lecture 15
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Lecture 15. Defining climate, climate controls Climate classification Past climates Historical climate paleoclimate Data and mechanism for change. Climate, the collective state of the atmosphere for a given location and over a specified time interval. - PowerPoint PPT PresentationTRANSCRIPT
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Lecture 15
Defining climate, climate controls Climate classification Past climates
Historical climatepaleoclimate
Data and mechanism for change
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Climate, the collective state of the atmosphere for a given location and
over a specified time interval
• Location, regional or global scale climate
• Time
• Averages and extremes of variables– Temperature– Precipitation– winds
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Climate controls
• Latitude
• Elevation
• Topography
• Proximity to large bodies of water
• Prevailing atmospheric circulation
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Classifying the climate zones (ancient Greek)
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Classifying climate zones --- Koppen
• A. Humid tropical• B. Dry• C. Humid middle-latitude, mild winters• D. Humid middle-latitude, severe winters• E. Polar• H. HighlandNote that boundaries fluctuate from year to
year
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Fluctuating boundaries of dry/humid
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Tropical humid climates (A)
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Dry climates (B)
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Dry climates (B), not tropical
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Moist subtropical to Mid-Latitude (C)Marine west coast climates
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Humid subtropical (C)
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Mediterranean climates (C)
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Severe midlatitude climates (D) (humid, continental)
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Subarctic (D)
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Polar climates (E)
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Past climates
• Historical climate (past several K years)– Instrumental record (measurements)– Historical data (for example diaries, ship logs)
• Paleoclimate, study of climate of the distant past– Use environmental records, such as– Tree rings– Pollen records– Air bubbles and dust in ice– Marine sediments– Fossil record
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Concentration of atm CO2 and CH4 from ice bubbles in the Vostok ice core
2083 m long ice core. Dated by counting the number of ice layers
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Ice cores
• Dust in ice sheets can be caused by volcanoes
• Or by dry windy conditions that lead to soil erosion
• Colder periods in Earth’s history are usually much dustier
• Did the dust block the sun or did the colder temperatures cause drier conditions?
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Past climates, the change mechanisms
• Volcanic eruptions• Asteroid impacts• Solar variability• Variations in Earth’s orbit: Milankovitch
cycles– Precession– Obliquity– Eccentricity
• Plate tectonics
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Volcanic activity and climate change
• Explosive eruptions emit huge quantities of gases and fine grained debris into the atmosphere
• The greatest eruptions at low latitudes are powerful enough to inject the material into stratosphere where it will filter out a portion of the incoming solar radiation– Mount St Helens– El Chichon– Mount Pinatubo
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Solar variability
• Variations in the amount of energy from the sun
• Variations in number of sunspots follow an 11 year cycle
• Maunder minimum– some believe that a reduction in output of the sun during this time cooled Earth
• Little Ice Age, 1400--1850
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Yearly averaged sunspot numbers, 1610-2000
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Precession: Earth’s axis wobbles (like that of a spinning top) every 27K years
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Obliquity: the angle Earth’s axis makes with the plane of Earth’s orbit (41K years)
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Eccentricity: change in the shape of Earth’s orbit around the sun (100K years)
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Plate tectonics and climate change
300million years ago
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Ice age is a period global cooling that leads to the creation of vast ice sheets across land