The Little Ice Age - How Human Cultures Respond to Climate Change

Human Responses to the Medieval Climate Shift

Sunburst over Grand Pacific Glacier, Alaska
Sunburst over Grand Pacific Glacier, Alaska. Altrendo Travel / Altrendo / Getty Images

The Little Ice Age is the name of a small but painful climate shift which occurred in the middle ages, when glaciers re-advanced into Europe and North America, and variable but cooler and somewhat stormier climate conditions occurred throughout the Northern Hemisphere. The LIA, as it sometimes abbreviated, is one of the most prominent climate modulations over the past 5,000 years, and the most recent rapid climate change prior to the modern era.

Ice in Antarctica, the Andes mountains and the Tibetan plateau also expanded during this period, at different rates and at different times depending on local conditions.

Dates for the Little Ice Age vary from region to region, but in general, dates for the LIA and the preceding and succeeding stages are:

  • Medieval Warm Period 800-1300 AD
  • Little Ice Age 1300-1850 AD
  • Modern Era 1850-present day

How Cool Was It?

Global estimates from Bertler et al. indicate that, relative to 1975 AD, the snowline was 100 meters (328 feet) lower in elevation and the average temperature about .5 to 1.5 degree Celsius (°C) or about 1-2.5 degrees Fahrenheit (°F) cooler. As a comparison, during the Last Glacial Maximum of about 24,000 years ago, the snowline was 900-950 meters (3000-3100 ft) lower, and about 6°C (10°F) cooler; and during the Younger Dryas about 12,000 years ago, the snowline was 350 meters (1100 ft) lower, with 3-4°C (5-7°F) cooler temperatures.

Conditions during the LIA in the northern hemisphere were not uniformly cool, and numerous reconstructions show there was a considerable variability with marked regional differences in style and timing of the changes.

Causes: and Human Responses

Three major known climate modulators have been suggested to have caused the LIA: changes in solar output, increased volcanic activity, and changes in ocean currents (or, more specifically, "thermohaline circulation"): all of that is debated in the climatology literature.

For archaeologists, the most interesting part of the LIA is that it occurred during a recent enough period that we have historic records of what humans saw and did as a response to the climate change.

This article describes four of the stories that archaeological investigation and reports of the locals can tell us about what the climate change was like and how they responded.

Xakwnoowú Fort (Alaska)

Xakwnoowú Fort ("Dry Fort" in the Tlingit language), located on Dundas Bay in what today is Glacier Bay National Park and Preserve in Alaska, has Tlingit history associated with the LIA. Reportedly founded by the L’uknax.ádi clan (with a radiocarbon site on initial founding of ~AD 1150), Xakwoonwú Fort was used until the mid-eighteenth century. The narrative oral history of the Tlingit people report that a climatic battle of the "Bow and Arrow Wars" or "The First War in the World" took place here; and that the fort was destroyed by a surge of the Grand Pacific Glacier (called Sit Tlein in Tlingit).

Tree ring studies on overridden and buried trees indicate the Grand Pacific Glacier surge occurred on nearby Lester Island and throughout the bay between 1720-1735. The ice caused isotatic depression and a corresponding increase in relative sea level to about 4 meters (13 feet) above its current height, the highest level in the last 8,000 years.

The pronounced climate change forced people out of the bay; Tlingit oral history reports that there was a "great flood" when rising sea levels forced people to climb into the adjacent mountains. Glacial retreat began in 1794, and isostatic rebound has resulted in a relative sea level drop at a rate of 1.4-2 cm (.5-.75 in) a year since. See Crowell and Howell for further information.

Ship Logs during the Anglo-Dutch Wars

On the other side of the world from the Bow and Arrow Wars, a different war was being conducted: the Anglo-Dutch Wars between the trading concerns of England and the Netherlands. Fought in the North Sea between 1652 and 1674, the war was conducted by ship captains who rigorously, as they do today, record weather changes.

DeGroot (2014) investigated surviving ships' journals (logs) from both sides during the period.

DeGroot discovered that the logs recorded an increase in the westerlies over time, periods of prolonged freezing of the waters, heavy fogs and fierce storms, particularly in the last Anglo-Dutch War (1672-1674), when gales and high winds were quite common.

DeGroot could find no reference to any recognition on board that a climate change was in process: the captains were simply recording day-to-day circumstances and were involved in naval battles. Increased storm activity is also recorded for the LIA in the French Mediterranean coast, by geochemical means and the use of historical archives of townships in region, the latter of which is mentioned but not discussed in detail by Sabatier et al.

Greenland Walrus Hunters and Polynya

According to a recent study of Thule walrus hunters on Clavering Island, Greenland, during the LIA, the people exploited a "hot spot" of marine resources, the Sirius Water Polynya. Polynyas are semi-permanent openings in the arctic pack ice which are relatively rare, but carefully mapped today: without them ships would find it very difficult to find safe passage across the arctic circle.

Rhodes et al. report that during the LIA, at least some of the polynyas expanded in size. The marine mammal populations of the polynyas also expanded, as walruses and seals and the like migrated to the open water. According to Grønnow et al., there is ample evidence that Thule hunters on Clavering Island in turn came in larger numbers to exploit the walrus. The Clavering Island site includes nearly 2,100 stone-built summer structures--meat caches, wall shelters and tent rings--dated to the Paleo-Eskimo and Thule periods.

No semi-subterranean turf houses were found, but over 1,000 cache pits were, stone boxes and lined pits where meat and blubber were stored for the winter. Based on Grønnow et al's investigations, for hundreds of years the Thule hunted near the polynya during the summer and cached food, and at the end of the summer returned to their winter homes, using Clavering Island as an enormous larder.

The polynya remained relatively stable throughout the LIA, with ice-rich conditions in coastal waters and little snow coverage, allowing caribou and musk oxen to sustain viable populations.

According to Grønnow et al., similar Thule summer sites have been found close to other primary polynyas, such as Scoresby Sound, 500 km (310 mi) south of Walrus island.

Qijurittuq site (Canada)

The Qijurittuq Paleo-eskimo and Thule site is located on Drayton Island in Hudson Bay, Nunavik province in the Canadian Low Arctic (Lemieux et al.). Here the LIA co-occurred with the inmigration of Thule whale hunters into the region, and for the most part, Thule people abandoned semi-subterranean houses for snowhouses: not so in Qijuittuq.

Qijurittuq is a multi-component Paleo-eskimo and Thule/Inuit site; during the LIA there were 13 semi-subterranean sod houses, a cache, a tent ring and a shallow rectangular depression. Elders at the nearby town of Inukjuak were interviewed about environmental changes, land occupations, semi-subterranean houses and Inuit identity, and about what they recalled of the site's settlement. Although none were alive when Qijurittuq was founded, the elders noted that their ancestors located the village in a valley protected from strong winds and in an area that was good for sealing.

Similar findings were reported by Roy et al. at Oakes Bay, Labrador, where Thule/Inuit people continued to use semi-subterranean houses because they were able to take advantage of small polynyas (called "rattles").

Sources

This article is a part of the About.com guide to the Dictionary of Archaeology.

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