METEOROLOGY

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METEOROLOGY

• GEL-1370

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Chapter Fourteen

• Climate Change

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Goal for this Chapter

• We are going to learn answers to the following
  questions
• How the global climate has changed in the past
• Theories on why the global climate has changed?

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If all the ice locked up in glaciers and ice
sheets were to melt, what would happen to this
town in coastal south Florida? (65m or 213 ft
rise)
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If all the ice melts what happens??
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Existence of Land Bridge in the Bering Strait
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Changing Climate

• Glaciers cover 10 of earths land surface
  (mainly Greenland and Antarctic ice sheets)
• If the all glaciers and ice sheets melt, global
  sea level rise will be 65 m (213 feet)
• Fossil pollen of a tundra plant in sediment layer
  in New England dated to be 12,000 yrs --- climate
  was much colder ocean sediment records and ice
  core records---
• 18 kyr ago, alpine glaciers extended to river
  valleys and huge ice sheets covered vast areas of
  North America and Europe New and Ohio River
  Valley were also covered with ice
• Glaciers advanced and retreated 10 times during
  the last 2 million years Are we still in the
  ice age (warmer part of it??)

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Past climate changes

• CLIMAP (Climate Long-range Investigation Mapping
  and Prediction) brought wealth of information
• Studies on Oxygen isotope ratios ---
• d18O (18O/16O)sam - (18O/16O)sam/
  (18O/16O)samx 1000
• Reconstruction of earths surface ocean
  temperature for various times during the past
• Vertical ice cores in Antarctica and Greenland
  --- info on past temperature patterns
• Glacier formation Snow accumulates ---
  compaction --- recrystallize into ice --- ice
  begins to move by gravity glacier is born
• In CLIMAP, the earths surface ocean temp for
  various times in the past was reconstructed

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Sea surface isotherms during August 18 kyr ago
and today (Left 18 kyr ago)
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Earths changing climate

• Global climate was much warmer (8-15 C) than
  today in the geological time frame polar region
  was ice-free
• 700 and 300 myr ago glacial periods existed
• 65 million years ago, the earth was warmer than
  now polar ice did not exist beginning 55
  million yrs, the earth entered a long cooling
  trend and polar ice caps appeared 10 myr ago,
  deep blanket of ice covered Antarctic snow and
  ice began to accumulate in high mountain valleys
  of the Northern Hemisphere, and alpine or valley
  glaciers soon appeared
• The Pleistocene epoch or the Ice Age began about
  2 myr ago glaciers appeared in the Northern
  Hemisphere, marking the beginning of the
  Pleistocene Epoch

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Earth Changing Climate contd.

• Pleistocene Glaciers advanced and retreated over
  large portions of North America and Europe
• Between the glacial advances , warmer periods
  that lasted for 10 kyr or more (interglacial
  periods)
• During the last glacial maximum (LGM), 18-22 kyr,
  sea level was 126 m before present --- vast areas
  exposed Siberia Alaska were connected
  (migration of animals and humans from Asia to
  North America)

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Past climate contd.

• Bubbles of air trapped in the ice --- past
  composition of the atmosphere, wind direction and
  intensity
• Dendrochronology Changes in the thickness of the
  rings indicate climatic changes from one year to
  the next (useful in trees that are stressed by
  temp or moisture during their growing season)
• Reconstruction of past climate is based on a)
  lake and ocean sediments b) loess and other soil
  deposits c) pollen in the ocean sediments, deep
  ice caves, soil deposits d) fossils in
  sediments e) oxygen isotope ratios of corals and
  other carbonate species (foram, etc) f) cave
  deposits (stalactites stalagmites)

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Pollen concentration vs depth
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Coiling pattern vs climate
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Oxygen isotope composition
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Climate change during the last 2 myr
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Climate through Ages 18 kyr

• Ice began to retreat 14 kyr ago as surface temp
  slowly rose 11 kyr ago, average temp suddenly
  dropped and northeastern North America and
  northern Europe reverted back to glacial
  conditions (Younger Dryas)
• 10 kyr ago, the cold spell ended and 8 kyr,
  continental ice sheets over North America
  disappeared
• 5-6 kyr BP, climate was 1C warmer than at
  present (Mid-Holocene maximum
• Holocene Epoch The second epoch of the
  Quaternary Period, beginning 10 kyr ago and
  continuing to the present time
• 5 kyr BP, cooling trend set in, alpine glaciers
  returned, but not continental ice sheets

