A critical factor in global climate change is the extent of ice on the Earth. Currently, there is a certain balance between ice and non-frozen water. While ice caps and glaciers constitute over 2/3 (68.7%) of fresh water, this represents only 1.7% of all the water on Earth. The oceans contain most of the water - 96.5%(source of data: US Geological Service). However, the oceans are also thousands of feet deep, and the continental ice deposits contain enough frozen water, if melted, to raise ocean levels more than 70 meters (more than 230 feet). This would flood much of the heavily-populated area of the planet.
The globe has been experiencing extreme retreats of montane glaciers. Glaciers and other ice have almost completely disappeared from some sites such as Mount Kilimanjaro in Africa. But the amount of ice in these glaciers is miniscule compared to oceanic ice and the ice caps on Antarctica and Greenland.
Since oceanic ice is already floating on the ocean, it is essentially in isostatic balance. This means that its melting will have no significant effect on sea level because the ice is already balanced out by floating.
However, the ice caps are something else again. The Greenland ice cap alone contains more than 1.7 million cubic kilometers of ice (over 400,000 cubic miles of ice), enough to raise sea level 7.4 meters (about 24 feet). The Antarctic ice cap is far larger, with 26.5 million cubic kilometers (6.35 cubic miles), which is about 61% of all the fresh water on Earth, enough to raise se level by over 63 meters (almost 210 feet).
These ice caps are clearly melting. Climate change deniers sometimes claim that it’s due to volcanic or subsurface activity, not due to human action. This appears to be true only in an area of northeast Greenland, where there is an acknowledged hot spot, but the rest are all melting in response to atmospheric and oceanic warming. In fact, in Greenland, the greatest ice melt is at the other side of the land mass, not at the hot spot.
Current ice loss from Antarctica appears to be about 83 gigatonnes (about 91.5 billion tons). This is enough ice loss that there has been a measurable shift in the Earth’s gravity in the area. There is currently about 500 cubic kilometers of ice volume lost from Antarctica and Greenland combined each year, and it’s accelerating.