Brown et al. (1999) studied siliciclastic sediment grain size, planktonic foraminiferal and pteropod relative frequencies, and the carbon and oxygen isotopic compositions of two species of planktonic foraminifera in cored sequences of hemipelagic muds deposited over the past 5300 years in the northern Gulf of Mexico for evidence of variations in Mississippi River outflow characteristics over this time period. The results of their research indicated the occurrence of large megafloods - which they describe as having been "almost certainly larger than historical floods in the Mississippi watershed" - at 4700, 3500, 3000, 2500, 2000, 1200 and 300 years before present. These fluvial events, in their estimation, were likely "episodes of multidecadal duration," spawned by an export of extremely moist gulf air to midcontinental North America that was driven by naturally-occurring same-time-scale oscillations in Gulf of Mexico ocean currents.

Think what would happen if, in the words of the three researchers, the United States began to experience a multidecadal episode of "historically unprecedented precipitation and flooding in the Mississippi watershed." Before it was even in full-swing, the IPCC-inspired media would probably have driven the U.S. Senate to unanimous ratification of a dozen Kyoto protocols. But would they have been right to do so? Such an occurrence of "historically unprecedented" extreme weather sure sounds like what the climate models are predicting to occur as a consequence of the ongoing rise in the air's CO2 content; but it is clear that these particular extreme events were in no way related to variations in atmospheric CO2 concentration, as they occurred over a period of near-constancy in this atmospheric property. And if it's happened before, it can happen again. How easy it would be, therefore, to make a monumental mistake in our stewardship of the planet! Brown et al.'s study thus reminds us that we must not to rush to judgment in matters of such great importance.

Hidalgo et al. (2000) used a new form of principal components analysis to reconstruct a history of streamflow in the Upper Colorado River Basin from information obtained from tree-ring data, after which they compared their results with the streamflow reconstruction of Stockton and Jacoby (1976). In doing so, they found their results were similar to those of the earlier 1976 study, but that their newer reconstruction responded with better fidelity to periods of below-average streamflow or regional drought. Hence, it was easier for them to see there had been "a near-centennial return period of extreme drought events in this region," going all the way back to the early 1500s, providing another demonstration of the cyclical nature of climate.

Also of great importance, Hidalgo et al.'s work provided additional evidence for the existence of past droughts that surpassed the worst of the 20th century. Consequently, it would not be surprising to see such a drought occur again; and if it lasted as long as such droughts have lasted in the past, it would likely be claimed by climate alarmists to have been caused by CO2-induced global warming. However, such need not be the case, since the most severe droughts of the past 500 years occurred at times when the air temperature and atmospheric CO2 concentration were much lower than they are today; and, hence, they could just as easily occur now without any help from rising air temperatures and CO2 concentrations as they did then.

Working in the same general area a few years later, Woodhouse et al. (2006) generated updated proxy reconstructions of water-year streamflow for four key streamflow gauges in the Upper Colorado River Basin (Green River at Green River, Utah; Colorado near Cisco, Utah; San Juan near Bluff, Utah; and Colorado at Lees Ferry, Arizona), "using an expanded tree-ring network and longer calibration records than in previous efforts." By these means they determined that the major drought of 2000-2004, "as measured by 5-year running means of water-year total flow at Lees Ferry ... is not without precedence in the tree ring record," and that "average reconstructed annual flow for the period 1844-1848 was lower." They also report that "two additional periods, in the early 1500s and early 1600s, have a 25% or greater chance of being as dry as 1999-2004," and that six other periods "have a 10% or greater chance of being drier." In addition, their work revealed that "longer duration droughts have occurred in the past," and that "the Lees Ferry reconstruction contains one sequence each of six, eight, and eleven consecutive years with flows below the 1906-1995 average."

"Overall," in the words of the three researchers, "these analyses demonstrate that severe, sustained droughts are a defining feature of Upper Colorado River hydroclimate." In fact, they conclude that "droughts more severe than any 20th to 21st century event occurred in the past," meaning the preceding few centuries. Interestingly, this finding is just the opposite of what climate alarmists would have one believe, i.e., that global warming brings with it more frequent and longer-lasting droughts of much greater severity. In stark contrast to this climate-model-based claim, the real-world record of the USA's Upper Colorado River Basin suggests that such droughts were more strongly associated with the much colder temperatures of the Little Ice Age.

Expanding the scope of investigation just a bit, and noting that "paleoclimatic studies indicate that the natural variability in 20th century [streamflow] gage records is likely only a subset of the full range of natural variability," while citing in support of this statement the studies of Stockton and Jacoby (1976), Smith and Stockton (1981), Meko et al. (2001) and Woodhouse (2001), Woodhouse and Lukas (2006) developed "a network of 14 annual streamflow reconstructions, 300-600 years long, for gages in the Upper Colorado and South Platte River basins in Colorado generated from new and existing tree-ring chronologies." The results indicated, as they describe it, that "the 20th century gage record does not fully represent the range of streamflow characteristics seen in the prior two to five centuries." Of greatest significance, in this regard, was probably the fact that "multi-year drought events more severe than the 1950s drought have occurred," and that "the greatest frequency of extreme low flow events occurred in the 19th century," with a "clustering of extreme event years in the 1840s and 1850s."

