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Little Ice Age (Regional - Europe: Mediterranean) -- Summary
The 21st century has seen a developing interest in paleoclimate studies, primarily driven by the need to derive a long-term baseline of global temperature variability against which to evaluate the uniqueness of 20th-century warming. Within this context, the Little Ice Age figures prominently, since it was a multi-century period of significantly reduced air temperature that serves as the baseline from which modern warming is computed. In like manner, the preceding Medieval Warm Period serves as the baseline from which the cooling that led to the Little Ice Age is computed. In this summary, we thus report on what has been learned about the Little Ice Age and the warm periods that preceded and followed it, based on a number of paleoclimate studies conducted in countries bordering the Mediterranean Sea.

D'Orefice et al. (2000) assembled and analyzed a wealth of historical evidence to derive a history of the post-Little Ice Age shrinkage of the surface area of the Ghiacciaio del Calderone, which is the southernmost glacier of Europe. From these materials they determined that from the time of the first available information about the glacier's surface area (AD 1794), there was a slow shrinkage that lasted until 1884, whereupon the glacier's surface area began to experience a more rapid reduction that prevailed, with some irregularities, to 1990, resulting in the loss of a little more than half of the Ghiacciaio's Little Ice Age extent.

Schilman et al. (2002) analyzed high-resolution δ18O values from a speleothem in Soreq Cave, central Israel (31°45'N, 35°03'E), as well as from planktonic foraminifera in two marine sediment cores retrieved just off the Ashdod coast (31°56.41'N, 34°22.13'E and 31°56.61'N, 34°19.79'E), to obtain a record of climate in this region over the past 3600 years. The δ18O values of the speleothem and marine cores showed "striking similarity" over the period of study, according to Schilman et al., and they were found to be primarily representative of historic changes in precipitation. Interpreted in this light, six major precipitation intervals were found to have occurred over the course of the 3600-year record, including three that were relatively wet and three that were relatively dry. The peaks of the humid events occurred at 3200, 1300 and 700 years BP, the latter of which was said by the researchers to be "associated with the global Medieval Warm Period humid event," which association is supported by additional evidence from the surrounding region in the form of (1) high Nile floods (Bell and Menzel, 1972; Hassan, 1981), (2) high Saharan lake levels (Nicholson, 1980), and (3) high water levels in the Dead Sea and Sea of Galilee (Frumkin et al., 1991). The peaks of the dry events occurred at 2100, 900 and 300 years BP, the last of which, in the words Schilman et al., "coincides with the Little Ice Age." These observations provide strong evidence for the natural climatic oscillation that was responsible for bringing the world the Little Ice Age, Medieval Warm Period, Dark Ages Cold Period, Roman Warm Period and the numerous sets of cold and warm periods that occurred before that. Hence, it is highly likely that this phenomenon also produced the majority of the temperature increase associated with the development of the Current Warm Period.

Sousa and Garcia-Murillo (2003) studied proxy indicators of climatic change in Doņana Natural Park in the Andalusia region of southwest Spain, comparing their results with those of several other such studies conducted in neighboring regions. They determined that the Little Ice Age was by no means uniform in their region of study, including periods of both wetter and drier conditions. Nevertheless, the two scientists cite Rodrigo et al. (2000) as indicating that "the Little Ice Age was characterized in the southern Iberian Peninsula by increased rainfall." Their own work complements this assessment by indicating "an aridization of the climatic conditions after the last peak of the Little Ice Age (1830-1870)." Therefore, although there was in increase in temperature on the order of 0.7°C since the end of the Little Ice Age in various parts of Spain (Lampre, 1994; Garcia Barron, 2000), Sousa and Garcia-Murillo conclude that precipitation differences were more significant in delineating the Little Ice Age in this part of the world than were temperature differences.

Desprat et al. (2003) 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. This work revealed that 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 Desprat et al. 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)." Desprat et al. additionally state that "solar radiative budget and oceanic circulation seem to be the main mechanisms forcing this cyclicity in NW Iberia."

