Greenland Ice Sheet Surface Mass Budget: DMI
The amount of snow/ice which accumulates on Greenland’s surface is much greater than the amount of melt. This autumn, accumulation is at a record high.
Some skeptics fall into the trap of believing alarmist BS about “total mass balance” and “basal melt” Those are things which can’t be measured accurately, and are a response to the surface mass balance. If the amount of ice accumulating on the surface increases or decreases, then the amount of ice flowing to the sea will eventually adjust to match the surface mass balance – and return to steady state equilibrium. Over the long term, the amount of snow accumulation, melt and glacial loss has to be a net zero.
The only interesting long-term metric is the surface mass balance. which shows that more snow falls on Greenland’s surface every year than melts from Greenland’s surface. This tells us that Greenland is absolutely not melting down. It is possible that there is a temporary imbalance between accumulation and calving, but this will eventually adjust back to a net zero.
Do not forget that Greenland is bowl shaped with a lake under the ice.
Massive Lake Found Under Greenland Ice (Usual screaming about the Ice is Melting)
http://www.csmonitor.com/var/ezflow_site/storage/images/media/content/2013/0830-greenland-canyon-topographic/16859445-1-eng-US/0830-Greenland-canyon-topographic_full_600.jpg
Gail,
Love the map! That is an interesting thing I found out about some time back, that Greenland is geographically, a bowl-shape.
The biggest glaciers flow out of the gaps in the mountains.
The source page seems to be saying that the graph does not include calving:
Did you not understand the entire point of my post?
I did. I don’t completely agree with it, though I certainly agree that Greenland is not threatened.
But consider a hypothetical: An ice-covered island where the temperature never gets warm enough to melt, consisting of one steep mountain that is now glaciated but receiving little further snowfall (for whatever reason). The snowfall would be greater than the melt, but the ice will still flow down to the sea and calve away, eventually. The chart would look even better than the one you’re showing, but the island mountain would still eventually wind up bare of ice.
Greenland has in common with this only that it never gets very warm there, especially in the last few hundred years. So there is little melt, per se. Greenland is very different because of its topology; with the low center, that ice is not going anywhere in a hurry. But it does still calve at the margins, and the total mass balance should be net of that, i.e. snow accumulation less (melt and calving). Greenland could have less melt than snow, and still lose ice every year for thousands of years. It probably did after the end of the most recent glaciation.
In practice, Greenland appears to be stable or growing slightly, in addition to rising out of the ocean at about a quarter-inch per year from the loss of huge amounts of ice thousands of years ago. But it seems to me that showing only the melt on the reducing side is only part of the story, since melt is one of only two modes.
I understand your point that calving is a response to increased snowfall, and that is certainly likely to be true. But it is not the only aspect going on, and the catastrophists insist that the calving rate is very large 400 to 500 gigatonnes per year. This number is evidently incorrect, and probably double the real number, but their argument should not be ignored, I think. Counter it with good data for calving, as you generally do for other metrics.
===|==============/ Keith DeHavelle
Calving is a response to excess accumulation of snow. If the amount of snow accumulation decreases, the amount of calving will eventually decrease. That is the point.
“Calving is a response to excess accumulation of snow.”
Well, sort of. But not only that. Were it to stop snowing, calving would continue as long as ice is pushed to the sea by its own weight. The rate of calving would decrease — until it reaches zero, when all of the glaciers with a path to the sea exhaust themselves.
So, snowfall turning to ice produces glaciers which calve when they hit the water, and produce meltwater (and sublimation) when temps and insulation support it. This is all trivially true. But the response is evidently elastic, and the coupling spans centuries, and there are tens of thousands of years of ice which have been draining into the sea from the last glaciation when Greenland had much more ice.
Has the calving rate changed much? Is there a problem? The GRACE folks assert an enthusiastic yes, as if their funding depended upon it. They’ve got a poor track record, and were found wrong with regard to Antarctica.
But my point is simply that snowfall could exceed melt, every year, and the ice could still be a net loss, every year. Not that this is happening — it does not appear to be — but your chart is only part of the story, and the mere snowfall to melt ratio is not enough to decide things, in my opinion.
===|==============/ Keith DeHavelle
The surface mass balance shows that the amount of snowfall is much greater than the amount of surface melt. That is the whole point of the blog post.
Steven is right about being careful what type of “___ mass balance” is being used. The warmers have about 5 different ways of measuring it (including or excluding certain components). They will trumpet the ice calving mass balance component when that excludes accumulation etc. This is actually way more common than most people realize and every second mass balance paper is only about certain components rather than the entire mass balance and the warming supporters fall for it every time.
If the depth of the ice is rising at the summit of Greenland, then there is a positive mass accumulation overall. (Note there is some post-glacial rebound occurring so it is not a matter of the measuring the elevation but it needs to be the thickness of the ice).
Well, it looks like Summit Camp is sinking at a rate of about 80 cm/yr according to this data set:
ftp://data-out.unavco.org/pub/products/velocity/pbo.final_igs08.vel
There are no other Greenland stations in that data so nothing with which to compare the rate but it could be because it is heading west at 166 cm/yr and north at 14 cm/yr. It could also be the runway building, the camp and other activities compacting the firn.