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CKA Uber
CKA Uber
 Vancouver Canucks

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PostPosted: Sat Aug 03, 2019 1:01 pm

herbie wrote:
11 billion tons melted in one day?Is that all?

Greenland Endures


Now, I’ve gotta admit that that sounds like a lot of ice, eleven billion with a “b” tonnes melted in one single day. However, I’m a tropical boy, so I’m kinda prejudiced in these matters. Here’s my conflict of interest statement. When I’m in a place where the ice jumps up out of my adult beverage and starts running around the landscape, I consider that to be “water behaving badly” whether it’s one cube or eleven billion tonnes, and I try to avoid such locations … but I digress.

To return to the question, is eleven billion tons of ice really a big number or not?

Well, to start with, it’s a one-day loss in the warmest part of the year. Snow builds up on the ice sheet in the winter, and melts, sublimates, and is lost in icebergs in the summer. So this one-day loss tells us very little about the longer-term changes, what is called the “mass balance” of an ice sheet over an entire year or a longer period.

So what is happening in the longer term? A source for some information on this question is the Polar Portal. There’s a good article to start with, the annual report for 2018. (It also has an interesting article on the various phenomena involved in the mass balance here.)

Let me start with a look at the mass balance of the Greenland ice sheet since 1972. Here’s that data.

From that data, we find that the 1981 – 2010 thirty-year average mass balance for the Greenland ice sheet was a net loss of 103 billion tonnes. Again, this is a very large number, it seems like a big deal that would demand our attention … but is it really?

In order to ask the question “How big is 103 billion tonnes?”, we have to ask a related question:

“Compared to what?”

In this case, the answer is, “Compared to the total amount of ice on Greenland”.

Here’s one way of looking at that. We can ask, IF Greenland were to continue losing ice mass at a rate of 103 billion tonnes per year, how long would it take to melt say half of the ice sheet? Not all of it, mind you, but half of it. (Note that I am NOT saying that extending a current trend is a way to estimate the future evolution of the ice sheet—I’m merely using it as a way to compare large numbers.)

To answer our question if 103 billion tonnes lost per year is a big number, we have to compare the annual ice mass loss to the amount of ice in the Greenland ice sheet. The Greenland ice sheet contains about 2.6E+15 (2,600,000,000,000,000) tonnes of water in the form of snow and ice.

So IF the Greenland ice sheet were to lose 103 billion tonnes per year into the indefinite future, it would take about twelve thousand five hundred years to lose half of it …

And even if the loss were to jump to ten times the long-term average, it would still take twelve hundred years to melt half the ice on the Greenland ice sheet. Even my great-great-great-great-great-great-great-great-great-great grandchildren won’t live long enough to see that.

However … there has been no big trend in mass losses in Greenland. As you can see in the graph above, it went down starting in 1980 but has generally risen since about 2010 … go figure.

Let me close with another way to visualize the mass loss of the Greenland ice sheet using two graphs. The first graph shows the cumulative loss over the forty-six year period of the record. This is how it would commonly be shown.


It’s shown that way because, well, it looks pretty scary. It looks like the ice sheet is about to disappear.

By contrast, here’s a more honest way to display the loss, by showing not the annual or cumulative anomalies, but instead showing the changes in the total mass of the Greenland ice sheet:


Not as scary, huh?

CKA Uber
CKA Uber
 Vancouver Canucks

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Posts: 25162
PostPosted: Sat Aug 03, 2019 1:29 pm

DrCaleb wrote:
PublicAnimalNo9 wrote:
Oh noes. An ice sheet that didn't exist 1100 years ago might melt some more. What a disaster.

So, if it didn't exist 1100 years ago, why can they get 800,000 years of ice data from it? [huh] ... elp-solve/

Wouldn't PAN9 be talking about the ice that wasn't there in Greenland during the Medieval Warm Period? I see nothing in your article offering any information on the Greenland ice during that period and how it compares to today's.

I do remember hearing a news story about recent warming melting some ice in Greenland and revealing a Viking colony that was there about the time PAN9 refers to though.

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