Terry Fields wrote:


Perhaps the mistake I really made was to make a throwaway remark about
stone spears to illustrate that 20000 years ago the ice cap extended
down to circa mid north atlantic levels, and followed with a question
that asked what mechanisms warmed the planet at that time, and whether
they operate today.

I think it was more like the cessation of an effect that profoundly
cooled the planet.

Fr instance the sort of effect a meteorite impact of sufficient size
might have is to cool the earth susbstantially for several years: if
that then resulted in excessive snowfall, and increased albedo, then
even when the dust settlled, you have an icebound planet. That might e
a stable state until e.g. a large volcanic eruption spews dust into the
air..causing rapid cooling, then emits vast amounts of Co2, which sets
the planet on a longer term warming course. Solar radiation is not a
constant, nor is the screening effect of the earths magnetic field,
which wanders about, changes strength, and occasionally flips altogether.

Thee are all known effects as its orbital perturbations: the exact
impact of them is somewhat hard to say, because we never had a need to
really try and work things out, and its hard to actually do the
experiments without wrecking the planet. We are engaged in the
experiment now 'let's see what happens if we burn all the fossil fuel we
can dig up'

Its likely to be very instructive, and potentially very destructive.


Whatever you think, I can almost guarantee that it won't have any
measurable effect.

Man has been screwing the environment ever since he got clever enough to
do it, and kill off any predators that might have stopped him. Hes not
alone in this: Overgrazing and deforestation probably created most of
the sahara..its as easy for sheep to wreck a field and goats a forest,
as it is for humans...
..