What was done
The authors of these two "perspectives" review the state of our knowledge relative to millennial-scale climate oscillations and their possible causes and consequences.

What was learned
The authors introduce us to some of the substantial evidence for the existence of millennial-scale climatic excursions that have been a stable feature of our planet in glacial and interglacial times alike.  They note that the warming phases of these oscillations have sometimes been extremely abrupt, occurring over periods of but a few years or decades, particularly during glacial times.  They also discuss a number of hypotheses that have served as fruitful springboards for research programs designed to discover the cause or causes of these climate cycles.  Both note, however, that it is premature to say that we have anything more than a superficial understanding of what drives them.  In fact, Stocker suggests that we may actually have a "chicken-and-egg problem" in this regard, not even knowing what is cause and what is consequence.

What it means
If we are unsure about cause and effect with respect to multiple climatic excursions of the past, some of which truly dwarf the modest transition in which we may currently be embedded, is it reasonable to believe that we know what is likely to occur in earth's climatic future?  We believe not.