We begin with the study of Holzhauser et al. (2005), who presented high-resolution records of variations in glacier size in the Swiss Alps together with lake-level fluctuations in the Jura mountains, the northern French Pre-Alps and the Swiss Plateau in developing a 3500-year climate history of west-central Europe, beginning with an in-depth analysis of the Great Aletsch glacier, which is the largest of all glaciers located in the European Alps.

Near the beginning of the time period studied, the three researchers report that "during the late Bronze Age Optimum from 1350 to 1250 BC, the Great Aletsch glacier was approximately 1000 m shorter than it is today," noting that "the period from 1450 to 1250 BC has been recognized as a warm-dry phase in other Alpine and Northern Hemisphere proxies (Tinner et al., 2003)." Then, after an intervening unnamed cold-wet phase, when the glacier grew in both mass and length, they say that "during the Iron/Roman Age Optimum between c. 200 BC and AD 50," which is perhaps better known as the Roman Warm Period, the glacier again retreated and "reached today's extent or was even somewhat shorter than today." Next came the Dark Ages Cold Period, which they say was followed by "the Medieval Warm Period, from around AD 800 to the onset of the Little Ice Age around AD 1300," which latter cold-wet phase was "characterized by three successive [glacier length] peaks: a first maximum after 1369 (in the late 1370s), a second between 1670 and 1680, and a third at 1859/60," following which the glacier began its latest and still-ongoing recession in 1865. In addition, they state that written documents from the fifteenth century AD indicate that at some time during that hundred-year interval "the glacier was of a size similar to that of the 1930s," which latter period in many parts of the world was as warm as, or even warmer than, it is today.

Data pertaining to the Gorner glacier (the second largest of the Swiss Alps) and the Lower Grindelwald glacier of the Bernese Alps tell much the same story, as Holzhauser et al. report that these glaciers and the Great Aletsch glacier "experienced nearly synchronous advances" throughout the study period.

With respect to what was responsible for the millennial-scale climatic oscillation that produced the alternating periods of cold-wet and warm-dry conditions that fostered the similarly-paced cycle of glacier growth and retreat, the Swiss and French scientists report that "glacier maximums coincided with radiocarbon peaks, i.e., periods of weaker solar activity," which in their estimation "suggests a possible solar origin of the climate oscillations punctuating the last 3500 years in west-central Europe, in agreement with previous studies (Denton and Karlen, 1973; Magny, 1993; van Geel et al., 1996; Bond et al., 2001)." And to underscore that point, they conclude their paper by stating that "a comparison between the fluctuations of the Great Aletsch glacier and the variations in the atmospheric residual ¹⁴C records supports the hypothesis that variations in solar activity were a major forcing factor of climate oscillations in west-central Europe during the late Holocene."

In another study of paleoclimate in western Europe, Mauquoy et al. (2002a) extracted peat monoliths from ombrotrophic mires at Lille Vildmose, Denmark (56°50'N, 10°15'E) and Walton Moss, UK (54°59'N, 02°46'W), which sites, being separated by about 800 km "offer the possibility of detecting supraregional changes in climate." From these monoliths, vegetative macrofossils were extracted at contiguous 1-cm intervals and examined using light microscopy. Where increases in the abundances of Sphagnum tenellum and Sphagnum cuspidatum were found, a closely spaced series of ¹⁴C AMS-dated samples immediately preceding and following each increase was used to "wiggle-match" date them (van Geel and Mook, 1989), thereby enabling comparison of the climate-induced shifts with the history of ¹⁴C production during the Holocene.

Results indicated the existence of a climatic deterioration that marked the beginning of a period of inferred cool, wet conditions that correspond fairly closely in time with the Wolf, Sporer and Maunder Minima of solar activity, as manifest in contemporary δ¹⁴C data. The authors further reported that "these time intervals correspond to periods of peak cooling in 1000-year Northern Hemisphere climate records," adding to the "increasing body of evidence" that "variations in solar activity may well have been an important factor driving Holocene climate change."

