Transcript Proxy Climate Data - University of Texas at Austin

Lecture 20: Orbital Variations in Ice Sheets
(Milankovitch Cycles)
Chapter 9 (p. 163-174)
Milankovitch Theory
Milutin Milankovitch first proposed
the following idea in the 1930s.
High summer insolation heats land
 glacier ablates
Low summer insolation keeps land
cool  glacier persists or grows
Changes in climatic
cycles of glacialinterglacial periods
were initiated by
variations in the
Earth’s orbital
parameters (EarthSun geometry factors)
Milankovitch Theory of Climate Change
Climate change may be driven by
changes in earth's a) orbit
(eccentricity), from ellipse to circle at
100,000 year cycles, b) wobble
(precession), from the north pole
pointing toward or away from the sun
in June at 23,000 year cycles, and
c) tilt (obliquity), from 22.2° to 24.5°
at 41,000 year cycles.
Milankovitch Theory of Climate Change
The precession of the
earth’s axis changes
seasonal variations.
Presently the earth is
closest to the sun
(perihelion) in January
(the N.H. winter), most
distant from the sun
(aphelion) in July.
Return to modern position after
23,000 years
In about 11,500 years, the
earth will be closer to the
sun in July (the N.H.
summer), most distant
from the sun in January.
Testing the Milankovitch Theory
Calculated June
insolation at 65˚N
-
Measured Ice
volume
Kump et al., 1999
Testing the Milankovitch Theory
Permanent
Glaciation
Phase
Large Glaciation Phase
-
Preglaciation Phase
-
Small Glaciation Phase
Ocean sediments have 2
key indicators of past
glaciations.
Last Glacial and Interglacial Cycle
Climate surprises:
Dominate 100,000 yr cycle
Sawtoothed features:
Slow glaciation & rapid deglaciation
> 50 glacial maxima
-
Slow shift toward a colder,
more glacial world
The Earth’s Climate History
1.
Over the last century, the earth’s surface temperature has increased by
about 0.75°C (about 1.35°F).
2.
Little Ice Age = 1350 A.D. – 1850 A.D. (N.H. temperature was lower by 0.5°C,
alpine glaciers increased; few sunspots, low solar output)
3.
Medieval Warm Period = 950 A.D. – 1,250 A.D. (N.H. warm and dry, Vikings
colonized Iceland & Greenland)
4.
Holocene Maximum = 5,000-6,000 ybp (1°C warmer than now, warmest of the
current interglacial period)
5.
Younger-Dryas Event = 11,000 ybp (sudden drop in temperature and portions of
N.H. reverted back to glacial conditions)
6.
Last Glacial Maximum = 18,000 ybp (maximum North American continental
glaciers, lower sea level exposed Bering land bridge allowing human migration
from Asia to North America)
7.
We are presently living in a long-term Icehouse climate period, which is
comprised of shorter-term glacial (e.g., 18,000 ybp) and interglacial (e.g., today)
periods. There were four periods of Icehouse prior to the current one.
8.
For most of the earth’s history, the climate was much warmer than today.