Climatic Changes
1.  Evidences from fossils
    (1).  Hippopotamus in England: 100,000 years ago
    (2).  Coal beds in Antarctica.
    (3).  Armeria sibirica (pollen of tundra plant) in SE 
                Massachusetts: 12,000 years ago.
2.  Dating Techniques
    (1).  Oxygen isotope analysis ( O18/O16 ratio)
                 A.  isotopes:          Elements having same number of protons but
                                              different number of neutrons.   
                     8O16, 8O17, 8O18
                     8O16 ---> number of protons and neutrons (8 protons)
                     6C12, 6C14
                 B.  Glacial period (ice age):   
                      (A).  Greater O18/O16 ratio in the ocean mud cores.
                               Smaller O18/O16 ratio in the ice core in Greenland and Antarctica.
                     (B).   less atmospheric evaporative power:  
                               O16 evaporated into air to produce snow leaving heavier O18 in 
                               the ocean.
                 C.  Interglacial period (warm period):
                     (A).   Smaller O18/O16 ratio in the ocean mud core.  Greater O18/O16
                               ratio in the ice cores in Greenland and Antarctica.
                     (B).   Higher atmospheric evaporative power (warm air):
                               more O18 evaporated into air and deposited in ice cores.
                 D.  To date sea temperatures extending back to 400 million years.      
    (2).  Carbon-14 method (by Libby)   
                 A.  Applicable to animals and plants.
                 B.  C14/C12 ratio is a constant (as C14/C12 ratio in the air) for a life animal 
                       or plant.          
                 C.  C14 content decreases by half for a period of 5730 years. 
3.  Geological Time Scale
    (1).  Era, Period, and Epoch.
    (2).  Era
                 A.  Precambrian Era:  4700 millions of years (Myr) to 570 Myr before 
                       present (BP):  Myr = milliom years.
                 B.  Paleozoic Era: 570 Myr to 225 Myr BP.
                 C.  Mesozoic Era:  225 Myr to 65 Myr BP.
                 D.  Cenozoic Era:   65 Myr to present.
                      (A).  Quaternary Period:  2 Myr BP to present.
                      (B).  Holocene Epoch:     0.01 Myr (10,000 years) BP to present.
                 E.  Last Ice Age:  Pleistocene Epoch (2 to 0.01 Myr BP).
    (3).  Climatic change in the past
                 A.  Much of the earth’s history: The global temperature was about 8 oC to 
                      15 oC warmer than at present (free of ice in polar region).
                 B.  Periods of glaciation
                      (A).  700 million years BP.
                      (B).  300 million years BP.
                               65 million years BP: no polar ice cap (interglacial period).
                      (C).  55 million years BP: began cooling trend.
                      (D).  45 million years BP: Antarctica ice sheet appeared.
                      (E).   2 million years BP (Pleistocene Ice Age):               
                               a.  Continental glaciers appeared in the Northern Hemisphere: 
                                    The ice sheet of several km thick extended as far south as 
                                    New York and the Ohio River Valley.
                               b.  4 major ice advances and retreats:
                               c.  Interglacial period:  lasted  about 10,000 years or more.
                               d.  Eemian interglacial period from 133,000 to
                                    114,000 years ago (lasted 19,000 years): two cold spells 
                                     lasting 2000 years and 6000 years(analysis of Greenland ice 
                       (F).  The most recent North American glaciers reached
                                their maximum thickness and extent about 18,000-22,000 years 
                                a.  Sea level: 125 m (395 ft) lower than at present.
                                b.  Human migration from Asia to North America through the 
                                     Bering land bridge.
                       (G). 14,000 years BP: Ice began to retreat (warming).
                       (H). Younger-Dryas (an arctic flower): 
                               a.  A cold spell (glacial condition) between 12,900 years and 
                                    11,600 years BP in northeastern North America and northern 
                               b.  Rapid Shifts from glacial to warm climates in Greenland around 
                                    the end of Younger-Dryas (ice core data): 3 years. 
                        (J). 8,000 years BP:  disappearance of the north American continental 
                               ice sheet.
