Ice Caps and Ice Belts: The Effects of Obliquity on Ice-Albedo Feedback
Planetary obliquity plays a crucial role in determining the meridional distribution of annual mean insolation. When obliquity exceeds 55°, the weakest insolation occurs at the equator. On such a planet, stable partial snow and ice cover would form a belt around the equator rather than polar caps. Let's delve into the details:
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Background
Earth's surface temperature decreases from the equator to the poles due to the meridional distribution of insolation.
For a planet with high obliquity (obliquities greater than 55°), the situation is reversed: annual mean insolation is largest at the poles and smallest at the equator.
Analytical Model
We use an analytical model of planetary climate to explore the stability of ice caps and ice belts across a wide range of parameters.
The model incorporates insolation, heat transport, and ice-albedo feedback on a spherical planet.
Key Findings
Equilibrium States:
Multiple equilibria exist, including ice-free, Snowball (complete ice cover), and ice cap/belt states.
Stable partial ice cover can take the form of Earth-like polar caps.
Instabilities:
At high obliquity, we observe the "Large Ice-Belt Instability" and the "Small Ice-Belt Instability."
The Snowball catastrophe is avoided under specific conditions (weak radiative forcing):
Weak albedo feedback and inefficient heat transport favor stable partial ice cover.
Efficient transport at high obliquity favors ice-free conditions.
Conclusion
Understanding the interplay between obliquity, insolation, and ice cover is essential for predicting planetary climates. While Earth's polar caps dominate today, other planets may exhibit intriguing ice belts around their equators.