CO2 and Northern Hemisphere ice volume variations over the middle and late Quaternary

 The atmospheric CO₂ concentrations have been reconstructed over the past 600 ka based on regression between the Vostok CO₂ data and the SPECMAP oxygen isotope values. A lag of 4.5 ka (CO₂ preceding δ¹⁸O) gives the best results. A polynomial of order 5 explains 66% of the Vostok CO₂ variance over the last 220 ka. The Northern Hemisphere ice-sheet volume was simulated over the past 575 ka using the LLN 2-D model, forced by insolation and these statistically reconstructed atmospheric CO₂ concentrations. The simulated ice volume fluctuations resemble the deep-sea oxygen isotope variations. CO₂ of interglacial level is necessary for explaining both the interglacial at oxygen isotopic stage 11 and our present-day interglacial.