Two years later, Mauquoy et al. (2004) reviewed the principles of ¹⁴C wiggle-match dating, its limitations, and the insights it has provided about the timing and possible causes of climate change during the Holocene. Based upon their review, the authors stated that "analyses of microfossils and macrofossils from raised peat bogs by Kilian et al. (1995), van Geel et al. (1996), Speranza et al. (2000), Speranza (2000) and Mauquoy et al. (2002a, 2002b) have shown that climatic deteriorations [to cooler and wetter conditions] occurred during periods of transition from low to high delta ¹⁴C (the relative deviation of the measured ¹⁴C activity from the standard after correction for isotope fractionation and radioactive decay; Stuiver and Polach, 1977)." This close correspondence, in the words of the authors, again suggests that "changes in solar activity may well have driven these changes during the Bronze Age/Iron Age transition around c. 850 cal. BC (discussed in detail by van Geel et al., 1996, 1998, 1999, 2000) and the 'Little Ice Age' series of palaeoclimatic changes."

Working with a marine sediment core retrieved from the southern Norwegian continental margin, Berstad et al. (2003) reconstructed sea surface temperatures (SSTs) from δ¹⁸O data derived from the remains of the planktonic foraminifera species Neogloboquadrina pachyderma (summer temperatures) and Globigerina bulloides (spring temperatures). Among other things, the researchers' work depicted a clear connection between the cold temperatures of the Little Ice Age and the reduced solar activity of the concomitant Maunder and Sporer solar minima, as well as between the warm temperatures of the most recent 70 years and the enhanced solar activity of the concomitant Modern solar maximum, which they clearly implied in their paper is a causative connection, as is also implied by the recent sunspot number reconstruction of Usoskin et al. (2003). Hence, the work of Berstad et al. adds to the ever-accumulating mountain of evidence that argues strongly against a human-induced cause of 20th-century warming, and strongly for a solar one.

Nearby in Finland, Haltia-Hovi et al. (2007) extracted sediment cores from beneath the 0.7-m-thick ice platform on Lake Lehmilampi (63°37'N, 29°06'E) in North Karelia, eastern Finland, after which they identified and counted the approximately 2000 annual varves contained in the cores and measured their individual thicknesses and mineral and organic matter contents. These climate-related data were then compared with residual δ¹⁴C data derived from tree rings, which serve as a proxy for solar activity.

According to Haltia-Hovi et al., their "comparison of varve parameters (varve thickness, mineral and organic matter accumulation) and the activity of the sun, as reflected in residual Δ¹⁴C [data] appears to coincide remarkably well in Lake Lehmilampi during the last 2000 years, suggesting solar forcing of the climate," as depicted in the figure below for the case of varve thickness. What is more, to further quote the Finnish researchers, the low deposition rate of mineral matter in Lake Lehmilampi in AD 1060-1280 [shown in another of their figures] "possibly implies mild winters with a short ice cover period during that time with minor snow accumulation interrupted by thawing periods." Likewise, they say that the low accumulation of organic matter during this period [also shown in another of their figures] "suggests a long open water season and a high decomposition rate of organic matter." Consequently, since the AD 1060-1280 period shows by far the lowest levels of both mineral and organic matter content, and since "the thinnest varves of the last 2000 years were deposited during [the] solar activity maxima in the Middle Ages," it is difficult not to conclude that that period was likely the warmest of the past two millennia in the part of the world studied by the three scientists.

Hanna et al. (2004) analyzed several climatic variables over the past century in Iceland in an effort to determine if there is "possible evidence of recent climatic changes" in that cold island nation. Results indicated that for the period 1923-2002, no trend was found in either annual or monthly sunshine data. Similar results were reported for annual and monthly pressure data, which exhibited semi-decadal oscillations throughout the 1820-2002 period but no significant upward or downward trend. Precipitation, on the other hand, appears to have increased slightly, although the researchers question the veracity of the trend, citing a number of biases that have potentially corrupted the data base.

