Date of Award




Document Type


Degree Name

Doctor of Philosophy (PhD)


Department of Atmospheric and Environmental Sciences

Content Description

1 online resource (ii, ix, 230 pages)

Dissertation/Thesis Chair

Oliver Elison Timm

Committee Members

Brian E. J. Rose, Andrei Lapenas, Robert G. Keesee, Abigail L. S. Swann


boreal forest, feedback, glacial inception, Pliocene, taiga, tundra, Tundra plants, Timberline, Climatic changes, Orbital mechanics, Radiative forcing, Vegetation dynamics, Paleoclimatology

Subject Categories

Archaeological Anthropology | Climate | Physical and Environmental Geography


The forest-tundra-short wave feedback is the dominant short wave (SW) vegetation feedback at mid-to-high northern latitudes and is an important feedback in Earth’s climate system, especially due to its potential role in modulating glacial cycles. Little research has been done on how the strength of this feedback might vary with the background climate state. It is hypothesized that the feedback has generally strengthened over the last four million years. The feedback mechanism is hypothesized to be weaker under warm Northern Hemispheric conditions when tundra is primarily confined to the high Arctic than under cooler conditions in which the forest-tundra boundary lies generally south across the interiors of the large continental land masses. To test the hypothesis of the weakened/strengthened feedback, an Earth System Model of Intermediate Complexity is used that consists of a newly-developed simple dynamic terrestrial vegetation model coupled to a general circulation atmospheric model and a slab ocean. The response to the same orbital forcing ("cold orbit", favorable to Northern Hemispheric glacial inception) is analyzed for two eras: the PRISM mid-Pliocene Warm Period and the pre-industrial Holocene.