Ecology And Environment

What Caused the little Ice Age



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The little ice age is the name given to the global cool period that lasted between approximately 1350 and 1850. Exact dates are uncertain, and vary from place to place (and from scientist to scientist!). They are estimated from historical records, tree rings, economic indicators such as grain prices, and so on.

The causes of the little ice age are not certain, but the major theories are:

Variations in sunspot activity
Changes in ocean currents
Volcanic eruptions
Changes in the Earth's albedo

It is likely that a combination of these phenomena came together to create the little ice age.

Variation in sunspot activity

The sun is the major source of energy for the Earth and drives circulation of the atmosphere. Any change in the output of the sun affects the climate, and the number of sunspots has been shown to correspond to variations in the output of solar energy. More sunspots = higher energy. Fewer sunspots = lower energy.
During the little ice age two periods (called the Sporer minimum and Maunder minimum) of very low sunspot numbers occurred, suggesting the solar output was lowered as a result.

Changes in ocean currents

Ocean currents are like conveyor belts. Warm waters flow north to near Iceland, where the water cools. Like cold air, cold water sinks, and as it does so it draws more warm water along. The cold water at the bottom flows south, rising again when it reaches warmer climes. Thus a conveyor belt effect is established.
The atmosphere above the sea currents are affected by any changes in those currents, and the ocean can at different times act both as an absorber and emitter of heat. During the little ice age the currents were removing heat from the atmosphere.

Volcanic eruptions

Volcanic eruptions produce ash and other fine particulates that can shield the surface of the Earth from solar radiation. Even when the ash has cleared, sulphur droplets produced in the eruption form clouds that can shield the surface for years.

There was an increase in volcanic activity through the little ice age, and the coolest years correspond quite well with the largest eruptions. For example, Mount Tambora (in Indonesia) erupted in 1815, and the following year was called 'the year with no summer' across much of Europe and America.

Changes in albedo

Earth's albedo is the reflectivity of the surface. Snow and ice are highly reflective, and therefore have high albedo. After the Earth has begun to cool, more ice is present and glaciers and ice-sheets grow, thus increasing the Earth's albedo.

Changes to albedo do not cause the ice to form, but once formed, it causes more sunlight to be reflected, which causes even more cooling.



The effects of the little ice age are less uncertain than the causes, and those in the seventeenth century were most extreme.

During this period agriculture was severely affected, with resulting food shortages and famines. Millions died, for example, when harvests in Western Europe, Scandinavia, Great Britain and Eastern Europe failed. In Greenland and Iceland, the Viking culture declined catastrophically. The extremely cold climate affected general health and had massive, and mostly detrimental economic effects. It even had an impact on art and literature. There were migrations to escape starvation, to escape social upheaval, and simply to look for food (Eskimos were seen paddling off the coast of England, for example).

The coolest period of the little ice age (the 17th century), also possibly had another remarkable effect. The growth of trees was slowed considerably, producing a wood that would later be used by Stradivarius to produce the greatest, and most sought after violins in the world. See http://news.nationalgeographic.com/news/2004/01/0107_040107_violin.html for more information on this theory.

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