The obliquity of Earth is stabilized by the size and proximity of the Moon. The formation of the Moon through a giant impact may be a relatively improbable outcome of planetary accretion. Thus, many Earth-like planets around other stars may not be well configured for spin-axis stability, which could allow their obliquities to vary wildly and to episodically approach 90 degrees. A natural question is whether Earth-like planets with high obliquities might still be climatically suitable for life. Past work using an energy-balance climate model has revealed that climate at high obliquity would be made regionally severe by large-scale seasonal changes to insolation received in the middle and upper latitudes. The extraordinary seasonal temperature fluctuations that would result might be damaging to many forms of life that depend on liquid water. The response of other Earth-like planets will depend primarily on their land-sea fractions and continental geographies, which affect the rate of seasonal heating and cooling, as well as levels of greenhouse gases such as H2O and CO2.
Dr. Williams and colleagues will use a three-dimensional general circulation model (GCM) to simulate extreme climates at high obliquity. These models are better suited to examining changes to climate caused by high obliquity because they simulate heat transport by winds and other processes more realistically than do simpler one-dimensional models. The GMC that will be employed includes a coupled ice-sheet model equipped to monitor the growth and ablation of glaciers. This will enable an investigation of whether high obliquity could have been the cause for low-latitude glaciation in the Precambrian Era of Earth's history. A suite of experiments will be performed for different continental arrangements, CO2 levels, and obliquities to place constraints on possible climates of early Earth and on the habitability of planets around other stars.