With respect to temperature, however, Hanna et al. indicate that of the handful of locations they examined for this variable, all stations experienced a net warming since the mid-1800s. The warming, however, was not linear over the entire time period. Rather, temperatures rose from their coldest levels in the mid-1800s to their warmest levels in the 1930s, whereupon they remained fairly constant for approximately three decades. Then came a period of rapid cooling, which ultimately gave way to the warming of the 1980s and 90s. However, it is important to note that the warming of the past two decades has not resulted in temperatures rising above those observed in the 1930s. In this point the authors are particularly clear, stating emphatically that "the 1990s was definitely not the warmest decade of the 20th century in Iceland, in contrast to the Northern Hemisphere land average." In fact, a linear trend fit to the post-1930 data would actually indicate an overall temperature decrease since that time.

As for what may be responsible for the various trends evident in the data, Hanna et al. note the likely influence of the sun on temperature and pressure values in consequence of their finding a significant correlation between 11-year running temperature means and sunspot numbers, plus the presence of a 12-year peak in their spectral analysis of the pressure data, which they say is "suggestive of solar activity."

In another study, Mangini et al. (2005) developed a highly-resolved 2000-year δ¹⁸O proxy record of temperature obtained from a stalagmite recovered from Spannagel Cave in the Central Alps of Austria. Results indicated that the lowest temperatures of the past two millennia occurred during the Little Ice Age (AD 1400-1850), while the highest temperatures were found in the Medieval Warm Period (MWP: AD 800-1300). Furthermore, Mangini et al. say that the highest temperatures of the MWP were "slightly higher than those of the top section of the stalagmite (1950 AD) and higher than the present-day temperature." In fact, at three different points during the MWP, their data indicate temperature spikes in excess of 1°C above present (1995-1998) temperatures.

Mangini et al. additionally report that their temperature reconstruction compares well with reconstructions developed from Greenland ice cores (Muller and Gordon, 2000), Bermuda Rise ocean-bottom sediments (Keigwin, 1996), and glacier tongue advances and retreats in the Alps (Holzhauser, 1997; Wanner et al., 2000), as well as with the Northern Hemispheric temperature reconstruction of Moberg et al. (2005). Considered together, they say these several data sets "indicate that the MWP was a climatically distinct period in the Northern Hemisphere," emphasizing that "this conclusion is in strong contradiction to the temperature reconstruction by the IPCC, which only sees the last 100 years as a period of increased temperature during the last 2000 years."

In a second severe blow to CO2-induced global warming alarmists, Mangini et al. found "a high correlation between δ¹⁸O and δ¹⁴C, that reflects the amount of radiocarbon in the upper atmosphere," and they note that this correlation "suggests that solar variability was a major driver of climate in Central Europe during the past 2 millennia." In this regard, they report that "the maxima of δ¹⁸O coincide with solar minima (Dalton, Maunder, Sporer, Wolf, as well as with minima at around AD 700, 500 and 300)," and that "the coldest period between 1688 and 1698 coincided with the Maunder Minimum." Also, in a linear-model analysis of the percent of variance of their full temperature reconstruction that is individually explained by solar and CO2 forcing, they found that the impact of the sun was fully 279 times greater than that of the air's CO2 concentration, noting that "the flat evolution of CO2 during the first 19 centuries yields almost vanishing correlation coefficients with the temperature reconstructions."

Two years later, Mangini et al. (2007) updated the 2005 study with additional data, after which they compared it with the Hematite-Stained-Grain (HSG) history of ice-rafted debris in North Atlantic Ocean sediments developed by Bond et al. (2001), finding an undeniably good correspondence between the peaks and valleys of their δ¹⁸O curve and the HSG curve. The significance of such correspondence is evidenced by the fact that Bond et al. reported that "over the last 12,000 years virtually every centennial time-scale increase in drift ice documented in our North Atlantic records was tied to a solar minimum."

