Text

theses

By altering the seasonal and latitudinal distribution of insolation, variations in the Earth’s orbital parameters have likely produced large climate changes in the past. To better understand the effect of orbital forcings, the GFDL Climate Model, version 2.1 (CM2.1), is used to perform idealized simulations in which only orbital parameters are altered while ice sheets, atmospheric composition, and other climate forcings are prescribed at preindustrial levels. These idealized simulations isolate the climate response to changes in obliquity and longitude of the perihelion alone. Additional simulations are conducted with a slab ocean model to assess the importance of ocean dynamics in parts of the climate response, and a water table model to study changes in groundwater. Though orbital forcing affects many aspects of the climate system, this research focuses on radiative feedbacks, the equatorial Pacific Ocean, and groundwater. Analysis shows that, despite being forced only by a redistribution of insolation with no global annual-mean component, feedbacks induce significant global-mean climate change, resulting in mean temperature changes of -0.5K in a lowered obliquity experiment and +0.6K in a precession experiment. At times when the orbital configuration favors glaciation, cloud feedbacks partially counteract changes in summer insolation, posing an additional challenge to understanding glacial inception. Precession can significantly affect the equatorial Pacific seasonal cycle, especially in the east, through thermodynamic and dynamic mechanisms. In addition to the direct thermodynamic effect of insolation anomalies, heat is redistributed across the basin by way of thermocline signals in the precession experiments, which appear to result from changes in the strength of subtropical anticyclones and shifts in the regions of convection in the western equatorial Pacific. On land, groundwater responds to orbitally-forced changes in monsoon circulations and other precipitation anomalies, and the relationships between net water flux, groundwater in the CM2.1, and shallow water table extent are explored. These three aspects of the climate system -- radiative feedbacks, the equatorial Pacific Ocean, and groundwater -- all may have played important roles in past climate variations.

ETD_5177

Ph.D.

Includes bibliographical references

by Michael Philip Erb

doi:10.7282/T3X928D1

ETD doctoral

The author owns the copyright to this work.