Introduction to Climatology (Geog 300 - 2009-02-05) - Paleoclimatology - Oliver Timm - IPRC-SOEST...
-
Upload
elfrieda-gilmore -
Category
Documents
-
view
221 -
download
2
Transcript of Introduction to Climatology (Geog 300 - 2009-02-05) - Paleoclimatology - Oliver Timm - IPRC-SOEST...
Introduction to Climatology(Geog 300 - 2009-02-05) - Paleoclimatology -
Oliver Timm - IPRC-SOEST1680 EAST WEST RD POST Bldg 413G
Online introduction: http://www.ncdc.noaa.gov/paleo/primer.html Textbooks:
Bradley, R.S., 1999. "Paleoclimatology: Reconstructing Climates of the Quaternary". Academic Press, San Diego.
“Ice ages : solving the mystery” by John Imbrie and Katherine Palmer
Imbrie.
Tilt of the Ecliptic
Ecliptic: The apparent path of the Sun's motion on the celestial sphere as seen from Earth.
The ecliptic plane is tilted 23.5° with respect to the plane of the
celestial equator.
(The Earth's spin axis is tilted 23.5° with respect to its orbit around the sun.)
What causes the seasons?
Tilted ecliptic Cause for annual cycle in solar declination
angle
Incoming solar raditation S
0 (1367 W/m2)
Received energy per unit area on Earth surface:
I= S0 cos()
1m
1m
Zeta
Basic Geometry
Declination angle δ (delta)
Solar zenith angle ζ (zeta)
Elevation angle η (eta)
Zenith Angle + Elevation Angle = 90o
Eq
δ
ϕ
Honolulu latitudeϕ (phi) =21.5oN ζ
η
http://www.analemma.com/Pages/framesPage.html
http://en.wikipedia.org/wiki/Equation_of_time
Typical solar insolation annual cycle in Hawaii
DecJan Jun
Observed rainfall (satellite and station data) present day annual cycle
x
VE (vernal equinox)
AE (autumn equinox)
summer solstice
WS
Causes for our seasons:
tilt of the ecliptic relative to the plane of the celestial equator
The difference in the distance Sun-Earth is not the primary factor (6% changes in insolation) Earth closest to sun (Perihelion) on January 3rd, and most distant point (Aphelion) on July 4th
wintersolstice
P A
x
VE
AE
SS
WS
Kepler's second law and the length of seasons:
The speed of the planet in its orbit is such thatthe connecting line from the planet to the sun
skims over an equal area in equal time
Kepler's second law and the length of seasons:
The speed of the planet in its orbit is such thatthe connecting line from the planet to the sun
skims over an equal area in equal time
Johannes Kepler (1571-1630)
What would be the meansurface temperature
according to Stefan-Boltzmann-Law?
global mean climate state is described through the global mean air temperature at 2m
to be in an equilibrium: incoming energy = outgoing energy Iin = Iout
Iin = (1-a)*So/4 = (1-a) * 1367 Wm-2 / 4 Iin = (1-a) * 342 Wm-2
a is the albedo of the Earth: a ≈ 0.3 about 30% of incoming solar radiation is reflected
into spaceIin ≈ 240 Wm-2
Radiative Equilibrium Temperature
Iin = Iout
Iout = εσT4
Emissivity of Earth surface in infrared wavelength (10 micron) is close to ε≈1
T4=Iin /(εσ) = 240 Wm-2/(5.67*10-8 Wm-2K-
4)
Radiative Equilibrium Temperature
Iin = Iout
Iout = εσT4
Emissivity of Earth surface in infrared (10 micron) is close to ε≈1
T4=Iin /(εσ) =240 Wm-2/(5.67*10-8 Wm-2K-4)
T= 253K = -18oC = 0oF
Thanks to the atmospheric greenhouse effect we live in more friendly environment with about 15oC global mean temperature
Balance between incoming and outgoing energy
Energy balance of the Earth Climate system
How can the mean global climate change?
Imbalance in incoming and outgoing radiation
Iin < Iout : global temperature decrease
Iin > Iout : global temperature increase
NOTE: THIS IS AN IDEALIZED WORLD!
OCEAN HEAT CAPACITY CAN BUFFERTHE HEAT LOSS/GAIN!
climate shows different regional, seasonal characteristics
anthropogenic CO2 increase reduces Iout
Energy balance of the Earth Climate system
instrumental observations
indirect paleo observations
Why has the study of past climates (Paleoclimatology)
become so important for future climate change research?
1) We can look into the past to find climate analogs for the expected CO2 levels2) We can test the climate models how good they can reproduce past climates (e.g. ice-ages, warm phases) 3) Learn about the response of Greenland and Antarctic ice-sheets, vegetation, ocean acidification to rapid climate change
Glacial-Interglacial cycles
In 18th and early 19th century acceptance of the idea of past ice ages.
