Ice Ages and Climate Change

1. Ice Ages and Climate Change GLY 2010 – Summer 2014 Lecture 21

2. Discovery of an Ice Age • Louis Agassiz, a Swiss-American scientist and physician, was the first to recognize evidence for an ice age • Trained in medicine and natural history, he was the first to propose, in 1837, that earth had been subjected to a past ice age • 1807 - 1873

3. Louis Agassiz • Agassiz moved to the United States in 1846 • He became professor of zoology and geology at Harvard University, and founded the Museum of Comparative Zoology • He became interested in the last glacial advance in North America, and studied it for the remainder of his life

4. Ice Ages • Ice ages - are times when the entire Earth experiences notably colder climatic conditions • During an ice age • The polar regions are cold • There are large differences in temperature from the equator to the pole • Large, continental-size glaciers or ice sheets can cover enormous regions of the earth

5. Previous Ice Ages • The climate history of earth is under active investagation • Two Precambrian ice ages are known • 2000 MYBP • 600 MYBP • Late Paleozoic ice age, about 250 MYBP • Pleistocene ice age

6. LatePaleozoicGlaciation

7. Plate Tectonics and Climate • Glaciers can only form on land • As plates move, evidence for a cold climate, in the form of glaciation, can only exist when land masses are present at high latitudes • Movement of land masses also alters the oceanic circulation pattern, a vital factor in determining climate conditions

8. Pleistocene Glaciation • Began about 1.6 MYBP • There were at least 4 glacial advances • Climate cooled 5-10ºC during glacial episodes, warming in between • Last episode peaked 18,000 years ago, ice covering about 30% of the earth’s surface

9. North American Ice Cover • Figure shows the extent of ice cover from 18,000 to 8000 years ago • White is ice, blue is glacial meltwater lakes

10. Remnants of the Ice • Loess is very fine sediment • Extensive, thick loess deposits generally formed in areas bordering large, continental glaciers • Loess is thickest just downwind of major river valleys

11. U.S. Loess Deposits

12. Climate Questions • What causes the onset of glacial conditions? • What caused the alternation of glacial and interglacial conditions during the Pleistocene?

13. Orbital Influence on Climate • The earth’s orbit around the sun, and rotation around its own axis, influence climate • Milutin Milankovitch proposed on theory of climate modification based on variations in incoming solar radiation, caused by orbital variations • 1879-1958

14. Variation in Orbital Eccentricity • The shape of the orbit changes over a period of about 100,000 years • The change is exaggerated in the drawing for clarity

15. Tilt of the Rotation Axis • Varies over a 41,000 year period • Varies from 21.5 to 24.5 degrees

16. Precession of the Axis • Earth’s axis wobbles, or precesses, over time, like a spinning top • This means the axis points to different places in the sky over a 26,000 year period

17. Milankovitch Hypothesis • Milankovitch combined these ideas in a mathematical formulation that predicted their combined effect on climate fluctuations of the Pleistocene • The three factors have almost no effect on the total amount of solar energy reaching the earth

18. Orbital Variations and Climate Change

19. Effects of the Milankovitch Hypothesis • The effect of the various cycles is to change the contrast between seasons • Milder winters in high latitudes lead to climate warming, and greater snowfall • Cooler summers would reduce snowmelt • Combined, this might trigger ice formation, and lead to an ice age • This can explain the alternating glacial-interglacial effects seen in the Pleistocene

20. Other Factors Effecting Climate • Composition of the earth’s atmosphere • Variations in reflectivity of the earth’s surface

21. Composition of the Earth’s Atmosphere • We know the present composition of the atmosphere • How can we measure it in the past? • One method is to analyze gas bubbles trapped in glacial ice at the time of formation • Gas bubbles trapped in other substances, such as amber, can also be analyzed • Certain gases, such as carbon dioxide, methane, and freon, are greenhouse gases

22. Greenhouse Effect • Sun emits ultraviolet (UV - purple), visible (green) and infrared (IR -red) wavelengths • Earth emits ONLY emits IR energy • CO2 traps IR, and greenhouse (earth) warms

23. Greenhouse Gases • Polyatomic gases with three of more atoms may trap infrared radiation leaving the earth • This radiation is earth’s cooling system • The gases act like a blanket, warming earth

