The theory of the Quaternary climate will be incomplete unless it is embedded in a more general theory for the fuller Cenozoic that can accommodate the onset of the ice-age fluctuations. Here we construct a simple mathematical model for the late Cenozoic climatic changes based on the hypothesis that forced and free variations of the concentration of atmospheric greenhouse gases (notably CO2) coupled with changes in the global ocean state and ice mass, under the additional influence or earth-orbital forcing, are primary determinants of the climatic state over this long period. Our goal is to illustrate how a single model governing both very long-term variations and higher frequency oscillatory variations in the Pleistocene can be formulated with relatively few adjustable parameters. Although the details of this model are speculative, and other factors neglected here are undoubtedly of importance, it is hoped that the formalism described can provide a basis for developing a comprehensive theory and systematically extending and improving it. According to our model the major near-100 ka period ice-age oscillations of the Pleistocene were caused by the downdraw of atmospheric CO2 (possibly a result of weathering of rapidly uplifted topography) to low enough levels for the ‘slow climatic system’, including glacial ice and the deep ocean state, to become unstable.

We welcome the views of A. D. Stewart (1990) on our interpretation of the unusual lithology and contact relations of the Stac Fada Member at Stoer. Stewart contends that our lower breccia body is a down-faulted outlier of the main breccia body and is therefore not a feeder. He thus rejects our notion that the Member is a peperitic extrusion: he also rejects the previously published view that the Member is a volcanic mudflow. Instead he suggests that the Stac Fada Member is one of several muddy volcanic horizons in the Stoer Group, all of which underwent post-depositional disturbance.

Study of satellite images from most of the area of the Canadian mainland once covered by the Laurentide ice sheet reveals a complex pattern of superimposed drift lineations. They are believed to have formed subglacially and parallel to ice flow. Aerial photographs reveal patterns of superimposition which permit the sequence of lineation patterns to be identified. The sequential lineation patterns are interpreted as evidence of shifting patterns of flow in an evolving ice sheet. Flow stages are recognised which reflect roughly synchronous integrated patterns of ice sheet flow. Comparison with stratigraphic sections in the Hudson Bay Lowlands suggests that all the principal stages may have formed during the last, Wisconsinan, glacial cycle. Analogy between Flow stage lineation patterns and the form and flow patterns of modern ice sheets permits reconstruction of patterns of ice divides and centres of mass which moved by 1000–2000 km during the glacial period. There is evidence that during the early Wisconsinan, ice sheet formation in Keewatin may have been independent of that in Labrador–Quebec, and that these two ice masses joined to form a major early Wisconsinan ice sheet. Subsequently the western dome decayed whilst the eastern dome remained relatively stable. A western dome then re-formed, and fused with the eastern dome to form the late Wisconsinan ice sheet before final decay.

Because of strong coupling between three-dimensional ice sheet geometry and atmospheric circulation, it is suggested that the major changes of geometry must have been associated with large scale atmospheric circulation changes.

Lineation patterns suggest very little erosional/depositional activity in ice divide regions, and can be used to reconstruct large scale patterns of erosion/deposition.

The sequence of flow stages through time provides an integrative framework allowing sparse stratigraphic data to be used most efficiently in reconstructing ice sheet history in time and space.

Ice deposits from Greenland and Antarctic ice sheets have stored over long periods of time information about the climate and environment of our planet. Attention will be focused on the 2083 m Vostok Antarctic ice core which represents a unusually long record (160 000 ka) due to the low accumulation rate (∼2 g cm−2a−1) and the rather uniform conditions of ice flow. This ice core provides a unique opportunity to obtain several palaeo-data such as temperature, accumulation (precipitation), aerosol loading, CO2 and trace gases over a full glacial-interglacial climatic cycle.

The Vostok temperature, deduced from the interpretation of the deuterium content, and the CO2 records show a large 100 ka signal with a change of the order of 10°C and 70 ppmv respectively. The two records are closely correlated and both display shorter periodicities characteristic of the earth orbital parameters. CH4 concentrations also show variations from about 0·35 to about 0·65 ppmv linked with the glacial-interglacial warming. These features suggest a fundamental link between the climatic system and the carbon cycle and stress the role of radiatively active gases in climatic changes.

The accumulation (precipitation) record appears to be governed by temperature with values during the coldest stages reduced by a factor of 2 with respect to the present rate. Ice deposited during these coldest stage is also characterised by high concentration of marine and terrestrial aerosols; these peaks probably reflect strengthened sources and meridional transport during full glacial conditions, linked to higher wind speed, more extensive arid areas on surrounding continent and a greater exposure of continental shelves.

A two-dimensional (2-D) seasonal model has been developed for simulating the transient response of the climate system to the astronomical forcing. The atmosphere is represented by a zonally averaged quasi-geostrophic model which includes accurate treatment of radiative transfer. The atmospheric model interacts with the other components of the climate system (ocean, sea-ice and land surface covered or not by snow and ice) through vertical fluxes of momentum, heat and humidity. The model explicitly incorporates surface energy balances and has snow and sea-ice mass budgets. The vertical profile of the upper-ocean temperature is computed by an interactive mixed-layer model which takes into account the meridional turbulent diffusion of heat. This model is asynchronously coupled to a model which simulates the dynamics of the Greenland, the northern American and the Eurasian ice sheets. Over the last glacial–interglacial cycle, the coupled model simulates climatic changes which are in general agreement with the low frequency part of deep-sea, ice and sea-level records. However, after 6000 yBP, the remaining ice volume of the Greenland and northern American ice sheets is overestimated in the simulation. The simulated climate is sensitive to the initial size of the Greenland ice sheet, to the ice-albedo positive feedback, to the precipitation-altitude negative feedback over the ice sheets, to the albedo of the aging snow and to the insolation increase, particularly at the southern edge of the ice sheets, which is important for their collapse or surge.

