What does precession (wobble of Earth) change the most?

• A. timing of the seasons throughout the year
• B. global average temperature
• C. poleward heat transport
• D. moisture distribution in the tropics

Answer: (A)

The wobble of Earth’s axis shifts when the solstices and equinoxes occur in the annual orbit, so the most direct effect is the timing of the seasons. Because precession changes the orientation of the axis relative to perihelion, the season that a hemisphere experiences during closest approach to the Sun can move from one hemisphere’s summer to another or occur earlier or later in the year. This alters how long and how intensely summers and winters feel, more than it changes the overall average global temperature. The other factors—poleward heat transport and tropical moisture distribution—are climate responses that depend on how insolation is distributed, but they are not changed as directly by precession as the calendar timing of seasons.