The Sun, Water, and Air

By the end of this lesson, you will be able to describe how energy from the Sun, the hydrosphere, and the atmosphere work together to shape weather and climate.

Almost all of Earth's weather starts with energy from the Sun. Sunlight warms the land, the air, and the water in the hydrosphere, which is all of the water on Earth, including oceans, lakes, rivers, ice, and water vapor. The Sun does not heat Earth evenly, though. The equator receives more direct sunlight than the poles, and dark ocean water absorbs energy differently than light-colored land. This uneven heating is what sets air and water in motion.

When water is heated, some of it evaporates, changing from liquid into an invisible gas called water vapor that rises into the atmosphere, the layer of gases surrounding Earth. As that moist air rises, it cools, the vapor condenses into tiny droplets, and clouds form. Warm air is less dense, so it rises and leaves lower pressure behind, while cooler, denser air sinks and flows in to take its place. That movement is wind, and it carries both heat and moisture across the planet.

You can see this every summer along the Texas Gulf Coast. The Sun heats the warm water of the Gulf, huge amounts of water vapor rise into the air, and sea breezes push that humid air inland. By afternoon, it often builds into towering thunderstorms over Houston or San Antonio. The same warm water and moist air can also feed hurricanes, which is why coastal Texas has a hurricane season at all.

Repeat those patterns for many years and you get climate, the average weather of a place over about thirty years or more. That is why the coast stays humid while West Texas stays dry.

Try it: Why do you think a city right next to the Gulf usually has milder winter temperatures than a city far inland at the same latitude?