Floods and solar variability
From ClimateWiki
From Climate Change Reconsidered, a work of the Nongovernmental International Panel on Climate Change
The IPCC claims that floods will become more variable and extreme as a result of CO2-induced global warming. Research shows modern flood frequency and severity fall well within the range of natural variability. The analysis in this section is limited to the issue of attribution, specifically investigating the influence of the sun on floods.
Contents |
Research
According to Starkel (2002), in general, more extreme fluvial activity, of both the erosional and depositional type, is associated with cooler climates. “Continuous rains and high-intensity downpours,” writes Starkel, were most common during the Little Ice Age. Such “flood phases,” the researcher reports, “were periods of very unstable weather and frequent extremes of various kinds.” More related to the present discussion, Starkel also notes that “most of the phases of high frequency of extreme events during the Holocene coincide with the periods of declined solar activity.”
Noren et al. (2002) extracted sediment cores from 13 small lakes distributed across a 20,000-km2 region in Vermont and eastern New York, after which several techniques were used to identify and date terrigenous in-wash layers that depict the frequency of storm-related floods. Results of the analysis showed that “the frequency of storm-related floods in the northeastern United States has varied in regular cycles during the past 13,000 years (13 kyr), with a characteristic period of about 3 kyr.” There were four major storminess peaks during this period; they occurred approximately 2.6, 5.8, 9.1, and 11.9 kyr ago, with the most recent upswing in storminess beginning “at about 600 yr BP [before present], coincident with the beginning of the Little Ice Age.” With respect to the causative factor(s) behind the cyclic behavior, Noren et al. state that the pattern they observed “is consistent with long-term changes in the average sign of the Arctic Oscillation [AO],” further suggesting that “changes in the AO, perhaps modulated by solar forcing, may explain a significant portion of Holocene climate variability in the North Atlantic region.”
Also working in the United States, Schimmelmann et al. (2003) identified conspicuous gray clay-rich flood deposits in the predominantly olive varved sediments of the Santa Barbara Basin off the coast of California, which they accurately dated by varve-counting. Analysis of the record revealed six prominent flood events that occurred at approximately AD 212, 440, 603, 1029, 1418, and 1605, “suggesting,” in their words, “a quasi-periodicity of ~200 years,” with “skipped” flooding just after AD 800, 1200, and 1800. They further note that “the floods of ~AD 1029 and 1605 seem to have been associated with brief cold spells,” that “the flood of ~AD 440 dates to the onset of the most unstable marine climatic interval of the Holocene (Kennett and Kennett, 2000),” and that “the flood of ~AD 1418 occurred at a time when the global atmospheric circulation pattern underwent fundamental reorganization at the beginning of the ‘Little Ice Age’ (Kreutz et al., 1997; Meeker and Mayewski, 2002).” Lastly, they report that “the quasi-periodicity of ~200 years for southern California floods matches the ~200-year periodicities found in a variety of high-resolution palaeoclimate archives and, more importantly, a c.208-year cycle of solar activity and inferred changes in atmospheric circulation.”
As a result of these findings, Schimmelmann et al. “hypothesize that solar-modulated climatic background conditions are opening a ~40-year window of opportunity for flooding every ~200 years,” and that “during each window, the danger of flooding is exacerbated by additional climatic and environmental cofactors.” They also note that “extrapolation of the ~200-year spacing of floods into the future raises the uncomfortable possibility for historically unprecedented flooding in southern California during the first half of this century.” When such flooding occurs, there will be no need to suppose it came as a consequence of what the IPCC calls the unprecedented warming of the past century.
References
Climate Change Reconsidered: Website of the Nongovernmental International Panel on Climate Change. http://www.nipccreport.org/archive/archive.html
Kennett, D.J. and Kennett, J.P. 2000. Competitive and cooperative responses to climatic instability in coastal southern California. American Antiquity 65: 379-395.
Kreutz, K.J., Mayewski, P.A., Meeker, L.D., Twickler, M.S., Whitlow, S.I. and Pittalwala, I.I. 1997. Bipolar changes in atmospheric circulation during the Little Ice Age. Science 277: 1294-1296.
Meeker, L.D. and Mayewski, P.A. 2002. A 1400-year high-resolution record of atmospheric circulation over the North Atlantic and Asia. The Holocene 12: 257-266.
Noren, A.J., Bierman, P.R., Steig, E.J., Lini, A. and Southon, J. 2002. Millennial-scale storminess variability in the northeastern Unites States during the Holocene epoch. Nature 419: 821-824.
Schimmelmann, A., Lange, C.B. and Meggers, B.J. 2003. Palaeoclimatic and archaeological evidence for a 200-yr recurrence of floods and droughts linking California, Mesoamerica and South America over the past 2000 years. The Holocene 13: 763-778.
Starkel, L. 2002. Change in the frequency of extreme events as the indicator of climatic change in the Holocene (in fluvial systems). Quaternary International 91: 25-32.
