19 July 2012
Last updated at 12:18 GMT
Floating "tongues" of ice, like the one that has broken off the Petermann glacier reported on Thursday, extend beyond the glaciers, and are constantly fed by ice pouring off the ice sheet.
Eventually parts of these tongues break off under the forces surrounding them and become free-floating icebergs.
Thousands of these "calving events" - in which chunks of ice break off glaciers - happen in Greenland each year, ranging from the unremarkable to the striking.
This most recent calving at is neither of the two in terms of size; with an area of roughly 120 sq km (46 sq mi), it is about half the size of the iceberg that broke off the same glacier in 2010.
Looming far larger in the future is the breakup of the Pine Island Glacier in Antarctica, which already shows a 30km-long crack - hinting at a catastrophic event that will release an 800 sq km iceberg.
Northern exposure It is important to keep in mind that this is a natural and periodic process that has been going on since long before we were here to snap satellite photos. What is at issue is whether or not the frequency of the events is changing, and why.
In the debate surrounding those questions, there are facts, educated guesses, and worrying trends.
The truth is that the questions are devilishly difficult to answer - the stability of ice sheets at both the Earth's poles depends on a wide range of factors, from atmospheric temperatures to the temperatures of the surface of the sea, to the degree of sea ice cover.
The Pine Island glacier will eventually cut loose an 800sq km iceberg
One fact is that the Petermann glacier's margins have now retreated to a point not seen in the last 150 years.
Another is that Greenland has over the last two decades experienced a significantly higher atmospheric warming than the global average.
Yet another is that over that same period, the south of Greenland has seen "mass loss" - both the kind of calving seen at Petermann and simple melting of surface ice - increasing year on year.
But from there, it becomes educated guesses as to whether that same worrying trend is making its way northward.
"To date, we've not really seen such a strong signal in northern Greenland - and Petermann is right at the northern limit of the ice sheet," said Jonathan Bamber, director of the Bristol Glaciology Centre at the University of Bristol.
"I think it's too early to say that this is the start of increased mass loss from northern Greenland - but it's certainly not good news," he told BBC News.
"Whether it's news that we should be particularly concerned about I think is difficult to answer at this stage."
'Not surprising' In truth, the buildup and breakup of glaciers can change over timescales ranging from months to millennia, and scientists simply haven't been watching this closely for very long.
As is so often the case in science, what is needed are more observations.
"If we start seeing patterns of the calving front retreating over a range of quite a few glaciers in northern Greenland in the same sector, then we would be quite concerned - and that would be a strong indicator that there's a change taking place, related to either atmospheric warming or ocean warming," Prof Bamber said.
For now, glaciologists - working with Earth and climate scientists of every stripe - are loath to make an explicit connection between iceberg formation and the broader debate around climate change, and this is where worrying trends come in again.
"I can't say that yes, this calving event is a consequence of the marked atmospheric warming that's been taking place over Greenland in the recent decades, but it is certainly more likely to take place as a consequence of that warming," Prof Bamber said.
"You don't have to be a rocket scientist to realise that in a warming world, ice is going to melt - so it's not surprising that Greenland is responding."
Petermann glacier in Greenland: Is it serious?
Petermann has been the site of two notable calving events in two years
The
increasingly detailed and immediate pictures that we get of vast
movements of ice at the Earth's poles make for a dramatic sight.
But whether that drama is cause for worry is an open question.Floating "tongues" of ice, like the one that has broken off the Petermann glacier reported on Thursday, extend beyond the glaciers, and are constantly fed by ice pouring off the ice sheet.
Eventually parts of these tongues break off under the forces surrounding them and become free-floating icebergs.
Thousands of these "calving events" - in which chunks of ice break off glaciers - happen in Greenland each year, ranging from the unremarkable to the striking.
This most recent calving at is neither of the two in terms of size; with an area of roughly 120 sq km (46 sq mi), it is about half the size of the iceberg that broke off the same glacier in 2010.
Looming far larger in the future is the breakup of the Pine Island Glacier in Antarctica, which already shows a 30km-long crack - hinting at a catastrophic event that will release an 800 sq km iceberg.
Northern exposure It is important to keep in mind that this is a natural and periodic process that has been going on since long before we were here to snap satellite photos. What is at issue is whether or not the frequency of the events is changing, and why.
In the debate surrounding those questions, there are facts, educated guesses, and worrying trends.
The truth is that the questions are devilishly difficult to answer - the stability of ice sheets at both the Earth's poles depends on a wide range of factors, from atmospheric temperatures to the temperatures of the surface of the sea, to the degree of sea ice cover.
The Pine Island glacier will eventually cut loose an 800sq km iceberg
Another is that Greenland has over the last two decades experienced a significantly higher atmospheric warming than the global average.
Yet another is that over that same period, the south of Greenland has seen "mass loss" - both the kind of calving seen at Petermann and simple melting of surface ice - increasing year on year.
But from there, it becomes educated guesses as to whether that same worrying trend is making its way northward.
"To date, we've not really seen such a strong signal in northern Greenland - and Petermann is right at the northern limit of the ice sheet," said Jonathan Bamber, director of the Bristol Glaciology Centre at the University of Bristol.
"I think it's too early to say that this is the start of increased mass loss from northern Greenland - but it's certainly not good news," he told BBC News.
"Whether it's news that we should be particularly concerned about I think is difficult to answer at this stage."
'Not surprising' In truth, the buildup and breakup of glaciers can change over timescales ranging from months to millennia, and scientists simply haven't been watching this closely for very long.
As is so often the case in science, what is needed are more observations.
"If we start seeing patterns of the calving front retreating over a range of quite a few glaciers in northern Greenland in the same sector, then we would be quite concerned - and that would be a strong indicator that there's a change taking place, related to either atmospheric warming or ocean warming," Prof Bamber said.
For now, glaciologists - working with Earth and climate scientists of every stripe - are loath to make an explicit connection between iceberg formation and the broader debate around climate change, and this is where worrying trends come in again.
"I can't say that yes, this calving event is a consequence of the marked atmospheric warming that's been taking place over Greenland in the recent decades, but it is certainly more likely to take place as a consequence of that warming," Prof Bamber said.
"You don't have to be a rocket scientist to realise that in a warming world, ice is going to melt - so it's not surprising that Greenland is responding."
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