There is evidence that climate change is already having observable impacts in both the Arctic and the Antarctic: some polar ice is melting.

Polar regions (see map left) include the Arctic in the Northern Hemisphere and Antarctic in the Southern Hemisphere.




There are two kinds of polar ice: 1) ice that floats on the sea or 2) ice that sits on land.
And which kind is melting determines if and how much sea level is impacted.

    
Because sea ice already floats on the water, it does not impact sea-level rise when it melts into the ocean.Because land ice sits on the land, it does add to sea-level rise when it melts into the ocean.


Both types of polar ice increase and decrease naturally during the year. In the summer, sea and land ice melt, and in the winter the ice builds, or reforms. That pattern is shifting with climate change, however, since both summers and winters are becoming warmer. This means that there is more melting in the summer, and less freezing in the winter, so the amount of total ice will decrease.

Arctic ice
The Greenland Ice Sheet (land ice) is a frozen reservoir for 8 percent of all freshwater on the planet. As the ice melts into water, this water enters the ocean and adds to the total volume of the ocean causing sea level to rise. Since Greenland has such a large amount of land-based ice, this is a big problem. Scientists estimate that if the entire ice sheet melted, sea level would rise 7 meters (23 feet).

Greenland melting.

Antarctic ice
In 2002, large fragments of the Larsen Ice Shelf (sea ice) broke off the Antarctic's West Ice Sheet. Ice shelves such as those around Antarctica are important because they support the much larger, land-based ice sheets. The loss of any of the continent’s ice shelves are likely to increase the flow of ice sheets off the land and into the ocean, which would, in turn, raise sea level.

Larsen Ice Sheet meltingfloating ice plain