How does warm water affect the weather?

But why all the fuss anyway about some hot water in the tropical Pacific Ocean? Well, it's not just the hot water. It's also the hot air.

Try this: take two cups that are the same. Fill one with cool water. Fill the other with hot water. (Not boiling, just good and hot.) Place them on a table. Hold each of your hands over one cup and feel the difference in the air above the water. (Don't actually touch the water. Just feel the air.) The hot water warms the air above it. The cool water doesn't.

Now, imagine you fill your bathtub with hot water. Think about how warm and steamy the air in the bathroom gets. Now, imagine millions and millions of bathtubs-ful of hot water.

All of that moist, hot air has to go somewhere. Scientists know that hot air rises and carries the moisture with it. Once the moisture gets into the air and starts to cool, rainclouds start to form.
 

Now try this: hold a small mirror over the cup of hot water for a few minutes. The moisture in the air should collect on the mirror, and, as it cools, form tiny droplets.

Imagine the bathroom mirror after you fill the bathtub with hot water. The "water" on the mirror is caused by the water vapour in the air gathering and cooling. Now imagine the air over the hot water of the tropical Pacific Ocean. Huge rainclouds start to form and flooding results in South American countries along the coast.

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