Lecture 15 Defining climate climate controls Climate classification
- Slides: 28
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 • 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 the climate zones (ancient Greek)
Classifying climate zones --- Koppen • A. Humid tropical • B. Dry • C. Humid middle-latitude, mild winters • D. Humid middle-latitude, severe winters • E. Polar • H. Highland Note that boundaries fluctuate from year to year
Fluctuating boundaries of dry/humid
Tropical humid climates (A)
Dry climates (B)
Dry climates (B), not tropical
Moist subtropical to Mid-Latitude (C) Marine west coast climates
Humid subtropical (C)
Mediterranean climates (C)
Severe midlatitude climates (D) (humid, continental)
Subarctic (D)
Polar climates (E)
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 CO 2 and CH 4 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
Yearly averaged sunspot numbers, 16102000
Precession: Earth’s axis wobbles (like that of a spinning top) every 27 K years
Obliquity: the angle Earth’s axis makes with the plane of Earth’s orbit (41 K years)
Eccentricity: change in the shape of Earth’s orbit around the sun (100 K years)
Plate tectonics and climate change 300 million years ago
Ice age is a period global cooling that leads to the creation of vast ice sheets across land
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