Test your knowledge of the many varieties of frozen water and how these icy realms are connected to climate change.
The salty ocean contains more than 97 percent of all the water on Earth, which means that freshwater is relatively scarce. About 70 percent of Earth's freshwater is held in ice caps and glaciers. The rest of the planet's freshwater resides in lakes (27 percent), swamps (3 percent) and rivers (less than 1 percent).
Ten to 11 percent of the land is covered by ice today. The vast majority of Earth's ice is found in Antarctica. It has an ice sheet more than 1.8 kilometers (1.1 miles) thick on average, and can be more than 4 kilometers (2.5 miles) thick in some places.
There are no glaciers on mainland Australia today. However, during the last glacial ice age, which ended 10,000 years ago, Mount Kosciuszko had a small glacier and Tasmania had many glaciers. The South Island of New Zealand still has thousands of glaciers.
Because glaciers are made of ice, they are normally associated with cold regions such as Iceland, Canada and Alaska, but tropical glaciers also exist in Earth's equatorial mountain ranges where the elevation is high enough and cold enough for ice accumulation. Tropical glaciers can be found at the tops of mountains in Colombia, Venezuela, Ecuador, Peru, Bolivia, East Africa and Indonesia.
Ice sheets are large glaciers that cover much of Greenland and Antarctica. Mountain glaciers, smaller than ice sheets, flow from high alpine areas. Even though Antarctica holds the majority of Earth's ice, Greenland, which contains only 10 percent, loses the most ice every year. If all 2.9 million cubic kilometers (0.7 million cubic miles) of Greenland's ice sheet were to melt, it would cause sea level to rise by 7.2 meters (23.6 feet).
California, Colorado, Montana, Oregon, Utah, Wyoming and Washington State all have glaciers. Emmons Glacier in Washington State is the largest, with an area of 11 square kilometers (4.2 square miles). Glacier National Park in Montana has 26 named glaciers, which are all shrinking in size. Alaska, not part of the lower 48, has tens of thousands of glaciers.
At high elevations, snow builds up to form glaciers, which flow downhill, extend into warm areas and melt. An 'equilibrium line' separates areas that melt in summer from areas that stay ice covered all year. If more ice melts than accumulates, the glacier retreats. In the past few decades, 400 billion tons of ice, enough to fill 160 million Olympic-size swimming pools, vanish from mountain glaciers around the world every year.
Roughly 30 to 50 trillion tons of ice has been lost over the past century worldwide. That's equivalent to the water contained in about 16 billion Olympic-size swimming pools. It has caused the world's oceans to rise by 17 centimeters (6.7 inches) on average. If all of the world's ice melted, the seas would rise about 70 meters (230 feet).
The Arctic Ocean, located in the Northern Hemisphere, is a small sea almost completely surrounded by land. Ice in the Arctic Ocean is made mostly of frozen seawater, called "sea ice." Most icebergs found in the Northern Hemisphere break (calve) off the Greenland Ice Sheet and then flow into the North Atlantic Ocean, where they eventually melt.
Antarctica is a continental land mass surrounded by ice shelves that flow into the ocean. Although icebergs around the world come in different shapes and sizes, tabular icebergs (large flat-topped ice masses) calve off Antarctic ice shelves in the Southern Ocean and are carried away by winds and currents. Many of these are massive in size, up to 80 kilometers (50 miles) long.