Heat can cause more pressure on a substance. This is because when heat is applied on a substance, it causes the molecules of the substance to move farther apart, making the substance occupy more space. For instance, if air is filled in a balloon and the balloon is heated, it will lead to the increase of volume of air, thus causing the balloon to expand more or burst. Learn more from http://science.howstuffworks.com/dictionary/physics-terms/expansion-info.htm.
Heat cause more pressure because it cause molecules to spread out, therefore, occupying more space. When in a contained area, such as earth, enclosed in our atmosphere, heat causes higher air pressure.