What was done
The authors present a brief overview of what is known about recurrent millennial-scale oscillations of earth's climate.

What was learned
The authors discuss the evidence for a climate oscillation with a return period on the order of 1,500 to 2,000 years that is evident in proxy climate data pertaining to the last deglaciation and which has continued (with reduced amplitude) through the Holocene, along with its association with contemporaneous changes - demonstrable for the last deglaciation but tenuous for the Holocene - in the thermohaline circulation of the North Atlantic Ocean.  The Little Ice Age (LIA) is the most recent cold phase of this persistent climatic phenomenon that may be induced by variations in the production rate of North Atlantic Deep Water.  According to Keigwin and Boyle, "mounting evidence indicates that the LIA was a global event, and that its onset was synchronous within a few years in both Greenland and Antarctica."  In the Northern Hemishpere, they say, it was expressed as a 1°C cooling between approximately 1500 and 1900 AD, with a cooling of approximately 1.7°C in Greenland.

What it means
Although the immediate cause or causes of the phenomenon have yet to be definitively identified, there is little question but what earth's climate oscillates globally on a millennial time-scale independent of the activities of man, and that the most recent cold phase of that natural oscillation was what we call the Little Ice Age, which was centered at approximately 1700 AD and lasted until about 1900 AD.  Hence, it is only to be expected that temperatures should have risen over the last century or so, as they indeed have, and that they will continue to rise even further until a warm epoch analogous to the Medieval Warm Period is reached a few hundred years from now.  To thus say, as the climate alarmists do, that any warming that may currently be occurring is due to anthropogenic CO2 emissions is deceitful at worst or an expression of ignorance at best.  The same goes for their infamous "hockey stick history" of earth's temperature variation over the past millennium (see our year 2000 Editorials of 15 June, 1 July, 15 July and 2 August), which does not even depict the existence of the Little Ice Age! Oh where, oh where, has our common sense gone?