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Lecture 30: Historical Climate

Lecture 30: Historical Climate. Part V, 270-271; Ch. 17, p. 287-308. Historical Climate: The Little Ice Age. Part V, 270-271; Ch. 17, p. 287-308. Were climate changes during the last 1000 years similar in pattern across the globe, or did they vary from region to region?.

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Lecture 30: Historical Climate

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  1. Lecture 30: Historical Climate Part V, 270-271; Ch. 17, p. 287-308

  2. Historical Climate: The Little Ice Age Part V, 270-271; Ch. 17, p. 287-308 • Were climate changes during the last 1000 years similar in pattern across the globe, or did they vary from region to region? • Can we see an imprint from millennial-scale and orbital-scale changes during this interval? • What evidence indicates a cooler climate in Europe and nearby regions during the Little Ice Age? What were its causes? • Why are climate changes during the last millennium difficult to detect?

  3. Climate Change at Different Time Scales Tectonic-scale Millennial-scale Orbital-scale Hundreds of millions of years (Oscillations) (Cycles) Tens to hundreds of thousands of years Thousands of years Historical-scale Decades to hundreds of years

  4. Proxy Records of Climate • Proxies that record annual growth patterns can indicate year to year variations in climate • -tree rings • -ice cores • -deep lake sediments • -coral reefs

  5. Climate Change Since the Last Glacial Maximum Data important for estimating past climate include: lake bottom sediment, ice cores, fossil evidence, written documents, coral isotopes, calcium carbonate layers in caves, borehole temperature, and dendrochronology or tree ring data. These data have helped identify several important climate change events in the past 18,000 years.

  6. The Little Ice Age: Local or Global? Sea ice on the coast of Iceland The cooling in Europe (1400-1900): colder winters and shorter growing seasons Evidence Lakes, rivers, and ports in Europe froze. The European population seriously affected. Mountain glaciers in the Alps of Switzerland and Austria advanced. The Little Ice Age was not a true ice age. Major ice sheets did not develop. Small (<1°C) drop in global temperature. Widely scattered land-based records, but few records from the oceans.

  7. The Little Ice Age(~1270-1850) The Hunters in the Snow by Pieter Brueghel the Elder (Kunshistorisches Museum, Vienna) Historical documents

  8. Little Ice Age February, from the Très Riches Heures du duc de Berry, ca.1410

  9. Little Ice Age The Reverend Robert WalkerSkating on Duddingston Loch attributed to Henry Raeburn, 1790's

  10. Two Interpretations of The Little Ice Age The Little Ice Age in Europe could have resulted from A continuation of slow orbital-scale cooling Part of a millennial-scale oscillation

  11. Causes of The Little Ice Age Low solar activity (1645-1715): 50 sunspots over a 30-yr period compared to normally 40,000 to 50,000 spots.

  12. Causes of The Little Ice Age (2) More volcanic eruptions The Year without summer in 1816 caused by the 1815 eruption of Mt Tambora Mt Tambora in Indonesia Ice Core in Greenland

  13. Causes of The Little Ice Age (3) Shutdown of thermohaline circulation

  14. Yearly Temperature Change for the Last 2000 Years Red: recent estimates; Blue: earlier estimates Global Warming Data from tree rings, corals, ice cores, and historical records are shown in various colors. Thermometers data in black. About 1000 y.a., Medieval Warm Period. Certain regions were warmer than others.Warm and dry summers in England (1000-1300):vineyards flourished and wine was produced. Vikings colonized Iceland and Greenland. http://upload.wikimedia.org/wikipedia/commons/b/bb/1000_Year_Temperature_Comparison.png

  15. Yearly Temperature Change Since 1850 1998 Data from thermometers http://commons.wikimedia.org/wiki/Image:Instrumental_Temperature_Record.png

  16. The Earth’s Climate History • Over the last century, the earth’s surface temperature has increased by about 0.75°C (about 1.35°F). • Little Ice Age = Cooling during 1,400 A.D. – 1,900 A.D. (N.H. temperature was lower by 0.5°C, alpine glaciers increased; few sunspots, low solar output) • Medieval Climate Optimum (Warm Period) = Warming during 1,000 A.D. – 1,300 A.D. in Europe and the high-latitudes of North Atlantic (N.H. warm and dry, Nordic people or Vikings colonized Iceland & Greenland) • Holocene Maximum = 5,000-6,000 ybp (1°C warmer than now, warmest of the current interglacial period) • Younger-Dryas Event = 12,000 ybp (sudden drop in temperature and portions of N.H. reverted back to glacial conditions) • Last Glacial Maximum = 21,000 ybp (maximum North American continental glaciers, lower sea level exposed Bering land bridge allowing human migration from Asia to North America) • We are presently living in a long-term Icehouse climate period, which is comprised of shorter-term glacial (e.g., 21,000 ybp) and interglacial (e.g., today) periods. There were four periods of Icehouse prior to the current one. • For most of the earth’s history, the climate was much warmer than today.

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