Volume 6, Number 31: 30 July 2003
Nearly everyone knows about the Vikings -- from whom we, the authors of this editorial (being of Norwegian extraction), presume we are descended -- and how their fortunes were tied to the millennial-scale climatic oscillation that has reverberated throughout the Holocene (Bond et al., 2001; Viau et al., 2002) and beyond (Oppo et al., 1998; Raymo et al., 1998). With the dawning of the Medieval Warm Period in the latter part of the 10th century AD, which was the most recent prior warm node of this climate cycle, the Vikings successfully settled a portion of coastal Greenland and maintained a colony there, until they succumbed to the bitter cold that arrived with the Little Ice Age, which was the most recent cold node of the millennial climate cycle.
Less well known is the analogous impact of cyclical climate change on the history of another people -- the Maya of Mesoamerica and northern tropical South America -- who were similarly influenced by the preceding full cycle of this same millennial-scale climatic oscillation, which in this case brought the world the Roman Warm Period and subsequent Dark Ages Cold Period, as demonstrated by the work of McDermott et al. (2001), who derived a detailed climate history of the entire Holocene from a high-resolution oxygen isotope study of a well-dated stalagmite found in a cave in southwest Ireland.
This new interpretive description of the history of the Maya comes to us courtesy of Haug et al. (2003), who used the study of Haug et al. (2001) as a springboard for their more recent work. Based on a study of titanium and iron concentrations in an ocean sediment core extracted from the Cariaco Basin on the Northern Shelf of Venezuela, the earlier of the two studies developed a hydrologic history of the entire Holocene for Mesoamerica and northern tropical South America. Then, based on a more detailed study of the titanium content of a smaller portion of this record, the more recent of the two studies developed a hydrologic history of pertinent portions of the extended record that yielded, in the words of the authors, "roughly bi-monthly resolution and clear resolution of the annual signal."
How is this detailed hydrologic history related to the history of the Mayas? Haug et al. (2003) tell us that the Pre-Classic period of Maya civilization flourished "before about 150 A.D.," which, according to the climate history of McDermott et al., corresponds to the latter portion of the Roman Warm Period (RWP). However, during the transition to the Dark Ages Cold Period (DACP), which was accompanied by a slow but long decline in precipitation, Haug et al. report that "the first documented historical crisis hit the lowlands, which led to the 'Pre-Classic abandonment' (Webster, 2002) of major cities."
This crisis occurred during the first intense multi-year drought of the RWP-to-DACP transition, which was centered on about the year 250 A.D. Although the drought was devastating to the Maya, Haug et al. report that when it was over, "populations recovered, cities were reoccupied, and Maya culture blossomed in the following centuries during the so-called Classic period."
Ultimately, however, there came a time of total reckoning, between about 750 and 950 A.D., during what Haug et al. determined was the driest interval of the entire first millennium A.D., when they report that "the Maya experienced a demographic disaster as profound as any other in human history," in response to a number of other intense multi-year droughts. During this Terminal Classic Collapse, as it is called, Haug et al. say that "many of the densely populated urban centers were abandoned permanently, and Classic Maya civilization came to an end."
As they assess the significance of these several observations near the end of their paper, Haug et al. conclude that, "given the perspective of our long time series, it would appear that the droughts we have highlighted were the most severe to affect this region in the first millennium A.D." Although some of these spectacular droughts were "brief," lasting only between three and nine years, Haug et al. note "they occurred during an extended period of reduced overall precipitation that may have already pushed the Maya system to the verge of collapse," which suggests to us that these droughts within dry periods were likely the proverbial straws that broke the camel's back.
The Mayan civilization thus faded away sometime during the transition from the Dark Ages Cold Period to the Medieval Warm Period, when the Vikings established their historic settlement on Greenland. Then came the Little Ice Age, which just as quickly led to the Vikings' demise in that part of the world. But this last cold node of the planet's millennial-scale climatic oscillation must have also led to hard times for the people of Mesoamerica and northern tropical South America; for according to the data of Haug et al., the Little Ice Age produced by far the lowest precipitation regime (of several hundred years duration) of the last two millennia in that part of the world.
There are a number of conclusions that may be drawn from these several observations. One is that both climatic and human history tend to repeat themselves. Another is that the millennial-scale climatic oscillation, which manifests itself throughout glacial and interglacial periods alike, does so totally independently of what the atmosphere's CO2 concentration is doing. Yet another is that the two nodes of this climate cycle, of which the Medieval Warm Period and Little Ice Age are typical, are truly global phenomena, manifesting themselves in some parts of the world primarily in terms of thermal extremes and in other parts of the world primarily in terms of moisture extremes. Most important of all is that all of these conclusions clearly demonstrate there was nothing abnormal or unusual about the warming of the 20th century, which was simply the natural transition from cool-node to warm-node global climate that was only to be expected with the scheduled -- and right on time -- demise of the Little Ice Age.
| Sherwood, Keith and Craig Idso |
References
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Haug, G.H., Gunther, D., Peterson, L.C., Sigman, D.M., Hughen, K.A. and Aeschlimann, B. 2003. Climate and the collapse of Maya civilization. Science 299: 1731-1735.
Haug, G.H., Hughen, K.A., Sigman, D.M., Peterson, L.C. and Rohl, U. 2001. Southward migration of the intertropical convergence zone through the Holocene. Science 293: 1304-1308.
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Webster, D. 2002. The Fall of the Ancient Maya. Thames and Hudson, London, UK.