Hubertus Fischer Dr. Hubertus Fischer Alfred Wegener Institute for Polar and Marine Research Germany If you would like to interview this scientist, please contact Leah Christen. > biographical information > abstract > paper

Biographical Information:

My passion for ice sheets and paleoclimate started with my work on aerosol and water isotopic composition in Greenland ice cores during my diploma and PhD work at the Institute for Environmental Physics, University of Heidelberg. In 1997, I became PostDoc at the Scripps Institution for Oceanography, University of San Diego, working with Martin Wahlen on carbon dioxide and its carbon isotopic signature in Antarctic ice cores. In 1999, I started at the Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, where I became head of the young research group RESPIC, funded by the German Secretary of Research and Education. RESPIC aims at a quantitative understanding of the global carbon cycle in the past based on new observational and modeling approaches. The research on bubble enclosures in ice is also an outstanding part of EPICA, where I head the consortium of European laboratories working in close collaboration to reconstruct the atmospheric composition of the past.

Abstract:

Global Biogeochemical Cycles and Greenhouse Gas Emissions in the Ice Core Paleoperspective

Hubertus Fischer and the EPICA gas consortium

Carbon dioxide and methane represent the most important greenhouse gases, second and third only to the natural water vapor content of the atmosphere. Accordingly, they play a major role in the radiative budget of the earth and, thus, are mainly responsible for an ongoing and future anthropogenic warming. However, they represented also a crucial ingredient for climate changes and the buildup of large ice sheets in climate history. In return, bubble enclosures in the ice sheets from both polar regions represent a unique direct archive of atmospheric composition in the past. As a matter of fact, most of what is known about the temporal evolution of the anthropogenic increase in greenhouse gases over the last 150 years is derived from ice cores. But Antarctic ice-core records also reach far back in time and only recently the EPICA (European Project for Ice Coring in Antarctica) Dome C ice core allowed for a reconstruction of climate changes and atmospheric composition over the last eight glacial cycles. Here, latest results on atmospheric paleorecords from ice cores are presented, extending the carbon dioxide and methane record back in time to approximately 650,000 years before present, a time characterized by glacial cycles of significantly reduced amplitude in the EPICA Dome C ice core. In addition, recent developments in the interpretation of those records, in terms of glacial/interglacial changes in biogeochemical cycles, are presented using high-resolution carbon dioxide and methane data from (bipolar) ice cores and other records, the carbon isotopic signature as well as simplified models.

Paper:

Ice core archives: The relationship of climate and greenhouse gases in the past 650,000 years

Hubertus Fischer and the EPICA gas consortium

Carbon dioxide (CO₂) and methane (CH₄) represent the most important greenhouse gases, second and third only to the natural water vapor content of the atmosphere. Accordingly, they play a major role in the radiative budget of the Earth and the current increase of their atmospheric concentrations is mainly responsible for an ongoing and future anthropogenic warming. They have also represented a crucial ingredient for climate changes and the buildup of large ice sheets in climate history.

Air bubbles enclosed in ice cores represent the only direct archive of the past atmosphere. In addition, the isotope thermometer (δ¹⁸O, δD) in polar ice cores provides information on temperature variations in high latitudes. Consequently, we can use the ice core climate archive to study the relationship of climate and greenhouse gases in the past.

Up to now, reconstruction of CO₂ and CH₄ concentrations in high resolution has been possible over the last approx. 400,000 years from Antarctic ice cores. Only recently has much older ice from the EPICA Dome C ice core (Antarctica) become available. It reaches back in time more than 900,000 years. Previous ice core studies have revealed a natural glacial/interglacial range of CO₂ from 180-300 ppmv, and of CH₄ from 350-750 ppbv. This is significantly less than the current CO₂ and CH₄ levels of about 375 ppmv and 1750 ppbv, respectively, caused by the anthropogenic emission of greenhouse gases during the last century. In addition to the mean atmospheric level, the current rate of increase in the concentration of these gases is also unprecedented over the last 400,000 years.

Comparison of CO₂ and CH₄ records with ice core temperature reconstructions shows an extraordinary correlation of CO₂ with the Southern Ocean temperature (Fig. 1), while CH₄ during the last ice age reflects rapid temperature variations in the northern hemisphere (Fig. 2). Therefore, understanding the influence of changing climate conditions on the global carbon (e.g., changes in the terrestrial biomass or in ocean circulation) and methane (e.g., changes in precipitation rates or melting of permafrost) cycles is a prerequisite to predicting how anthropogenic warming will feedback on those cycles. By reconstructing new ice core records for carbon dioxide, methane and temperature from both polar regions over an extended time scale and in higher resolution, by using the isotopic composition of these trace gases, and by applying computer models for the carbon and methane cycles, the observed changes in the past can be quantitatively explained.



Figure 1. Proxy for temperature changes in the Southern Ocean region (?D) vs. CO₂ concentration changes recorded in the Vostok ice core, Antarctica (Fischer, et al., 1999; Petit, et al., 1999).

Figure 2. Proxy for temperature changes in the North Atlantic region (?¹⁸O) vs. CH₄ concentration changes as recorded in the GISP2 ice core, Central Greenland (Blunier and Brook, 2001).