MET 112 Global Climate Change -

1. MET 112 Global Climate Change - Natural Climate Forcing Professor Menglin Jin San Jose State University Outline – • Paleoclimate – temperature and CO2 • Natural forcing for temperature change • Features for Glacier and inter-glacier • Activity MET 112 Global Climate Change

2. Paleoclimate A lead to MET 112 Global Climate Change

3. Earth geological time scale Paleo : Greek root means “ancient” Modern age, ice age, last 2 million years Age of dinosaurs Animal explosion of diversity From the formation of earth to the evolution of macroscopic hard-shelled animals MET 112 Global Climate Change

4. Climate record resolution (years) 1 ,000,000 100,000 10,000 1000 100 10 1 1mon 1day Satellite, in-situ observation Historical data Tree rings Lake core, pollen Ice core Glacial features Ocean sediment, isotopes Fossils, sedimentary rocks MET 112 Global Climate Change 1 ,000,000 100,000 10,000 1000 100 10 1 1mon 1day

5. Climate record distribution from 1000 to 1750 AR4 6.11 MET 112 Global Climate Change

6. C14 and O18 proxy C14 dating proxy • Cosmic rays produce C14 • C14 has half-life of 5730 years and constitutes about one percent of the carbon in an organism. • When an organism dies, its C14 continues to decay. • The older the organism, the less C14 O18 temperature proxy • O18 is heavier, harder to evaporate. As temperature decreases (in an ice age), snow deposits contains lessO18 while ocean water and marine organisms (CaCO3) contain more O18 • The O18/ O16 ratio or δO18 in ice and marine deposits constitutes a proxy thermometer that indicates ice ages and interglacials. • Low O18 in ice indicates it was deposited during cold conditions worldwide, while low O18 in marine deposits indicates warmth MET 112 Global Climate Change

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9. External Forcing: Internal Forcing: Natural Climate Change The agent of change is outside of the Earth-atmosphere system • The agent of change is within the Earth-atmosphere system itself MET 112 Global Climate Change

10. Faint-sun paradox According to solar models, solar luminosity is 30% stronger nowadays than 4.5 billion years ago due to thermonuclear H to He makes the sun denser and hotter There should be glaciations up to 2 billion years ago Temperature should be 25K lower However According to record, glaciations are absent from 2 to 3 billion years ago Possible reasons: • Higher CO2 concentration (Kuhn & Kasting 1983, Kasting 1993) or CH4 causing greenhouse gas effect • Less continent and faster rotation of earth increase temperature by 4k and 1.5K respectively (Jenckins 1993) • Stronger solar wind stopped cosmic rays reaching earth leading to heating (harrison & Aplin 2001, Eichkorn et al.2002, Shaviv 2003) MET 112 Global Climate Change

11. Ice-covered earth Ice-free earth 700 million years ago due to very low CO2 concentration Hypothesis: plate tectonics and lack of weathering and photosynthesis left great amount of CO2 in the atmosphere (Kirshvink 1992) Support: thick layer of carbonate and banded iron formation on top of tropic glaciations Rapid transition from cold to warm climate would bring great changes in life on earth MET 112 Global Climate Change

12. Continental drift http://www.mun.ca/biology/scarr/Pangaea.html In 1915, German scientist Alfred Wengener first proposed continental drift theory and published book On the Origin of Continents and Oceans Continental drift states: In the beginning, a supercontinent called Pangaea. During Jurrasic, Pangaea breaks up into two smaller supercontinents, Laurasia and Gondwanaland,. By the end of the Cretaceous period, the continents were separating into land masses that look like our modern-day continents MET 112 Global Climate Change

13. Consequences of continental drift on climate • Polarward drifting of continents provides land area for ice formation  cold climate • Antarctica separated from South America reduced oceanic heat transport  cold climate • Joint of North and South America strengthens Gulf Stream and increased oceanic heat transport  warm climate • Uplift of Tibetan Plateau  Indian monsoon MET 112 Global Climate Change

