The Little Ice Age: Climate Change and Geographic Impact

Introduction

The Little Ice Age (LIA) is considered by some researchers to extend over several generations of time. Estimates show that the period began around the 13th and 14th centuries; another period under consideration is between the mid-16th and the mid-19th century (Grove, 1988). The significance of conducting additional research into the LIA lies in hopes of gaining a better understanding of the period's timeline, its causes, and where it occurred. It is hoped that this research will provide clarity about the timeframe of the LIA and what caused its occurrence, in addition to understanding the global impact it had. The method of research is a compilation of previously collected data and studies conducted on the subject of the LIA, in an attempt to bring necessary clarity to the questions surrounding the subject. The areas included in this research are Greenland, Iceland, and Alaska. There is little agreement among professionals in the field as to the exact dates and extent of the LIA (Syszygyastro, n.d.).

The study of glacial landforms and deposits is important because it is difficult to observe processes under modern glaciers and ice sheets. Landscapes and sediments that are the product of present glaciations can, therefore, give insight into processes that occurred during Pleistocene times. This study investigates the genesis of Little Ice Age glacial landforms present in Portage Glacier, south-central Alaska. The moderately sorted gray sandy boulder gravel present on the 1900 and 1922 moraines is interpreted as an ice-marginal deposit with a mixture of supraglacial and glaciofluvial sediments deposited by slumping and stream-sorting processes. All of these features are interpreted as ablation moraines representing glacier retreat and moraine building in 1900 and 1922 (Santos, Joao, & Cordova, 2009).

Background and Data

Beginning around 1450 AD, an interval of relative cold often called the Little Ice Age has been identified. Occurring within the current warm interglacial period, the Little Ice Age cannot be regarded as a full glacial episode, since the high latitudes of the Northern Hemisphere landmasses remained largely free of permanent ice cover. Nevertheless, the term has been used to describe an epoch of renewed glacial advance. Although many regions of the world experienced cooling during the period 1450 to 1890 AD — with average surface temperatures in many regions at least 1°C lower than those of today — its use has been criticized because it has not conclusively been considered an event of global significance ("Little Ice Age," 2010).

The Little Ice Age, a period of glacier expansion in alpine regions that began sometime between the twelfth and sixteenth centuries and lasted until late in the nineteenth century, was recorded not only in glacial features dated by geologic techniques but also in historical documents such as field sketches, land values, and weather records, especially in the Alps. Indirect evidence of its impact in other parts of the world includes records of sea-ice extent near Iceland and Greenland, the fate of the Viking settlements in Greenland, and many other indications that the climate was colder in the recent past than it is today (Wright, 1990). During the Little Ice Age, the climate of northern Europe turned volatile and markedly cooler. While this did not directly cause major historical events, it catalyzed significant social, political, and economic changes throughout the region. Widespread reliance on subsistence farming meant that bad weather and shortened growing seasons led to food shortages and even famines. Hunger, along with disease, war, crime, and economic forces, provoked widespread sociopolitical upheaval, including the collapse of Norse settlements in Greenland, the French Revolution, and the Irish Famine (Curtis, 2001).

Lateral, medial, recessional, push, and terminal moraines are common features in Portage Valley, Alaska. They are the product of ice recession and advance that occurred from 1810 to the present. All of these features have different orientations. End and recessional moraines have a southwest–northeast orientation and are perpendicular to ice flow. Lateral and medial moraines have a southeast–northwest orientation and are parallel to the ice flow direction in Portage Valley. The shape of these moraines is similar; they have sharp crests with steep slopes, showing that they are very recent. Recessional moraines such as those deposited in 1900 and 1922 are the smallest features in Portage Valley and represent short periods of standstill or ice retreat. This type of glacial regime allowed small amounts of morainal deposition. In contrast, terminal moraines such as the 1852 moraine are the largest features present in this area; they are generally the product of longer periods of deposition and moraine building (Santos, Joao, & Cordova, 2009).

Research on global climate change, drawn from tree rings and Greenland ice cores, provides detailed information on weather and climate history. This information can be correlated with historical accounts of major weather events and their influence on human conditions. When Europe became colder, wetter, and stormier, abrupt changes in weather could mean the difference between prosperity and poverty — or even between life and death — especially for people living near subsistence levels, as most Europeans did before 1800, particularly when such changes lasted more than one season (Cooper, 2001).

Hunt (2006) explains that the LIA was an episode of below-average temperatures from 1550 to 1850 AD. However, there is no universal agreement regarding the precise dates of these events, and they were not episodes of continuous above- or below-average temperatures. Controversy continues to exist over the reality of both the Medieval Warm Period (MWP) and the LIA. The principal concerns of researchers include the lack of temporal correspondence between climatic variability in different regions, regional variability itself, the modest amplitude of hemispheric mean temperature anomalies, and the sparseness and derivative nature of the observations. Many observational studies document climatic perturbations, primarily temperature changes, that support the occurrence of these events (Hunt, 2006).

During the past 4,000 years, there have been several multi-centennial cold periods during which glacier fronts have notably advanced. This sequence of cold periods is referred to as the LIA, though today this epoch is also called Neoglaciation. The more familiar term "LIA" is used to describe the latest and most dramatic cold event of the Neoglaciation, during which there were substantial glacier advances. However, the exact timing of the LIA is not well defined. Paleoclimatologists use the term LIA to describe the coldest interval of their reconstructions over the last 1,000 years. Some researchers argue that the beginning of the LIA should be placed around 1450, based on data from Greenland and Antarctica, while others define the LIA as the period between 1550 and 1850 — a definition adopted by a large number of researchers (Sedláček & Mysak, 2009).

