Continued emissions of carbon dioxide to the atmosphere will affect climate and ocean chemistry. These consequences can be anticipated by consideration of basic physical principles, past climates, and calculations. Emission of 5,000 PgC (= amount of carbon in conventional fossil-fuel resources) over a few centuries could produce radiative forcing of climate of about 10 W m­^-2 which could be expected to produce global mean warming of ~4 to 12 °C. Warming in this range would have large biological and human consequences. It could threaten the ice sheets and lead to a long-term sea-level rise of 70 m. Ocean pH could decrease by 0.7 units, making the oceans more corrosive to carbonate minerals than they have been for many millions of years. From the perspective of geology and biological evolution, these changes would occur rapidly, overwhelming most natural processes that would buffer CO₂ changes occurring over longer time intervals, and thus may produce changes at a rate and of a magnitude that exceed the adaptive capacity of at least some biological systems. To find comparable events in Earth history, we need to look back tens of millions of years to rare catastrophic events.

IMPACT OF CLIMATE-CARBON CYCLE FEEDBACKS ON EMISSIONS SCENARIOS TO ACHIEVE STABILISATION  
Description:

At present, approximately half of anthropogenic CO₂ emissions are absorbed by the land and oceans [Jones and Cox, 2005], but climate changes may act to reduce this uptake, leading to higher CO₂ levels for a given emission scenario [Cox et al., 2000, Friedlingstein et al., 2005, in prep.]. Less attention has been paid to the potential impact of carbon cycle feedbacks on the emissions reductions required to achieve stabilisation (the so called “permissible emissions”), although this is arguably more pertinent to the issue of avoiding dangerous climate change in the context of the United Nations Framework Convention on Climate change.

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Category: Abstracts/Managing the Carbon Cycle

  GREENHOUSE GAS CO2, CH4 AND CLIMATE EVOLUTION SINCE 650KYRS DEDUCED FROM ANTARCTIC ICE CORES  
Description:

Ice cores are unique archives of past climatic and atmospheric conditions through the isotopic composition of the ice and the analysis of the air bubbles trapped. In 1999 Petit et al published the reconstruction of the Antarctic climate and atmospheric composition over the last 420 000 years from the Vostok ice core. This record covered the last four glacial inter glacial cycles back to the end of the marine interstadial 11 (MIS 11). It has revealed the close relationship between the atmospheric part of the carbon cycle and the climate. With CO₂ concentration oscillating between 180 and 280 ppmv during the last 4 climatic cycles. In a similar way the methane concentration followed closely temperature on glacial interglacial time scales, with millennial-scale structures during glacial times which appear out of phased with Antarctic temperature but, at least for the last glaciation, in phase with the Greenland rapid climatic oscillations, as revealed by the GISP and GRIP ice cores.

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Category: Abstracts/Carbon Cycle Response to Environmental Change