When a system is driven cyclically or harmonically, the solution is also cyclic.
Well, the earth is such an example. There are daily and yearly driving forces because the earth rotates around its own axis in a day and around the sun in a year.
Therefore, it only makes sense that climate change is cyclic and is not a hockey stick1.
The hockey stick model, of Michael Mann, shows that temperature has been slighly decreasing for ever and then rising up because of the activity of man to
constitute the blade of the hockey stick.
This is false according to Mark Steyn. He spoke June 12th at
the International Conference on Climate Change.
Vineyards used to exist in England in the medieval warm period (13th century).
1https://en.wikipedia.org/wiki/Hockey_stick_graph accessed January 26th, 2018.