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.