AOSC 200 Lesson 12

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AOSC 200Lesson 12
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Past and present climates

• weather - short time fluctuations
• climate long-term behavior
• - location
• - time
• - average and extremes
• climate controls
• - latitude
• - elevation
• - topography
• - proximity to large bodies of water
• - atmospheric circulation

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THE CHANGING CLIMATE

• Climate involves more than just the atmosphere.
• Climate may be broadly defined as the long-term
  behavior of global environmental system
• To understand fully and to predict changes in
  the atmospheric component of the climate system.
  one must first understand the sun, oceans, ice
  sheets, solid earth, and all forms of life"
• Thus we talk about a climate system consisting of
  the atmosphere, hydrosphere, solid earth,
  biosphere and cryosphere.
• Climate system involves the exchange of energy
  and moisture among these components

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Fig. 14-3, p. 414
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Climate Zones

• In the three cell model discussed before the
  intersections were shown at 30 and 60 degrees
  latitude.
• However these intersections move over the year.
• In the winter they move South. In the summer they
  move North. This is because the axis of rotation
  of the earth is tilted with respect to the
  sun-earth plane. Seasons.
• This gives a variation in the climate at any
  latitude.
• A variation can also be induced by other effects.

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Effect of the Olympic Mountains on average annual
rainfall. Rain Shadow effect
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Annual precipitation for three cities across the
US
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CLIMATE ZONES

• VLADIMAR KOPPEN ZONES
• TROPICAL MOIST A
• DRY B
• MOIST WITH MILD WINTERS C
• MOIST WITH SEVERE WINTERS D
• POLAR E
• HIGHLAND H

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World map of the Kopper climate classification
scheme
Fig. 14-2, p. 413
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Tropical Humid Climates - A

• High mean monthly temperature, at least 18.3 C.
• Rage of temperature is small, less than 10
  degrees.
• Divided into three sub-types
• Tropical wet climates (Af)
• Tropical wet and dry climates (Aw)
• Tropical monsoon climates (Am)

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Tropical Humid Climates
Iquitos, Peru (Af), Pirenopolis, Brazil, Aw,
Rochambeau French Guiana, Am
Fig. 14.4
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Tropical rain forest near Iquitos, Peru, (Af)
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Baobob and Acacia trees in grassland savanna (Aw)
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Dry Climates

• Evaporation plus transpiration exceeds
  precipitation. Descending branch of the Hadley
  cell.
• Mainly over land, diurnal variation larger than
  annual variation.
• Two subtypes
• Steppe or semi-arid (BS)
• Arid or desert (BW)
• BSh and BWh are warm dry climates
• BSk and BWk are cold dry climates

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Dry Subtropical Climates
Dakar, Senegal BSh, Cairo, Egypt BWh
Fig. 14.5
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Warm Dry Climates
San Diego, Calif.BSk, Santa Cruz, Argentina, BWk
Fig. 14.6
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Rain streamers are common in warm dry climates.
Rain evaporates before it reaches the ground.
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Creosote bushes and cactus in the arid
southwestern deserts (BWh)
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Steppe grasslands of western North America (BS)
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Moist Subtropical and Midlatitude Climates

• Characterized by humid and mild winters.
• Lie between the tropics and mid-latitudes
• Three major subgroups
• Marine West Coast Cfb and Cfc
• Humid Subtropical Cfa and Cwa
• Mediterranean Csa or Csb

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Marine West Coast Cfb, Cfc
Bergen, Norway Cfb, Reykjavik, Iceland Cfc
Fig. 14.7
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Humid Subtropical Cfa, Cwa
New Orleans, Louisiana, Cfa, Hong Kong China, Cwa
Fig. 14.8
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Mediterranean , Csa, Csb
Lisbon, Portugal, Csa, Santiago, Chile, Csb
Fig. 14.9
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Mediterranean-type climate of North America.
Chaparral foothill pine, chamise and manzanita.
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Severe Midlatitude Climates, D

• Tend to be located in the eastern regions of
  continents.
• Temperature range is generally greater than seen
  in the western climates (C)
• To be classified as D the average cold
  temperature must be less than -3 C, and the
  average summer temperature must exceed 10 C.
• Two basic types
• Humid Continental (Dfa/b and Dwa/b)
• Subarctic (Dfc/d and Dwc/d)
• a,b,c, - hot summers, d - severe winter and cold
  summer