                       (K). Holocene Maximum (Climatic Optimum)
                               a.  6,000 to 5,000 years BP.
                               b.  The global temperature was 1 oC warmer than at present.
                       (L).  Medieval Climatic Optimum
                               a.  Around 1,000 years BP: lasted for several hundred years.
                               b.  Northern Hemisphere
                                    (a).     warm and dry summers (absences of cold springs).
                                    (b).     Vineyards flourished and wine was produced in 
                                    (c).  Colonization of Iceland and Greenland by Vikings.
                       (M). Around A.D. 1200 (800 years BP)
                                a.  Mild climate of western Europe.
                                b.  Climatic extremes: cold winters followed by warm ones.
                                c.  several famines during the 1300s.
                       (N). Little Ice Age
                               a.  A.D. 1400 to 1850.
                               b.  Cold and severe winters, short and wet summers.
                               c.  The vineyards in England vanished.
                               d.  The Viking colony in Greenland perished.
                               e.  1816 (The year without a summer or eighteen hundred and 
                                    frozen to death).
                       (O). 1850 to present
                               a.  Average warming: 0.6 oC.
                               b.  Slightly cooling  between the 1940s and 1970s.                
                               c.  The 1980s and 1990s: warming trend
                               e.  The eight hottest years of this century occurring since 1979.
4.  Theories of Climatic Changes                                                                                        
    (1).  The Plate Tectonic Theory (Continental Drift Theory)
           A.  The earth crust is made of several major plates due to the convection cells 
                 of magma (partially molten material) below the crust.
           B.  The plates move slowly (1 inch/year) in relation to one another upon magma 
           C.  Pangaea (supercontinent): 6 major continents (plates) joined together in the 
                 higher latitudes than they are today (Tethys Sea is today’s Mediterranean 
           D.  Explains the near-sea level glacial landscapes over today’s tropical areas of 
                Africa, India, South America, and Australia near the end of Paleozoic Era 
                (250 Myr BP).
                (A).  Laurasia: northern hemisphere.
                (B).  Gondwana: southern hemisphere.
           E.  The continents (plates) has gradually separated from one another to form 
                today’s situations.
                (A). Ice sheets are more likely to form when land masses are concentrated 
                       in middle and high latitudes (more reflection of sun light).
                (B). The plate movement cuts off the warm water from moving toward high 
                       latitude ocean (promote winter glaciation).     
               (C). Subduction                      
                       a. An oceanic plate dives under a continental plate:
                           Heat and pressure melt a portion of the subducting rock (volcanic 
                           rock and calcium-rich ocean sediment).
                       b. Degassing: the release of volcanic gases (CO2, water).
                (D). Mountain buildings (Himalayan Mountains and Tibet plateau) due to 
                        the collision between two continental plates (the Indian plate vs the 
                        Eurasian plate: Change the global circulation patterns).
           F.  Explains gradual climatic change for a scale of million  years.
          G.   Mid-Atlantic Ridge: 
                (A). Trough (Fault) between North America plate moving toward west and 
                       Eurasian and African plates, both moving toward east.
                (B). The magma currents below the crust have been rising and splitting 
                       toward west and east (a tension force on the crust) along the bottom 
                       of the crust.                    
                (C). Magma erupted to the ocean floor to form ridge.
           H.  San Andreas Fault
                (A). The joint between North America Plate moving toward west and 
                        North Pacific Plate moving toward northwest (a compressional force).
                (B). The land over Palmdale was uplifted by more than one foot during the 
                        past several decades (a major earthquake is eminent at any moment): 
                        buy insurance.               
                 (C). Satellite measurement
                         a. Measurement of the distance between Quincy (North
                             California, North America Plate) and Otay Mountain 
                             (near San Diego, Pacific Plate) by sending Laser beams from 
                             satellite to these two locations.
                         b. Los Angeles is moving closer to San Francisco about 1 inch per 
  (2).    Volcanic Dust Theory
            A.  Suspended fine particles (sulfur rich) in the stratosphere
                  reduced solar radiation reaching the surface:
                  (A). A warming of the stratosphere (absorption of energy).
