There has been much worry about the possibility that global warming will cause the polar ice caps to melt and flood many coastal cities. Coastal flooding could be catastrophic because virtually all of the world's metropolitan areas that have more than 10 million people are located on or near coasts. In short, if both polar ice caps melted, sea level would indeed rise enough to flood many coastal areas and change the world's coastlines. Most scientists, however, believe that the process would take thousands of years.
Most of the world's ice — almost 90 percent — is in Antarctica. The continent is covered by an ice shelf that is about 7,000 feet (2,133 m) thick. Depending on the time of year, there is about 800 to 1,000 times as much as covering Antarctica than in the Arctic circle, where the ice cap is floating rather than covering land.
The effects caused by the melting of Arctic ice, if the polar ice caps melted, would be relatively small. Mostly because water from the Antarctic ice cap would run into the ocean, the world's oceans would rise by about 200 feet (61 m) if the polar ice caps melted. The average temperature in Antarctica is minus-35&def; Fahrenheit (minus-37° Celsius) — well below the temperature at which water freezes — so any significant melting of the Antarctic ice cap is considered very unlikely to happen. It is considered more likely that only a portion of the ice will melt, even over a long period of time, and that sea levels will increase by no more than a few feet or meters.
If the polar ice caps melted enough to cause the ocean levels to rise several feet or a few meters, however, the results would be significant. The streets of many current coastal cities would be underwater. Low-lying countries, such as many of those in Indonesia, could become almost entirely submerged. Flooding also could cover much farmland and affect the world's food supply. Farmers in the flooded areas would need to move to more elevated, likely rockier land, which might be less suited to growing crops.
What is not possible is that all the world's land would be covered if the polar ice caps melted. There simply is not enough ice on Earth for this to happen. Even in a severe flood, only a small percentage of the world's land would be lost.