The story so far.
We have
solar cycles, about which not much is known over the long term, because the records cannot be read through the inferred influences of the atmosphere. We know that solar radiation varies with the eleven year sunspot cycle, and another 100 year cycle, and we infer from. We also know from astronomical study of main sequence stars, that
the sun is getting hotter, by about 25% over 3billion years or so.
Insolation of Earth is further modified by
Milankovitch cycles. These have periods of 26000, 41,000, and 100,000 yrs. The reason why the North polar region is the influential one for these cycles is that most of the land mass is in the Northern hemisphere and the land heats and cools more quickly than the sea, and ice forms more easily on land, because sea has salt as antifreeze. So the Antarctic is more stable.
The temperature of Earth's surface is produced by insolation modified by transparency and insulation effects of the atmosphere, and the reflectivity of the surface itself, and by the absorption of heat by photosynthesis. (Forests also have a large cooling influence through transpiration and associated cloud production.)
The lesson I take from the 2 billion yr old story of cyanobacteria poisoning the atmosphere with oxygen and producing a snowball Earth, which might have remained stable until the present because of the reflectivity of ice, but for some vulcanism restoring a bit of CO2 and maybe darkening the ice a bit with ash, is that the Gaia hypothesis is not true. The living planet is not self regulating.
Rather, there have been wild fluctuations of climate through geological time far larger than can be accounted for by variations of insolation. The history of humanity has been one of unusual climate stability sufficiently long for the effects of milankovitch cycles to become noticeable.
When Prime Minister Harold Macmillan was asked what was the greatest challenge for a statesman, he replied: 'Events, dear boy, events'.
Vulcanism, asteroids, continental drift, and changes to the biome. Human civilisation is a change to the biome that has affected every region and every species. It is events that destabilise the climate and send it careering off to a heating or cooling until it arrives at a new semi-stable climate maybe tens of degrees hotter or cooler. This happens because of positive feedback and tipping points, which complex systems analysts will be familiar with.