Evidence Of Past Abrupt Climate Change

Scientists use various forms of proxy data as evidence of past abrupt climate change. The proxies most commonly used include tree rings, cor als, speleothems (cave deposits), glacial deposits, polar ice caps, lake and marine sediments, and pollens. It was through the use of proxies (ice cores) that scientists were able to determine that the Younger Dryas had occurred around 12,800 years ago. The event was an unusual break in the climate cycle of Earth's warming up after the Ice Age. The Earth returned to a glacial-like climate and persisted as a glacial ecosystem for the next 1,200 years. Then, around 11,600 years ago, the climate phase abruptly ended, and the temperature increased 17°F (10°C) in just a 10-year interval.

There have been other events over the past 50,000 years. The Heinrich events occurred during the last ice age and involved multitudes of icebergs broken from glaciers that melted and added freshwater to the ocean. This freshwater was believed to have played a role in moderating the circulation of the Atlantic Ocean and causing a sudden cooling in the climate. The Dansgaard/Oeschger events were rapid fluctuations of temperature that also occurred during the last ice age. Scientists have recorded 23 fluctuations that occurred 23,000 to 110,000 years ago where the atmosphere warmed up quickly, then cooled down over longer periods of time.

Another episode, called the 8,200-year event, lasted only 100 years, but temperatures in the North Atlantic region dropped an average of 5°F (3°C) and caused widespread dry conditions. Scientists speculate this was caused by freshwater being added to the Atlantic and slowing the thermohaline circulation. More recently, the interval known as the medieval warm period was a time of abrupt warming (0.3°F, or 0.2°C) about 1,000 years ago. This period ended 700 years ago with the start of the Little Ice Age, another abrupt climate change. The Little Ice Age existed from the 1300s to the mid-1800s. Its cooling was not as severe-only about 1.7°F (1°C).

Abrupt climate change has also been documented by archaeologists and climatologists as one of the chief causes for the fall of great civilizations. Among these are the Maya, the Anasazi, the Akkadian Empire, and civilizations in Mesopotamia, Egypt, India, and China, as well as cultures in Europe such as the Vikings.

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