400
450
500
550
W m
−2
W m
−2
(a)
−500
−450
−400
−350
−300
−250
−200
−150
−100
−50
0
400
450
500
550
Time before present (millenia)
(b)
Figure 7 Summer solstice insolation at (a) 651 N and (b) 251 N for the past 500 000 years.
300
400
500
600
700
800
0
100 000
200 000
300 000
400 000
500 000
600 000
Time (years before 1950)
160
180
200
220
240
260
280
300
−460
−440
−420
−400
−380
−360
CO
2 (ppmv)
CH
4 (ppbv)
%
D ice (% )
Figure 8 Variations in deuterium (dD; black), a proxy for local temperature, and atmospheric concentrations of the greenhouse
gases carbon dioxide (CO 2 ; red), and methane (CH 4 ; green), from measurements of air trapped within Antarctic ice cores. Data from
Spahni R, Chappellaz J, Stocker TF, et al. (2005) Atmospheric methane and nitrous oxide of the late Pleistocene from Antarctica ice
cores. Science 310: 1317–1321 and Siegenthaler U, Stocker TF, Monnin E, et al. (2005) Stable carbon cycle-climate relationship
during the late Pleistocene. Science 310: 1313–1317.
440 PLIO-PLEISTOCENE GLACIAL CYCLES AND MILANKOVITCH VARIABILITY