Ch 7b: Atmosphere Flashcards
Climate:
time-average weather conditions at a place on the Earth’s surface.
climate records typically include
temperature, precipitation, humidity, wind, cloud cover
Climate change over geological time
cenozoic record of cooling, cretacenous warm interval.
Koppen scheme of climate classification:
tropical, dry, temperate humid (mesothermal), temperate cold (microthermal), polar
Deserts:
Semi-deserts:
250-500 mm
Distribution of deserts:
belts of low rainfall correspond to regions of divergence.
Types of deserts:
subtropical, continental, rainshadow, coastal, polar
Subtropical desert eg
Sahara, Kalahari, Great Australian
Continental desert eg
Gobi, Takla Makan
Rainshadow desert eg
Sonoran
Coastal desert eg
Atacama, Namib
Polar desert eg
Antarctica
Instrumental records
Short term, weather records
Proxy records
short to long term: historical, biological, geological, chemical
Average weather records
Global correlation, overall warming trend over last 150 yrs.
Geological: Glacier ice records
records of glacier extents, geological or historical.
Longer-term change: hundreds to thousands of years
climate is inferred indirectly, requires validation by other sources. Similar proxy data types as earlier changes.
Historical proxy records include
agriculture or shipping records, pictures, sketches, paintings, writings, personal letters.
Biological Climate proxies:
dendrochronology: ring widths show correlation with climate
Palynology
pollen: record of land vegetation
Last 2 Ma: Quaternary Period
marked by cold climates worldwide, glacial erosion and deposition in areas no longer glaciated
Extent of ice cover:
records indicate at least 4 advances and retreats, separated by interglacial periods.
Ocean sedimentary records:
6 layers of ice-rafted debris deposited during last glaciation (between 70-10ka)
Heinrich events:
catastrophic calving of ice sheet
Ocean sediment records: marine micro-organisms
many species of plankton have restricted temperature range. Species alternate in cores, indicating changing temperature changes.
Isotopes:
O18:O16.
When water evaportes:
vapor contains slightly less O18.
As ice sheets grow, O18:
increases in ocean water, decreases in continental ice sheets.
O18 is heavier
land rain is O16 enriched.
Cycles of climate change:
isotopes record many glacial and interglacial intervals in last 2Ma. Dominant period in last 800000 years is 100000 years.
Earlier glaciations:
late paleozoic, late proterozioc time
Late paleozoic
gondwanaland, glacial and interglacial intervals
Late proterozoic time
difficult to reconstruct, snowball Earth hypothesis
Milankovitch cycles
affect the distribution of solar energy over Earth’s surface. Affect climate: global totals, seasons
Causes of Climate change:
milankovich cycles, changes in solar energy output, plate tectonics, volcanic events, degassing of sediments, asteroid/comet impact.
Plate tectonics:
position of continents, redistribution of heat
Volcanic Events:
short term: dust particles in atmosphere reduce solar energy reaching the ground.
Long term: major volcanic episodes, ash to the atmosphere: cooling effect, carbon dioxide: greenhouse warming effect.
Degassing of sediments
hydrocarbons, esp methane, trapped in sediments may be released. Gas hydrates on continental margins. Methane burps.
Asteroid
triggering of the younger dryas cooling by ET impact.
