On Dec 28, 3:04*pm, "Alastair McDonald"
wrote:
"Pete L" wrote in message

...

Yes, I know about Milankovitch - is it not a case that we are
about (+/-) a few hundred years, to go into the next downturn?
I've often wondered if man's input of CO2 is actually holding
off the next Ice Age. Would be ironic really!

The two main theories about the next glacial a

1) Mankind has already prevented it with the introduction of farming. Crops
do not drawdown the CO2 that forests do and so the widespread clearing of
land for farming has kept the CO2 levels high. Moreover, the rice paddies
produce methane which is an even more powerful greenhouse gas. Thus our
influence on climate goes back thousands of years. [http://en.wikipedia.org/wiki/William_Ruddiman]

2) The ellipticity of the Earth is decreasing and so the next Milankovitch
cooling will not happen for about 40 thousand years anyway. [http://www.sciencemag.org/content/297/5585/1287]

Recently, Berger & Loutre have proposed that the next glacial may have been
banished forever.http://www.nature.com/news/2002/0208...20819-9..htmlI am not sure
that would be ironic. It will result in a sea level rise of over 60 m (200
feet) which will flood most farmland since it is mainly situated on coastal
plains. A 6 metre sea level rise might be held back with flood defences but
not 60 m.

Cheers, Alastair.

Sorry guys,Milankovitch as an assertion is obsolete while precession
as a long term axial trait is untenable also - this is a conclusion
drawn from direct observation where the polar latitudes are carried
around in a circle to the central Sun and act like a beacon for the
orbital behavior of a planet -

http://www.daviddarling.info/images/...gs_changes.jpg

Axial precession goes from a long term axial trait to an orbital
orbital trait and the degree of inclination is given a new role in
assigning a planetary climate spectrum between polar (90 degree
inclination) to equatorial (0 degree inclination).

The old 'no tilt/no seasons' is replaced by a 21st century perspective
which introduces a planetary climate spectrum with the Earth having a
largely equatorial climate.Meteorology is a subset of astronomy and
although it is possible to predict short term weather using known
components of the atmosphere,land and sea,it is impossible to study
climate proper outside astronomy.

Milankovitch indeed ! - try understanding the cause for the annual
Arctic sea ice fluctuations as the polar latitude is carried around in
a circle to the central Sun about an ecliptic axis that runs
coincident with the circle of illumination -

http://www.msss.com/mars_images/moc/...mericas250.jpg