The AVAS and ACE techniques allow us to model the possible nonlinearity suggested by linear models. Comparison of AVAS and ACE led us to concentrate on application of AVAS, for theoretical and practical reasons. Results indicate that the effect of precession is linear, with perihelion near vernal equinox corresponding with warmer climate. Obliquity's effect is also generally linear, though with a stronger warming for very high values. The role of eccentricity is more difficult to interpret. Northern hemisphere summer insolation variations were prescribed as a regression variable but proved to be redundant. Interaction modelling, using Generalised Additive Models, allows us to visualise the combined effect of two orbital variables. This confirms the combined role of high obliquity and vernal perihelion in the deglaciations, and also permitted the last 200 ka to be reproduced independently of eccentricity. The cause of the deglaciations, and therefore the Earth's 100 ka ice age cycle, is the combined warming effect due to precession and obliquity variations (during a glacial period), and not eccentricity (other than through its modulation of the precession effect). We therefore conclude that the Earth's ice age cycle operates as follows: • The Earth naturally accumulates ice; • When the ice sheets have reached a certain threshold size then their feedback mechanisms become strong enough to precipitate a glacial collapse; • This collapse is triggered by the warming pulse which results from high obliquity and autumnal perihelion, possibly due to the extended summer experienced in the Northern hemisphere during such an orbital configuration.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:649082 |
| Date | January 1996 |
| Creators | Dalgleish, Alexander Norman |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13548 |
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