What could cause a turn from global warming to global cooling? Except a hypothesized orbital forcing! Ice cores shows that there are several irregular sharp temperature peaks in between of the big 100,000 years glaciations. What could cause those peaks? 

Almost all energy excess is stored in the oceans and common sense says that there have to be a threshold for how much energy the oceans can take up without drastically changing the climate. There are two possibilities: either there is a turn to cooling down the oceans or there isn't.

Could the energy from the oceans take over the climate system totally for a time long enough to be cooled down? Could the energy from the oceans, if big enough cause global storms independent of the insolation? Convective clouds transport warm vapor high up in troposphere where condensation release an enormous amount of energy - mostly as heat energy that spreads from there. Could a global cover of convective clouds be maintained entirely by the ocean heat content, if big enough? 



In the diagram, there is a well defined peek about 50,000 years ago, for example. Sudden up and sudden down. Increased insolation (or something else) caused a sudden warming, that "immediately" turned back. Could it have been caused by a long time of storms and convection?
Pleistocene's climate variations are well correlated with Milhankovitch Cycles. 


  "Variations in eccentricity, axial tilt, and precession of the Earth's
  orbit resulted in cyclical variation in the solar radiation reaching
  the Earth, and that this orbital forcing strongly influenced climatic
  patterns on Earth."
  
  Source: Milhankovitch Cycles, Wikipedia


At this graph you can see eccentricity explains major Oxygen $δ18$ variations at Pleistocene oceans. $δ18$ is a known proxy for temperature.


   
  
  Source: euanmearns.com


The minor peaks are Earth's internal forces reaction to changes on solar radiation. Earth has subsystems that store and interchange the energy received from the Sun, resulting oscillatory climate tendencies.

Aswell as the atmospere and the hydrosphere, cryosphere has internal forces as a subsystem; and oscillatory events (development of ice-break of ice). One example of punctual changes due to cryosphere internal forces dynamics are Heinrich Events, that can influence climate at minor scale than eccentricity does and be correlated with some of the peaks your graph shows.