Geologists and other scientists have been studying Earth's climate history for centuries.
A few decades ago, some computer gamers with science degrees decided to call themselves "climate scientists".
They generally ignore 99.999% of Earth's climate history, because they prefer to get lots of attention, and government grants, by making scary predictions about the future climate.
Their climate predictions are non-science (nonsense) -- just their personal opinions, based on their false belief that CO2 in the air is the "climate controller".
The climate modelers' personal opinions are disguised … by converting them into assumptions used in computer models ... that reach exactly the same conclusions (opinions) the modelers had before they wrote the assumptions.
Their computer model assumptions merely repeat their personal opinions.
This article summarizes climate history discoveries of real scientists, who collect real data in the field to explain Earth's past climate (computer models are not data, so they are not science).
Explaining the past climate has been difficult work, but easier than predicting the future climate, which is impossible.
There is one possible exception:
If scientists discover a repeating natural climate cycle in Earth's history, then predicting the cycle will continue in the future has a decent chance of being right.
The only alternative would be to discover historical natural climate cycles, but then claim 'the future will be different'.
'The future climate will be different than anything in the past', is exactly what climate doomsayers have been predicting for 40 years … and they have been making grossly inaccurate predictions of the future climate for all 40 years.
Natural Climate Cycles
Discovered by Real Scientists
No one knows exactly how much each of these cycles affects the climate.
Numbers(2), (3) and (4) are called Milankovitch Cycles.
(1) 143 million year galactic cycle
(2) 100,000-year elliptical orbit cycle:
Earth's orbit becomes more elliptical, and then less elliptical, on a 100,000 year cycle.
This changes the distance between the Earth and the Sun, which forces solar energy to travel a longer distance, making Earth much cooler, at 100,000 year intervals.
Today, Earth's orbit is not very elliptical.
(3) 41,000-year axial tilt cycle:
Earth has an axial tilt that varies from 21.5 to 24.5 degrees, affecting the angle that the Sun's energy strikes the surface.
This affects the differences between solar energy received at the poles and the equator.
Today, Earth's axial tilt 23.5 degrees, not far from the middle of the range.
(4) 23,000-year precession (wobble) cycle:
Earth has a slow wobble, or "precession".
At one extreme, Earth has milder summers, so more winter ice sheets survive those mild summers = ice sheet growth.
Today, Earth should be beginning, or close to beginning, a period of ice sheet growth, exactly the opposite of what Al Gore always predicts.
(5) 1,500 (+/- 500 years) Dansgaard-Oeschger solar cycle
Discovered in the 1980s, and revealed by climate proxy studies of Greenland ice cores, Vostok, Antarctica ice cores, seabed sediment cores, cave stalagmites, fossilized pollen, etc.
(6) 210-year solar cycle
(7) 87-year solar cycle
(8) 22-year solar cycle
(9) 18.6 years lunar cycle
(10) 11 year solar cycle