IF THE whole Earth froze over about 650 million years ago鈥攁s some
believe it did鈥攊t would have taken a massive build-up of atmospheric
carbon dioxide to thaw it out again, according to climatologists in
Pennsylvania
Rocks in Namibia suggest that glaciation once reached the tropics
(This Week, 5 September 1998, p 11).
To investigate this 鈥渟nowball Earth鈥� theory, Gregory
Jenkins and Steven Smith of Penn State University in College Park ran a computer
simulation of the climate.
Their model indicates that the big chill could have happened. But their
results indicate that thawing the frozen planet by greenhouse warming would have
required levels of atmospheric CO2 to rise to a staggering 12 per cent,
which is 400 times the present level (Geophysical Research Letters, vol
26, p 2263). As a result, Jenkins is sceptical that the whole planet actually
froze.
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