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Updated 12 October, 2003
CO2 and Temperature over the Last 420,000 Years: Present and Projected Climate Changes in Perspective
USGCRP Seminar, 30 September 1999
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How have global surface temperatures and concentrations of greenhouse gases such as carbon dioxide (CO2) and methane (CH4) varied over the last 420,000 years, relative to the last 150-200 years? How did "ice ages" and intervening warm periods come and go during this period of time? Is there evidence that changes in the concentration of CO2 and other greenhouse gases bring about changes in the surface temperature of the Earth? By comparison, how do the recent (the last 150-200 years) global trends in CO2, CH4, and surface temperature compare to these historic trends? From an historical perspective, how large an impact, if any, is society having on the Earth's climate system?

INTRODUCTION:

Dr. Julie Palais
Program Manager for Antarctic Glaciology, National Science Foundation, Arlington, VA

SPEAKERS:

Dr. Jean Jouzel
Laboratoire des Sciences du Climat et de l'Environnement, Gif-sur-Yvette, France

Dr. Dominique Raynaud
Laboratoire de Glaciologie et Geophysique de l'Environnement, Saint Martin d'Heres, France


Overview

Vostok, one of the coldest places on Earth, is a permanent Russian station in East Antarctica where annual precipitation in the form of snow represents the equivalent of 2 cm of water.

A collaborative, international research program involving Russia, the U.S. and France was deployed from 1989 to 1998, to study ice core records of climate change from deep drilling. This project achieved both a technical and scientific milestone by reaching 3623 meters below the surface, the deepest ice core ever drilled, representing the longest, continuous, annual climate record extracted from the ice, encapsulating the last 420,000 years of Earth history.

Ice-core records of temperature, oceanic and desert aerosols, and air composition (concentrations of oxygen, nitrogen, carbon dioxide, and methane) allow one to describe in detail the natural variability of climate and the environment, sometimes on a year-by-year basis. Among a host of implications, the newest Vostok ice-core record, spanning 420,000 years, underscores the importance of the role of greenhouse gases in climatic change. In addition, these new data can now be incorporated into climate models for the purpose of simulating and assessing the potential impact of human activities on future climates.

The latest Vostok records of climate change provide a unique context or backdrop for examining human-induced changes in the concentrations of important greenhouse gases such as CO2 (carbon dioxide) and CH4 (methane) over the last 200 years. Comparatively speaking, human activities have resulted in present-day concentrations of CO2 and CH4 that are unprecedented over the last 420,000 years of Earth history. By extension of this comparison, the present rate of CO2 build-up also seems to be greater than what has been observed in ice-core records of climate change spanning the last 420,000 years.


Climate over the Last 420,000 Years: Results and Implications

The extended Vostok record of climate now enables scientists and others to compare the climatic evolution of the present-day interglacial period (often referred to as the Holocene warm period) in which we are living, with previous periods of global climate warming. As judged from this detailed record which encapsulates the main trends in global climate change, the long, stable Holocene period (the last 10,000 years) appears to be a unique feature of the Earth's climate during the last 420,000 years.

The Vostok results show an overall remarkable correlation between greenhouse gases and climate over the four glacial-interglacial cycles (naturally recurring at intervals of approximately 100,000 years) which, in particular, confirm that the periods of CO2 build-up have most likely contributed to the major global warming transitions at the Earth's surface. The results further indicate that the succession of changes in climate parameters such as temperature, greenhouse gases and continental ice volume during each of the major warming periods corresponding to four glacial-interglacial (cold-warm) transitions, are similar. This suggests that the same sequence of climate triggers and feedbacks occurred in each instance as follows –– changes in solar insolation (as a result of changes in the Earth's orbit) is typically followed by two strong amplifiers of climate warming, with greenhouse gases acting first, followed by deglaciation (melting) due to feedbacks related to changes in the reflectivity of glacial ice (Snow and ice typically reflect sunlight, but as ice melts the amount of solar radiation absorbed at the Earth's surface increases, resulting in further warming). During these major transitions in the Earth's climate, Antarctic warming appears to precede warming in the Northern Hemisphere.