Other researchers have found similar periodicities in their climate proxies. Turner et al. (2008), for example, found an ~1500 year cycle in a climate history reconstructed from sediment cores extracted from two crater lake basins in central Turkey, which they indicate "may be linked with large-scale climate forcing" such as that found in the North Atlantic by Bond et al. (1997, 2001). McDermott et al. (2001) found evidence of millennial-scale climate cycles in a δ¹⁸O record from a stalagmite in southwestern Ireland, as did Sbaffi et al. (2004) from two deep-sea sediment cores recovered from the Tyrrhenian Sea, which latter proxy corresponded well with the North Atlantic solar-driven cycles of Bond et al. (1997).

Nearby in the Mediterranean Sea, Cini Castagnoli et al. (2002) searched for possible solar-induced variations in the δ¹³C record of the foraminifera Globigerinoides rubber obtained from a sea core located in the Gallipoli terrace of the Gulf of Taranto (39°45'53"N, 17°53'33"E, depth of 178 m) over the past 1400 years. Starting at the beginning of the 1400-year record, the δ¹³C values increased from about 0.4 per mil around AD 600 to a value of 0.8 per mil by AD 900. Thereafter, the δ¹³C record remained relatively constant until about 1800, when it rose another 0.2 per mil to its present day value of around 1.0 per mil.

Using statistical procedures, the researchers were able to identify three important cyclical components in their record, with periods of approximately 11.3, 100 and 200 years. Comparison of both the raw δ¹³C and component data with the historical aurorae and sunspot time series, respectively, revealed that the records are "associable in phase" and "disclose a statistically significant imprint of the solar activity in a climate record." Three years later, Cini Castagnoli et al. (2005) extended the δ¹³C temperature proxy from the Gulf of Taranto an additional 600 years, reporting an overall phase agreement between the climate reconstruction and variations in the sunspot number series that "favors the hypothesis that the [multi-decadal] oscillation revealed in δ¹³C is connected to the solar activity."

Finally, we report on the study of Desprat et al. (2003), who studied the climatic variability of the last three millennia in northwest Iberia via a high-resolution pollen analysis of a sediment core retrieved from the central axis of the Ria de Vigo in the south of Galicia (42°14.07'N, 8°47.37'W). As they describe it, over the past 3000 years there was "an alternation of three relatively cold periods with three relatively warm episodes." In order of their occurrence, these periods are described by them as the "first cold phase of the Subatlantic period (975-250 BC)," which was "followed by the Roman Warm Period (250 BC-450 AD)," which was followed by "a successive cold period (450-950 AD), the Dark Ages," which "was terminated by the onset of the Medieval Warm Period (950-1400 AD)," which was followed by "the Little Ice Age (1400-1850 AD), including the Maunder Minimum (at around 1700 AD)," which "was succeeded by the recent warming (1850 AD to the present)." Based upon this "millennial-scale climatic cyclicity over the last 3000 years," which parallels "global climatic changes recorded in North Atlantic marine records (Bond et al., 1997; Bianchi and McCave, 1999; Chapman and Shackelton, 2000)," Desprat et al. concluded that "solar radiative budget and oceanic circulation seem to be the main mechanisms forcing this cyclicity in NW Iberia."

In conclusion, as time progresses and paleoclimatic studies increase in both number and sophistication, ever more evidence is accumulating for the global reality of the solar-induced millennial-scale oscillation of climate that pervades both glacial and interglacial periods alike. As a result, the establishment of the Current Warm Period over the course of the past century is seen to be nothing more than the most recent manifestation of this ever-recurring phenomenon and, hence, is likely totally unrelated to the concurrent historical increase in the air's CO2 content.

References
Berstad, I.M., Sejrup, H.P., Klitgaard-Kristensen, D. and Haflidason, H. 2003. Variability in temperature and geometry of the Norwegian Current over the past 600 yr; stable isotope and grain size evidence from the Norwegian margin. Journal of Quaternary Science 18: 591-602.

Bianchi, G.G. and McCave, I.N. 1999. Holocene periodicity in North Atlantic climate and deep-ocean flow south of Iceland. Nature 397: 515-517.

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.

