søndag den 16. december 2007

The Last 2,000 Years

During the last 2,000 years, the climate has been relatively stable. Scientists have identified three departures from this stability, known as the Medieval Climate Anomaly (also referred to as the Medieval Warm Period), the Little Ice Age and the Industrial Era:

The Medieval Climate Anomaly: Between roughly 900 and 1300 AD, evidence suggests Europe, Greenland and Asia experienced relative warmth. While historical accounts and other evidence document the warmth that occurred in some regions, the geographical extent, magnitude and timing of the warmth during this period is uncertain (NRC, 2006). The American West experienced very dry conditions around this time.

The Little Ice Age: A wide variety of evidence supports the global existence of a "Little Ice Age" (this was not a true "ice age" since major ice sheets did not develop) between about 1500 and 1850 (NRC, 2006). Average temperatures were possibly up to 2ºF colder than today, but varied by region.

The Industrial Era: An additional warm period has emerged in the last 100 years, coinciding with substantially increasing emissions of greenhouse gases from human activities.

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