Transcript ppt
Climate Change Daily Question – Records of Climate Change There are a number of methods available to determine past climates. With the methods listed below indicate whether they provide direct evidence or proxy evidence and list the extent of time they cover. Finally, rank them in order of usefulness. A. B. C. D. E. F. Weather Record Tree Rings Lake Sediments Cultural Recordings Ice Layers Oxygen Isotopes Daily Question – Records of Climate Change There are a number of methods available to determine past climates. With the methods listed below indicate whether they provide direct evidence or proxy evidence and list the extent of time they cover. Finally, rank them in order of usefulness. Ranking is problem specific (what is the time frame of interest) A. Weather Record – direct, 150 years B. Tree Rings – proxy, ~8,000 years C. Lake Sediments – proxy, ~30,000 years D. Cultural Recordings – proxy, ~9,000 years E. Ice Cores – proxy, ~1,000,000 years F. Oxygen Isotopes – proxy, ~10,000,000 years Causes of Glaciation Full Reasoning is not known Theory of Glaciation needs to include: Interglacial periods – periods of warm climate separating periods of glacial advancements. Causes of Glaciation Full Reasoning is not known Theory of Glaciation needs to include: Interglacial periods – periods of warm climate separating periods of glacial advancements. Glacial episodes in the Paleozoic (200-300 mya) and Precambrian time (700 mya). Causes of Glaciation Full Reasoning is not known Theory of Glaciation needs to include: Interglacial periods – periods of warm climate separating periods of glacial advancements. Glacial episodes in the Paleozoic (200-300 mya) and Precambrian time (700 mya). Earth’s average global is 14oC, in the geologic past it was 22oC – Glaciation requires a temp. of about 10oC. Continental glaciers originate in polar or elevated land. Sufficient precipitation needs to occur. Continental Movement – Plate Tectonics Land Masses need to be near poles ~ 700 million years ago ~200- 300 million years ago Ocean Circulation Gulf Stream has “turned off” Warm water is not able to get to poles. Earth’s Orbit Milankovitch cycles Eccentricity Measure of the noncircularity of Earth's orbit Cycle is about 100,000 years Milankovitch cycles Eccentricity Inclination or Tilt The changes in the axial tilt (22o to 24.5o) of the Earth The greater the tilt, the greater the contrast between summer and winter temperatures Cycle is about 41,000 years Milankovitch cycles Eccentricity Inclination Precession The wobble of the Earth as it spins on its axis Cycle is about 26,000 years Milankovitch cycles Main effect of cycles is to change the contrast in the temperature of the summer and winter. Glaciation would occur when the summer temperature is closer to the winter temperature, but winter temperature are not colder than usual. Rather the mild summers melt less ice than is received in the winter.