Comprehensible explanations of the operation of earth climate systems should consist of descriptions of the operation of a few degrees of freedoms. Qualitative interpretations of results from large-scale numerical models generally follow this principle, but do not render formal definitions of the precise nature of such degrees of freedom.

At its simplest, ice-sheet kinematics requires knowledge of the evolving height and span. Rheology and surface mass-balance impose different requirements upon the co-evolution of these variables, meaning a two-degree of freedom model is over-prescribed. By means of a perturbation expansion about the analytic similarity solution for viscous spreading, eigenfunctions corresponding to degrees of freedom in the ice-sheet profile are obtained, and are used to decompose mass-balance distributions. Only a few eigenfunctions are needed to replicate numerical models, implying that ice-sheets in plane flow may operate with fewer than ten degrees of freedom.

Unstable evolution of ice-sheets can occur, when the operation of a very large number of degrees of freedom can be manifested. Previous work is reviewed and new results for the unstable transformation of valley glaciers into ice-sheets are presented. Phasing of initiation may be an unpredictable phenomenon.

Water of southerly origin replaced polar water very rapidly on the coast of NW Europe and an interstadial marine circulation with a weak North Atlantic Drift was fully established off both west Scotland and southern Scandinavia by roughly 12 800BP. A ‘warm’ interval detected in marine strata on the western Scottish coast at the beginning of the Windermere (Bølling plus Allerød) Interstadial lasted from this date to perhaps 12 400 BP and another towards its close from about 11 250 to shortly after 11 000 BP. During the Younger Dryas Stadial polar water returned by about 10 850 BP and was present until about 10 200–10 100 BP. The changes in water circulation at the beginning and end of the Windermere Interstadial and at the end of the Younger Dryas seem to have taken place within the limits of radiocarbon dating, perhaps within a few decades. Warming at the beginning of the Holocene Interglacial may have taken place in two phases, during the first of which, from about 10 100 BP to possibly 9600 BP, marine temperatures seem to have been lower than at present, more especially on the east coast of Scotland and in southern Sweden. Full marine interglacial circulation may not have been established until 9500 BP. Water depth in the Faeroe–Shetland Channel may have been a major factor in controlling sea and air temperature from Scotland northwards during the Windermere Interstadial and Holocene Interglacial and, by implication, during earlier interglacials and interstadials.

The ocean/sea-ice interaction of the Antarctic open ocean region is described through a one-dimensional model. The model includes processes responsible for maintaining stability in this marginally stable region and reveals the importance of the various processes controlling deep water formation/ventilation and sea-ice thickness and their sensitivity to climate change. This information is used to estimate changes, as they impact water column stability, induced by glacial conditions. Increased stability is conducive to greater ice cover and less deep water formation/ventilation; decreased stability conducive to the opposite.

Sensitivity studies show that the system is destabilised given: (1) shallowing of the pycnocline (induced by increased gyre vigor); (2) decrease in the ratio of heat to salt through the pycnocline (induced by introducing a colder and/or saltier deep water or by increasing the salinity of the surface water); (3) decreased pycnocline strength (induced by a fresher deep water or saltier surface water) and (4) increased atmospheric heat loss. Most of the assumed glacial conditions drive the system toward destabilisation, but the critical effect of changes in NADW characteristics depends strongly on the temperature and salinity of the replacement water. The importance of this deep water influence is evident today—as little as 3Wm−2 in the upper ocean heat balance or an additional 15 cm of ice growth is sufficient to overturn the water column in some regions.

Lake-level and palaeoecological evidence from Africa, Arabia and southern Asia for 9000 yBP suggests an intensification and increased poleward penetration of the northern monsoons. The vegetation belts shifted north by 4–6° latitude on the south side of the Sahara. In contrast, the monsoon over southern Africa was weaker than today. Calculations based on the new palaeogeographical map of Mali by Petit-Maire et al. (1988) indicated that the areaaveraged surface albedo decreased by 0·10–0·14 in the zone 16–24°N and that total annual precipitation increased by 150–320 mm north of the inland delta of the Niger (20–24° 15′N). Experiments with atmospheric general-circulation models suggest that this asymmetrical pattern of anomalies in the strength of the tropical monsoons can be explained in broad terms by the different orbital configuration of the Earth at 9000 yBP. Here, we describe a hitherto unpublished sensitivity experiment with the low-resolution (5° × 7·5°) version of the U.K. Meteorological Office 11-layer model, in which the albedo over Africa and Arabia between 15 and 30°N was reduced by between 0·04 and 0·06 to simulate the increase in vegetation cover at 9000 yBP. The results indicate that the surface-albedo change provides a significant positive feedback enhancing the direct climatic effects of Milankovitch forcing in the tropics.