In real science,
when you don't know
the answer, the FIRST
item in the list of suspects
( I call them "the usual suspects" )
must be "Unknown".
And that's why "Unknown"
is first on both lists below.
The remaining suspects are
NOT listed in order
of importance
-- no one would know that,
although a lot of liars will
claim they do.
They are just typed in a way
I thought was easy to read !
My list of likely causes,
of the minor, and harmless
warming / cooling cycles
( such as + 1 or 2 degrees C.
over a century or two ),
where a full cycle
seems to last
hundreds of years,
per ice core studies:
Natural Causes: Unknown
Natural: The Sun
Natural: The Oceans
Natural: The Clouds
Natural: Volcanoes
Man Made: Unknown
Man Made: Land Use Changes
Man Made: Air Pollution / Aerosols
Man Made: CO2 / Methane / Other
Man Made: Measurement Error
and / or Measurement Bias
My list of likely causes,
for the very long term,
40,000 to 150,000-year
cycles of glaciation.
"Planetary Geometry"
is listed as (2) because
it has no competition:
(1) Natural Causes: Unknown
(2) Natural Causes: Planetary Geometry
( aka Milankovitch Cycles)