Changing Climate
In our discussion of climate change we can consider change of three types
- Gradual change of mean temperature, precipitation, etc. (e.g. global warming)
- Changes in climate variability (changes in frequency of floods, droughts, hurricanes, etc.)
- Climate surprises (abrupt changes in climate conditions not seen before in our recorded climate
history)
Both the written record of history and the geological record give
plenty of evidence that climate has changed many times and in many ways
over the surface of the earth, so climate change is not new. Twenty
thousand years ago ice several kilometers thick covers parts of the
Northern Hemisphere as far south as 40
(Schneider and Dickinson, 1974:
Rev. Geophys and Space Phys., 12, 447-493). About 1,000 years ago, a
relatively mild period permitted Viking explorers to travel throughout the
region of the North Atlantic. Harsh winters during a "little ice age" in
the 1700s wiped out Nordic colonies on Greenland. The 20th century has
been one of the mildest on record with temperatures at the end of this
century being warmer than anytime in the last 130,000 years. Biblical records
describe 7-year cycles of good years and bad years, and archeological
evidence points to past civilizations that became extinct, some due to
changing climate.
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