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Discussion
Climate
Change
- From a geological
perspective
Did the Earth
once turn into a
snow-ball?
Jim Hedfors, Dept. of Earth Sciences
Examples of thick beds of
marbles indicative of hot
environment intemixed by
tillites showing ice ages
of neoproterozoic age in
Billefjorden, Svalbard
1. The sun was ~ 30 % weaker in the early history of
Earth, but the sun have grown stronger with time.
700 million years ago the sun was ~ 6 % weaker than
today.
Why was not the Earth an
ice ball during it´s earliest
history?
The early atmosphere during the first 2 billion years of the
Earth´s history probably had an atmosphere of upto 50%
greenhouse gases.
2. At about 2-3 billion years ago
cyanobacteria started to change the
atmposhere by reducing carbon dioxode
and to oxygenate the atmosphere photosythesis.
3. The majority of the continents
was at this time massed into the
super-continent Rodinia.
If high mountain ranges at the Equator gets iced, the Earth will be
more chilled than if these mountains were located at the poles due
to the albedo effect (brighter surfaces reflects more of the incoming
short wave radiation).
If the ice limits to the tropics (latitude 30˚) will
the planetary albedo be so high that it
overcomes the incoming solar energy, and the
planet freezes up.
4. And, since the continents were lacking vegetation the weathering of
the bedrock was high, and more nutrients were delivered into the
oceans, which in turn increased the bio-productivity by the
photosynthetic planctons down-drawing carbon from the atmosphere.
The Earth freezes
into a snow ball!
But, if the Earth was completely
iced, how could the Earth slip out
of it´s icey armour? Would not
the high albedo on the Earth´s
surface reflect most of the
incoming solar heat and such
stay frozen for ever?
Well, the help came from the Volcanoes! They were
leaking carbondioxide all through the ice age, and
accumulated greenhouse gases in the atmosphere.
When enough heat was retained on Earth the ice started to ablate
in a increasing pace, which in turn increased the plant- and
plancton colonies, which pumped our carbon from the
atmosphere …. and there we go again….
Rocks from this age tells that snow balls and
sauna stages came intechanged at least four
times during the Neoproterozoic epoch.
Human causes?
- What we know from
the past, we must put
into use for the future...
The cryosphere: Glaciers & ice sheets
Accelerated melt?
Since the Great Ocean Conveyor Belt is driven in part by differences in ocean
water density, if one can pump enough fresh water into the ocean in the key
areas on either side of Greenland where the Gulf Stream waters cool and sink,
this will lower the ocean's salinity (and therefore its density) enough so that the
waters can no longer sink. As a result, the Atlantic conveyor belt and Gulf Stream
current would shut down in just a few years, dramatically altering the climate.
Approaching… desert or ice age?