Section 4.4.2, "Encumbrance, Gravity, and Movement" doesn't actually mention the effects of gravity.

If I had to guess:

"Multiply the character's weight by the local gravity, expressed as Earth-gravities. In higher than normal gravity fields, this is the extra weight the character must 'carry.' In lower than normal gravity, the result is the resulting increase in carrying capacity."

And in Section 4.4.3, "Leaping:" add after the first paragraph:

"If other-than-Earth gravity is in effect, multiply the character's weight by the local gravity first."

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I've come up with this for movement in microgravity; suggestions welcome.

Microgravity Maneuvers

Fighting in microgravity ("Zero-G") can be challenging. It's easy to start soaring through space, but unless a character has flight powers, a hero can find herself floundering mid-air, unable to find a hand-hold to change directions, or worse zooming on a ballistic trajectory directly for an enemy, with no way to stop.
In a relatively contained place, such as the deck of a ship with 10' ceilings, it isn't necessary to track a character's "altitude." In a large space with a high ceiling (or none, such as in deep space or above an asteroid) a character's path may include a vertical as well as horizontal component. If you wish can use this simplified chart to break down total velocity into horizontal and vertical components:

A character pushing off a solid surface with her legs has a velocity of their normal move; with just arms, halve that. Pushing off another floating object – a piece of debris or another character for example – halves this velocity. (The other object takes off in the opposite direction, at a percentage of the character’s speed proportional to their relative mass. A 200 lb. character pushing off a 400 lb. crate at 20” will send the crate flying at 10”/turn.) The character moves in a straight line until she encounters another object. A save vs. AG is required to safely and accurately stop or change course.
After a collision, or a fumbled grab at a handhold, roll 1d8 to determine a random direction (1 = "north," 2 = "northeast", etc) and a 1d6 to determine altitude change (1-2= "Up," 3-4= Maintain altitude, 5-6="Down" toward the floor of the space). The character's new velocity is 1d10 x 10% of his former velocity.