For a site on the northwest coast of Sicily near Capo Gallo promontory, Silenzi et al. (2004) "present new data on sea climate trend fluctuations that could be interpreted as Sea Surface Temperature (SST) variations, recorded on Vermetid reefs, by means of [oxygen] isotopic analysis." Their data depict the existence of the Little Ice Age, with a "temperature variation of about delta T = 1.99 ą 0.37°C between the Little Ice Age and present day." Following the Little Ice Age was what they call "the warming trend that characterized the last century," which according to their findings "ended around the years 1930-1940 AD, and was followed by a relatively cold period between the years 1940 and 1995." Their results thus disagree with the Northern Hemispheric temperature history of Mann et al. (1999) in two different ways: they indicate that the Little Ice Age was significantly colder than what Mann et al. suggest, and they do not find any sign of the dramatic late-20th century warming claimed by Mann et al.

Pla and Catalan (2005) analyzed chrysophyte cyst data collected from 105 lakes in the Central and Eastern Pyrenees of northeast Spain to produce a history of winter/spring temperature in which the region's climate alternated between warm and cold phases over the past several thousand years. Of particular note were the Little Ice Age, Medieval Warm Period, Dark Ages Cold Period and Roman Warm Period, the warmest of which intervals was the Medieval Warm Period, which started around 900 AD and was about 0.25°C warmer than it is currently. Following the Medieval Warm Period, temperatures fell to their lowest values of the entire record (about 1.0°C below present), whereupon they began to warm, but remained below present-day values until the early 19th and 20th centuries, except between 1350 and 1400, when temperatures rose a full degree Celsius to a value about 0.15°C warmer than at present. Further examination of Pla and Catalan's data reveals that modern temperatures peaked in the 1970s-80s and declined throughout the 1990s.

Giraudi (2005) studied various properties of alternating layers of organic-matter-rich soils and alluvial, glacial and periglacial sediments on higher Apennine massifs in Italy, reconstructing a history of relative changes in temperature for this region over the past 6000 years. This work revealed that organic-matter-rich soils formed on slopes currently subject to periglacial and glacial processes around 5740-5590, 1560-1370 and 1300-970 cal yr BP. Based upon current relationships between elevation and soil periglacial and glacial processes, Giraudi estimated that the mean annual temperature during these three periods "must therefore have been higher than at present," and that winter temperatures were at least 0.9-1.2°C higher than those of today. In addition, it was determined that the lowest wintertime temperatures, which were reached during the Little Ice Age (ca. 790-150 cal yr B.P.), were as much as 3.0°C colder than at present.

Cini Castagnoli et al. (2005) produced a high-precision record of climate variability over the past two millennia based on a δ13C profile of Globigerinoides rubber that was extracted from a shallow-water core in the Gulf of Taranto (39°45'53"N, 17°53'33"E). This high-precision record was statistically analyzed, together with a second two-millennia-long tree-ring record obtained from Japanese cedars (Kitagawa and Matsumoto, 1995), for evidence of recurring cycles using Singular Spectrum Analysis and Wavelet Transform, after which both records were compared with a 300-year record of sunspots. Plots of the two two-thousand-year series revealed the existence of the Dark Ages Cold Period (~400-800 AD), Medieval Warm Period (~800-1200 AD), Little Ice Age (~1500-1800 AD), and Current Warm Period, the roots of which can be traced to an upswing in temperature that began in the depths of the Little Ice Age "about 1700 AD." Results of the statistical analyses also showed a common 11-year oscillation in phase with the Schwabe cycle of solar activity, plus a second multi-decadal oscillation (of about 93 years for the shallow-water G. rubber series and 87 years for the tree-ring series) in phase with the amplitude modulation of the sunspot number series over the last 300 years.

According to the three researchers, the overall phase agreement between the two climate reconstructions and the variations in the sunspot number series "favors the hypothesis that the [multi-decadal] oscillation revealed in δ13C from the two different environments is connected to the solar activity," which further suggests that a solar forcing was at work in both terrestrial and oceanic domains over the past two millennia. Thus, and once again, we have additional evidence for solar forcing of climate at decadal and multi-decadal time scales, as well as for the millennial-scale oscillation of climate that likely has been responsible for the 20th-century warming of the globe that led to the demise of the Little Ice Age and ushered in the Current Warm Period.