These findings are of great importance to water resource planners. In addition, they provide a huge "security net" for climate-alarmists who predict the occurrence of both extreme droughts and floods in response to anthropogenic-produced increases in air temperature. This "assurance of fulfillment" of their prophetic pronouncements arises from the fact that historic streamflow variability is "only a subset of the full range of natural variability." This being the case, it can be appreciated that predictions of abnormal perturbations (relative to the past hundred or so years) of both wet and dry conditions likely will see fulfillment some time in the future ... but it need not be due to CO2-induced global warming, for atmospheric CO2 concentration and air temperature were both significantly lower than they are now - and will be throughout the 21th century - during the prior centuries of the Little Ice Age, when the greater natural variability in streamflow detected by Woodhouse and others occurred.

Working in an adjacent region of the western United States, Carson and Munroe (2005) used tree-ring data collected by Stockton and Jacoby (1976) from the Uinta Mountains of Utah to reconstruct mean annual discharge in the Ashley Creek watershed for the period 1637 to 1970. As a result of their efforts, significant persistent departures from the long-term mean were noted throughout the 334-year record of reconstructed streamflow. The periods 1637-1691 and 1741-1897 experienced reduced numbers of extremely large flows and increased numbers of extremely small flows, indicative of persistent drought or near-drought conditions. In contrast, there was an overall abundance of extremely large flows and relatively few extremely small flows during the periods 1692-1740 and 1898-1945, indicative of wetter conditions. These results provide yet another indication of the cyclical nature of climate. In addition, they provide still more evidence for the existence of past periods of extreme wetness and dryness with accompanying floods and droughts, when both air temperatures and atmospheric CO2 concentrations were much lower than they were throughout the bulk of the 20th century.

Working entirely within Canada Campbell (2002) analyzed the grain sizes of sediment cores obtained from Pine Lake, Alberta, to provide a non-vegetation-based high-resolution record of climate variability for this part of North America over the past 4000 years. This research effort revealed the existence of periods of both increasing and decreasing grain size (a proxy for moisture availability) throughout the 4000-year record at decadal, centennial and millennial time scales. The most predominant departures included several-centuries-long epochs that corresponded to the Little Ice Age (about AD 1500-1900), the Medieval Warm Period (about AD 700-1300), the Dark Ages Cold Period (about BC 100 to AD 700) and the Roman Warm Period (about BC 900-100). In addition, a standardized median grain-size history revealed that the highest rates of stream discharge during the past 4000 years occurred during the Little Ice Age approximately 300-350 years ago. During this time, grain sizes were about 2.5 standard deviations above the 4000-year mean. In contrast, the lowest rates of streamflow were observed around AD 1100, when median grain sizes were nearly 2 standard deviations below the 4000-year mean, while most recently, grain size over the past 150 years has generally remained above average.

The Pine Lake sediment record convincingly demonstrates the reality of the non-CO2-induced millennial-scale climatic oscillation that has alternately brought several-century-long periods of dryness and wetness to the southern Alberta region of North America during concomitant periods of relative global warmth and coolness, respectively, revealing a relationship that was not evident in the prior streamflow studies reviewed here that did not stretch all the way back in time to the Medieval Warm Period. It also demonstrates there is nothing unusual about the region's current moisture status, which suggests that the planet may still have a bit of warming to do before the Current Warm Period is fully developed.

In summing up the gist of what was learned by the studies described in this Summary, it can be said they provide no support at all for the climate-alarmist contention that CO2-induced global warming will lead to the occurrence of more severe and longer-lasting droughts and floods throughout North America. These climatic phenomena clearly possess the potential to occur on their own without any help from the "twin evils" of the radical environmentalist movement. And occur again they likely will, if the past is truly prologue to the future, even though hydrologic variability appears to have been somewhat muted throughout the 20th century compared to previous centuries, in contradiction of what climate alarmists typically contend should be the case.

References
Brown, P., Kennett, J.P. and Ingram B.L. 1999. Marine evidence for episodic Holocene megafloods in North America and the northern Gulf of Mexico. Paleoceanography 14: 498-510.

Campbell, C. 2002. Late Holocene lake sedimentology and climate change in southern Alberta, Canada. Quaternary Research 49: 96-101.

Carson, E.C and Munroe, J.S. 2005. Tree-ring based streamflow reconstruction for Ashley Creek, northeastern Utah: Implications for palaeohydrology of the southern Uinta Mountains. The Holocene 15: 602-611.

Hidalgo, H.G., Piechota, T.C. and Dracup, J.A. 2000. Alternative principal components regression procedures for dendrohydrologic reconstructions. Water Resources Research 36: 3241-3249.

Meko, D.M., Therrell, M.D., Baisan, C.H. and Hughes, M.K. 2001. Sacramento River flow reconstructed to A.D. 869 from tree rings. Journal of the American Water Resources Association 37: 1029-1039.

Smith, L.P. and Stockton, C.W. 1981. Reconstructed stream flow for the Salt and Verde Rivers from tree-ring data. Water Resources Bulletin 17: 939-947.

Stockton, C.W. and Jacoby Jr., G.C. 1976. Long-term surface-water supply and streamflow trends in the Upper Colorado River Basin based on tree-ring analysis. Lake Powell Research Project Bulletin 18, Institute of Geophysics and Planetary Physics, University of California, Los Angeles.

Woodhouse, C.A. 2001. Tree-ring reconstruction of mean annual streamflow for Middle Boulder Creek, Colorado, USA. Journal of the American Water Resources Association 37: 561-570.

Woodhouse, C.A., Gray, S.T. and Meko, D.M. 2006. Updated streamflow reconstructions for the Upper Colorado River Basin. Water Resources Research 42: 10.1029/2005WR004455.

Woodhouse, C.A. and Lukas, J.J. 2006. Multi-century tree-ring reconstructions of Colorado streamflow for water resource planning. Climatic Change 78: 293-315.