Fig. 2: Time series of forcing and responses of Northern Hemisphere ice sheets.
From: Astronomical forcing shaped the timing of early Pleistocene glacial cycles
a–g Time series across the period of interest and i–o corresponding normalised amplitude spectra, respectively. a Eccentricity77. b Climatic precession, where the envelope corresponds to eccentricity77. c Obliquity77. d Insolation at 65°N on June 2177. e CO2 forcing used as model input: constant value of 230 ppm (black) and variable CO2 (red: van de Wal et al.36, blue: Lisiecki37). f δ18O signature relative to the mean value of this period (black: Lisiecki and Raymo (2005)3, purple: U1308 core8). Data from Hodell et al.8 were filtered using a zero-phase low-pass Butterworth filter. g Simulated North American and Eurasian ice sheet volume (unit: m, in sea level equivalent; SLE) calculated with different CO2 forcings, shown in the same colours as in (e). h Duration of each glacial/interglacial period (blue/red lines) under a constant CO2 concentration of 230 ppm.