(rock formations, moraines in the Alpes, Agassiz, 1837)
North America: similar geological formations
Agassiz (1807-1873)
Alaska, Mendenhall Glacier
http://pubs.usgs.gov/of/2004/1216/
Northern Germany
Glacial-Interglacial cycles
In 18th and early 19th century first evidence (and acceptance as proof) for an ice age (rock formations in the Alpes, Agassiz, 1837)
Early (19th century) explanations for ice ages:
Solar insolation changes Volcanic dust Interstellar dust Changes in the ocean circulation Vertical movements of the earth's crust
CO2 reduction
Orbitally driven solar forcing
Agassiz (1807-1873)
x
VE (vernal equinox)
AE (autumn equinox)
summer solstice
WS
Causes for our seasons:
tilt of the ecliptic relative to the plane of the celestial equator
The difference in the distance Sun-Earth is not the primary factor (6% changes in insolation) Earth closest to sun (Perihelion) on January 3rd, and most distant point (Aphelion) on July 4th
wintersolstice
P A
Orbital Theory
Orbitally driven solar forcing:
Adhemar 1839(?): Length of cold seasons (eccentricity + precession)
Croll, 1867: Eccentricity + precession change in winter insolation
Croll, 1875: additional factor: obliquity Milankovitch 1910s: quantification of orbitally
driven insolation changes 1924: Koeppen, Wegener, Milankovitch:
summer half-year high latitude insolation responsible for ice-ages
1941: Milankovitch: “Canon of the Insolation and the Ice Age Problem”
James Croll(1821-1890)
Milutin Milankovitch(1879-1958)
Precession 19,000+23,000 yearperiods
Strong seasonaleffect
Eccentricity
100,000 yr period
Weak effect on annual insolation
Obliquity 41,000 year period pole-equator contrast in insolation seasonal changes
Precession depends on eccentricity
Images: http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/
more
less
Northern Hemisphere summer Insolation
more
less
summer insolation at poles
Orbital forcing over the last 150,000 years
time
Eccentricity
Obliquity
Eccentricity*Precession
A. Berger (1978)
Effect of the Precession changes the position of Perihelion and Aphelion with respect to the
Vernal Equinox point
causes changes in the annual cycle of incoming solar radiation
a change in the length of the seasons
Typical solar insolation annual cycle in Hawaii
DecJan Jun
present12,000 years ago
Evidence for 'Milankovitch Cycles'
From 1950s on: finding evidence for orbital cycles in terrestrial and oceanic sediment records
From 1990s to present Antarctic ice cores:Vostok, EPICA Dome C, Dome Fuji etc., covering last 800,000 years
Cesare Emiliani(1922-1995)
Sir Nickolas Shackelton(1937-2006)
Wallace Broecker John Imbrie
Ice ages : solving the mystery / John Imbrie and Katherine Palmer Imbrie.!
source http://www.ngdc.noaa.gov/paleo/ctl/index.html
Glacial-Interglacial sea level changes:from the LGM to present about 120m sea level rise
(about 400ft!!!)
time
120m sea level rise
Simulated Ice Sheets 130,000-present(Abe et al., 2007)
Simulated Ice Sheets 130,000-present(Abe et al., 2007)
back
Sources of climatic information: climate proxies
Any indirect information about the past climate!
Ice cores: isotopes, trace metals, annual layer thickness
Marine sediment cores: foraminifera assemblages, isotopes, trace metals, grain size, pollen
Tree ring width reflects climate of the growth season Isotopes and trace metals from coral skeletons,
speleothems (Historical records: weather descriptions, harvest
reports, famines etc.)
What are climate proxies?
Climate proxies:A physical or chemical property of a given medium that is
influenced by one or more components of the climate
system.
Antarctic ice core record from EPICA
time
cooler
Figure from http://www.realclimate.org/index.php?p=221
warmer
CO2 Greenhouse effect
weaker
stronger
Last Glacial Maximum 20,000 years ago
Antarctic ice core record from EPICA
warmer
cooler
Figure from http://www.realclimate.org/index.php?p=221
Last Glacial Maximum (LGM) 20,000 years ago
CO2between 190-300 ppmv
Jouzel et al., Science 317, 2007
800,000 years climate history from Antarctica, Dome C
present day climate part of the Holocence (present-10,000yrs ago)
Last 10,000 years relatively stable.
Pleistocene (10,000-1,800,000 yrs ago)
LGM
Temperature and CO2 relationship: Lead and lags in the climate system
Monnin et al., Science, 291, pp. 112-114, 2001 Temperature
CO2
increasebegins
warming starts
Antarctica warmingstarts 18000 BP,CO2 increase follows 800yr later
LGMHolocene starts
Temperature and CO2 relationship: Lead and lags in the climate system
Ahn and Brook , Science, 322, 83-85, 2008
Millennial climate fluctuations:Antarctica warming and CO2 increase in phasebut Greenland warms after CO2 increase
Understand climate change:Combination of paleoproxies
Lowell Stott, Axel Timmermann and R. Thunell, Science, 317, 2007
A new study co-authored by
paleoclimatologist Lowell Stott
of earth sciences indicates that carbon
dioxide was not the main cause of the
last ice age's meltdown.http://college.usc.edu/news/september_2007/stott.html
Lowell Stott, USC
Axel Timmerma
nnUH Manoa
Summary
Orbital theory of ice ages (glacials) warm ages (interglacials): precessional cycle (21,000 yr), obliquity (tilt of the axis of rotation, 41,000 yr), eccentricity (100,000 yr)
Last glacial maximum (LGM) ended 20,000 years ago sea level rose by 120m from the LGM
to present the recent Holocene epoch is relatively stable Paleoclimatogists still try to understand what caused
the CO2 changes during the glacial cycles from 190-300 ppmv.
Antarctic warming starts around 18,000 BP
due to local insolation changes and CO2 increase
Southern hemispherictemperature evolution
Only 35% of glacial-interglacialTransition can beExplained by CO2
Forcing
Another 35% can be Explained in terms ofSpring time insolation
Southern hemispherictemperature evolution
Only 35% of glacial-interglacialTransition can beExplained by CO2
Forcing
Another 35% can be Explained in terms ofSpring time insolation