As pointed out in a November 21 letter to the editor, Earth has been hotter than it is now, so how is current warming different? Past warmings have been caused either by well-understood variations in the Earth’s orbit around the Sun and / or oscillations in the Earth’s tilt, or by emissions of carbon dioxide and methane, usually due to widespread volcanism. Today’s temperature rise comes at a time when the Earth’s orbit and tilt cycles are not expected to warm Earth, and there is no widespread volcanism. Human activities are the cause of warming.
Additionally, in the past, most global warming was gradual, taking thousands of years. It gave animals and plants time to adapt. When the Earth warmed rapidly, events were almost always very destructive to life. Sometimes there have been massive extinctions, such as at the end of the Permian geological period, when 96% of marine species and 70% of terrestrial vertebrate species became extinct. According to information online from NASA, the current rate of warming is similar to past rapid and disruptive warming events and 20 times faster than warming caused by natural cycles. It is true and it is a source of concern.
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