Rising sea levels are a result of melting ice in the polar regions, right? Green Houses gasses are making the melting problem worse.
According to How Things Work, when you look at a regular outside bulb thermometer, you'll see a thin red or silver line that grows longer when it is hotter. The line goes down in cold weather.
This liquid is sometimes colored alcohol but can also be a metallic liquid called mercury. Both mercury and alcohol grow bigger when heated and smaller when cooled. Inside the glass tube of a thermometer, the liquid has no place to go but up when the temperature is hot and down when the temperature is cold.
As the temperature of the liquid in a thermometer increases, its volume increases. Nearly all substances exhibit this behavior of thermal expansion. It is the basis of the design and operation of thermometers.
What does this have to do with global warming, watch this video: