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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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

  • Lower temperature gradient between

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

  • Warming mechanism unknown


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.


Experimental Set-Up

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

  • Ran 5 Pliocene experiments with EdGCM:


14.6°

11.1°

12.9°

12.5°

15.0°

14.6°


14.6°

11.1°

lesstilt

12.9°

12.5°

moretilt

15.0°

14.6°


precession = 270°

precession = 90°

12.9°

12.5°

15.0°

14.6°


global: -2.1°

global: -1.7°

global: +0.0°

global: +0.6°


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


Effect of Varying Only Obliquity

Precession = 270°

Avg. global warming of 2.3°C

Precession = 90°

Avg. global warming of 2.1°C


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°


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


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).


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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