Little Ice Age

The Little Ice Age was a period of regionally cold conditions between about AD 1300 and 1850. The Little Ice Age was a period of regionally cold conditions between roughly AD 1350 and 1850. The term "Little Ice Age" is somewhat questionable, because there was no single, well-defined period of prolonged cold. There were two phases of the Little Ice Age, the first beginning around 1290 and continuing until the late 1400s. There was a slightly warmer period in the 1500s, after which the climate deteriorated substantially. After 1600, there are indications that average winter temperatures in Europe and North America were as much as 2°C lower than at present.

There is substantial historical evidence for the Little Ice Age. The Baltic Sea froze over, as did many of the rivers and lakes in Europe. Pack ice expanded far south into the Atlantic making shipping to Iceland and Greenland impossible for months on end. Winters were bitterly cold and summers were often cool and wet. These conditions led to widespread crop failure, famine, and population decline. The tree line and snowline dropped and glaciers advanced, overrunning towns and farms in the process. There was a lot of social unrest as large portions of the population were reduced to starvation and poverty.

The period between 1600 and 1800 marks the height of the Little Ice Age and is characterized by cold and long winters as well as well as some unusual warmth during the summer. Climate variability in Northern Europe became more pronounced than before. The period was also characterized by the expansion of European trade and the formation of European sea born Empires. This was directly linked to advances in technology harnessing more of nature's power and towards the end of the period of fossil-fuelled power. The 17th and 18th centuries also saw the specialization of agricultural regions, which produced specific products for local and international markets.

The height of the Little Ice Age was also the period in which glaciers advanced rapidly and threatened to crush complete villages in the Alps.

On balance, the Little Ice Age affected northern European history in different ways. Regions that diversified agriculture and had good access to the international trade network, like Britain and the Low Countries, could cope quite easily with increasingly severe weather conditions. They could import food when harvests failed. Trade also gave them the financial base to develop technological responses.

In isolated regions, like high alpine areas of Switzerland, the Highlands of Scotland or Iceland, the unfavorable condition of the Little Ice Age, especially cold springs and harvest rains as well as longer winters, strongly influenced grain prices and were drivers for local famines. In central Europe the Little Ice Age was characterized by increased droughts as well as by increased flood frequency. In general the impact on different parts of Europe differed considerably. Some regions thrived while others struggled.

What caused the Little Ice Age?
The earth does not have some magical average natural temperature to which it always returns. If it warms, the earth must be receiving more heat or retaining more heat. If it cools, then it must be receiving less heat from the Sun or radiating more into space, or both. Is that what happened during the Little Ice Age?

Maunder Minimum
The exact cause of the Little Ice Age is unknown, but there is a striking coincidence in the sunspot cycle and the timing of the Little Ice Age. During the Little Ice Age, there is a minimum in sunspots, indicating an inactive and possibly cooler sun. This absence of sunspots is called the Maunder Minimum.

Sunspot numbers graph
Source: Wikipedia/ Robert A. Rohde

The Maunder Minimum occurred during the coldest period of the Little Ice Age between 1645 and 1715 AD, when the number of sunspots was very low. It is named after British astronomer E.W. Maunder who discovered the dearth of sunspots during that period. The lack of sunspots meant that solar radiation was probably lower at this time, but models and temperature reconstructions suggest this would have reduced average global temperatures by 0.4ºC at most, which does not explain the regional cooling of the climate in Europe and North America.

North Atlantic Oscillation
What does explain a drop of up to 2 degrees C in winter temperatures? The North Atlantic is one of the most climatically unstable regions in the world. This is caused by a complex interaction between the atmosphere and the ocean. The main feature of this is the North Atlantic Oscillation (NAO), a seesaw of atmospheric pressure between a persistent high over the Azores and an equally persistent low over Iceland. Sometimes the pressure cells weaken and that has severe consequences for the weather in Europe.

Positive NAO
Positive North Atlantic Oscillation.
Image Courtesy Martin Visbeck

When the Azores high pressure grows stronger than usual and the Icelandic low becomes deeper than normal, this results in warm and wet winters in Europe and in cold and dry winters in northern Canada and Greenland. This also means that the North Atlantic Storm track move north, directing more frequent and severe stroms over northern Europe. This situation is called a Positive NAO Index.

Positive NAO
Negative North Atlantic Oscillation.
Image Courtesy Martin Visbeck

When both pressure systems are weak, cold air can reach Northern Europe more easily during the winter months resulting in cold winters and the North Atlantic strom track is pushed south, causing wet weather in the Mediterranean. This situation is called a Negative NAO Index.

It is now thought that during the Little Ice Age NAO Index was more persistent in a negative mode. For this reason the regional variability during the Little Ice Age can be understood in terms of changes in atmospheric circulation patterns in the North Atlantic region.

 

Further reading
Dodgshon, Robert A., ‘The little ice age in the Scottish Highlands and Islands: Documenting its human impact’, Scottish Geographical Journal, Vol. 121, No. 4 (2005), 321

Fagan, Brian M., The Little Ice Age: how climate made history, 1300-1850 (New York: Basic Books, 2000)

Le Roy Ladurie, Emmanuel, Times of feast, times of famine: a history of climate since the year 1000 (LinkLondon: Allen & Unwin, 1972)

Mann, M. E., ‘Medieval Climatic Optimum’, in Michael C. MacCracken and John S. Perry (eds.), Encyclopedia of Global Environmental Change
 (vol. 1, Chichester: John Wiley & Sons, Ltd, 2002), 514–516. Access at: http://holocene.meteo.psu.edu/shared/articles/medclimopt.pdf

Pfister, C. and Brazdil, R., ‘Social vulnerability to climate in the “Little Ice Age”: an example from Central Europe in the early 1770s’, Climate of the Past Discussions, Vol. 2 (2006), 123-155. Access at: http://www.clim-past.net/2/115/2006/cp-2-115-2006.html

Robinson, Peter J., ‘Ice and snow in paintings of Little Ice Age winters’, Weather, Vol. 60, No. 2 (2005), 37-41