Borehole measurements from Greenland suggest temperatures were 0.5 to 0.7°C colder than they are now (Dahl-Jensen et al., 1998).  In South Africa, mean annual temperatures reached values that were about 1°C cooler than today (Tyson et al., 2000); while sea surface temperatures in the Caribbean plummeted by as much as 3°C (Winter et al., 2000).  Additional cooling during this time has been reported in Switzerland (Filippi et al., 1999) and Russia (Naurzbaev and Vaganov, 2000).

Perhaps the best evidence to date that the Little Ice Age was indeed a global phenomenon comes from the study of Huang and Pollack (1997).  Using 6,144 sets of heat flow measurements from every continent of the globe, these authors produced a global reconstruction of ground surface temperatures over the past 20,000 years.  Describing their dataset as "independent of other proxy interpretations [and] of any preconceptions or biases as to the nature of the actual climate history," they found strong evidence that the Little Ice Age indeed existed, was global in extent, and was perhaps as much as 0.7°C colder than it was at the time of their study.

As a result of the lower temperatures of this cool climatic excursion, snowfall occurred at lower latitudes and elevations throughout most of the world (Manley, 1969, 1971; Hastenrath, 1981; Grove, 1988).  In some places, such as the Ben Nevis area of Scotland, snowlines were 300-400 meters lower in the 17th and 18th centuries then they are presently (Grove, 1988).  The combination of lower snowlines and cooler temperatures provided excellent conditions for glacial growth; and a vast array of studies indicate that alpine glaciers advanced in virtually all mountainous regions of the globe during this period (Luckman, 1994; Villalba, 1994; Smith et al., 1995; Naftz et al., 1996; D'Orefice et al., 2000; Harrison and Winchester, 2000).

Glacial advances during the Little Ice Age typically eroded large areas of land and produced masses of debris.  Like an army of tractors and bulldozers, streams of ice flowed down mountain slopes, carving paths through the landscape, moving rocks, and destroying all vegetation in their paths (Smith and Laroque, 1995).  These advances often were relatively swift, with one Norwegian account recording a glacial advance of 200 meters in just 10 years (Grove, 1988).

Continental glaciers and sea ice expanded their ranges as well (Grove, 1988; Crowley and North, 1991).  Near Iceland and Greenland, in fact, the expansion of sea ice during the Little Ice Age was so great that it essentially isolated the Viking colony established in Greenland during the Medieval Warm Period, leading to its ultimate demise (Bergthorsson, 1969; Dansgaard et al., 1975; Pringle, 1997).

Two closely associated phenomena that often occurred during the Little Ice Age were glacial landslides and avalanches (Porter and Orombelli, 1981; Innes, 1985).  In Norway, an unprecedented number of petitions for tax and land rent relief were granted in the 17th and 18th centuries on account of the considerable damage that was caused by landslides, rockfalls, avalanches, floods and ice movement (Grove, 1988).  In one example of catastrophic force and destruction, the Italian settlements of Ameiron and Triolet were destroyed by a rockfall of boulders, water, and ice in 1717.  The evidence suggests that the rockfall had a volume of 16-20 million cubic meters and descended 1860 meters over a distance of 7 kilometers in but a few minutes, destroying homes, livestock and vegetation (Porter and Orombelli, 1980).  Other data suggest rockslides and avalanches were also frequent hazards in mountainous regions during this period (Porter and Orombelli, 1981; Innes, 1985).

Flooding was another catastrophic hazard of the Little Ice Age, with meltwater streams from glaciers eroding farmland throughout Norway (Blyth, 1982; Grove, 1988).  In Iceland, flooding also wreaked havoc on the landscape when, on occasion, subglacial volcanic activity melted large portions of continental glaciers (Thoroddsen, 1905-06; Thorarinsson, 1959).  Peak discharge rates during these episodes have been estimated to have been as high as 100,000 cubic meters per second - a value comparable in magnitude to the mean discharge rate of the Amazon River (Thorarinsson, 1957).  During one such eruption-flood in 1660, glacial meltwater streams carried enough rock and debris from the land to the sea to create a dry beach where fishing boats had previously operated in 120 feet (36.6 m) of water (Grove, 1988); while flooding from a later eruption carried enough sediment seaward to fill waters 240 feet (73.2 m) deep (Henderson, 1819).

There is also evidence to suggest that some regions of the globe experienced severe drought during the Little Ice Age as a result of large-scale changes in atmospheric circulation patterns (Crowley and North, 1991; Stahle and Cleaveland, 1994).  In Chile, for example, dendrochronology studies have revealed that the most intense droughts of the past 1,000 years occurred during this period of time (Villalba, 1994).  In Africa, droughts occurred that were "more severe than any recorded drought of the twentieth century" (Verschuren et al., 2000).

Similar findings have been obtained from tree-ring analyses in the southeastern United States, where the most prolonged dry episode of spring drought in the last 1,000 years occurred during the mid-18th century (Stahle and Cleaveland, 1994).  Elsewhere in the southwestern United States, dendrochronology data indicate that the warm and moist conditions experienced during the Medieval Warm Period gave way to progressively cooler and drier conditions during the Little Ice Age; and it is suspected that this transformation of the climate led to the demise of the Anasazi Indian civilization by reducing the area of land on the Colorado Plateau that was suitable for agriculture (Petersen, 1994).  Indeed, cold temperatures and glacial advances resulted in problematic farming in many areas of the world during the Little Ice Age; and failed crops and disrupted ecosystems produced much human misery (Bernabo, 1981; Grimm, 1983; Payette et al., 1985; Campbell and McAndrews, 1991; Cambpell and McAndrews, 1993).

So what was the cause of this globally-chilled period?  One possibility has to do with changes in the global thermohaline circulation (Broecker et al., 1999).  Another possibility relates to an increase in volcanic acticity (Briffa et al., 1998).  Perhaps the most viable explanation, however, rests in changes in the energy output of the sun.  In a review of the role of solar forcing on climate, Van Geel et al. (1999) state that "there is mounting evidence suggesting that the variation in solar activity is a cause for millennial scale climate change," and that "the climate system is far more sensitive to small variations in solar activity that generally believed."  Such conclusions are buttressed by Cioccale (1999) and Tyson et al. (2000), who note that the cold temperatures observed during the Little Ice Age in Argentina and South Africa, respectively, correspond well with the Maunder Minimum in solar sunspot activity.  Similarly, Hong et al. (2000) note that "there is a remarkable, nearly one to one," correspondence between solar variability and climate observed in China during this time.

In light of the above evidence, the Little Ice Age does indeed appear to have been a time in which near-surface air and water temperatures were cooler than they are presently; and there would seem to be sufficient evidence to also conclude that this severe climatic epoch was global in scale.

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