The only two high confidence
facts in real climate science are:
(1)
Earth's climate has
always been changing,
and
(2)
There's no scientific
evidence that
CO2 levels CAUSED
any temperature changes
in the past 4.5 billion years.
Climate proxy studies
of the past 800,000 years,
using Antarctica ice cores,
found that temperature changes
FOLLOWED the CO2 changes,
hundreds of years later.
Explanation:
Some natural cause of
global warming affected
the oceans, causing them
to release some of their
dissolved CO2 as they
warmed, just like a soda pop
sitting outdoors in a cup
on a warm day will release
CO2, as the soda warms up.
The Milankovitch Theory
describes the effects
of Earth’s orbital variations
on the glacial cycle.
It has been a popular theory
since the early 1970’s.
An ice age is a period
with extensive ice sheets
over vast land regions,
as we have now
over Antarctica.
The last four ice ages
have taken place roughly
150 million years apart.
We do know about 10%
of the time there is a
milder condition known
as an interglacial.
We are living in the Holocene
interglacial, which has existed
for about 10,000 years.
Milankovitch Theory:
In the 1920s,
the Serbian genius,
Milutin Milankovitch,
calculated the Earth's
insolation (incoming
solar energy)
at different latitudes
due to orbital variations
... without computers !
His theory was not accepted
until 1970, when geological
evidence was found on
multiple glacial-interglacial
cycles.
Proper dating of glaciations
during the past 3 million years
showed they usually take place
at intervals of 41,000 years.
Three types of orbital changes
affect Earth’s insolation
( incoming solar energy )
over the long term:
Eccentricity:
Movements of the other planets,
especially Jupiter and Saturn,
cause the Earth’s orbit to
slightly change its eccentricity.
The eccentricity changes
have a major beat of 413,000 years,
and two minor beats of 95,000
and 125,000 years.
The changes in eccentricity
alter the amount of solar energy
Earth receives as the distance
from the Sun changes.
Earth’s orbit is close enough
to being circular that the
change in insolation is small,
currently about 6.4%
peak to trough.
Changes in eccentricity
shorten and lengthen
the seasons as the Earth
speeds up at Perihelion
and slows down at Aphelion.
Obliquity:
This cycle is from changes
in the inclination of Earth’s axis,
or axial tilt, that varies between
22.1° and 24.3°, in a cycle
that takes 41,000 years.
The higher the obliquity,
the more insolation
in the poles
during the summer,
and the
less insolation
in the poles
during the winter.
High obliquity
promotes interglacials,
while low obliquity
is associated with
glacial periods.
Obliquity changes
add a significant amount
of warming at high latitudes
year after year over
thousands of years,
and can have an
enormous cumulative effect.
The temperature proxy record
shows temperatures decreasing
during periods of low obliquity
and increasing during periods
of high obliquity.
When obliquity starts rising
during a glacial period,
it starts moving energy
from tropical to polar areas.
Its effects on global average
temperatures are not noticeable
for many thousands of years.
The hypothesis that obliquity
drives the glacial cycle
solves problems of
Milankovitch Theory.
The 100,000 year problem
is solved because there is no
100,000 year cycle,
just a 41,000 year cycle
that skips one or two beats.
Precession:
There are two precessional
movements.
The axial precession
is Earth’s slow wobble
as it spins on its axis
due to the gravitational pull
on its equator
by other solar bodies.
Precession doesn’t change
the amount of insolation
that the Earth receives
from the sun during the year.
The interaction of the
various components
of precession produce
cycles at 19,000 22,000
and 24,000 years, with
an average of roughly
23,000 years.
Precessional changes
greatly affect the amount
of insolation during
a three-month period,
but that change is offset
over the following
three months, leaving
total annual radiation
unchanged.
Problems with
Milankovitch Theory:
The current theory
explaining glaciations
paced by the 100,000 year
eccentricity cycle
is supported by
a scientific consensus.
In the past one million years,
glaciations have taken place
at 100,000 year intervals.
But between one and three
million years ago,
glaciations were
taking place
at 41,000 year intervals,
pointing to obliquity
as the main factor.