This issue is not merely an academic disagreement, as it has entered into discussions of the credibility of attributing current warming to the greenhouse effect. Studies based largely on proxy data have derived a Northern Hemispheric temperature time series from 1000 AD to the present. This time series has the shape of a hockey stick, with the blade representing global warming over the past few decades and the shaft representing a relatively stationary series of hemispheric temperature anomalies back to 1000 AD. The crucial point is that no MWP is identified by the time series, thus supporting the claim that 1998 was the warmest year and the 1990s the warmest decade of the past millennium in the Northern Hemisphere. This implies that natural climatic variability cannot fully account for present observed global warming (Hunt, 2006).

Reconstructing the temporal and spatial climate development on a seasonal basis during the last few centuries, including the LIA, may help researchers better understand the modern interplay between natural and anthropogenic climate variability. The conventional view of climate development during the last millennium has been that it followed a sequence of a Medieval Warm Period, a cool Little Ice Age, and a warming during the latter part of the 19th century and especially during the late 20th and early 21st centuries. However, recent research has challenged this rather simple sequence. Up to the present, it had been considered most likely that Little Ice Age glacial expansion in western Scandinavia was caused by lower summer temperatures. Data from more recent research, however, indicates that the main cause of the early 18th-century glacial advance in western Scandinavia was mild and humid winters associated with increased precipitation and high snowfall on the glaciers (Nesje et al., 2008).

Glaciers and small ice caps in temperate environments are sensitive indicators of climatic change. Iceland is an important location for the study of North Atlantic climate change owing to its proximity to both atmospheric and oceanic polar fronts. Geomorphologic evidence of glacier fluctuations in Iceland during the Late Holocene is abundant. Furthermore, Iceland has a unique documentary record of ice-front positions spanning from the time of settlement around AD 870 to the early 20th century. Many of Iceland's larger outlet glaciers have been systematically monitored since 1930. Consequently, a general description of glacier conditions exists for the past 1,000 years, in addition to detailed knowledge of ice-front fluctuations for the past 70 years, and the idea of a broadly synchronous late 19th-century glacier maximum in Iceland has been widely accepted (Bradwell, Dugmore, & Sugden, 2006).

The difficulty in specifying the timing of the LIA arises because the coldest period of the last 1,000 years was not uniformly cold, and cold events around the globe were not synchronous. For example, the seventeenth century was the coldest LIA period in eastern Asia, while in Europe the nineteenth century was the coldest. Even on a regional scale, differences exist: in the late 1700s, the Czech Republic experienced a warm period while the Low Countries underwent cooling. However, a few cool periods may have been synchronous on a hemispheric or even global scale. An additional complication is that different seasons do not necessarily show temperature anomalies of the same sign over time. For instance, between 1750 and 1800, winter temperature anomalies in Switzerland show a cooling while summer temperature anomalies show a warming. Several model studies have investigated the forcing that could have caused the LIA and assessed its impact on different components of the climate system. Researchers have shown, using simple energy-balance models, that volcanic and solar forcing is important for a realistic simulation of the LIA, and have concluded that greenhouse gas changes must also be taken into account to simulate the warming observed over the twentieth century (Sedláček & Mysak, 2009).

Another area affected by the LIA is the Greenland Ice Sheet in the Kangerlussuaq area of west Greenland, a relatively stable passive ice margin with small outlet glaciers. Throughout southern Greenland, abundant evidence in the form of fresh erosion features and erratics on islands and coastal hills indicates that ice during the last glaciation covered most of the present unglaciated land area and extended onto the continental shelf. The bottom sediments on the banks of the shelf are sands and gravels with coarse clasts typical of glacial or glaciomarine facies. Moraine systems have not been positively identified, although geophysical surveys have shown their presence on the West Greenland shelf to the north. Despite this, the outer parts of the banks are generally considered to correspond to the limit of the last glaciation. While this can be crudely correlated with the Last Glacial Maximum (LGM), the history of glaciations of the shelf is likely to have been long and complex. Some confirmation of a shelf-break location of the ice-sheet margin at the LGM comes from the modeling of the relative sea-level curve for the southern sector, which requires this marginal position as well as the existence of a 1,500-meter-thick ice cover over the outer coast, completely covering the coastal mountains (Weidick, Anker, Kelly, & Ole Bennike, 2004).

Syszygyastro (n.d.) discusses several suspected causes of the LIA, suggesting that it could have been caused by: (A) asteroid or comet impacts; (B) cooling of the sun through sunspot minima; (C) drying cycles that introduced large amounts of dust into the atmosphere; (D) increased albedo of the Earth; (E) shutdown of the Mid-Atlantic conveyor current; or (F) mankind's industrial and warlike activities.

Conclusion

The compilation of data in this research makes clear that a definitive period for the Little Ice Age has not yet been established. It is also clear that researchers continue to seek additional explanations for the climatic phenomena observed in the regions discussed. One thing, however, is certain: the LIA occurred, it is well documented, and strong associations have been made between its patterns and the dynamics of global warming — evidenced by the recession of glaciers during warming intervals.

More detailed research is needed not only to determine the full effects of the LIA but also to explore what can be done to slow or prevent similar episodes from occurring again. Relatively little attention has been paid in the existing literature to possible methods of prevention, and this is an important dimension that deserves recognition and serious consideration. The effects of global warming on the planet as a whole are already visible, and the ongoing melting of glaciers worldwide is a clear call to action. Waiting until conditions become irreversible before developing prevention or mitigation strategies would be deeply unwise. If we do not learn what history has to teach us, we risk repeating its worst outcomes — and once the glaciers are gone, options for response will be severely limited.