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Humid Continental
Vladosvostok, Russia Dwb, Fargo, North Dakota,
Dfb
Fig. 14.10
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Adirondack Park - humid continental climate (Dfa)
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Subarctic
Fairbanks, Alaska, Dfc, Verkhoyansk, Siberia, Dfd
Fig. 14.11
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Coniferous forests occur where winter
temperatures are low and precipitation is
abundant (Dfc)
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Polar Climates, E

• Occur poleward of the Arctic and Antarctic
  circles
• Mean temperatures are less than 10 C for all
  months.
• Annual precipitation is less than 10 inches.
• Two polar climate types are identified
• Tundra (ET) and Ice Caps (EF)
• EF have essentially no vegetation

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Polar Climates, E
Barrow, Alaska, ET, Eismitte, Greenland, EF
Fig. 14.12
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Tundra vegetation in Alaska sedges and dwarfed
wildflowers (ET)
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Highland climate (H)
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DETECTING CLIMATE CHANGE

• DIFFICULT TO DETECT CLIMATE CHANGE EXCEPT OVER
  LONG PERIODS OF TIME.
• INSTRUMENTAL RECORDS GO BACK ONLY A COUPLE OF
  CENTURIES. THE FURTHER BACK, THE LESS RELIABLE
  ARE THE DATA.
• SCIENTISTS MUST DECIPHER CHANGES FROM INDIRECT
  EVIDENCE
• HISTORICAL DOCUMENTS
• TREE RINGS
• POLLEN RECORDS
• GLACIAL ICE AIR BUBBLES AND DUST
• SEA-FLOOR, MATINE SEDIMENTS. OXYGEN ISOTOPE
  RATIOS IN FOSSIL SHELLS
• FOSSIL RECORDS

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CLIMATE CLUES
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Cave drawing from the Sahara Desert
Fig. 14-14, p. 422
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TREE RINGS

• In regions with distinct growing seasons, trees
  growth appears as distinct rings. Typically one
  ring per year.
• Dendrochronology
• Width of the ring is a function of available
  water, temperature, and solar radiation.
• Tree species have different responses to these
  three factors hence the factors can be
  separated by looking at different species

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TREE RINGS
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Plot of annual precipitation in Iowa derived from
the analysis of tree rings
Fig. 14-16, p. 423
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POLLEN RECORDS

• Pollen degrades slowly and each species can be
  identified by the shape of its pollen
• Radioactive carbon dating gives the age of the
  pollen.
• As the climate changes, different types of
  species become dominant
• Hence the pollen record can be used to identify
  the type of climate that existed

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POLLEN RECORDS
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ICE SHEETS

• Each year snow falls on the ice sheets and
  glaciers. As it accumulates it compresses and
  traps air bubbles.
• These bubbles of air trapped in ice can be
  analyzed to determine atmospheric composition.
• Glaciers that exist today can hold bubbles that
  are tens or hundreds of thousand of years old.
• Dust in the ice sheets can be caused by
  climate-changing volcanoes, or dry windy
  conditions that lead to soil erosion.
• Find that the colder periods of the Earth history
  (20000, 60,000 and 100,000 years ago) are usually
  much dustier

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Concentration of Carbon Dioxide and Methane
determined from air bubbles in ice cores.
Fig. 14-18, p. 426
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MARINE SEDIMENTS/FOSSIL RECORDS

• Foraminifera are micro-organisms that live in the
  sea and have a calcium carbonate shell. CaCO3
• As the foraminifera die they sink to the ocean
  floor to form chalk deposits.
• Among these chalk deposits one also find fossil
  shells.
• Oxygen has two isotopes which have an atomic mass
  of 16 and 18
• The ratio of these two isotopes in the shells and
  foraminifera is a function of the sea temperature
• Fossils reveal ancient animal and plant life that
  can be used to infer climate characteristics of
  the past

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Variation in average temperature determined from
O18/O16 ratio in fossil shells
Fig. 14-20, p. 428
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ICE SHEETS