                  (B). A cooling of the surface air (reflection reduces solar energy reaching 
            B.  A period of high volcanic activity was followed by a period of cool climate:
                 (A). 1915 to 1963 (the year Mt. Agung, Bali Island, erupted): low 
                         frequency of volcanic eruptions and rising mean global temperature 
                         up to 1940’s.               
                 (B).  Mt. Tambora (Indonesian Island) erupted in 1815
                         ejecting 150 km3 of ash.  This was followed by a cool year in 1816 
                         (the year without summer in USA and Europe).           
                 (C). An intense volcanic activity 30,000 to 17,000 years ago established 
                         an ash layer over the Antarctic ice.  Global temperature cooled by 
                         3 oC.
                  (D). Glomar Challenger (NSF Deep Sea Drilling Project Ship) research 
                          project shows active volcanic eruption during the past 2 million years.
                  (E).  Recent Major volcanic eruptions
                          a.   Iceland’s Laki volcanic eruption in the summer of 1783:  the 
                                severe winter of 1783-84 (Benjamin Franklin).
                          b.  Krakatau eruption: 1883 in the strait of Sunda;
                                produced red sun for several months; associated with 
                                severe winters following the eruption.
                           c.  Katami: 1912, Alaska.           
                           d. Agung: 1963, Bali: lower the mean atmospheric
                                temperature of the Northern Hemisphere by about 0.3 oC.
                           e.  Mount St. Helens:  May 18, 1980 
                                (a).  Not much sulfur released to the atmosphere (more dusts).
                                (b).  Aerosols settled to ground quickly (not much climatic 
                                (c).  Global cooling :0.1 oC.
                                (d).  Large local effect: lower temperature by 8 oC during the day.
                            f. Mount. El Chichon (Mexico): 1982 (1982-83 is the strongest 
                                El Nino in the century).
                                (a).  40% more sulfuric aerosols than from the eruption of Mount 
                                       St. Helens.
                                 (b). Global cooling: 0.3 oC.
                            g. Mount Pinatubo (Philippines): June 12, 1991.
                                 (a). Sulfur dioxide plume girdled the lower stratosphere (25 Km) 
                                       over the equator (sulfuous aerosol layers found by Junge).
                                 (b). Mean global temperature had cooled by 0.8 oC by July 
                                 (c). El Nino since 1990 peaking in 1992 and ending in late 1995: 
                                       Offset the cooling caused by the Mount Pinatubo eruption.
               C. Acidity of annual ice layers in Greenland and Antarctica
                    (A). Little ice Age
                           Relatively acidic ice has been uncovered from about A.D.1350 to 
                           about 1700.
                    (B). Sulfur-rich volcanic eruptions may have trigger the cool period.
            D. Ocean floor core samples from the northern Pacific
                    (A). Active volcanic eruptions (10 times larger than at any other times) 
                           2.6 million years ago.
                    (B). A time when the Northern Hemisphere glaciation began.
  (3).  Aerosols (particulate) in the troposphere      
         A.  Any solid and liquid particles (not gases).
         B.  Sources of sulfate aerosols (most common and most important).
              (A).  Combustion of sulfur-containing fossil fuels.
              (B).  Ocean: Dimehtylsulphide (DMS) released by phytoplankton
                      (drifting aquatic plants).
         C.  Sulfate aerosols
               Brightening the clouds (condensation nuclei increases the number of cloud 
               droplets) and increasing reflection.
         D.  Lower the earth’s surface temperature during the daytime and may offset the 
               global warming induced by CO2.
               (A).  Less temperature warming in the Northern Hemisphere than in the 
                       Southern Hemisphere: more sulfate aerosols in the Northern 
               (B).  Little temperature warming in the United States compared to the rest 
                       of the world.    
               (C).  Most of the global warming has occurred at night and not during the day.
   (4).  Energy-Balance Theory 
          A.  Variation in Solar constant (Simpson’s theory)
                (A).  Moderate increase in solar radiation would permit higher moisture 
                        content of the air, causing a stronger meridian transfer of air and 
                        increasing precipitation in the polar region.
                (B). Greater summer cloudiness could inhibit melting snow and ice.
