All weather comes from the sun

Have you ever stepped barefoot on pavement on a hot, sunny day? The ground is warm from the Sun. But… the Sun is so far away! How does it heat the pavement? Nuclear reactions in the Sun’s core release massive amounts of energy.

The energy travels through space via electromagnetic waves called radiation, and a small portion reaches Earth. But the Sun is responsible for much more than heating the ground. In fact, it is the driving force behind all our planet’s weather! Let’s find out why. When energy from the Sun nears Earth, it hits the mixture of gases that surround our planet: the atmosphere.

The atmosphere reflects some of the energy back into space. The rest passes through and is absorbed by the land and the oceans, heating them up. As the Earth heats up, it radiates some of the heat energy back towards space. But not all of the energy makes it: some of it is trapped by certain gases in the atmosphere, like ozone and water vapour. This is called the greenhouse effect.

The greenhouse effect keeps the Earth warm enough to sustain life. And yet… the Earth isn’t the same temperature everywhere. Why is that? Because the Earth is round, the Sun’s rays don’t fall evenly around the globe. At the equator, the Sun’s energy is concentrated over a small area.

The air here is warm. At the north and south poles, the Sun’s energy is spread out over a larger area and the air is colder. These regional differences affect more than just air temperature... The warm air near the equator is less dense, so it rises. As it rises, it creates an area of low pressure.

The cold air at the poles is more dense, so it sinks. The cold, sinking air creates an area of high pressure. The pressure differences across the atmosphere cause air to move, generally from areas of high pressure to areas of low pressure This flow of air is called a convection current. Convection currents cause large-scale winds across the surface of the Earth. Smaller, more localised pressure differences give us the wind we feel day to day.

We’ve seen how the Sun is responsible for temperature and wind. What about rain, snow, and hail — precipitation? The Sun’s energy hitting the Earth’s oceans, lakes, and rivers heats the liquid water, turning it to a gas — water vapour. This process is called evaporation. The water vapour rises into the air, where cooler temperatures cause it to turn back into water droplets.

This is condensation. The water droplets suspended in the air form clouds. As more and more droplets join a cloud, it becomes too heavy to remain in the air. The droplets fall back to Earth as rain — or if the temperature is cold enough, as hail or snow. Some lands in oceans and lakes… and the cycle begins again.

So it’s the water cycle, driven by the Sun, that gives us precipitation. Without the Sun, Earth would be a very different place. There would be no energy for the atmosphere to absorb, so no greenhouse effect. Everything would be frozen. There would be no uneven heating of the air to create convection currents — no wind.

And there would be no warming of bodies of water to drive the water cycle — no precipitation. Without the Sun, Earth would be a dark, still, frozen planet... unable to support life as we know it.