Earth Sciences 240A - Lecture 32 - Climate I
Introduction
Climate vs. Weather
It’s just a matter
of time/scale
21 thousand years ago: Glacial
period
Enormous ice
sheets; sea level down ~110 m
100 mya: No ice anywhere
Why
the variations?
Climate System
‘Forcing’
Factors that cause change
‘Response’
Result of forcing factors
Some Forcing Factors:
Tectonic Processes
Dictated by Earth’s internal heat
engine
Very slow to change climate
Ocean currents partly directed by
placement of continent blocks
Earth Orbital Changes “Milankovitch Factors”
Circular to oval orbit about Sun: 100,000
year period
Earth’s axis tilt; 21.5o
to 24.5o: 41,000 year period
Earth’s axis
wobble (‘precession’): 26,000 year period
Combine to produce cyclical solar radiation variation
Sun Energy Change
Long-term
Sun’s radiation
has increased since ‘birth’
Short-term
‘Sun spots’: 11
year period
Climate Change
Responses
Importance of time of forcing vs.
time of response
Full on – full off: never in nature
“Rate of response is fastest when
‘system’ is far from equilibrium”
“Each component of climate responds
at a different rate”
Feedback
Case: global cooling
Positive feedback
Example: spread of
snow/ice strengthens glacial growth
Negative feedback
Example: increase of ice sheets
means decreased weathering, which means more CO2 left in greenhouse
Earth’s Surface Heat
Sun Radiation
Latitude variation
Albedo : % of incoming radiation that is reflected
rather than absorbed by a surface
Snow/vegetation
Climate Data Archives
Historical Data
Quality of harvests
Distribution of
pollen
Tree rings
Pre-Historical Data
Sediment and Ice
Cores
Oxygen Isotopes
Oxygen Isotopes
16O (99.8%) and 18O (17O
too rare)
Stronger bonds - heavier isotopes
Fractionation
Evaporation
Temperature dependency
Geothermometer
Climate Models
”Models put numbers on ideas”
Types
Physical
Most simulate
today’s climate
‘control case’
Geochemical
Follow material
masses through climate systems
Geochemical
tracers
Past Glaciations
Terminology confusing, so use:
Icehouse
Time of
continental ice somewhere
May be
glacial/interglacial periods
Greenhouse
Time of no
continental ice
Next: Climate II
26 November
Climate III
28 November
End of course
Review of previous exam
1 December