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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. 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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  1. The Effects of Orbital Forcings During Mid-Pliocene Global Warming AOS 528, Fall 2007 Semester Project Group 10: Morgan Franklin, Libby Obbink, Ian Orland

  2. 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

  3. 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.

  4. Experimental Set-Up • Pliocene control run with Pre-Industrial GHG and solar luminosity values • Ran 5 Pliocene experiments with EdGCM:

  5. 14.6° 11.1° 12.9° 12.5° 15.0° 14.6°

  6. 14.6° 11.1° lesstilt 12.9° 12.5° moretilt 15.0° 14.6°

  7. precession = 270° precession = 90° 12.9° 12.5° 15.0° 14.6°

  8. global: -2.1° global: -1.7° global: +0.0° global: +0.6°

  9. 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

  10. Effect of Varying Only Obliquity Precession = 270° Avg. global warming of 2.3°C Precession = 90° Avg. global warming of 2.1°C

  11. 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°

  12. 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

  13. 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).

  14. 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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