The Little Ice Age

Between roughly 1300 and 1850, many parts of the world, especially Europe and North America, experienced a period of cooler temperatures known as the Little Ice Age. It was not a true ice age, since average temperatures fell by less than one degree Celsius. Even so, the change had noticeable effects. Glaciers in the Alps advanced and destroyed farms and villages, and harvests failed more often.

One famous sign of the cold was the frost fairs held on the River Thames in London. In several especially cold winters, the river froze so solidly that people set up shops, played games, and even cooked meat on the ice. The last frost fair took place in 1814. Part of the reason the river no longer freezes is that the old London Bridge, whose many narrow arches slowed the flow of the water, was replaced in the 1830s.

Scientists are still debating what caused the Little Ice Age. A series of large volcanic eruptions probably played a role, since volcanic ash and gases can block sunlight for years. A period of unusually low activity on the sun may also have contributed. Whatever its causes, the Little Ice Age shows how even small changes in average temperature can affect human societies.