Although we question their claim about recent warming being unprecedented within this context (see both our Medieval Warm Period Project and the materials we have archived under Roman Warm Period (Europe) in our Subject Index), we will not argue this subject further here. Instead, we will concentrate on the primary conclusion that Buntgen et al. draw from their work, which is that their data "may provide a basis for counteracting the recent political and fiscal reluctance to mitigate projected climate change."

In the abstract of their paper, the twelve researchers state that "wet and warm summers occurred during periods of Roman and medieval prosperity," which is indeed correct; and in the body of their paper they write that "average precipitation and temperature showed fewer fluctuations during the period of peak medieval and economic growth, ~1000 to 1200 C.E. (Kaplan et al., 2009; McCormick, 2001), which is also correct, but which is something that suggests to us that warmer is better than colder, especially when it comes to assessing what could be called the wellness-state of humanity.

Support for this point of view is provided by Buntgen et al.'s description of what happened as temperatures declined and the Medial Warm Period gave way to the Little Ice Age, with its onset "likely contributing," in their words, "to widespread famine across central Europe," when they say that "unfavorable climate may have even played a role in debilitating the underlying health conditions that contributed to the devastating economic crisis that arose from the second plague pandemic, the Black Death, which reduced the central European population after 1347 C.E. by 40 to 60% (Buntgen et al., 2010; Kaplan et al., 2009; Kausrud et al., 2010)."

In addition, the team of Austrian, German, Swiss and U.S. scientists notes that this period "is also associated with a temperature decline in the North Atlantic and the abrupt desertion of former Greenland settlements (Patterson et al., 2010)," and that "temperature minima in the early 17th and 19th centuries accompanied sustained settlement abandonment during the Thirty Years' War and the modern migrations from Europe to America." And a quick trip to the heading of War and Social Unrest in our Subject Index will provide many more real-world examples of cold times typically leading to bad times in terms of the wellness-state of humanity in many other parts of the planet.

Clearly, maintaining the planet's current level of warmth is a good thing for earth's inhabitants, as is maintaining -- and actually increasing -- the atmosphere's CO2 concentration, because of CO2's impressive aerial fertilization effect and its anti-transpiration effect, which working together significantly boost the water use efficiencies of nearly all plants, including those that supply us and the rest of the planet's animal life with the food we need to sustain ourselves. And since there is no compelling reason to attribute the planet's current level of warmth to its current level of atmospheric CO2 -- seeing there was much less CO2 in the air during the comparable (or even greater) warmth of the Roman and Medieval Warm Periods -- there is no reason to believe that attempting to reduce the air's CO2 content (which we can't do anyway) or even slow its rate-of-rise (which we cannot do to any significant degree) would alter the planet's temperature to any significant degree. In addition, the planet's temperature has remained essentially level for the past decade or more; and some scientists believe we are facing a future cooling. Consequently, we believe that the work of Buntgen et al. "may provide a basis for [not] counteracting the recent political and fiscal reluctance to mitigate projected climate change," as those mitigating efforts are known to likely have but a miniscule thermal impact even if successful, and they would come at an ungodly economic cost at a time when the world's economy is in an ungodly world of hurt.

Sherwood, Keith and Craig Idso

References
Buntgen, U., Tegel, W., Nicolussi, K., McCormick, M., Frank, D., Trouet, V., Kaplan, J.O., Herzig, F., Heussner, K.-U., Wanner, H., Luterbacher, J. and Esper, J. 2011. 2500 years of European climate variability and human susceptibility. Science 331: 578-582.

Buntgen, U., Trouet, V., Frank, D., Leuschner, H.H., Friedrichs, D., Luterbacher, J. and Esper, J. 2010. Tree-ring indicators of German summer drought over the last millennium. Quaternary Science Reviews 29: 1005-1016.

Kaplan, J.O., Krumhardt, K.M. and Zimmermann, N. 2009. The prehistoric and preindustrial deforestation of Europe. Quaternary Science Reviews 28: 3016-3034.

Kausrud, K.L., Begon, M., Ben Ari, T., Viljugrein, H., Esper, J., Büntgen, U., Leirs, H., Junge, C., Yang, B., Yang, M., Xu, L. and Stenseth, N.C. 2010. Modeling the epidemiological history of plague in Central Asia: Palaeoclimatic forcing on a disease system over the past millennium. BMC Biology 8: 10.1186/1741-7007-8-112.

McCormick, M. 2001. Origins of the European Economy: Communications and Commerce, A.D. 300-900. Cambridge University Press, Cambridge, United Kingdom.

Patterson, W.P., Dietrich, K.A., Holmden, C. and Andrews, J.T. 2010. Two millennia of North Atlantic seasonality and implications for Norse colonies. Proceedings of the National Academy of Sciences USA 107: 5306-5310.