[sologoub]

That's exactly the detail missing from this article!

The other bit of information that I would really find useful as a lay person is how temperature distribution varied during the "greenhouse" climates. For example, was it linear to todays differential, implying that if I can directly apply an increase of 20C to today's temp and say that the avg. CA temp would be 34C from the 14C referenced currently or is it more even and the jump at extremes will be significantly larger or smaller than at equator?

[jofer]

It's probably very spatially variable, but beyond that, I'm out of my depth.

Ocean circulation plays a large role in regional (and global) variations in climate. If nothing else, the changes in the shape of the ocean basins over time would result in very different regional climate patterns, even if the average global temperature stayed the same.

On top of that, changes in average global temperature tend to vary strongly by latitude, if I remember correctly.

[dragop]

In the current ice age, the cycle between glacials and inter-glacials is primarily driven by variations in the Earth's orbit, and therefore the distribution of incoming solar radiation over the Earth's surface by season and latitude. Obviously, as you mention, this then interacts with global climate through atmospheric and ocean circulation. They're called Milankovitch cycles after Milutin Milanković, who calculated them all (by hand!) at the beginning of the 20th century.

Obviously orbital forcing would exist in "greenhouse" times, to answer the parent comment.

If you are interested, there are three variations:

- eccentricity, change in the ellipticity of the orbit around the Sun, ie how close to a circular orbit it is. So if it's close to circular, temperature variations by season will be low. If it's more eccentric, you will get greater variation by season.

- tilt of the axis of rotation, which varies around 22-24 degrees. So when the Earth is tilted over more, at the poles it will be hotter when facing the Sun, colder when facing away.

- axial precession, which is the wobble of the axis of rotation, a bit like if you put a toy gyroscope on a table. This has a latitudinal and seasonal effect, particularly at the poles.

These cycles are approximately 100, 41 an 25 thousand years respectively. Put them together and the periods very closely follow the current ice age climate variations.