Many researchers have examined historical proxy temperature changes over the past millennium in an attempt to quantify the magnitude, frequency and causes of natural climate variability. However, temperature is not the only measure of climate; and few studies have examined the ranges and rates of change of hydrologic and atmospheric circulation properties; yet changes in these factors are important because they are involved in more than half of the planet's poleward transfer of heat (Peixoto and Oort, 1992). Hence, in what follows we review some studies that have taken a much broader look at global climate change based on a wide spectrum of observations and climatic phenomena, emphasizing what they reveal about the Little Ice Age.
Mayewski et al. (2004) examined some fifty globally distributed paleoclimate records in search of evidence for what they call rapid climate change (RCC) over the Holocene. This terminology is not to be confused with the rapid climate changes typical of glacial periods, but is used in the place of what the authors call the "more geographically or temporally restrictive terminology such as 'Little Ice Age' and 'Medieval Warm Period'." Hence, RCC events, as they also call them, are multi-century periods of time characterized by extremes of thermal and/or hydrological properties, rather than the much shorter periods of time during which the changes that led to these different climatic states took place.
Within this context Mayewski et al. identified six RCCs that occurred during the Holocene over the following periods: 9000-8000, 6000-5000, 4200-3800, 3500-2500, 1200-1000 and 600-150 cal yr BP, the last two of which were the "globally distributed" Medieval Warm Period and Little Ice Age, respectively. In speaking further of these two periods, they say that "the short-lived 1200-1000 cal yr BP RCC event coincided with the drought-related collapse of Maya civilization and was accompanied by a loss of several million lives (Hodell et al., 2001; Gill, 2000), while the collapse of Greenland's Norse colonies at ~600 cal yr BP (Buckland et al., 1995) coincides with a period of polar cooling."
With respect to the causes of these and the other Holocene RCCs, the international team of sixteen scientists says that "of all the potential climate forcing mechanisms, solar variability superimposed on long-term changes in insolation (Bond et al., 2001; Denton and Karlen, 1973; Mayewski et al., 1997; O'Brien et al., 1995) seems to be the most likely important forcing mechanism." In addition, they note that "negligible forcing roles are played by CH4 and CO2," and they say that "changes in the concentrations of CO2 and CH4 appear to have been more the result than the cause of the RCCs."
In light of these findings, it is becoming ever more clear that the millennial-scale oscillation of climate that has reverberated throughout the Holocene is indeed the result of similar-scale oscillations in some aspect of solar activity. Consequently, Mayewski et al. suggest that "significantly more research into the potential role of solar variability is warranted, involving new assessments of potential transmission mechanisms to induce climate change and potential enhancement of natural feedbacks that may amplify the relatively weak forcing related to fluctuations in solar output." We couldn't agree more, for until these mechanisms have been elucidated to everyone's satisfaction, the world's climate alarmists will continue to ignore the mountains of evidence that link millennial-scale climate change with similar-scale solar variability, pushing the adoption of wrong-headed energy policies to the serious detriment of man and nature alike.
Maasch et al. (2005) examined changes in eight well-dated high-resolution non-temperature records over the past two millennia: (1) K+ concentrations from the GISP2 ice core in Greenland, (2) Na+ concentrations from the Siple Dome ice core in Antarctica, (3) percent Ti from an ocean sediment core in the Cariaco basin, (4) Fe intensity from a marine core near the coast of mid-latitude Chile, (5) oxygen isotope fractions from Punta Laguna near the Yucatan, (6) carbon isotope data from a speleothem in Makapansgat, South Africa, (7) percent of shallow water diatoms from Lake Victoria, and (8) lake levels from Lake Naivasha in equatorial Africa. These eight data sets were then compared with a history of atmospheric 14C, a proxy for solar variability obtained from tree rings, in order to ascertain what, if any, solar influence operated on these parameters.
Comparison of the 14C solar proxy data with the eight climate-related data sets revealed that over the past 2000 years there has been, in the words of the researchers, a "strong association between solar variability and globally distributed climate change." This "remarkable coherence" among the data sets was particularly noticeable in the Medieval Warm Period to Little Ice Age transition, as well as throughout the Little Ice Age. Hence, as we continue to report here at CO2 Science, and contrary to the strident claims of climate alarmists, the results of this and the preceding study clearly suggest that the Medieval Warm Period and Little Ice Age were indeed global phenomena that were likely the products of natural climate variability driven by changes in solar activity, which further implies that the Current Warm Period is merely another of the long line of RCCs that has characterized the Holocene, perhaps made more dramatic by the fact that it represents the recovery of the planet from the coldest period of the current interglacial, i.e., the Little Ice Age.
References
Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M.N., Showers, W., Hoffmann, S., Lotti-Bond, R., Hajdas, I. and Bonani, G. 2001. Persistent solar influence on North Atlantic climate during the Holocene. Science 294: 2130-2136.
Buckland, P.C., Amorosi, T., Barlow, L.K., Dugmore, A.J., Mayewski, P.A., McGovern, T.H., Ogilvie, A.E.J., Sadler, J.P. and Skidmore, P. 1995. Bioarchaeological evidence and climatological evidence for the fate of Norse farmers in medieval Greenland. Antiquity 70: 88-96.
Denton, G.H. and Karlen, W. 1973. Holocene climatic variations: their pattern and possible cause. Quaternary Research 3: 155-205.
Gill, R.B. 2000. The Great Maya Droughts: Water, Life, and Death. University of New Mexico Press, Albuquerque, New Mexico, USA.
Maasch, K.A., Mayewski, P.A., Rohling, E.J., Stager, J.C., Karlén, W., Meeker, L.D. and Meyerson, E.A. 2005. A 2000-year context for modern climate change. Geografiska Annaler 87 A: 7-15.
Mayewski, P.A., Meeker, L.D., Twickler, M.S., Whitlow, S., Yang, Q., Lyons, W.B. and Prentice, M. 1997. Major features and forcing of high-latitude northern hemisphere atmospheric circulation using a 110,000-year-long glaciochemical series. Journal of Geophysical Research 102: 26,345-26,366.
Mayewski, P.A., Rohling, E.E., Stager, J.C., Karlen, W., Maasch, K.A., Meeker, L.D., Meyerson, E.A., Gasse, F., van Kreveld, S., Holmgren, K., Lee-Thorp, J., Rosqvist, G. Rack, F., Staubwasser, M., Schneider, R.R. and Steig, E.J. 2004. Holocene climate variability. Quaternary Research 62: 243-255.
O'Brien, S.R., Mayewski, P.A., Meeker, L.D., Meese, D.A., Twickler, M.S. and Whitlow, S.E. 1995. Complexity of Holocene climate as reconstructed from a Greenland ice core. Science 270: 1962-1964.
Peixoto, J.P. and Oort, A.H. 1992. Physics of Climate. American Institute of Physics, New York.
Last updated 17 May 2006