Human Influences on Climate

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Human Influences on Climate

• Greenhouse effect
• Feedbacks
• Northward movement of the jet streams
• Changing Land Surfaces
• Heat Islands
• Consequences of Greenhouse Effect

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Simple Greenhouse Model
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Greenhouse Effect
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Greenhouse Effect
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Greenhouse Effect
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Ice-albedo feedback effect
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Positive Feedback
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Negative Feedback
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CLIMATE FEEDBACK MECHANISMS

• POSITIVE AND NEGATIVE FEEDBACKS
• WATER VAPOR - POSITIVE
• ICE COVER - POSITIVE
• .CLOUDS - POSITIVE AND NEGATIVE - MAINLY NEGATIVE
  

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Positions of the jet streams
Fig. 7-27, p. 191
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Jet Streams on March 11, 1990Sub-tropical
Blue, Polar Red
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Relation between jet stream and high and low
pressure systems
Fig. 8-30, p. 231
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DAYS WHEN JETSREAM WITHIN 150 MILES OF BALTIMORE
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Frontal Movement and Climate Change

• Increasing evidence that the Polar and
  Sub-tropical jet streams in the Northern
  Hemisphere are moving northward.
• This implies that the weather patterns associated
  with the jets (fronts) are also moving northward
• As the sub-tropical jet moves northward so do the
  high pressure systems associated with this jet.
• Expect drier summers
• Could increase in greenhouse forcing in the
  tropics lead to a stronger Hadley cell
  circulation, and hence to a movement of the jet?

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Disappearance of the Aral Sea, during the period
from 1973 to 2000. Largely due to diversion of
water from the rivers feeding the sea for
irrigation.
Fig. 15.8
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Aral Sea

• Government of the Soviet Union diverted waters
  feeding this inland lake to provide water for the
  growing of cotton.
• Aral Sea began shrinking rapidly
• Climate has also changed in the region
• Asian Dust Bowl
• Increased salinity destroyed fishing industry

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Roadways and buildings reduce evapor-transpiration
and absorb more solar radiation than the
surrounding rural regions.
Fig. 15.9
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Washington DC Heat Island
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THE CLIMATE OF CITIES

• URBAN HEAT ISLAND
• TEMPERATURES ARE GENERALLY HIGHER THAN IN RURAL
  AREAS, CREATING AN 'ISLAND' OF WARMER AIR.
• CITIES ARE GENERALLY CLOUDIER, FOGGIER, WARMER,
  WETTER
• WHY?
• ROCK-LIKE MATERIALS OF CITY HAVE HIGH THERMAL
  CAPACITY
• IMPERVIOUS SURFACES REMOVE PRECIPITATION QUICKLY
• LARGE SOURCES OF HEAT
• ATMOSPHERIC POLLUTION TRAPS RADIATION
• TALL BUILDINGS ALTER THE AIR FLOW
• INCREASED PRECIPITATION
• THERMALLY INDUCED UPWARD MOTIONS

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Fig. 15-1, p. 442
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CONSEQUENCES OF GREENHOUSE WARMING

• .WATER RESOURCES AND AGRICULTURE - CHANGES IN
  PRECIPITATION PATTERNS - LENGTH OF GROWING SEASON
  
• .SEA LEVEL RISE - .MELTING OF GLACIERS PLUS THE
  THERMAL EXPANSION OF THE OCEANS - HAS RISEN 10-25
  CM OVER PAST CENTURY
• .NEW WEATHER PATTERNS - HIGHER FREQUENCY AND
  GREATER INTENSITY OF HURRICANES BECAUSE OF WARMER
  SEA SURFACE TEMPERATURES.
• SHIFTS IN PATHS OF CYCLONIC STORMS -
  PRECIPITATION PATTERNS.
• .SHIFTS OF OCCURRENCES OF TORNADOES.
• .MORE INTENSE HEAT WAVES AND DROUGHTS IN SOME
  REGIONS AND LESS IN OTHERS.