Studying Paleoclimate to Reduce Climate Uncertainty Dorian S. Abbot.
Lecture 15 Defining climate, climate controls Climate classification Past climates Historical...
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Transcript of Lecture 15 Defining climate, climate controls Climate classification Past climates Historical...
Lecture 15
Defining climate, climate controls Climate classification Past climates
Historical climatepaleoclimate
Data and mechanism for change
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
Climate controls
• Latitude
• Elevation
• Topography
• Proximity to large bodies of water
• Prevailing atmospheric circulation
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
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
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
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?
Past climates, the change mechanisms
• Volcanic eruptions• Asteroid impacts• Solar variability• Variations in Earth’s orbit: Milankovitch
cycles– Precession– Obliquity– Eccentricity
• Plate tectonics
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
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