Bond, G., Showers, W., Cheseby, M., Lotti, R., Almasi, P., deMenocal, P., Priore, P., Cullen, H., Hajdas, L. and Bonani, G. 1997. A pervasive millennial-scale cycle in North Atlantic Holocene and Glacial climates. Science 278: 1257-1266.

Chapman, M.R. and Shackelton, N.L. 2000. Evidence of 550-year and 1000-year cyclicities in North Atlantic circulation patterns during the Holocene. The Holocene 10: 287-291.

Cini Castagnoli, G.C., Bonino, G., Taricco, C. and Bernasconi, S.M. 2002. Solar radiation variability in the last 1400 years recorded in the carbon isotope ratio of a Mediterranean sea core. Advances in Space Research 29: 1989-1994.

Cini Castagnoli, G., Taricco, C. and Alessio, S. 2005. Isotopic record in a marine shallow-water core: Imprint of solar centennial cycles in the past 2 millennia. Advances in Space Research 35: 504-508.

Denton, G.H. and Karlen, W. 1973. Holocene climate variations - their pattern and possible cause. Quaternary Research 3: 155-205.

Desprat, S., Gońi, M.F.S. and Loutre, M.-F. 2003. Revealing climatic variability of the last three millennia in northwestern Iberia using pollen influx data. Earth and Planetary Science Letters 213: 63-78.

Haltia-Hovi, E., Saarinen, T. and Kukkonen, M. 2007. A 2000-year record of solar forcing on varved lake sediment in eastern Finland. Quaternary Science Reviews 26: 678-689.

Hanna, H., Jónsson, T. and Box, J.E. 2004. An analysis of Icelandic climate since the nineteenth century. International Journal of Climatology 24: 1193-1210.

Holzhauser, H. 1997. Fluctuations of the Grosser Aletsch Glacier and the Gorner Glacier during the last 3200 years: new results. In: Frenzel, B. (Ed.) Glacier Fluctuations During the Holocene. Fischer, Stuttgart, Germany, pp. 35-58.

Holzhauser, H., Magny, M. and Zumbuhl, H.J. 2005. Glacier and lake-level variations in west-central Europe over the last 3500 years. The Holocene 15: 789-801.

Keigwin, L.D. 1996. The Little Ice Age and Medieval Warm Period in the Sargasso Sea. Science 274: 1503-1508.

Kilian, M.R., van der Plicht, J. and van Geel, B. 1995. Dating raised bogs: new aspects of AMS ¹⁴C wiggle matching, a reservoir effect and climatic change. Quaternary Science Reviews 14: 959-966.

Magny, M. 1993. Solar influences on Holocene climatic changes illustrated by correlations between past lake-level fluctuations and the atmospheric ¹⁴C record. Quaternary Research 40: 1-9.

Mann, M.E., Bradley, R.S. and Hughes, M.K. 1998. Global-scale temperature patterns and climate forcing over the past six centuries. Nature 392: 779-787.

Mann, M.E., Bradley, R.S. and Hughes, M.K. 1999. Northern Hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations. Geophysical Research Letters 26: 759-762.

Mann, M.E. and Jones, P.D. 2003. Global surface temperatures over the past two millennia. Geophysical Research Letters 30: 10.1029/2003GL017814.

Mangini, A., Spotl, C. and Verdes, P. 2005. Reconstruction of temperature in the Central Alps during the past 2000 yr from a δ¹⁸O stalagmite record. Earth and Planetary Science Letters 235: 741-751.

Mangini, A., Verdes, P., Spotl, C., Scholz, D., Vollweiler, N. and Kromer, B. 2007. Persistent influence of the North Atlantic hydrography on central European winter temperature during the last 9000 years. Geophysical Research Letters 34: 10.1029/2006GL028600.

Mauquoy, D., Engelkes, T., Groot, M.H.M., Markesteijn, F., Oudejans, M.G., van der Plicht, J. and van Geel, B. 2002b. High resolution records of late Holocene climate change and carbon accumulation in two north-west European ombrotrophic peat bogs. Palaeogeography, Palaeoclimatology, Palaeoecology 186: 275-310.

