Can anybody tell me what the 'normal' climate of the planet is supposed to be?

Before the Ice Age, Greenland had a similar climate to what is now the US Great Plains, and fossils show aquatic species lived well above what is now sea level.

Maybe the planet went in to a period of colder-than-normal and is now returning to its normal average. Here's a hint---dig in to solar activity (i.e., the sun has become extremely active with flares and such in the not so recent past).
Dig through the news archives from the 70s---there was a lot of worry 35 years ago we were retuning to a new Ice Age!!