As the world heats up, the sea levels are rising. Many experts warn that dramatic sea-level rise is global warming's biggest danger. Two main factors are behind this: thermal expansion of the ocean and melting Ice. First, as the ocean gets wanner from global warming, its volume expands. This is basic science: water expands as it heats up. Thermal expansion has raised the oceans about 10 to 20 centimeters (4 to 8 inches), according to the International Panel on Climate Change (IPCC). The melting of polar ice caps, glaciers and the ice sheets in Greenland and the Antarctic are another Factor. Greenland's massive Ice sheet, which has begun to show signs of early melting, may disappear completely within the next thousand years If global warming continues at its present rate, according to National Geographic. Wind surges are also an important factor in the formation and presence of sea ice, says the International Arctic Science Committee. Strong winds