of the Antarctic ice sheet about 14 million years ago, sea surface temperatures in the Southern Ocean rose. Climate model simulations suggest that this short-lived warming was related to changes in ocean–atmosphere circulation induced by the growth of the ice sheet.

Coinciding with global warming, Arctic sea ice has rapidly decreased during the last four decades. Here, using biomarker records, the authors show that permanent sea ice was still present in the central Arctic Ocean during the last interglacial, when high latitudes were warmer than present.

During the Cenozoic the Arctic Ocean change from a restricted freshwater regime towards more saline modern ocean conditions is supposedly driven by the subsidence of the Greenland-Scotland Ridge. Here, the authors derive a threshold for this shift, constrained by the characteristic depth of wind mixing.

Melting from below is crucial for the future evolution of Antarctic ice shelves. Here the authors use an Earth system model with explicit simulations of ice-shelf cavities to show how regional hydrography and topography determine when an ice shelf will undergo rapid melting.

Arctic warming will decrease sea ice cover and increase the possibility of intensified marine heatwaves. Using a high-resolution model, the authors show that this intensification, combined with strengthened short-term temperature variability and enhanced stratification, could threaten the ecosystem.

Oscillating human population growth in all continents from 9000 to 3000 years ago is identified. These population cycles reveal synchronicity with cycles in climate stability, which in turn were possibly driven by variations in solar activity.

According to the Milankovitch theory, glacial to interglacial climate variability — as recorded in Antarctica ice cores — is governed by summer insolation at high northern latitudes. It is now shown that accumulation of Antarctic snow is biased towards austral winter and may be explained simply by variations in local insolation, with no recourse to northern influences. Although not constituting a complete negative proof, the results show that the Antarctic ice core records do not, in themselves, provide sufficient support for the Milankovitch theory.

A global data set of proxy-based temperature estimates and biome reconstructions is used to assess the ability of eight climate models to simulate the warm environments of the Pliocene. Model results show a substantial cold bias in the Northern Hemisphere. Sensitivity tests identify temporal variability, the temperature difference over the proxy time range, as an important factor in model–data discrepancies, indicating that future comparisons should focus on time slices with the same orbital forcing

Based on marine multiproxy records, a new study outlines the role of larger heat discharge of the pan-Arctic Rivers in determining the pronounced sea ice retreat over the East Siberian Arctic Shelf in the mid-Holocene.

The size and shape of the North American ice sheet during the Last Glacial Maximum was set by atmospheric moisture transport feedbacks during summer, not by the geometry of the earlier intermediate-sized ice sheet, according to a coupled climate–ice sheet model.

Spatial changes in planktonic foraminifera species assemblages reveal steeper thermal gradients in the North Atlantic Ocean during the Last Glacial Maximum than simulated by climate models, according to a macroecological analysis of marine sediment cores.

Accurate forecasting of tropical precipitation is dependent on our understanding of the hydrological cycle. Here, the authors present a speleothem-derived record of Mesoamerican precipitation variability since the 1930s, and show that multi-decadal declines in rainfall coincide with major volcanic eruptions.

The last interglacial has been suggested as a test bed for models developed for future climate prediction, yet many climatic parameters remain unknown. Here, the authors present a precisely dated fossil coral and show that temperature seasonality in the southern Caribbean Sea 118 ka was similar to today.

Concurrent intensification of Bering Strait Inflow and associated stronger poleward heat caused a millennial-scale sea ice retreat in the Arctic, known as the ‘Pacificization’ effect, according to analysis of paleo-climate records, satellite-derived and modeling dataset of sea ice conditions.

Suppressed El Niño/Southern Oscillation variability during the mid-Pliocene Warm Period was caused mainly by a northward displacement of the intertropical convergence zone, according to an analysis of a large ensemble of climate model simulations.

The configuration of past ice sheets, and therefore sea level, is highly uncertain. Here, the authors provide a global reconstruction of ice sheets for the past 80,000 years that allows to test proxy based sea level reconstructions and helps to reconcile disagreements with sea level changes inferred from models.

Heat stored in the deep ocean due to salinity stratification contributed to rapid Antarctic warming during middle and late Pleistocene glacial terminations, according to coupled atmosphere–ocean general circulation model simulations.

In contrast to future projections, paleoclimate records often find wetter subtropics in tandem with elevated CO₂. Here, a compilation of proxies and simulations are used to reveal the climate dynamics and feedbacks responsible for generating wet subtropics during the mid-Pliocene.

Millennial-scale climate oscillations can arise from orbital forcing alone during relatively stable glacial climate states, according to an analysis of high- and low-latitude climate proxy records as well as climate modelling.

Ice core data show a breakdown in the long-term temperature-atmospheric CO₂ correlation during interglacial-glacial transitions. Here, via a novel modelling approach, the authors reveal marine volcanism, triggered by a fall in sea level, as a likely mechanism for the observed delayed decline in atmospheric CO₂.

Despite the importance of Arctic sea-ice in the global climate system, a paucity of pre-Quaternary sedimentary archives limits our understanding of its long-term history. Here, based on ancient sediments revealed by submarine landslides, the authors reconstruct Arctic sea-ice conditions during the Miocene.

Lower glacial atmospheric CO₂has been linked to enhanced carbon storage in the Southern Ocean, yet the associated biological and physical mechanisms are poorly understood. Here, the authors combine diatom and radiolarian isotope measurements, and model simulations to investigate surface–subsurface processes.

Despite their importance, the accuracy of the quantitative interpretation of Antarctic ice core stable water isotope records remains a matter of debate. Here, the authors use an isotope-enabled atmospheric general circulation model to test and validate the isotopic paleothermometer approach.

Multi-proxy core data and model simulations support the presence of temperate rainforests near the South Pole during mid-Cretaceous warmth, indicating very high CO₂ levels and the absence of Antarctic ice.

It has been postulated that there is a threshold temperature above which permafrost will reach a global tipping point, causing accelerated thaw and global collapse. Here it is argued that permafrost-thaw feedbacks are dominated by local- to regional-scale processes, but this also means there is no safety margin.

The volume of the Northern Hemisphere ice sheet controlled abrupt millennial-scale climate changes during the last glacial.

Laurentide ice-sheet retreat continued into the mid-Holocene. Speleothem-based precipitation records suggest the cessation of melt led to the establishment of the present precipitation patterns associated with the North Atlantic Oscillation.

The observed sea surface temperature pattern of strong warming concentrated in the subtropical oceans is likely to be an early signature of climate change, according to observations and model simulations, whereas ocean warming at high latitudes is expected to become dominant in the future.

Understudied in the Antarctic system are the subsurface interfaces between ice-sheet, ocean and geological substrate. Here, the authors review our understanding of these components and propose new avenues of holistic dynamic modeling to achieve a unified understanding of past, present and future polar climate.

A shift in Central Asian dust supply with a reduced dominance of the Gobi Desert occurred during Pliocene global cooling, according to a combination of multi-proxy records from a Pacific ferromanganese crust and climate simulations.