Up until the 1970s, the amount of sea ice - an aggregate seasonal high point amount of approximately 13.5 million square miles - was relatively constant. But since the 1980's, it has been decreasing.

The constantly evolving answer to this question is at the heart of the controversial Global Warming debate, a discussion re-ignited by the 2006 Oscar winning documentary An Inconvenient Truth.

Arctic Sea Ice 

Portions of the earth's surface that are permanently frozen are closely monitored by government and various scientific organizations. Arctic sea ice, which sits on an ocean basin at the North Pole surrounded by land, reaches its highest mass each March and its lowest mass each September.  Historically, spring and fall amounts range from six million square miles to 2.7 million square miles.

Antarctic Sea Ice 

The configuration of antarctic sea ice at the South Pole is the opposite of that of arctic sea ice; it sits on land that is surrounded by an ocean basin. Its winter-to-summer surface area ranges each year on average from 6.9 million square miles to 1.2 million square miles. So in the cases of both Poles, the answer to the question of how much surface area is frozen depends greatly on the time of the year when the question is being asked. The above amounts include a pair of major ice sheets floating off of Antarctica.

Greenland 

Along with a couple of floating ice shelves off Antarctica, the other major area of permanent terrestrial ice is Greenland.  Because this island nation is more easily accessible than the North and South Poles, measurements of its seasonal ice points are the most common current barometer used for the Global Warming debate. Recently, a 100-square mile sheet of ice detached from one of the island's glaciers, amounting to the largest such incident in half a century. Scientists estimate that a change in average temperature of just a few degrees could spell the end of Greenland 650,000 square mile frozen surface.