Robert et al. (2006) analyzed assemblages of minerals and microfossils from a sediment core taken from the Berre coastal lagoon in southeast France in an effort to reconstruct environmental changes in that region over the past 1500 years. The results of their analyses revealed three distinct climatic intervals: (1) a cold period that extended from about AD 400 to 900, (2) a warm interval between about AD 980 and 1370, and (3) a cold interval that peaked during the 16th and 17th centuries. These climatic intervals correspond, respectively, to the well-known Dark Ages Cold Period, Medieval Warm Period (MWP) and Little Ice Age; and with respect the MWP, the eight-member research team found evidence of a higher kaolinite content in the sediment core during that period, which suggests, in their words, the occurrence of "increased chemical weathering in relation to higher temperatures and/or precipitation." In addition, they report that the concentration of microfossils of the thermophilic taxon Spiniferites bentorii also peaked during the same time interval; and this finding provides additional evidence that the temperatures of that period were higher than those of the recent past.

In a contemporaneous study, Eiriksson et al. (2006) reconstructed the near-shore thermal history of the North Atlantic Current along the western coast of Europe over the last two millennia, based on measurements of stable isotopes, benthic and planktonic foraminifera, diatoms and dinoflagellates, as well as geochemical and sedimentological parameters, which they acquired on the Iberian margin and at several other locations. In addition to identifying the Roman Warm Period (nominally 50 BC- AD 400), which exhibited the warmest sea surface temperatures of the last two millennia on the Iberian margin, they too found evidence of the subsequent Dark Ages Cold Period (AD 400-800), Medieval Warm Period (AD 800-1300) and Little Ice Age (AD 1300-1900), which was followed by 20th-century warming that they say "does not appear to be unusual when the proxy records spanning the last two millennia are examined."

In introducing their analysis of the subject, Garcia et al. (2007) state that "despite many studies that have pointed to ... the validity of the classical climatic oscillations described for the Late Holocene (Medieval Warm Period, Little Ice Age, etc.), there is a research line that suggests the non-global signature of these periods (IPCC, 2001; Jones and Mann, 2004)." Noting that "the best way to solve this controversy would be to increase the number of high-resolution records covering the last millennia and to increase the spatial coverage of these records," they proceed to do just that.

Working with a number of sediment cores retrieved from a river-fed wetland that is flooded for approximately seven months of each year in Las Tablas de Daimiel National Park (39.4°N, 3.8°W, south central Iberian Peninsula, Spain), Garcia et al. employed "a high resolution pollen record in combination with geochemical data from sediments composed mainly of layers of charophytes alternating with layers of vegetal remains plus some detrital beds" to reconstruct "the environmental evolution of the last 3000 years." This work enabled them to identify five distinct climatic stages: "a cold and arid phase during the Subatlantic (Late Iron Cold Period, < BC 150), a warmer and wetter phase (Roman Warm Period, BC 150-AD 270), a new colder and drier period coinciding with the Dark Ages (AD 270-900), the warmer and wetter Medieval Warm Period (AD 900-1400), and finally a cooling phase (Little Ice Age, >AD 1400)."

Noting that "the Iberian Peninsula is unique, as it is located at the intersection between the Mediterranean and the Atlantic, Europe and Africa, and is consequently affected by all of them," Garcia et al. significantly advance the likelihood that "the classical climatic oscillations described for the Late Holocene (Medieval Warm Period, Little Ice Age, etc.)" were indeed both real and global in scope, as becomes ever more evident each and every week with our posting of the results of a new Medieval Warm Period study on our website. In addition, Garcia et al. state that the Medieval Warm Period "is identified at about a similar date all around the world (China: Chu et al., 2002; Arabia, Fleitmann et al., 2004; Africa: Filippi and Talbot, 2005; Iceland: Doner, 2003; central Europe: Filippi et al., 1999; New Guinea: Haberle and David, 2004; USA: Cabaniss Pederson et al., 2005: Argentina: Mauquoy et al., 2004; etc.," and that "comparable changes are described by Desprat et al. (2003), Julia et al. (1998) and Riera et al. (2004) in northwest, central and northeast Spain."

Truly, the evidence for the global scope of the Little Ice Age, Medieval Warm Period, Dark Ages Cold Period, Roman Warm Period, and etc., going back in time ad inifinitum, is overwhelming. And this, of course, suggests that 20th-century global warming was likely nothing more than the logical progression of this natural millennial-scale climatic oscillation, which fostered the Little Ice Age-to-Current Warm Period transition.

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Last updated 6 August 2008