                (C). Diminished insolation would weaker the general atmospheric circulation 
                       and thereby reduce precipitation at higher latitudes.
                (D). Paradoxically, a lowering of the mean atmospheric temperature  might 
                       cause the recession of ice sheets, whereas a temperature increase 
                       would cause ice sheets to advance.
                (E). 1981-1986 (NASA’s Solar Maximum Mission satellite)
                       a. Solar irradiance declined about 0.10% (0.018% per year).
                       b. Irradiance began to increase since fall of 1986 (the last sunspot 
                       c. Upper Atmospheric Research Satellite (UARS): since 1991.
                (F). 0.5% increase in solar constant could account for 0.5 oC warming in 
                       mean annual hemispheric temperature over the past century.
            B. Sunspot cycle (Eddy’s Theory)
                (A). A huge magnetic storm that shows up as a cooler region (darker area 
                       called umbra) on the sun’s surface (penumbra: ring around umbra).
                       a.     The sun emits about 0.1% more energy during periods of sunspot
                               maximum than during periods of sunspot minimum. 
                       b.    The greater number of bright areas (faculae or plages, hot or white 
                               spots) around the  sunspots radiate
                               more energy which offsets the effect of the dark spots.
                (B). Sporer Minimum: 1450 to 1550 A.D., cold spell in Europe Norse 
                        Viking settlements in Greenland perished.
               (C).  Maunder’s minimum : 1645 to 1715 A. D.    
                       a.     Little ice age (1350 to 1850 A.D.) in Europe with fewer or no 
                               sunspot number (increased carbon-14 in tree rings).                                             
                       b.    Global mean temperature decreased by about 0.5 oC over the 
                               long-term average (a reduction in solar brightness).                                                             
                       c.     Landsberg’s study:  Globally the coldest interval of the Little Ice 
                               Age occurred 100 years after the Maunder Minimum  
               (D). Active sunspot in 1100 to 1250 A. D.
                      Medieval Warm period (950 to 1250 A. D.)
               (E). 11-year cycle (7 to 17 years).
                      35-year cycle (Bruckner cycle).
                      80-year’s cycle.
               (F). Short sunspot cycles: 
                      a. Higher air temperatures over lands in the Northern Hemisphere 
                          (1860 to 1985): more solar output.
                      b. Reduction in sea ice around Iceland.
              (G). Sun’s magnetic cycle: 22 years (Magnetic field reverses every 11 years).
                     a.  Correlate to 20-year droughts on the Great Plains.
                     b. The Quasi-Biennial Oscillation (QBO)
                         It takes about two years for the completion of the cycle of reversing 
                         stratospheric winds (easterlies vs westerlies) over the tropics. 
              (H). Carbon-14 in tree rings
                     a. C-14 is generated when cosmic rays impact nitrogen in the upper 
                     b. More active sun (more sunspots): Less Carbon-14 in the tree rings 
                         because of strong magnetic fields in the solar wind, shielding the 
                         earth from cosmic rays 
                     c. Scuderi tree-ring study in Sierra Nevada, California for 2000 years: 
                         close correlation between solar activity and air temperature (records 
                         show the Little Ice Age and the medieval warming).
               C.  Willet’s theory
                   (A). Increased ultra-violet solar radiation:
                          a. warms up the tropical atmosphere.
                          b. Polar area remains unchanged in temperature.
                          c. Stronger zonal flow  .
                          d. less meridian exchange of masses of air.
                   (B). Increased corpuscular radiation
                          a. Heats the upper air of the polar region: Magnetic field directs 
                              particles to the poles).
                           b. Zonal circulation is disrupted.
                           c. Greater meridian transfer of air with accompanying storms of 
                              temperature extremes.
                    (C). No appreciable change in mean atmospheric temperature, simply the 
                           change in circulation patterns.
      (5).    Astronomical Theory (Milankovitch’s theory, a Yugoslavian
               astronomer): Toward global cooling.
               A.  Eccentricity:       
                     (A).  Variation of the shape of the earth’s orbit (ecliptic plane) about the 
                               sun that results in the change in the distance between the earth and 
                               the sun.
                               a.  Perfect circular ecliptic plane:  zero eccentricity.
