What was done
The author presents an overview of our knowledge about the speed and magnitude of major climate changes that have occurred over a span of time that includes the current and previous interglacial periods, as well as the intervening ice age.

What was learned
The author begins by noting that "as the world slid into and out of the last ice age, the general cooling and warming trends were punctuated by abrupt changes."  Many of these changes were very dramatic.  He states, for example, that "climate shifts up to half as large as the entire difference between ice age and modern conditions occurred over hemispheric or broader regions in mere years to decades."  Coolings were generally achieved "in a series of steep ramps or steps and warmings in single steps."  The more dramatic of the warmings were on the order of 8°C, and they were accompanied by several-fold decreases in wind-blown materials.

Although, in the words of the author, "climate changes in the past have been large, rapid, and synchronous over broad areas extending into low latitudes, with less variability over historical times," he does note the existence of one abrupt century-long cold event about 8200 years ago that occurred when "temperatures before and after this event ... were slightly higher than recently," which shows, he says, that "warmth is not a guarantee of climate stability."

What it means
As with many studies we have reviewed in the past, this brief overview of what we know about climate variability indicates that climate is much less stable during glacial and glacial/interglacial transition periods than it is during warmer interglacials.  In addition, the only current-interglacial perturbation noted in this review article is a temperature decrease, not a warming, suggesting that earth's climate just does not spike to the extremely high temperatures that are being predicted by climate modeling exercises during warm interglacials such as the one in which we are presently living.  Hence, whereas climate alarmists are attempting to create global anxiety - actually fear - over extremely weak climatic possibilities, strong climatic probabilities based on real-world data serve to remind us that although almost anything is possible, there should at least be some precedent for what is being predicted if it is to be considered tenable.  And in the case of dramatic CO2-induced global warming within an interglacial such is totally lacking.