The Effects of Orbital Forcings
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The Effects of Orbital Forcings During Mid-Pliocene Global Warming. AOS 528, Fall 2007 Semester Project Group 10: Morgan Franklin, Libby Obbink, Ian Orland. Mid-Pliocene Global Warming. 3.15 - 2.85 Ma Most recent period warmer than present Average warming is ~3°C globally

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AOS 528, Fall 2007 Semester Project Group 10: Morgan Franklin, Libby Obbink, Ian Orland

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Aos 528 fall 2007 semester project group 10 morgan franklin libby obbink ian orland

The Effects of Orbital Forcings

During Mid-Pliocene Global Warming

AOS 528, Fall 2007 Semester Project

Group 10: Morgan Franklin, Libby Obbink, Ian Orland


Aos 528 fall 2007 semester project group 10 morgan franklin libby obbink ian orland

Mid-Pliocene Global Warming

  • 3.15 - 2.85 Ma

  • Most recent period warmer than present

  • Average warming is ~3°C globally

  • Lower temperature gradient between

    • equator and poles (i.e. warmer poles). - No NH ice sheet

  • Warming mechanism unknown


Aos 528 fall 2007 semester project group 10 morgan franklin libby obbink ian orland

Orbital Forcings:

Milankovitch Cycles

  • Eccentricity has the least effect on solar insolation.

  • When the Northern Hemisphere ice sheet is absent, obliquity and precession dominate the climate signal.


Aos 528 fall 2007 semester project group 10 morgan franklin libby obbink ian orland

Experimental Set-Up

  • Pliocene control run with Pre-Industrial GHG and solar luminosity values

  • Ran 5 Pliocene experiments with EdGCM:


Aos 528 fall 2007 semester project group 10 morgan franklin libby obbink ian orland

14.6°

11.1°

12.9°

12.5°

15.0°

14.6°


Aos 528 fall 2007 semester project group 10 morgan franklin libby obbink ian orland

14.6°

11.1°

lesstilt

12.9°

12.5°

moretilt

15.0°

14.6°


Aos 528 fall 2007 semester project group 10 morgan franklin libby obbink ian orland

precession = 270°

precession = 90°

12.9°

12.5°

15.0°

14.6°


Aos 528 fall 2007 semester project group 10 morgan franklin libby obbink ian orland

global: -2.1°

global: -1.7°

global: +0.0°

global: +0.6°


Aos 528 fall 2007 semester project group 10 morgan franklin libby obbink ian orland

Obliquity

more tilt

  • More extreme seasons

    • - Poles affected most

  • Higher lat oceans absorb more solar radiation

less tilt

  • Less extreme seasons

    • - Poles affected most

  • High lat oceans absorb less solar radiation


Aos 528 fall 2007 semester project group 10 morgan franklin libby obbink ian orland

Effect of Varying Only Obliquity

Precession = 270°

Avg. global warming of 2.3°C

Precession = 90°

Avg. global warming of 2.1°C


Aos 528 fall 2007 semester project group 10 morgan franklin libby obbink ian orland

Precession

precession = 90°

  • Warmer NH summer & SH winter

  • Colder SH summer & NH winter

  • Warmer NH winter &

  • SH summer

  • Colder SH winter & NH summer

precession = 270°


Aos 528 fall 2007 semester project group 10 morgan franklin libby obbink ian orland

Effect of Varying Only Precession

Obliquity = 22.2°

Avg. global warming of 0.4°C

Obliquity = 24.5°

Avg. global warming of 0.6°C


Aos 528 fall 2007 semester project group 10 morgan franklin libby obbink ian orland

Conclusions

  • Variations in obliquity result in as much as 2.3°C change in model Pliocene SATs.

  • Variations in precession result in as much as 0.6°C change in model Pliocene SATs.

  • Globally averaged annual temperatures are warmest when obliquity is 24.5° (max) and precession is 270° (i.e. when SH summers are warmest).


Aos 528 fall 2007 semester project group 10 morgan franklin libby obbink ian orland

Implications for Climate Research

  • Our research isolates the influence of obliquity and precession on global climate before the presence of a NH ice sheet.

  • Future studies should concentrate on the effects of these two parameters with the addition of a NH ice sheet.


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