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Differential heating

What causes weather? Weather happens because of differences in temperature. We know that the Sun is our main source of heat, but why isn’t that heat evenly distributed across the surface of the Earth?

Well, firstly the curvature of the Earth means that at higher latitudes, the solar energy is spread over a much larger surface area, while the same amount of energy is much more concentrated at the equator.

Diagram showing two equal areas of solar energy equal solar energy heading toward the Earth; one near the equator, where the solar energy is spread over a short area of the Earth’s surface, and the other near the pole, where the energy is spread over a much larger area due to the curvature of the Earth The curvature of the Earth results in spreading out of solar energy towards the poles and a concentration near the equator

There is also a greater amount of scattering of the energy closer to the poles due to the energy having a much greater depth of atmosphere to travel through in comparison with nearer the equator. By scattering, we mean that some of the energy collides with atoms or particles on route, and so is sent in other directions that deviate from a straight line. The result being that some of the energy doesn’t reach the Earth’s surface.

Graphic showing two areas of equal solar energy heading toward the Earth; one near the equator, where the solar energy has a relatively short distance of atmosphere to travel through, and the other near the pole, where the energy has a much longer distance of atmosphere to travel through due to the curvature of the Earth The curvature of the Earth results in solar energy having a larger amount of atmosphere to travel through to reach the Earth’s surface near the poles than towards the equator

We also know that the spin and tilt of the Earth on its axis result in day and night, as well as seasons.

Diagram showing beams of solar energy radiating from the centre of the picture towards the Earth in Northern Hemisphere summer on the left, and the Earth in Northern Hemisphere winter on the right. The tilt of the Earth on its axis results in the seasons, and the spin of the Earth results in day and night The spin of the Earth results in day and night, and the tilt of the axis gives us our seasons

All of these things lead to temperature differences across the Earth’s surface.

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