and archaeological evidence,
of climate change,
long before man made
carbon dioxide was added
to the atmosphere,
in significant quantities,
after 1940.
Global warming and cooling,
before the Industrial Revolution,
certainly had natural causes,
and was not man made.
Earth's climate is always changing.
The 'why' and 'how",
is not yet known,
with any certainty,
but one theory involves
small changes in solar energy,
affecting cosmic rays,
which affect Earth's cloud cover.
1.
Magnetic activity of the sun decreases.
(fewer sunspots).
2.
More Galactic Cosmic Rays (GCR’s),
reach Earth's atmosphere.
3.
Cosmic rays are high-energy particles,
from exploded stars (supernovas).
4.
Cosmic rays knock electrons,
out of air molecules,
producing ions,
in the atmosphere.
5.
Ions in the atmosphere,
accelerate the growth,
of small aerosols,
into cloud condensation nuclei,
which are the "seeds" on which,
liquid water droplets form,
to make clouds.
6.
With more cloud cover,
less solar energy reaches Earth.
Below is a chart,
of cloud cover going down,
in green,
as global average temperature goes up,
in blue,
and then both are in a flat trend:
So far there is no evidence,
cosmic rays are now,
or ever were,
a major driver,
of climate change.
It certainly reasonable,
to assume,
there is no single,
"climate controller",
based on the fact that,
there is no,
scientific proof,
of a single "controller",
after many decades,
of searching for one.
With the current state,
of climate change knowledge,
it would be logical to assume,
there are many minor,
climate change variables,
from cosmic rays,
to carbon dioxide,
that when combined,
cause harmless mild warming,
alternating with,
harmless mild cooling.
And then every 100,000 years,
there is a huge glaciation,
that covers northern nations,
such as Canada,
with thick ice,
which eventually melts,
... but that cycle,
CAN be explained,
by long-term cyclical changes,
of the geometric relationship,
between the earth and the sun.
The Milankovitch Theory,
describes the effects,
of Earth’s orbital variations,
on the glacial cycle.
The theory has been popular,
since the early 1970’s,
(which certainly is no guarantee,
it is correct).
An ice age is a period,
with extensive ice sheets,
over vast land regions,
including Canada,
similar to ice we now have,
only over Antarctica.
The last four ice ages,
have taken place,
roughly 150 million years apart.
We know about 10% of the time,
there is a milder climate,
known as an interglacial,
such as the one we live in now!
Milankovitch Theory
In the 1920s Serbian genius.
Milutin Milankovitch,
calculated the solar energy,
reaching Earth,
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.
Three types of orbital changes
affect Earth’s reception,
of solar energy,
over the long term:
(1) 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.
(2) 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 current tilt is 23.44° and decreasing.
The temperature proxy record,
shows temperatures decreasing,
during periods of low obliquity,
and increasing during periods,
of high obliquity.
(3) Precession:
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.
The interactions,
of various components,
of precession,
produce cycles,
at 19,000, 22,000 and 24,000 years,
with an average of about 23,000 years.
Problems with The Milankovitch Theory
The current "consensus" theory,
explaining glaciations,
is the 100,000 year eccentricity cycle.
Because in the past one million years,
glaciations have taken place,
at 100,000 year intervals.
But in the two million year period,
between one and three million years ago,
glaciations were taking place,
at 41,000 year intervals,
pointing to obliquity,
as the main factor,
during that period.
As usual,
real climate science,
is complicated,
not simple,
and is never settled.