The lessons from the Vostok ice core can be summarized as follows. Past changes in greenhouse gases have been initially triggered by climatically induced changes in the oceanic and terrestrial pools or reservoirs of carbon Changes in these pools of carbon resulted in the amplification of the original weak, orbitally-driven changes in the amount of solar radiation reaching the Earth's surface. Once in the atmosphere, greenhouse gases then played an important role as amplifiers of climate change, accounting for about half of the global warming observed in the Vostok ice core, corresponding to the four glacial-interglacial (cold-warm) climate transitions. The main difference between the Vostok record of climate change and the present climate situation is that today the sharp increase in greenhouse gases (i.e., approaching unique levels of greenhouse gas concentrations relative to the last 420,000 years of climate change) is being triggered by human activities at an unprecedented rate. In addition, ice-core records (and other records) of past climates indicate that changes in the concentration of greenhouse gases, whatever the causes, induce important global climatic changes. By comparison, society's impact on the concentration of greenhouse gases during the last 150 years has already enhanced the CO2 concentration of the atmosphere by an amount equivalent to the glacial-interglacial CO2 increases documented in the Vostok ice-core records described above.


BIOGRAPHIES

Dr. Jean Jouzel currently serves as Head of the Climate Group at the Laboratoire des Sciences du Climat et de l'Environnement (LSCE), a joint laboratory of CEA (French Attomic Energy Agency) and CNRS (French National Center for Scientific Research) in Saclay, France. Dr. Jouzel formerly served as Associate Director of the Laboratoire de Glaciologie et Geophysique de l'Environnement (LGGE), and Director of the Laboratoire des Modelisation du Climat et de l'Environnement (LMCE).

Dr. Jouzel's research interests lie in reconstructing past climate changes from ice cores, on a variety of timescales, and in modeling the Earth's atmosphere using both dynamically simple as well as General Circulation models. He has participated in several major international ice-core projects such as Vostok in Antarctica, and GRIP (Greenland Ice Project) in Greenland. He is presently in charge of the European Program for Ice Coring in Antarctica (EPICA).

Dr Jouzel was a lead author for part of the 1995 IPCC (Intergovernmental Panel on Climate Change) report and is a lead author for part of the 2001 IPCC report. He serves as the French representative to IPCC Working Group I (the Science of Climate Change – for the 1995 and 2001 reports) and he is a Member of the CLIVAR (Climate Variability and Predictability) Scientific Steering Group.

Dr. Jouzel was selected to be a member of Academia Europea and was awarded the Milankovitch Medal by the European Geophysical Society in 1997. Dr. Jouzel received a degree in Engineering from Ecole Supérieure de Chimie Industrielle de Lyon, France in 1968, and received his Ph.D. in stable isotopes in 1974.

Dr. Dominique Raynaud is Director of Research at CNRS (French National Center for Scientific Research) and Director of the Laboratoire de Glaciologie et Geophysique de l'Environnement (LGGE) at Saint Martin d'Heres, near Grenoble, France. His research interests include the evolution of the atmosphere (especially greenhouse gases) and the carbon cycle as they pertain to climate, as well as ice core studies and the interactions between ice-sheets and climate. He has also participated in several scientific expeditions to Antarctica and Greenland.

Dr. Raynaud is a Lead Author for the Carbon Cycle chapter of the IPCC Third Assessment Report, and presently serves as a member of the following international programs: PAGES (Past Global Changes), IGBP (International Geosphere-Biosphere Program), and GLOCHANT (Global Changes and Antarctica). He has been the recipient of several scientific awards and is a member of Academia Europea. He is the author or co-author of more than 80 peer-reviewed, scientific publications. Dr. Raynaud received his Doctorat d'Etat degree in 1976 from the University of Grenoble, France.

 


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