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

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thickness sediment records, five tree-ring width records, five tree-ring maximum latewood
density records, and one δ 13 C tree-ring record, but not including tree-ring width records from
arid and semi-arid regions, since they may have been affected by drought stress, and they may
not show a linear response to warming if higher summer temperatures also reduce the
availability of water, as suggested by the work of D’Arrigo et al. (2006) and Loehle (2009).
The results of Ljungqvist’s stellar efforts are depicted in the following figure.
Reconstructed extra-tropical (30-90°N) mean decadal temperature variations relative to the
1961-1990 mean of the variance-adjusted 30-90°N CRUTEM3+HadSST2 instrumental
temperature data of Brohan et al. (2006) and Rayner et al. (2006), showing the approximate
locations of the Roman Warm Period (RWP), Dark Ages Cold Period (DACP), Medieval Warm
Period (MWP), Little Ice Age (LIA) and Current Warm Period (CEP). Adapted from Ljungqvist
(2010).
In discussing this temperature history, Ljungqvist states that it depicts “a Roman Warm Period
c. AD 1-300, a Dark Age Cold Period c. AD 300-800, a Medieval Warm Period c. AD 800-1300
and a Little Ice Age c. AD 1300-1900, followed by the twentieth-century warming.” These
alternating warm/cold periods, in his words, “probably represent the much discussed quasicyclical
c. 1470 ± 500-year Bond Cycles (Bond and Lotti, 1995; O’Brien et al., 1995; Bond et al.,
1997, 2001; Oppo, 1997),” which “affected both Scandinavia and northwest North America
synchronically (Denton and Karlen, 1973)” and have “subsequently also been observed in China
(Hong et al., 2009a,b), the mid-latitude North Pacific (Isono et al., 2009) and in North America
(Viau et al., 2006), and have been shown to very likely have affected the whole Northern
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