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Average air temp variations for the past 18 kyr
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Average temp variations of eastern Europe for the
last 1200 yrs
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Climate during the last 1 kyr

• Ice core date from Greenland reveal rapid shifts
  in climate (from ice stage conditions to a warm
  state)
• 1200 AD, mild climate of western Europe changed
  to extreme variations climate grew stormy great
  floods and great droughts occurred cold winters
  followed by relatively warm ones several famines
  during the 1300s
• Little Ice Age Period from 1550 to 1850 when
  average global temperatures were lower (0.5C),
  and alpine glaciers increased in size and
  advanced down mountain canyons
• 1816 Unusually cold summer followed by a
  bitterly cold winter

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Climate during the last 1-kyr contd.

• 1970s early 1980s Average yearly temp showed
  considerable fluctuation from year to year from
  region to region, with overall trend pointing to
  warming
• Warning trend continued into the 1990s
• 20th century warming is 0.7C warming is not
  uniform greatest warming over the mid-latitude
  continents in winter and spring while a few areas
  (North Atlantic Ocean) have actually cooled in
  recent decades US has experienced little warming
• Warming of 0.7C is quite significant, as the
  global temp have varied no more than 1.5C during
  the past 10,000 yrs
• Part of the warming is due to an enhanced
  Greenhouse effect caused by increasing levels of
  greenhouse gases

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Causes of Climate Change

• Intricate relationship between atmosphere-ocean-co
  ntinent coupling --- not fully known
• Feedback mechanisms is not fully characterized
• Positive Feedback Initial increase in
  temperature is reinforced by the other process
• Example Earth has entered a slow warming trend
  --- temperature rises --- ocean water evaporates
  rapidly --- water vapor content in the atmosphere
  increases --- more IR energy is absorbed ---
  leads to warming --- more water vapor evaporation
  --- and so on Water vapor-temperature rise
  feedback Such a chain reaction is called
  Runaway greenhouse effect no evidence that a
  runaway greenhouse effect ever occurred on earth!

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Causes of climatic change contd.

• There are checks and balances for example, when
  air temp increases, outgoing IR energy increases
  and this helps to slow the temp change and
  stabilize the climate
• Example for negative feedback Air warms --- more
  evaporation --- more moisture (and precipitation)
  --- global low cloudiness increases --- large
  percentage of incoming sunlight is reflected ---
  less energy to heat the surface --- cooling
• All feedback mechanisms work simultaneously in
  both directions example increase in global
  surface air temp --- to melt snow and ice more
  --- decrease in albedo --- more solar radiation
  to reach the surface

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Climate change and feedback mechanisms

• Lower temp --- greater snow cover --- increase in
  albedo --- more light reflected back --- further
  drop in temp ---runaway ice age --- not found on
  the earth
• CLIMATE CHANGE, PLATE TECTONICS,
  MOUNTAIN-BUILDING
• Glacial features found near the sea level in
  Africa today area underwent a period of
  glaciation hundreds of millions of years ago
• Fossil remains of tropical vegetation can be
  found under layers of ice in polar regions today
• If land masses are redistributed (concentrated in
  middle high latitudes), ice sheets are likely
  to form (more light reflected --- cooling)
  influence the path of ocean currents --- affect
  the transport of heat wind

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Relationship between global change and plate
tectonics

• Rate at which plates move (currently 1-10 cm/yr)
  might be related to the climatic changes took
  place in millions of years rapid spreading, a
  relatively wide ridge forms, causing sea level to
  rise relative to the continents at the same
  time, an increase in volcanic activity vents
  large quantities of CO2 into the atmosphere ---
  increased greenhouse effect --- increase in
  global temperature
• Increased temperature leads to high precipitation
  --- increased chemical weathering and hence
  faster removal of CO2
• Mountain building processes lead to collision of
  two continental plates --- can have a marked
  influence of global circulation patterns (e.g.,
  Tibetan Plateau)

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Geographical distribution of landmasses 180 myr
ago (a) today (direction of continental
movement)
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During times of rapid spreading, increased
volcanic activity may promote global warming by
increased CO2 emission
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Milankovitch Theory

