I was just transcribing a recent public talk by Prof Gavin Foster of the
NOC, Southampton and thought the 22 to 24 tilt and albedo process
described below, itself relatively small , might be analogous to the
absent sea-ice process. Perhaps connecting effects at both poles
concurrently, ie despite summer one pole , winter the other.
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.... On top of this grand 1/2 million year cycle
(pangea/break-up/pangea...), there is cycling of the
climate on shorter time scales , due to how the Earth orbits around
the Sun . This was recognised by Mulacan Milankovic ? , trying
to understand why we had cold climates relatively recently.
In 1920 he proposed that glaciations were driven by orbital
changes of the Earth. The Earth is influenced by the other planets,
every 41,000 years the tilt of the Earth changes from 24 degrees
to 22 degrees, a change in the elliptic nature of the orbit, and the
way the Earth spins , the precession like a spinning top .
It has little effect on the amount of sunlight reaching the Earth
but the distribution of that sunlight , through the year
and where the maximum insolation is, changes as the orbit
changes.
Examples of cold orbit and a warm orbit . A cold orbit is
when there is a small tilt , the north hemisphere is colder .
A warm orbit the northern hemisphere is tilted towards the Sun
i nthe summer. These orbits affect the local temp in the north
hemisphere. In a cold orbit phase you get some ice-growth one
summer , that ice stays , that increases the albedo because it is
reflective, more sunlight is reflected and then on a global
scale via a bunch of feedback effects also causes atmos CO2
to come down. That all leads to more cooloing , more ice
growth, more CO2 stored in the ocean, more cooloing and so on.
When we have a warm orbit, the ice retreats, decreases the
albedo, less CO2 stored in oceans, more warming ...
These orbital cycles are quite a small influence on the
earth's radiative budget, but through the bunch of feedbacks they
can cause dramatic climate change. ...
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