14. Warm during Cretaceous High CO2 may be responsible for the initiation of the warming • Higher water vapor concentration leads to increased latent heat transport to high latitudes • Decreased sensible heat transport to high latitudes results from decreased meridional temperature gradient • Thermal expansion of sea water increased oceanic heat transport to high latitudes Psulsen 2004, nature The Arctic SST was 15 oC or higher in mid and last Cretaceous. Global models can only represent this feature by restoring high level of CO2 MET 112 Global Climate Change

15. Cretaceous being the last period of the Mesozoic era characterized by continued dominance of reptiles, emergent dominance of angiosperms, diversification of mammals, and the extinction of many types of organisms at the close of the period

16. Asteroid impact initializes chain of forcing on climate Short-term forcing: The kinetic energy of thebollide is transferred to the atmosphere sufficient to warm the global mean temperature near the surface by 30 K over the first 30 days The ejecta that are thrown up by the impact return to Earth over several days to weeks produce radiative heating. Long-term forcing: Over several weeks to months, a global cloud of dust obscures the Sun, cooling the Earth’s surface, effectively eliminating photosynthesis and stabilizing the atmosphere to the degree that the hydrologic cycle is cut off. The sum of these effects together could kill most flora. The latter results in a large increase in atmospheric CO2, enabling a large warming of the climate in the period after the dust cloud has settled back to Earth This hypothesis is proposed to 65 Million years ago for one possible reason that kills the dinosaurs MET 112 Global Climate Change

17. Variations in solar output Orbital variations Meteors External Forcing MET 112 Global Climate Change

18. A meteor is a bright streak of light that appears briefly in the sky. Observers often call meteors shooting stars or falling stars because they look like stars falling from the sky • Meteor showers • http://www.nasa.gov/worldbook/meteor_worldbook.html MET 112 Global Climate Change

19. Sunspots are the most familiar type of solar activity. Solar Variations • Sunspots correlate with solar activity • More sunspots, more solar energy MET 112 Global Climate Change

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21. SOLAR ACTIVITY • Sunspots are the most familiar type of solar activity.

22. THE SOLAR CYCLE • Sunspot numbers increase and decrease • over an 11-year cycle • Observed for centuries. • Individual spots last from a few hours to months. • Studies show the Sun is in fact about • 0.1% brighter when solar activity is high.

23. SOLAR INFLUENCES ON CLIMATE • Solar activity appears to slightly change the Sun’s brightness and affect climate on the Earth...

24. THE MAUNDER MINIMUM • An absence of sunspots was well observed • from 1645 to 1715. • The so-called “Maunder minimum” coincided with a cool climatic period in Europe and North America: • “Little Ice Age” • The Maunder Minimum was not unique. • Increased medieval activity • correlated with climate change. MET 112 Global Climate Change

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26. Orbital forcing on climate change Coupled orbital variation and snow-albedo feedback to explain and predict ice age He suggested that when orbital eccentricity is high, then winters will tend to be colder when earth is farther from the sun in that season. During the periods of high orbital eccentricity, ice ages occur on 22,000 year cycles in each hemisphere, and alternate between southern and northern hemispheres, lasting approximately 10,000 years each. James Croll, 19th century Scottish scientist MET 112 Global Climate Change

27. Further development of orbital forcing by Milutin Milankovitch Mathematically calculated the timing and influence at different latitudes of changes in orbital eccentricity, precession of the equinoxes, and obliquity of the ecliptic. Deep Sea sediments in late 1970’s strengthen Milankovitch cycles theory. MET 112 Global Climate Change

28. Milankovitch theory: Serbian astrophysicist in 1920’s who studied effects of solar radiation on the irregularity of ice ages Variations in the Earth’s orbit Changes in shape of the earth’s orbit around sun: Eccentricity (100,000 years) Wobbling of the earth’s axis of rotation: Precession (22,000 years) Changes in the tilt of earth’s axis: Obliquity (41,000 years) Orbital changes MET 112 Global Climate Change

29. Earth’s orbit: an ellipse • Perihelion: place in the orbit closest to the Sun • Aphelion: place in the orbit farthest from the Sun MET 112 Global Climate Change

