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Welcome to Brain Stuff from howstuffworks.com, where smart happens.

Marshall Brain

Hi, I’m Marshall Brain with today’s question, if the polar ice caps melted how much would the oceans actually rise? You may have heard about global warming. It seems that in the last 100 years, the earth’s temperature has increased by about half a degree Celsius. This may not sound like much, but even half a degree can have an effect on our planet. According to the US Environmental Protection Agency, the sea level has risen 6-8 inches in the last 100 years.

This higher temperature may be causing some floating icebergs to melt, but this will not make the oceans rise. Icebergs are floating chunks of ice. In order to float, the iceberg displaces a volume of water that has a weight equal to that of the iceberg. So when an iceberg melts, nothing happens to sea level. But the rising temperature and icebergs could play a small role in the rising ocean level. Icebergs are chunks of frozen glaciers that break off from land masses and fall into the ocean. The rising temperature may be causing more icebergs to form by weakening the glaciers, causing more cracks and making ice more likely to break off.

As soon as the ice falls into the ocean, the ocean rises a little bit. If the rising temperature affects glaciers and icebergs, could the polar ice caps be in danger of melting and causing the oceans to rise even more? This could happen, but no one knows when. The main ice covered land mass is Antarctica at the South Pole, with about 90 percent of the world’s ice. Antarctica is covered with ice an average of 2,133 meters, or 7,000 feet thick – more than a mile in other words. If all of the Antarctic ice melted, sea levels around the world would rise about 61 meters, or 200 feet.

But the average temperature in Antarctica is -37 Celsius, so the ice there is in no danger of melting. In fact, in most parts of the continent it never gets above freezing any time during the year. At the other end of the world, the North Pole, the ice is not nearly as thick as at the South Pole. The ice floats on the Arctic Ocean. If it melted, sea levels wouldn’t be affected. There is a significant amount of ice covering Greenland, which would add another seven meters, or 20 feet, to the oceans if it melted. Because Greenland is closer to the equator than Antarctica, the temperatures there are higher, so the ice is more likely to melt.

But there might be a less dramatic reason than the polar ice caps melting for the higher ocean levels. The higher temperature of the water is actually having an effect. Water is most dense at four degrees Celsius. Above and below this temperature, the density of water decreases the same way the water occupies a bigger space. So as the overall temperature of the water increases, it naturally expands a little, making the oceans rise.

Scientists have tried to predict what the sea level will be in the year 2100. Different scientists come up with different predictions, but in general, they estimate that the sea will rise 50 centimeters, or 20 inches, with the lowest estimates in the 15 centimeter, or six inch, range and the highest in the 95 centimeter, or 37 inch, range. The rise will come from thermal expansion of the ocean and from melting glaciers and ice sheets. 20 inches is no small amount. It could have a big affect on coastal cities, especially during storms.

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