Changes

Evolutionary scientists Scientists who believe in global warming think that the Earth has experienced numerous [[Ice Age|ice age]]s over two million years, during which global temperatures dropped approximately {{temperature|6|11}} 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. It is often and possibly correctly argued by those such as Al Gore that artificial effects may compound with natural changes to produce a particularly dangerous temperature rise and that even if global warming is not wholly anthropogenic, humans may have the power to stop it.