• Three separate cyclic movements combine to
  produce variations in the amount of solar energy
  that falls on the earth
• Changes in the eccentricity of the earths orbit
  (100,000 yrs) the difference in distance is only
  3 while the increase in the solar energy is 7
  received at the top of the atmosphere from July
  to January when the difference in distance is
  9, the difference in solar energy will be 20
• Precession (23,000 yrs) of the equinoxes as the
  earth rotates on its axis, it wobbles like a
  spinning top Presently, the earth is closer to
  the sun in January and farther away in July. Due
  to precession, the reverse will be true in
  11,000 yrs
• Changes in the tilt of earth (41,000 yrs)
  present tilt is 23½, but during the 41,000 yr
  cycle it varied from about 22 to 24½ smaller
  the tilt, less variations between seasons

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Earths orbital changes (eccentricity) 100 kyr
cycle
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Milankovitch theory
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(a) Changes in the tilt (41 kyr) (b) presently
earth is closer to the sun when N.Hemisphere is
in winter (c) 11 kyr from now, earth will be
closer to sun in July when N. Hemisphere is in
summer
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Past climate changes

• CLIMAP project results during the past 800 kyr,
  ice sheets have peaked about every 100 kyr
  superimposed on this are smaller advances that
  show up at intervals of about 41 kyr and 23 kyr
• CO2 levels were about 30 lower during glacial
  periods than during interglacial periods ice
  core studies also reveal CH4 follows CO2 pattern
• Why CO2 levels have varied as glaciers expanded
  and contracted Due to changes in the biological
  productivity (phytoplankton productivity)
• Changing levels of CO2 indicate a shift in ocean
  circulation patterns---changes in the
  precipitation evaporation rates wind
  intensity and direction

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Climate Change - contd

• Other factors that can affect temperature
  variations are
• Dust and other aerosol contents in the atmosphere
• Changes in the albedo of the ice sheets and
  clouds
• Isostatic changes due to depression by ice
  (during interglacial period)
• Presence of other trace gases
• Aerosol sources Factories, auto emissions, wild
  fires, dust storms, etc some particles (soil
  dust sulfate particles) reflect and scatter
  incoming sunlight while others (smoky soot)
  absorb sunlight warming
• Overall net effect of human-induced aerosols on
  climate is to cool the climate
• Sulfate aerosols serve as cloud condensation
  nuclei, and scatter and reflect incoming sunlight

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Volcanic eruption and climate

• Sulfur-rich gases have the greatest impact
• Two largest volcanic eruptions in the last 100
  yrs are El Chichòn in Mexico (April 1982)
  Mount Pinatubo in Philippines (June 1991)
• Mathmatical models predict global mean temp can
  drop by 0.2 to 0.5C
• Acidic ice was uncovered from AD 1350 to 1700
  corresponding to Little Ice Age sulfur-rich
  volcanic eruptions may have played an important
  role in triggering this cool period? Other cool
  periods were also triggered by such events??

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Changes in average global air temp from 1990-1992
after eruption of Mt. Pinatubo, June 1991 temp
decreased by 0.5C
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Variations in Solar Output

• 11-year sunspot cycle
• Suns energy output appears to change slightly
  with sunspot activity
• Maunder minimum Between 1645 and 1715, there
  were few sunspots this period is called so
• Changes in suns energy output cause for
  climate change??

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CO2, Greenhouse effect and global warming

• Annual average in 1999 368 ppm 1.5 ppm/yr
  increase 500 ppm by end of this century
• Increase in CH4, N2) CFCs effect CO2 in their
  ability to increase greenhouse effect
• Temperature increase of 1-3.5C

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Human activity contributes to global warming
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Ocean conveyor belt in the N. Atlantic
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chapter 14- Summary

• Variations in the oxygen-18/16 ratios-climate
  info
• CLIMAP Project global climate change in the past
• Glaciers glacial and interglacial periods
• Effect of volcanoes on global change
• Positive and negative feedbacks
• Milankovitch theory 3 periodicities factors
  that cause
• Sunspot cycle and climatic changes
• Maunder minimum
• CO2 levels during glacial and interglacial
  periods
• Relationship between increased temp and amount of
  pptn
• Fertilization effect, ocean as a source/sink of
  CO2