Earth has been a wet, warm, greenhouse, volcanic planet for about 3.5 billion years, or about 80% of our 4.5 billion year history.
20% of the time there have been large ice sheets, or glaciers.
The Northern Hemisphere has had glaciers for the past 2 to 3 million years.
The Southern Hemisphere has had glaciers for the past 35 to 40 million years.
Glaciers are huge piles of snow that have been compressed into ice.
As more snow falls on a glacier, it spreads and thins under its own weight
We don't know what causes glaciers to replace an ice-free planet, even though that's Earth's largest climate change event.
We also don't know what caused the average temperature of Earth to warm by about 1 degree C. (+/- 1.0 degrees C.) since 1880, nor should we care, because a change of degree or two is a harmless minor climate change event.
People who claim they know CO2 controls the climate, causes all global warming, and +2 degree C. of warming after 1750 would be a catastrophe ... are liars, for the following four reasons:
(1) There have been glaciation peaks in the past with atmospheric CO2 levels much high than the present 400 ppmv level.
(2) There is no evidence that CO2 is, or was ever, the "climate controller".
(3) The average temperature has already risen at least +2 degrees C. (and possibly closer to +3 degrees C.) since the unusually cold Maunder Minimum period in the late 1600s, and that was very good news for people, and
(4) Antarctica has not had warming in the past 50 years, even though "greenhouse warming" from CO2 is claimed to most affect both poles, and least affect the tropics.
Sea level has risen about 400 feet from melting glaciers, since the last peak glaciation about 20,000 years ago.
The ice was not melting due to power plants burning coal, and SUVs burning gasoline.
Today some glaciers are retreating, and others are advancing, or static.
Glaciers are rivers of ice, not static piles of ice.
They constantly flow toward the sea.
They flow due to gravity.
Glaciers melt at the edges, and also underneath from the earth's heat.
Its normal for glaciers to 'calve off' large blocks of ice at the edges.
Calving is the end of a process that takes thousands of years.
When a large block of ice breaks off and falls into the sea, its called an iceberg.
Environmental "activists" who use pictures of calving glaciers to "prove" global warming are liars.
Calving happens during both global warming and global cooling periods.