You've probably heard a lot about global warming, but have you ever wondered how scientists take Earth's temperature?

Most of the excess heat trapped by greenhouse gasses like carbon dioxide actually ends up in the oceans. That's because the earth's oceans are kind of like a giant sponge that can hold a lot of heat for a long time.  The oceans are also huge-in fact, they cover most of the planet, and some parts of the oceans are warmer and some are colder. So it's not like you can just stick a thermometer in somewhere and say, "OK, that's the ocean's temperature."

Scientists take thousands of temperature readings from different parts of the oceans. They use a combination of heat sensitive satellites and thousands of floats that directly measure the temperature of ocean water at various depths. Together, these instruments allow scientists to calculate an average ocean temperature.  It's an ongoing process, and scientists are always trying to get more accurate measurements. But they've found that the oceans have in fact been warming at a rate that corresponds with how much heat scientists think has been trapped by greenhouse gasses.

This may not sound too bad; as long as the oceans are absorbing most of the extra heat, why worry? Unfortunately, higher ocean temperatures cause icebergs and ice shelves to melt, which raises sea level.  Plus, warmer oceans could affect weather patterns in ways that scientists don't fully understand.  In the end, warming of the oceans affects us all.