Claude Lorius

Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica

The recent completion of drilling at Vostok station in East Antarctica has allowed the extension of the ice record of atmospheric composition and climate to the past four glacial–interglacial cycles. The succession of changes through each climate cycle and termination was similar, and atmospheric and climate properties oscillated between stable bounds. Interglacial periods differed in temporal evolution and duration. Atmospheric concentrations of carbon dioxide and methane correlate well with Antarctic air-temperature throughout the record. Present-day atmospheric burdens of these two important greenhouse gases seem to have been unprecedented during the past 420,000 years.

Climatic interpretation of the recently extended Vostok ice records

A new ice core drilled at the Russian station of Vostok in Antarctica reached 2755 m depth in September 1993. At this depth, the glaciological time scale provides an age of 260 ky BP (±25). We refine this estimate using records of dust and deuterium in the ice and of δ18O of O2 in the entrapped air. δ18O of O2 is highly correlated with insolation over the last two climatic cycles if one assumes that the EGT chronology overestimates the increase of age with depth by 12% for ages older than 112 ky BP. This modified age-depth scale gives an age of 244 ky BP at 2755 m depth and agrees well with the age-depth scale of Walbroeck et al. (in press) derived by orbital tuning of the Vostok δD record. We discuss the temperature interpretation of this latter record accounting for the influence of the origin of the ice and using information derived from deuterium-excess data. We conclude that the warmest period of stage 7 was likely as warm as today in Antarctica. A remarkable feature of the Vostok record is the high level of similarity of proxy temperature records for the last two climatic cycles (stages 6 and 7 versus stages 1–5). This similarity has no equivalent in other paleorecords.

A comparison of the Vostok ice deuterium record and series from Southern Ocean core MD 88-770 over the last two glacial-interglacial cycles

Taking advantage of the fact that the Vostok deuterium (δD) record now covers almost two entire climatic cycles, we have applied the orbital tuning approach to derive an age-depth relation for the Vostok ice core, which is consistent with the SPECMAP marine time scale. A second age-depth relation for Vostok was obtained by correlating the ice isotope content with estimates of sea surface temperature from Southern Ocean core MD 88-770. Both methods lead to a close correspondence between Vostok and MD 88-770 time series. However, the coherence between the correlated δD and insolation is much lower than between the orbitally tuned 8D and insolation. This reflects the lower accuracy of the correlation method with respect to direct orbital tuning. We compared the ice and marine records, set in a common temporal framework, in the time and frequency domains. Our results indicate that changes in the Antarctic air temperature quite clearly lead variations in global ice volume in the obliquity and precession frequency bands. Moreover, the average phase we estimated between the filtered δD and insolation signals at precessional frequencies indicates that variations in the southern high latitude surface temperature could be induced by changes in insolation taking place during a large period of the summer in northern low latitudes or winter in southern low latitudes. The relatively large lag found between Vostok δD variations and obliquity-driven changes in insolation suggests that variations in the local radiative balance are not the only mechanism responsible for the variability in surface temperature at those frequencies. Finally, in contrast to the cross-spectral analysis method used in previous studies, the method we use here to estimate the phases can reveal errors in cross-correlations with orbitally tuned chronologies.

Evidence for an early Holocene climatic optimum in the Antarctic deep ice-core record

In the interpretation of the Antarctic deep ice-core data, little attention has been given to the Holocene part of the records. As far as translation of the stable isotope content in terms of temperature is concerned, this can be understood because expected temperature changes may be obscured by isotopic noise of various origins and because no 14C dating has yet been available for this type of sequence. In this article, we focus on the Dome C and Vostok cores and on a new 850-m long ice core drilled out at Komsomolskaïa by the Soviet Antarctic Expeditions. These three sites are located in East Antarctica, on the Antarctic plateau, in a region essentially undisturbed by ice-flow conditions, so that their detailed intercomparison may allow us to identify the climatically significant isotopic signal. Our results compare well with the proximal records of Southern Hemisphere high latitudes and support the existence of a warmer “climatic optimum” between 10 and 6 ka y BP. Maximum temperatures are reached just at the end of the last deglaciation, which confirms previous observations at high latitudes, in contrast with later dates for the Atlantic and hypsithermal optima in Europe and North America.

