In message
,
Alastair writes
On Sep 19, 5:43*pm, Lawrence13 wrote:
On Sep 18, 12:16*pm, Alastair wrote:









On Sep 18, 11:28*am, Lawrence13 wrote:

Now we have some vry bright minds using this group so here's a
question for them

If the accepted *cause of the *ice age which kicked of in earnest
around several million years ago is seen to be the Milankovitch theory
of earths orbital forcings causing, procession, tilt and wobble
(sounds like a double act that). Well we now know we are at the end of
a very short warm intermission called the interglacial so has there
been any evidence to date of the mechanism that Milankovitch
postulated, happening now?
I note wiki talks of another 50,000 years befor we should see these
changes but that really is guess work, others have said we could start
anytime soon . But I repeat shouldn't we be see evidence first of
orbital forcing?

The Pleistocene Ice Age, which began 2.6 or 1.8 Myrs ago, was not
caused by Milankovitch cycles. *They cause the glacial and
interglacial periods within an ice age, and existed long before this
ice age began, in fact since the Earth began circling the Sun. *The
reason the Ice Age began is possibly due to the closing of the Isthmus
of Panama which happened about 3 Myrs ago. There has also been an
erratic fall in atmospheric carbon dioxide since the Age of the
Dinosaurs, and that is possibly the underlying cause.

There are three main sets of Milankovitch cycles and it is only when
they act together that you get major changes in climate. The last time
this was happening was around 7,000 years ago and since then the
planet has been cooling.

HTH,

Cheers, Alastair.

Thanks Alastair.Those Milankovitch three cycles; I assume they are
observable and measurable?

Not in the same way as a tricycle.

Milankovitch calculated them and Hays et al found them by analysing
the delta18O isotope record in ocean cores. Now they can also be seen
in the Antarctic ice cores. The 100,000 kyr elliptical cycle is
obvious in the slides that Al Gore showed, but it should be the
weakest cycle. It is thought that it is amplified by carbon dioxide,
but no one knows where the CO2 comes from!

Not ocean-CO2 feedback?

Googling for Milankovitch will give you more information, and see
Wikipedia for the problem with the 100,000 kyr cycle.

Cheers, Alastair.

--
Stewart Robert Hinsley