30. Eccentricity: period ~ 100,000 years MET 112 Global Climate Change

32. Precession: period ~ 22,000 years MET 112 Global Climate Change

33. Axis tilt: period ~ 41,000 years MET 112 Global Climate Change

34. Eccentricity affects seasons Small eccentricity --> 7% energy difference between summer and winter Large eccentricity --> 20% energy difference between summer and winter Large eccentricity also changes the length of the seasons MET 112 Global Climate Change

35. Obliquity explain seasonal variations Ranges from 21.5 to 24.5 with current value of 23.439281 Small tilt = less seasonal variation cooler summers (less snow melt), warmer winters -> more snowfall because air can hold more moisture Source: http://www.solarviews.com/cap/misc/obliquity.htm

36. Precession of equinoxes • Vernal equinox has 24 000 period around the orbit. • Moon’s gravitational pull on Earth’s equatorial bulge causes wobling MET 112 Global Climate Change

37. Milankovitch cycles suggest changes in the mean temperatures of earth Source: Whyte (1995) MET 112 Global Climate Change

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39. Temperature: the last 400,000 years From the Vostok ice core (Antarctica)

40. Fig 4.5 High summer sunshine, lower ice volume

41. Formation of Glaciers • Glaciers - composed of fallen snow that is compressed into a large, thickened mass of ice over many years • Glacier Growth: When over a year snowfall (winter) is larger than snowmelt (summer) • Glacier Decay: When over a year snowfall (winter) is less than snowmelt (summer) • Glacier growth and decay largely influenced by summer temperatures. MET 112 Global Climate Change

42. ____________________________ ____________________________ Ocean changes Chemical changes in the atmosphere (i.e. CO2) Natural variations Internal Forcing Plate tectonics/mountain building Volcanoes MET 112 Global Climate Change

43. Activity Consider the fact that today, the perihelion of the Earth’s orbit around the sun occurs in the Northern Hemisphere winter. In 11,000 years, the perihelion will occur during Northern Hemisphere summer. A) Explain how the climate (i.e. temperature of summer compared to temperature of winter) of the Northern Hemisphere would change in 11,000 years just due to the precession. B) How would this affect the presence of Northern Hemisphere glaciers (growing or decaying)? Assume growth is largely controlled by summer temperature. MET 112 Global Climate Change

44. 42 of 70 If the earth’s tilt was to decrease, how would the summer temperature change at our latitude • Warmer summer • Cooler summer • Summer would stay the same • Impossible to tell

45. 42 of 70 A: How would climate change • Warmer winters, cooler summers • Warmer winters, warmer summers • Cooler winters, warmer summers • Cooler winter, cooler summer MET 112 Global Climate Change

46. 42 of 70 B: How would glaciers change? • Glaciers would grow • Glaciers would decay • Glaciers would stay about constant MET 112 Global Climate Change

47. Major features of ice age • Minimum insolation could be explained by • Milankovitch cycle followed by advancement • of glaciers • Polar front moves south • Salinity increases • Thermohaline circulation increases • Lower sea surface temperatures and sea • levels followed by reduced evaporation and • precipitation • Nutrients and biological productivity increase • Deep water sequesters CO2 from atmosphere • Cooling due to expanding ice caps and • decreased CO2 MET 112 Global Climate Change

48. Last Glacial Maximum (LGM) 22 ~ 14 K year • 3.5 –4 km thick • 50-60 x 106 km3 water • 120 m sea level reduction • 700 –800 m geosyncline depression (still rebounding) • Large changes in flora and fauna • Most of planet equatorward of ice sheets: • →colder and drier • →wind speed 20 –50% higher • →higher dust levels • →lower CO2 concentration (~200ppm) and CH4 concentration feedback MET 112 Global Climate Change

49. Major features of interglacial (Honocene) • Glaciers retreat • shows maximum insolation Milankovitch cycle • Higher sea levels • Higher sea surface temperatures • Enhanced evaporation and precipitation • Salinity decreases • Polar front moves north • Thermohaline circulation decreases • Nutrients and biological productivity decrease • Warming due to shrinking ice caps and increased CO2 • Abrupt warming: one of most rapid transitions • Interrupted by brief period of cold –YoungerDryas (~11 KABP) • Continuation of warming beginning in ~10 KABP MET 112 Global Climate Change

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