Your child may be interested to learn that when the ice caps melt, the level of the ocean rises, which can place coastal areas in danger. Freeze a bowl of water into a solid block of ice. Meanwhile, create a fairly flat island using plaster or Paris or clay that doesn't disintegrate when wet. Place the island on one end of a large plate or cookie sheet. Place the block of ice at the opposite edge. Over several hours, watch what happens when the ice melts and begins to rise over the edges of the island. Take progressive pictures and help your child keep an observation journal to turn in.
Fill a bowl with water, and add two or three drops of food coloring. Use a dark color, such as blue or purple, for best results. Place the bowl in the freezer and allow it to get completely solid, which may take up to 24 hours. Run the bottom of the bowl under warm water until the ice separates from the bowl. Place the ice into a larger bowl that has been filled with cool water. Examine what happens to the ice over a period of several days. Have your child record what the ice looks like a day later, three days later and five days later. Look at the way the food coloring blends into the water as a visible way for your child to see that the ice caps are melting. Take pictures to include with the finished project he turns in.
Even young children can understand that when the air gets hotter, the ice caps melt more quickly. Have your child do a project to demonstrate what happens to an ice cap when it's surrounded by warmer air. Give your child three ice cubes, each one set on a different plate. Leave one ice cube alone. Have your child use a blow-dryer to blow hot air around, but not directly on, the second ice cube. Place the third ice cube in a warm (100 degrees or less) oven. Watch the ice cubes together so your child sees that the warmer the air, the faster the ice melts. Help him take pictures and record his observations to turn in with his project.
Print out two or three large maps that show the ice caps and where they're located. Alternately, show your child a map and have him draw his own. On the first map, have your child color areas of land green and areas of water blue. Ask him to leave the ice caps white. Talk about what the map would look like many years from now when the ice caps have melted more. Give your child another map and have him draw what he thinks it will look like. Encourage him to consider that if they melt, the ice caps will be smaller. Use a third map to show a prediction even further into the future.