Europe and North America during last Ice Age, 110,000 to 12,000 years ago. Variations in Earths orbit (Milankovitch cycles). The Milankovitch cycles are a set of cyclic variations in characteristics of the Earths orbit around the Sun. Each cycle has a different length, so at some times their effects reinforce each other and at other times they (partially) cancel each other. Past and future of daily average insolation at top of the atmosphere on the day of the summer solstice, at 65 N latitude. There is strong evidence that the Milankovitch cycles affect the occurrence of glacial and interglacial periods within an ice age. The present ice age is the most studied and best understood, particularly the last 400,000 years, since this is the period covered by ice cores that record atmospheric composition and proxies for temperature and ice volume. Within this period, the match of glacial/interglacial frequencies to the Milanković orbital forcing periods is so close that orbital forcing is generally accepted. The combined effects of the changing distance to the Sun, the precession of the Earths axis, and the changing tilt of the Earths axis redistribute the sunlight received by the Earth. Of particular importance are changes in the tilt of the Earths axis, which affect the intensity of seasons. For example, the amount of solar influx in July at 65 degrees north latitude varies by as much as 22% (from 450 W/m² to 550 W/m²). It is widely believed that ice sheets advance when summers become too cool to melt all of the accumulated snowfall from the previous winter. Some believe that the strength of the orbital forcing is too small to trigger glaciations, but feedback mechanisms like CO 2 may explain this mismatch. iceagenow/Europe_During_Last_Ice_Age.gif
Posted on: Sat, 17 Jan 2015 09:17:57 +0000
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