Changes

==Natural variability of the climate system==

==Natural variability of the climate system==

[[Image:Climate cycle.png|right|thumb|Cycle of warming and cooling]]

[[Image:Climate cycle.png|right|thumb|Cycle of warming and cooling|300px]]

The Earth has experienced numerous [[Ice Age|ice age]]s over the past two million years, during which global temperatures dropped approximately 6 degrees Celsius and then returned to normal. The frigid temperatures allowed ice sheets to expand southward, covering much of [[Asia]], [[Europe]], and [[North America]]. The cooling associated with ice ages is gradual, while the terminations are relatively rapid. However, even the rapid terminations of ice ages take centuries to millennia, which contrasts with the effects predicted for anthropogenic global warming.

The Earth has experienced numerous [[Ice Age|ice age]]s over the past two million years, during which global temperatures dropped approximately 6 degrees Celsius and then returned to normal. The frigid temperatures allowed ice sheets to expand southward, covering much of [[Asia]], [[Europe]], and [[North America]]. The cooling associated with ice ages is gradual, while the terminations are relatively rapid. However, even the rapid terminations of ice ages take centuries to millennia, which contrasts with the effects predicted for anthropogenic global warming.