                               b.  Elliptical (oval or egg) ecliptic plane:  large eccentricity.
                               c.  Present time:   A period of low eccentricity.
                                    (a). The sun-earth distance is 3% more in July (Aphelion) than 
                                           in January (Perihelion) that leads to the increase of nearly 
                                           7% solar radiation from July to January.
                                     (b). Aphelion:  The position or time when the earth is farthest 
                                            away from the sun (July 4).
                                     (c). Perihelion:   The position or time when the earth is closest 
                                           to the sun (January 3)
                                d.  Highly eccentric orbit
                                     (a). 9% difference in the sun-earth distances between July and 
                                           January that leads to about 20% difference in the solar 
                                           energy received by the earth.
                                     (b). Change the length of season in each hemisphere (more 
                                            seasonal variation).
                  (B).   Hay’s theory:              
                               a.  Ice age occurred when the ecliptic plane is nearly circular.
                               b.  Smaller seasonal variation in air temperature for
                               a    circular ecliptic plane.        
                                     (a).    warm winter and cool summer
                                              More snowfall in winter that survives through summer.
                                     (b).    Smaller seasonal variation in solar radiation received by 
                                              the earth due to smaller seasonal variation of the sun-earth 
                  (C). Cycle of the eccentricity:  100,000 years.
             B.  Precession
                  (A).      The wobbling of the earth’s axis leading to the change in aphelion 
                               and perihelion with respect to seasons.
                  (B).      Cycle of precession: 23,000 years.
                               In 11,000 years, the perihelion will be in July (presently in January) 
                               and the seasonal variations in the
                               Northern Hemisphere should be greater than at present (vice versa 
                               for the Southern Hemisphere).
                  (C).     Glaciation (ice growth)
                              Greater distance between the earth and the sun in July
                              (colder summer) results in less snow melting.
            C.  Obliquity
                  (A).      The tilt of the earth’s axis varies between 22.1 to 24.5 degrees.
                  (B).       cycle:      41,000 years.
                  (C).       small tilt: reduced seasonal contrast which in turn could
                                promote the growth of ice sheet (warmer winter and cool 
                                summer favored glaciation, Hay’s theory).
                  (D).       The trend is now toward the minimum tilt and thus will favor 
                               glaciation in the future.
                  (E).        The peak tilt (24.5 degrees) occurred about 9,000 years ago.
    (6). Carbon dioxide theory (Global warming)
           A.  Greenhouse effect:  CO2 absorbs terrestrial (long-wave) radiation and 
                 warms up the atmosphere.
           B.  CO2 increased from 0.03% in 1860 to 0.033% in 1970, 0.035%
                 in 1990, 0.0355% in 1993, 0.036% in 1995, and 0.038% in 2005.
           C.  Global warming trend from 1860 to 1940s, cooling slightly until 1970 and 
                 then warming again to the present.
           D.  Between 1940s and 1970, the mean global temperature had declined 
                 (A). Would decline more had no CO2 increase.
                 (B). Increased dust particles slowed down the warming rate. 
                 Doubling CO2, raise surface temperature by 2 oC (1.5 to 4.5 oC).
            F.  Evidence from trapped air bubbles in the ice sheets of
                 Greenland and Antarctica:
                 CO2 levels were about 30% lower during glacial periods than during 
                 interglacial periods.
          G.  Methane (CH4), nitrous oxide (N2O), and chlorofluorocarbons
                (CFCs): equal greenhouse effect induced by CO2.
5.  Future Climate
    (1). warming trend (Budyko’s theory)
           A.  0.015% CO2 concentration: The polar ice cap extends to the equator.
           B.  0.033% CO2 concentration: The polar ice cap extends to 70 oN.
           C.  0.045% CO2 concentration: The polar ice completely melts: will occur 
                 by A.D. 2050.
    (2). Cooling trend (Bryson’s theory)
           Increased aerosols and moisture due to industrialization could reduce mean 
           atmospheric temperature.
    (3). Astronomical theory (Milankovitch’s theory) supports the cooling trend.
    (4). Most computer models based on greenhouse effect support the warming trend.
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