Abrupt Climatic Changes: The Antarctic Ice Record during the Late Pleistocene

The δ180 records from Antarctic (Dome C and Byrd) ice cores allow us to Investigate the possible existence of abrupt climatic changes as revealed by Greenland ice cores in the 40 to 10 ky BP time period. At the decade to century time-scale there is no firm conclusion about the presence of rapid climatic changes since seasonal oscillation is not completely averaged out.

Glacials-interglacials in Vostok: climate and greenhouse gases

Abstract The main message coming from long term ice core records may be the close association between changes in the atmospheric composition, and glacial/interglacial changes. When compared with the preanthropogenic levels, the Vostok paleorecords show lower CO 2 and CH 4 concentrations and significant variations in aerosols of both terrestrial and oceanic origins. These changes, in particular those associated with greenhouse gases, may account for about half of the temperature change over the last climatic cycle. Although the interplay between the physical atmospheric and oceanic systems and the biosphere has still to be clarified, this finding may provide a clue to help in the prediction of future greenhouse gases induced warming. In view of available paleodata, a warming of 3–4°C, at equilibrium, may be a realistic figure for a doubling of CO 2 concentrations or its equivalent.

Effet de serre : les lacunes du savoir et de la perception

Resume Les emissions anthropiques de gaz a effet de serre devraient conduire a un rechauffement marque de la planete. Malgre son flou quantitatif, ce message est bien percu par la Societe. Le developpement des recherches sur le climat et sur les sources denergies du futur devrait aider a limiter lampleur de ce risque. Pour citer cet article : C. Lorius, C. R. Geoscience 335 (2003).

Record of Past Atmospheric CO2 from Tree-Ring and Ice Core Studies

After assessing the need for data on past atmospheric CO2 and carbon isotope concentrations, we describe in this chapter results recently obtained from tree-ring and ice core studies. Some tree-ring data span the last 2 000 years or so but most deal with the last 200 years, covering the industrial period. A summary of δ13C records from the Northern Hemisphere is presented and compared with a few Southern Hemisphere and other data. Despite some controversy about the magnitude of the global decrease of the atmospheric δ13C in approximately the last 100 years, as recorded in tree-rings, results of calculations to estimate both the non-fossil fuel biospheric CO2 input to the atmosphere and the “pre-industrial” CO2 atmospheric concentration are presented.

Évolution du climat : du passé récent vers le futur

Abstract The aim of this article is twofold. We first summarize our current scientific knowledge about the potential influence of human activities on climate. This review is largely based on the conclusions of the 1995 IPCC report (International Panel on Climate Change). An increase in atmospheric concentrations of greenhouse gases has been observed since 1750 (CH4 = 145 %; CO2 = 30 %; N2O = 15 %) and in the temperature of the Earths surface since 1860 (between 0.3 and 0.6 °C). This report suggests a discernable human influence on climate and predicts significant global warming for the next century (1 to 3.5 °C) as a result of the anthropogenic increase of the greenhouse effect. We then show how studies of past climates have, over the last ten years, contributed to this problem by providing information relevant to the future of our climate. Important results concern the existence of a relationship between climate and concentrations of greenhouse gases for more than 200 000 years, the discovery of rapid climatic changes (∼10 °C in a few decades in Greenland) and the reconstruction of recent climate showing that the 20th century is the warmest since 1 400 AD.

Abrupt climatic changes: A global perspective from ice cores

On July 12 1992, the GRIP European deep drilling (GReenland Ice Core Project) reached the bedrock in Central Greenland (Summit region; altitude of the site above sea level, a.s.l, is 3250 m, Figure 1). One year later, the US Greenland Ice Sheet Project (GISP2) successfully completed a second drilling in the same region at a site located 28 km apart (3208 m a.s.l). These two, more than 3 km long, cores have now been continuously analysed for their ice oxygen 18 content. Before reviewing the important climatic information that has already been derived from those profiles and putting them in a global perspective through a comparison with the Vostok deuterium record, we briefly summarize why and how these isotopic changes provide a record of the local temperature at the time of formation of the precipitation.