Carbon Dioxide and Earth's Future Pursuing the ... - Magazooms

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part of the response of the global climate to persistent La Niña-like conditions in the tropical
Pacific Ocean.” And this conclusion contradicts the climate-alarmists’ primary but unfounded
claim that the world is currently warmer than it has been at any other time over the past two
millennia or more.
It is instructive to learn how Native Americans were impacted by different dry phases of the
Medieval Warm Period, which was the subject of the study of Benson et al. (2007), who
reviewed and discussed possible impacts of early-11th-, middle-12th-, and late-13th-century
droughts on three Native American cultures that occupied parts of the western United States
(Anasazi, Fremont, Lovelock) plus another culture that occupied parts of southwestern Illinois
(Cahokia). They report, in this regard, that “population declines among the various Native
American cultures were documented to have occurred either in the early-11th, middle-12th, or
late-13th centuries” -- AD 990-1060, 1135-1170, and 1276-1297, respectively -- and that “really
extensive droughts impacted the regions occupied by these prehistoric Native Americans during
one or more of these three time periods.” In particular, they say the middle-12th-century
drought “had the strongest impact on the Anasazi and Mississippian Cahokia cultures,” noting
that “by AD 1150, the Anasazi had abandoned 85% of their great houses in the Four Corners
region and most of their village sites, and the Cahokians had abandoned one or more of their
agricultural support centers, including the large Richland farming complex.” In addition, they
write that “the sedentary Fremont appear to have abandoned many of their southern area
habitation sites in the greater Unita Basin area by AD 1150 as well as the eastern Great Basin
and the Southern Colorado Plateau,” so that “in some sense, the 13th century drought may
simply have ‘finished off’ some cultures that were already in decline.” Lastly, they state that
these “major reductions in prehistoric Native American habitation sites/population” occurred
during “anomalously warm” climatic conditions, which characterized the Medieval Warm
Period throughout much of the world at that particular time. And the fact that the deadly
North American droughts of the MWP have never been equaled throughout all the ensuing
years argues strongly that what Benson et al. call the anomalous warmth of that period has also
“never been equaled throughout all the ensuing years,” which further suggests (since the air’s
CO2 content was so much less during the MWP than it is now) that the considerably lesser
warmth of today need not in any way be related to the much higher CO2 concentration of
earth’s current atmosphere.
At this point, we have covered large portions of the United States plus other parts of North
America; and we will discuss a few additional studies that consider this larger area, beginning
with that of Stahle et al. (2000). This team of eight researchers developed a long-term history
of drought over North America from reconstructions of the Palmer Drought Severity Index
(PDSI), based on analyses of many lengthy tree-ring records; and in doing so, they found that
the 1930s Dust Bowl drought in the United States -- which was the nation’s most severe,
sustained, and wide-spread drought of the past 300 years -- was eclipsed in all three of these
categories by a 16th-century “megadrought.” Although this drought has been mentioned in
some of the prior studies we have reviewed, it is worth noting the additional information that
Stahle et al. present.
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