This was caused during global warming, version 1.0. During these pitiful years....humans set too many campfires, killed too many turtles and mammoths....and refused to dig pits for toilet purposes.
Later...as Al Gorestone preached to Krog and Becky about their wasteful lifestyle...everyone got carbon in their lifestyle and agreed to buy carbon credits from Gorestone...with shiny black rocks. Sadly, Krog wasn’t honest about this business...and still lit too many campfires. Later, Becky got close to a member of the Gorestone society, and ran away with another caveman. This set Krog back a bit...and he had to visit with Dr Philstone who got Krog’s grove back into circulation.
Krog ended up on “Dancing with Cavmen”...where he placed 3rd and was offered a job with “Hot-Rocks-R-Us” and became a star salesman. As Krog made it big...he left in pursuit a new gal...and headed north out of the drought area...and met Carla who was a bit of a flirt but definitely Krog’s type
More like 2.0. There were probably two previous ice ages before the last one, beginning at the end of the Cambrian and occurring about every 200,000,000 (that's 200 million, for you "progressive lurkers) years. These were alternated with Global Warming 1.0 and 1.2.
Nowadays, we're probably up to Global Warming SE.