What causes differences in air pressure?

1. the windchill factor

2. the horizontal movement of air

3. the speed at which wind moves

4. the unequal heating of Earth's atmosphere

4.

Explanation:

Pressure differences are caused by uneven heating in the Earth's atmosphere. Cold air is denser than warm air and so tends to sink, while the less dense warm air rises. Because heat always moves from warmer to colder areas, the atmosphere (like the oceans) is constantly transferring heat from the Equatorial Regions to the Polar Regions.