1. Class #34: Wednesday, November 181 Climate Types (E, and H) Past Climates: Proxy Data and Mechanisms of Change

2. Class #34: Wednesday, November 182 The 6 major climate groups A: Tropical moist B: Dry (can be subtropical or mid latitude) C: Moist with mild winters (mid latitude) D: Moist with severe winters (mid latitude) E: Polar (high latitude) H: Highland (rapid climate change with elevation) 2 nd letter: usually latitude (except B) 3 rd letter: differences in temperature

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6. 6 D Climate type Severe (winter) Midlatitude Similar to C but severely cold winter Average temperature of coldest month <27ºF Snow on ground for extended periods Average temperature of warmest month >50ºF Overall, large change in temperature with season

7. Class #34: Wednesday, November 187 D climate subtypes 2 nd letter –“f” no dry season –“w” winter dry season 3 rd letter –“a” hot summer –“b” warm summer –“c” cool summer –“d” extremely severe winter

8. Class #34: Wednesday, November 188 D Climate Subtypes (continued) Humid continental –Dfa, Dfb, Dwa, Dwb –Dfa, for example, Chicago Subarctic –Dfc, Dfd, Dwc, Dwd –Long winter –Brief cool summer

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11. Class #34: Wednesday, November 1811 E climate type Polar climate, very dry and cold Poleward of Arctic/Antarctic Circle, latitude 66.5º E climate subtypes –ET Tundra: mosses, lichens, flowering plants, woody shrubs, small trees, permafrost –EF Ice caps: no vegetation; Greenland, Antarctic Plateau

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13. Class #34: Wednesday, November 1813 H climate type: Highland Large variation of temperature and precipitation over small horizontal distances Large diurnal temperature variation Can be dry or moist, depending on orientation, humidity, and whether prevailing winds are upslope or downslope

14. Class #34: Wednesday, November 1814 Have today’s climates always been the same? This question leads to the study of past climates. So do the questions: Can we predict future climates? What is the impact of humans on climate? Two kinds of past climate: –Historical, past few thousand years –Paleoclimate, ancient, back billions of years

15. Class #34: Wednesday, November 1815 Historical Climate Humans have kept records Instrumental record –Since about 1600 Historical data: proxy data –Humans have kept some sort of record of climate conditions –Examples: dates of freezes of lakes and rivers, farmers’ logs, animals in cave paintings, other documents

16. Class #34: Wednesday, November 1816 Another source of data for the historical period is trees Tree rings are rings of growth in tree trunks in regions with distinct growing seasons. A wider tree ring means more growth. Growth varies with temperature and precipitation, depending on the species. Information from various species is most helpful. The study of tree rings is dendrochronology, and is done by dendrochronologists. Figure shows dry periods in Iowa in 1700, 1740, 1820, 1820, 1890, and 1930 from tree rings.

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20. Class #34: Wednesday, November 1820 Proxy measurements of precipitation from tree rings Dry periods: 1930s, the “Dust Bowl” around 1700 1740 1820 1890

21. Class #34: Wednesday, November 1821 Pollen for proxy information Pollen degrade slowly, distinctive shapes for each species Oldest sediments are deepest Spruce need a cool climate Decline of spruce during warming Pine need a warm and moist climate Oak need it drier than pine

22. Class #34: Wednesday, November 1822 Dating ancient climates Living things all contain carbon C 14 begins to change to C 12 in a radioactive decay process at an exponential rate with a half-life of 5760 years as soon as living matter dies Carbon dating good to 50,000 yrs with an uncertainty of about 15%. For older samples and rocks need another method

23. Class #34: Wednesday, November 1823 Dating really ancient climates Uranium-238 decays into Lead-206 with a half-life of 4.5 billion years No other (except possibly human) sources of Lead-206 How we know how old the Earth and moon are If equal amounts of Uranium-238 and Lead- 206, then 4.5 billion years old.

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25. Class #34: Wednesday, November 1825 Glaciers, Icebergs, Bubbles, and Dust Climate clues buried in ice just as in lake sediments When snow and ice exceed melting, glaciers form. Ice crystals crush under pressure, trapped air expelled, and bubbles form Ice 30-m thick can flow downhill. At the coast, calving produces icebergs when the glacier breaks, with as much as 90% underwater Gas bubbles with CO 2 and CH 4

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28. Class #34: Wednesday, November 1828 Dust Dust in ice cores can be volcanic activity, or dry and windy conditions Acidic dust with sulfuric acid indicates volcanic activity Dust storms in Africa can be detected in polar ice cores

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