FIGURE 7.4 Earth's climate history during the previous 500,000 years based on atmospheric, marine, and terrestrial records that continuously cover the last five glacial-interglacial transitions (identified by dashed vertical lines with Roman numerals and the duration of the period in thousands of years, ka). Temperature profile from the Vostok ice core from Antarctica has been calculated in relation to the oxygen and hydrogen isotope content of the snow. Close correlation between atmospheric temperatures and greenhouse gases is further revealed by the carbon dioxide (CO2) concentrations in the Vostok ice core, which are higher today than at any previous period during the last four climate cycles. The calcium carbonate vein from Devils Hole (DH11) in North America and the SPECMAP composite of calcareous planktonic foraminifera in 17 sediment cores from the Atlantic Ocean reveal coupled climate shifts and interacting dynamics of air-sea-land reservoirs in the Earth system. All of these profiles are compared to variability of the Earth's insolation, which is forced by the orbital relationship with the Sun (Figs. 7.2 and 7.3). Units are ppmv (parts per million by volume), %o (parts per thousand), W m~2 (watts per square meter), and °C (degrees Celsius). Modified from published information on the Vostok ice core (Petit et al., 1999), Devils Hole core (Winograd et al., 1992) and SPECMAP composite core (Imbrie et al., 1989).

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