Honors 1360 Planet Earth
Last time:Measuring Earth’s Hydrosphere
Obs: Altimetric height changes on rivers & lakes (with strong seasonal cycle & dependence on precip)
Obs: Altimetric height changes in oceans (Steric plus mass sea level change > climate predictions!)
Obs: Satellite imaging of extent & thickness of sea ice (Arctic sea ice in a “new normal”; likely to be ice free in 5-15 years)
Today:• The Cryosphere
13 October 2008
Read for Wed: 351-363
Example IV: Satellite Gravity to Measure Mass Change:
Example IV: Satellite Gravity to Measure Mass Change:
The Cryosphere:
Frozen water at or near the Earth’s surface
Includes snow, alpine glaciers, ice caps (Greenland and Antarctica), sea ice (e.g. North Pole)
Earth is currently (past 12,000 to 15,000 years) in an interglacial period of a ~1.8 to 2.5 million year epoch of glaciation
Evidence for this in our back yard…
Pleistocene LakeBonneville Shorelines!
Deltaic Lake Deposits!
U-Shaped Glacial Valleys!
Cirques!
Moraines and Tills!
Pleistocene Ice Caps and Sea Level
From Surface Landforms (e.g., Moraines) & Sediment Record
Glacial Moraine on an Active Alpine Glacier, Swiss Alps
Also much wetter climate: Pleistocene Lakes evidencedby shoreline landforms,
salt flats.
Glacial-Interglacial Cycles Through Pliocene-Pleistocene
These are Natural cycles of climatic variation!
40,000–100,000 year cycles → Changes in Earth Insolation?
Milankovitch cycles: Variations in
(1) Eccentricity (“ellipticity”) of Earth orbit around the sun (T = 100,000 years)
(2) Obliquity (tilt of Earth’s spin axis relative to plane of orbit) (T = 41,000 years)
(3) Precession (changes in orientation of the spin axis) (T = 26,000 years)
The important factor: How much insolation does high latitude (particularly northern!) receive in summer?
Planetary orbits are ellipses with Sun at one focus:
Current Earth distance to Sun changes by ~3.4%Recall S = S0(R/R0)2
1.0342 = 1.069 (i.e. ~7% total change over a year!)
Min-Max distance varies between 0% to 12%
N
SJan 3Jul 4
Tilt of the Earth gives us seasons:
Precession determines what season in the year we are closest(Now, northern hemisphere has less insolation in summer,
more in winter, and a shorter winter than southern hemisphere)
• Glaciers form on continents• At latitudes 40-80º, very sensitive to seasonality • Right now, a very large fraction of continental area is in that range of northern hemisphere!