Mauquoy, D., van Geel, B., Blaauw, M., Speranza, A. and van der Plicht, J. 2004. Changes in solar activity and Holocene climatic shifts derived from ¹⁴C wiggle-match dated peat deposits. The Holocene 14: 45-52.

Mauquoy, D., van Geel, B., Blaauw, M. and van der Plicht, J. 2002a. Evidence from North-West European bogs shows 'Little Ice Age' climatic changes driven by changes in solar activity. The Holocene 12: 1-6.

McDermott, F., Mattey, D.P. and Hawkesworth, C. 2001. Centennial-scale Holocene climate variability revealed by a high-resolution speleothem δ¹⁸O record from SW Ireland. Science 294: 1328-1331.

Moberg, A., Sonechkin, D.M., Holmgren, K., Datsenko, N.M. and Karlen, W. 2005. Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data. Nature 433: 613-617.

Muller, R.A. and Gordon, J.M. 2000. Ice Ages and Astronomical Causes. Springer-Verlag, Berlin, Germany.

Sbaffi, L., Wezel, F.C., Curzi, G. and Zoppi, U. 2004. Millennial- to centennial-scale palaeoclimatic variations during Termination I and the Holocene in the central Mediterranean Sea. Global and Planetary Change 40: 201-217.

Speranza, A. 2000. Solar and Anthropogenic Forcing of Late-Holocene Vegetation Changes in the Czech Giant Mountains. PhD thesis. University of Amsterdam, Amsterdam, The Netherlands.

Speranza, A.O.M., van der Plicht, J. and van Geel, B. 2000. Improving the time control of the Subboreal/Subatlantic transition in a Czech peat sequence by ¹⁴C wiggle-matching. Quaternary Science Reviews 19: 1589-1604.

Stuiver, M. and Polach, H.A. 1977. Discussion: reporting ¹⁴C data. Radiocarbon 19: 355-363.

Tinner, W., Lotter, A.F., Ammann, B., Condera, M., Hubschmied, P., van Leeuwan, J.F.N. and Wehrli, M. 2003. Climatic change and contemporaneous land-use phases north and south of the Alps 2300 BC to AD 800. Quaternary Science Reviews 22: 1447-1460.

Turner, R., Roberts, N. and Jones, M.D. 2008. Climatic pacing of Mediterranean fire histories from lake sedimentary microcharcoal. Global and Planetary Change 63: 317-324.

Usoskin, I.G., Solanki, S.K., Schussler, M., Mursula, K. and Alanko, K. 2003. Millennium-scale sunspot number reconstruction: Evidence for an unusually active sun since the 1940s. Physical Review Letters 91: 10.1103/PhysRevLett.91.211101.

van Geel, B., Buurman, J. and Waterbolk, H.T. 1996. Archaeological and palaeoecological indications of an abrupt climate change in the Netherlands and evidence for climatological teleconnections around 2650 BP. Journal of Quaternary Science 11: 451-460.

van Geel, B., Heusser, C.J., Renssen, H. and Schuurmans, C.J.E. 2000. Climatic change in Chile at around 2700 BP and global evidence for solar forcing: a hypothesis. The Holocene 10: 659-664.

van Geel, B., Raspopov, O.M., Renssen, H., van der Plicht, J., Dergachev, V.A. and Meijer, H.A.J. 1999. The role of solar forcing upon climate change. Quaternary Science Reviews 18: 331-338.

van Geel, B., van der Plicht, J., Kilian, M.R., Klaver, E.R., Kouwenberg, J.H.M., Renssen, H., Reynaud-Farrera, I. and Waterbolk, H.T. 1998. The sharp rise of delta ¹⁴C c. 800 cal BC: possible causes, related climatic teleconnections and the impact on human environments. Radiocarbon 40: 535-550.

Wanner, H., Dimitrios, G., Luterbacher, J., Rickli, R., Salvisberg, E. and Schmutz, C. 2000. Klimawandel im Schweizer Alpenraum. VDF Hochschulverlag, Zurich, Switzerland.