• Each year snow falls on the ice sheets and
  glaciers. As it accumulates it compresses and
  traps air bubbles.
• These bubbles of air trapped in ice can be
  analyzed to determine atmospheric composition.
• Glaciers that exist today can hold bubbles that
  are tens or hundreds of thousand of years old.
• Dust in the ice sheets can be caused by
  climate-changing volcanoes, or dry windy
  conditions that lead to soil erosion.
• Find that the colder periods of the Earth history
  (20000, 60,000 and 100,000 years ago) are usually
  much dustier

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Concentration of Carbon Dioxide and Methane
determined from air bubbles in ice cores.
Fig. 14-18, p. 426
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MARINE SEDIMENTS/FOSSIL RECORDS

• Foraminifera are micro-organisms that live in the
  sea and have a calcium carbonate shell. CaCO3
• As the foraminifera die they sink to the ocean
  floor to form chalk deposits.
• Among these chalk deposits one also find fossil
  shells.
• Oxygen has two isotopes which have an atomic mass
  of 16 and 18
• The ratio of these two isotopes in the shells and
  foraminifera is a function of the sea temperature
• Fossils reveal ancient animal and plant life that
  can be used to infer climate characteristics of
  the past

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Variation in average temperature determined from
O18/O16 ratio in fossil shells
Fig. 14-20, p. 428
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NATURAL CAUSES OF CLIMATE CHANGE

• UNRELATED TO HUMAN ACTIVITY.
• VOLCANIC ACTIVITY
• ASTEROID IMPACTS
• SOLAR VARIABILITY
• VARIATIONS IN THE EARTH'S ORBIT
• PLATE TECTONICS
• CHANGES IN THE OCEAN CIRCULATION PATTERNS

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Annual acidity of layers of an ice core in
Greenland
Fig. 14-21, p. 430
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VOLCANIC ACTIVITY

• MOST VOLCANOES EJECT DUST ETC. INTO THE
  TROPOPSHERE WHERE IT IS QUICKLY RAINED OUT.
• HOWEVER LARGE VOLCANOES CAN EJECT GASES,
  ESPECIALLY SULFUR DIOXIDE, INTO THE STRATOSPHERE.
• IN THE STRATOSPHERE THE SULFUR DIOXIDE TRANSFORMS
  INTO AEROSOLS, WHICH REMAIN IN THE STRATOSPHERE
  FOR ONE TO TWO YEARS.
• THIS WILL TEND TO COOL THE TROPOSPHERE - SCATTERS
  SOLAR RADIATION BACK TO SPACE.
• ERUPTION OF MOUNT TAMBORA IN INDONESIA LED TO
  'YEAR WITHOUT A SUMMER'
• MOUNT PINATUBO, 1991, LOWERED TEMPERATURE BY 0.5 C

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Variations in the Earths orbit

• Over long time periods the shape of the earths
  orbit around the sun, and the tilt of its axis
  are not constant. We can identify three ways in
  which these factors change
• Precession the Earth wobbles on its axis
  similar to a spinning top. (27,000 years)
• Obliquity its inclination to the solar plane
  changes (41,000 years)
• Eccentricity the elliptical shape of the orbit
  changes (100,000 years)

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SUNSPOT NUMBERS 1600-2000
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SUNSPOT NUMBERS

• The output of energy from the Sun has an eleven
  year cycle which also follows the number of
  dark spots on the Sun sunspots.
• People have been observing sunspots since the
  invention of the telescope, 1600
• In the period 1645 and 1715 the number of
  sunspots was dramatically lower Maunder
  minimum.
• Coincided with the little ice age (1400-1850)

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Continental Drift
Fig. 14-26, p. 436
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Continental Drift

• The Appalachians are a major source of coal.
  Among the coal can be found fossil remains of
  ferns.
• The coal came from the decay of ferns. This
  requires a moist warm climate such as at the
  equator in order to grow at a rate to produce
  enough vegetative matter to produce coal.
• So the Appalachians had to be much close to the
  equator when coal was deposited
• Continental drift.

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North Atlantic ocean conveyor belt keeps Northern
Europe warm. Any disruption will mean colder
climate.
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Fig. 14.27
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Changes in the Ocean Circulation Patterns

• The ocean circulation tends to keep the northern
  latitudes warmer.
• However if the overall flow patterns are changed
  then the northern latitudes can get colder, and
  ice sheets can expand southward.