Introduction to Climatology(Geog 300 - 2009-02-05) - Paleoclimatology -

Oliver Timm - IPRC-SOEST1680 EAST WEST RD POST Bldg 413G

timm@hawaii.edu

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