Photo credit Michael Van Woert, NOAA NESDIS, ORA

The answer is, "It depends." If Earth’s surface gets warm enough to melt all the ice in Antarctica, it’s a big problem because it’s more than a mile thick. If you look at a globe, you can see that Antarctica is huge. If all of the Antarctic ice melted, sea levels around the world would rise about 200 feet. Two hundred feet might not seem like much, but think about this: some of the biggest cities in the world are right on the coast. Cities like Los Angels, New York, San Francisco and Miami. If the ocean level rose 200 feet, all of these cities would be under water. It would be a gigantic disaster.

The average surface temperature in Antarctica is minus 37°C right now. So, it seems like the ice there is safe. It’s in no danger of melting unless there are huge changes in the weather patterns all over the planet. But, what about the ice at the other end of the world, in the Arctic Circle? There is already evidence that it is melting to some degree. And, this ice is not nearly as thick as ice at the South Pole. But, the ice floats on the Arctic Ocean, rather than sitting on land. If all the ice at the North Pole melted, sea levels would not be affected.

What about Greenland? There’s a lot of ice there – look at a map. If it all melted, it would add another 20 feet to the oceans. Greenland is closer to the equator than Antarctica, the temperatures there are higher, so the ice is more likely to melt. A 20-foot rise in sea level would mean bad news for many big cities. They might be able to build dykes and sea walls, but it would be incredibly expensive.

Let’s say that the temperature of Earth’s surface rises by just a few degrees. It melts the glaciers at places like Glacier National Park in the United States, but the ice caps don’t melt and Greenland stays the same. A few degrees may not sound like much, but even half a degree can have an effect on our planet. It seems that in the last 100 years the Earth's surface temperature rose about half a degree Celsius. According to the U.S. Environmental Protection Agency (EPA), the sea level rose six to eight inches in the last 100 years. Part of that is melting ice, but a lot of it is simple expansion. Warm things are bigger than cool things. There’s a huge amount of water in the ocean. If you heat it even a little, it expands enough to notice.

So what will happen in the future? No one really knows for sure. In 1995, the International Panel on Climate Change asked scientists to make some predictions. They predicted how sea level might change by the year 2100. The lowest predictions were at six inches and the highest at 37 inches. The rise will come from thermal expansion of the ocean and from melting glaciers and ice sheets. Let’s say it’s somewhere in the middle of the predictions, say 20 inches. That’s no small amount -- it could have a big effect on coastal cities, especially during storms.