Orbital Hypothesis of Climate Change & Pleistocene Ice Ages

Peixoto & Oort (1992)

Imbrie & Imbrie (1979)

Eccentricity (e) x y a b Modern value of e is (insolation at perihelion = that at aphelion) e varied between and over the past 1.5 Myr or so e has quasi-periodicities near 100 kyrs & 413 kyrs Annual global insolation varies as (1 – e 2 ) -1/2

Berger & Loutre (2004) W m -2

Eccentricity over the Past 5 Myr Time (Myr) Laskar (2004)

Paillard (2001)

Obliquity (  ) Ecliptic plane Configuration of Sun and Earth during northern hemisphere summer Obliquity = angle between Earth rotation axis & normal to ecliptic plane Modern value of obliquity is 23.5 o  varied between about 22.2 o and 24.5 o over the past 1.5 Myr or so  has a quasi-periodicity of 41 kyrs   N S SUN

Effect of Obliquity on Latitudinal Distribution of Insolation Imbrie & Imbrie (1979)

Berger & Loutre (2004) W m -2

Paillard (2001)

Precession Ecliptic plane   N S SUN Orientation of Earth rotation axis near the aphelion today Earth rotation axis tipped toward the Sun near aphelion: cold NH summer & SH winter

Precession Ecliptic plane   N S SUN Orientation of Earth rotation axis near the aphelion at (26 kyr)/2 = 13 kyr ago Earth rotation axis tipped away from the Sun near aphelion: cold NH winter & SH summer

The Two Components of Precession Ruddiman (2014)

Precession of the Equinoxes Imbrie & Imbrie (1979)

Joint Effect of Eccentricity & Precession e = 0 e > 0 -> Eccentricity modulates the effect of precession on insolation Still seasons, but precession has no impact on seasonal distribution of solar radiation Precession has an impact seasonal distribution of solar radiation

Berger & Loutre (2004) Precessional index = e sin 

Berger & Loutre (2004) W m -2

Paillard (2001)

Berger & Loutre (2004) W m -2

Ruddiman (2013)

SUCCESSES & FAILURES OF ASTRONOMICAL THEORY

Paillard (2001) Joseph Adhémar James Croll Milutin Milankovitch

The SPECMAP  18 O Record Imbrie et al. (1984)

The SPECMAP  18 O Record Imbrie et al. (1984)

Paillard (2001)

Imbrie et al. (1984)

The Pliocene-Pleistocene  18 O Record (LR04) Lisiecki & Raymo (2005)

The Pliocene-Pleistocene  18 O Record (LR04) Lisiecki & Raymo (2005)

The Pliocene-Pleistocene  18 O Record (LR04) Lisiecki & Raymo (2005)

The Pliocene-Pleistocene  18 O Record (LR04) Lisiecki & Raymo (2005)

The Marine Isotopic Stages of the Last 200 kyrs Austin & Hibbert (2012)

The 100-kyr Cycle Problem Imbrie et al. (1993)

The Mid-Pleistocene Transition Problem

The Stage-11 Problem Imbrie et al. (1993)

  18 O in Cloud Vapor & Condensate Dansgaard (1964) Fig: Broecker (2002)

Clark & Fritz (1997) Changes in Air Parcel Properties

Dansgaard (1964) Fig: Broecker (2002) Precipitation  18 O versus Air Temperature

Grootes & Stuiver (1997)  18 O ( o / oo ) Dansgaard-Oeschger Events Ice  18 O Record from GISP2, Central Greenland

Orbitally-Forced Contribution to Quaternary Climate Change Wunsch (2004)  18 O Record from subpolar North Atlantic core DSDP 607

Orbitally-Forced Contribution to Quaternary Climate Change Wunsch (2004)

Conclusions The three orbital parameters that influence insolation are: - eccentricity (ca. 100 & 413 kyr) - obliquity (ca. 41 kyr) - longitude of perihelion (ca. 22 kyr) Eccentricity per se influences the global annual insolation Obliquity & precession index determine the seasonal & latitudinal distribution of insolation A fraction of climatic variance seems to be driven by orbitally-induced insolation changes Climate seems to respond - linearly to obliquity & precession changes - nonlinearly to eccentricity changes Challenges of orbital hypothesis of climate change: kyr problem - mid-Pleistocene transition problem - stage-11 problem - suborbital climate changes Climatic spectra are continuous & “red”, with relatively small variance in orbital bands