When used without qualification, "weather" is understood to be the weather of Earth. At large scales, weather results from temperature differences around the globe, which arise mainly because areas closer to the tropics receive more energy per unit area from the Sun than regions nearer to the Earth's poles. On local scales, temperature differences can occur because different surfaces (such as oceans, forests, or ice sheets) have differing physical characteristics such as reflectivity (albedo), roughness, or moisture content.

Surface temperature differences in turn cause pressure differences. A hot surface heats the air above it and the air expands, lowering the air pressure. The result is a horizontal pressure gradient which accelerates the air from high to low pressure, creating wind. The simple systems thus formed can then display emergent behaviour to produce more complex systems and thus other weather phenomena. A large scale example of this process can be seen in the Hadley cell and other forms of atmospheric circulation. A smaller scale example would be coastal breezes.

Because the Earth's axis is tilted (not perpendicular to its orbital plane), sunlight is incident at different angles at different times of the year. In June the Northern Hemisphere is tilted towards the sun, so at any given Northern Hemisphere latitude sunlight falls more directly on that spot than in December (see Effect of sun angle on climate). This effect causes seasons. Over very long periods of time, ranging from thousands to hundreds of thousands of years, changes in Earth's orbital parameters will affect the amount of solar energy received by the Earth and influence long-term climate (see Milankovitch cycles)...