Reference
Wanner, H., Beer, J., Butikofer, J., Crowley, T.J., Cubasch, U., Fluckiger, J., Goosse, H., Grosjean, M., Joos, F., Kaplan, J.O., Kuttel, M., Muller, S.A., Prentice, I.C., Solomina, O., Stocker, T.F., Tarasov, P., Wagner, M. and Widmann, M. 2008. Mid- to Late Holocene climate change: an overview. Quaternary Science Reviews 27: 1791-1828.
What was done
In a lengthy review paper, eighteen climate scientists -- hailing from thirteen research institutions scattered throughout Switzerland, Germany, the United Kingdom, Belgium and Russia -- develop what they describe as "a general framework for understanding climate changes during the last 6000 years," and when all is said and done, they end their analysis of the several hundred papers they cite with a summary consisting of two main points, of which we will only report the second and final point, as it is the one that is most germane to our interests.
What was learned
Wanner et al. conclude that "at decadal to multi-century timescales, climate variability shows a complex picture with indications of a possible role for (i) rapid changes of the natural forcing factors such as solar activity fluctuations and/or large tropical volcanic eruptions, (ii) internal variability including ENSO [El Niņo Southern Oscillation] and NAO [North Atlantic Oscillation], (iii) changes of the thermohaline circulation, and (iv) complex feedback mechanisms between ocean, atmosphere, sea ice and vegetation." They also report that "notable swings occurred between warm and cold periods, especially the hemispheric-scale warming leading into the Medieval Warm Period and subsequent cooling into the Little Ice Age," the latter of which periods they say "appears at least [our italics] to be a hemispheric phenomenon." Last of all, they say that model simulations support the inference that the Little Ice Age "may have been brought about by the coincidence of low Northern Hemisphere orbital forcing during the Late Holocene with unusually low solar activity and a high number of major volcanic events."
What it means
We find it gratifying that Wanner et al. acknowledge (1) the existence of the Medieval Warm Period and Little Ice Age, (2) their hemispheric (or greater) geographic impacts, and (3) the possible role played by variable solar activity in their development and demise, which three things have often been difficult for the world's climate alarmists to accept.