[blam]

"But there are also concerns that the Earth's climate may have changed very abruptly at times in the past, in complex interactions between the atmosphere, ocean currents and ice sheets."

All part of a normal cycle?

[cogitator]

All part of a normal cycle?

Abrupt changes might signal the end of the normal cycle and a transition to a new cyclic timing. Reading various sources indicates that there was a transition between a dominate 41,000 year cycle and a dominant 100,000 year cycle. The cause(s) of the 100,000 year cycle are harder to figure out.