Ice with everything - Antarctica: Global Science from a Frozen Continent - page 88

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Future Past Present

Figure 3.18 Past variations of, from top to bottom: green, methane concentration (parts per

billion in volume, ppbv); grey, carbon dioxide concentration (parts per million in volume),
derived from instrumental data and gas concentration measurements in EPICA Dome C ice
core; EPICA Dome C temperature ( C) derived from stable isotope measurements of water. The
colour shading is used to highlight the glacial periods (green to blue) and the interglacial periods
(red colour for periods warmer than the current interglacial period); blue, global sea level
change derived from deep ocean sediment Foraminifera isotopic composition. Note that cold
periods in Antarctica coincide with northern hemisphere ice sheet growth and reduced sea level.
The bottom curve (yellow) displays one component of past insolation changes, namely
anomalies of mid-June insolation at 65 N(Wm ²). At this timescale, past changes in our
planet's orbit around the Sun (its excentricity, obliquity and the position of the seasons)
modulate the seasonal and latitudinal distribution of incoming solar radiation. Astronomical
calculations of insolation are very precise for past and future changes, on timescales of tens
of millions of years. The horizontal dashed line shows the insolation threshold required for
the inception of an ice age. Such a threshold is not in view for the next tens of thousands
of years in the future!

constraints on the Greenland contribution: in a context where the Arctic was also
3to5 C warmer, the northern part of the Greenland ice sheet was probably
comparable to its modern extent. The southern part of the Greenland ice sheet
was probably strongly reduced, with a contribution of about 2m to the observed