Page 121 - Earth's Climate Past and Future
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CHAPTER 6
From Greenhouse to
Icehouse: The Last
50 Million Years
Today’s cold icehouse climate, marked by the presence of ice sheets and
extensive sea ice in both hemispheres, is the result of gradual cooling over
many tens of millions of years. Earth’s record of this transition is rich in informa-
tion, including the initial appearance of mountain glaciers and continental ice
sheets, the replacement of warm-adapted vegetation by cold-adapted forms,
and a range of evidence indicating progressively cooler ocean temperatures.
In this chapter we first examine evidence showing when this greenhouse-
to-icehouse cooling occurred. Then we explore three possible explanations for
the cooling: changes in ocean heat transport, the BLAG spreading rate hypoth-
esis, and the uplift weathering hypothesis.
