I would be nice to be able to demo Milankovic cycles, but I'm not sure how to do this.
just some graphics I found on a NZ site... http://www.seafriends.org.nz/issues/global/climate1.htm
Milankovic cycles summer and winterIn order to understand Milankovic cycles, it is important to first understand how summer and winter arise. In the diagram, Earth is shown rotating around the sun in a counter-clockwise direction when looking down from the north. The planet itself rotates around its axis in the same direction, but at a slight angle of 23.5º. Northern hemisphere summer occurs when the northern half tilts towards the sun in June, and likewise for the southern hemisphere in December. In the northern summer, Earth is also 1.7% closer to the sun, thus the northern summer gets 3.4% more sunlight (= 3.5% more heat) or 1.7x3= 5 degrees C (see above), and the difference between northern and southern hemispheres amounts to 7 % in heat or 10 degrees C. These differences are quite large and have an influence on the climate system.
Milankovic variationsMilutin Milankovic (28 May 1879 – 12 December 1958), was a Serbian civil engineer and geophysicist, best known for his theory of ice ages, relating variations of the Earth's orbit and long-term climate change, now known as Milankovitch cycles. The diagram (from Wikipedia) shows the nature of the cycles and how these influence solar radiation (solar forcing). Milankovic thought that the ice ages could be explained this way. However, the planet has known ice ages only during the Pleistocene, back to 1.6 million years ago whereas the Milankovic cycles must be very much older. Note also that there is no hard correspondence between the oscillations shown and the recorded ice ages. Remember also that the effects of the Milankovic cycles is very small (max +/-50W/m2 of 1370 W/m2 or +/- 3.5%), much smaller than changes in albedo can achieve. Note that the Milankovic cycles all assume that the power of the sun remains constant, but is this so?
- Earth's climate is subject to very slow cycles. but their influence is small, except for summer/winter. the north pole 'looks' at the opposite side of the universe, compared to the south pole, experiencing different amounts of cosmic radiation. the NH to SH difference is large Milankovic cycles may trigger ice ages but do not cause them.