24. Global Warming

25. Measuring Temperature Over Time • It is easy to measure current temperatures • How do we measure temperatures at some point in the past? • We use geothermometers • Most of these depend on the ratios of one isotope to another

26. Oxygen Isotopes As Geothermometers • There are three stable isotopes of oxygen, 16O, 17O, and 18O • 18O is heaviest, and moves the slowest, so it is less like to be incorporated into oxygen containing compounds, such as water (ice) • As temperatures increase, the probability of 18O being incorporated increases

27. 18O/16O Fractionation

28. Oxygen Geothermometer Data

29. Ice Cores • Ice cores in Greenland and at the Russian Antarctic station (Vostok) have provided radiometrically datable ice deposited more than 420,000 years ago • Oxygen isotope studies give us an essentially continuous climate record for that period

30. Other Climate Indicators • Calcite linings in underground channels provide much longer climate records • Calcite contains oxygen, so can be used as a geothermometer • Records may go back hundreds of thousands of years • Marine sediments have also been used for geothermometry studies

31. Stalagmite Evidence

32. Temperatures at Glacial Maximum Climate model calculation based on several sources of data • Differences between the annual mean near-ground air temperatures for present-day climate and for the climate during the last ice age approximately 18,000 years ago

33. Cenozoic Climate

34. Glacial Pair Photography • On the left is a photograph of Qori Kalis Glacier taken in July 1978, and on the right, a photograph taken from the same vantage in July 2004 • Both photographs taken by Lonnie G. Thompson, Byrd Polar Research Center, the Ohio State University

35. Muir Glacier • On the left is a photograph of Muir Glacier taken on August 13, 1941, by glaciologist William O. Field; on the right, a photograph taken from the same vantage on August 31, 2004, by geologist Bruce F. Molnia of the United States Geological Survey (USGS).

36. Sea-Level Changes • When temperature changes, sea-level rises or falls, due to the melting of glaciers, and thermal expansion of sea-water • Since 1900, sea-level has risen ~ 20 centimeters, and is estimated to rise as much as 100 centimeters by 2100

37. Post-Glacial Sea-Level Rise

38. Effect of Rising Sea-level • Uncontrolled, sea-level rise by the year 2100 could lead to the erosion or inundation of 38% to 61% of existing coastal wetlands in the United States.

39. Sea-level Rise: Florida

40. North America if All Ice Melted

41. Effects of Sea-Level Rise • Beach erosion • Salt water encroachment • Flooding of coastal areas • Changes to coastal wetlands • More information on climate change effects, including sea-level rise, in the southeast is available at: http://www.epa.gov/climatechange/impacts-adaptation/southeast.html

42. Bering Land Bridge • Increased glaciation results in lower sea-levels, and may result in land bridge formation • Ex - Bering Sea between Siberia and Alaska during Wisconsin glaciation • Humans, mastodons, and mammoths migrated from Asia to N. America this way • Camel and horse went the other way

43. Albedo • Albedo is the reflectivity of the earth surface • Ice reflects a lot of radiation • Forests or sea-water are much darker, and absorb more radiation • Absorption leads to heating, and reflection to cooling, of the earth’s atmosphere and surface

44. Effect of Albedo • As ice melts, albedo decreases • Ice has an albedo of about 0.7, which means 70 of the nergy hitting a surface is reflected to space • Ocean water has an albedo of 0.2 • Thus, as ice is converted to water, heating increases

45. Effect of Meltwater on Glacier

46. Arctic Ice Melt

47. Arctic Ice Levels • In June 2012, the Arctic lost a total of 2.86 million square kilometers (1.10 million square miles) of ice, the largest June ice loss in the satellite record. • Ice level in June, 2012 in the Arctic was the second lowest since satellite observations began in 1979 – this year isn’t far behind

48. Petermann Glacier - 2012 • The calving of a massive 46 square-mile iceberg two times the size of Manhattan from Greenland's Petermann Glacier on July 14 - 18, 2012, as seen using MODIS satellite imagery

49. Petermann Glacier - 2010 • The animation begins on August 5, 2010, and ends on September 21, with images spaced about 8 days apart • A 100 square-mile ice island broke off the Petermann Glacier • It was the largest iceberg in the Arctic since 1962

50. Geogenic or Anthropogenic Climate Change? • Is climate change due to man or is it natural? • Maps show predictions from climate models