Timelapse of Columbia Glacier in Alaska

how long was the time period for this video?

About 4-5 months.

7000 years

What would cause the cyclical activity of the glacier? Global warming?

When the English Channel was formed from the retreating arctic ice shelf in what is now the North Sea do you think cavemen were responsible for global warming? Maybe the mere proliferation of lifeforms digesting food and then farting en masse creates each ice age due to the build up of methane causing a greenhouse effect. Mass extinctions gone by could simply be the point at which the sheer numbers of farting animals causing a greenhouse effect. 6 billion people all fart daily so were doomed.

Over 20% of man made greenhouse gasses are from cow farts.

Whats the ratio of chicken farts to cow farts per kg of meat produced? Maybe we need an animal fart index to assess which is the least gas-producing animal to eat. Maybe fish fart the least?

Then again its still cooler now than during Roman times, if the records of growing grapes in the UK are to be believed. What exactly is the 'right' temperature or is it preferable to simply not have it any warmer than it is now?

The ice that is being lost during this sequence is due to melting and ice berg calving. This lost ice is simply being replaced by more ice that's flowing from higher up the glacier. Even if a glacier were advancing it would still be melting at its terminus, but there would be more ice being gained at the top of the glacier and so despite the loss the glacier would move forward. There is nothing shocking in this video.

Yeah it is hardly changing. It's only receeding very slightly. All glaciers ablate (loose mass) where they terminate and accumulate (gain mass) where they start high up in the mountains.

there aren't any... i looked :-(