The media blitz ahead of the Paris climate conference is well underway and you can expect sources like the New York Times to publish many stories along these lines. This one evokes the WWII headline, Paris is Burning, and it happens now to be all over Facebook.
Greenland Is Melting Away (link)
What you get is not science, but a compelling human interest story with great photos about a team of researchers working to study rivers on the ice sheet, and then an appeal to share in their fears. A scientific report would at least provide some snippets of findings, and then provide contextual facts for people to interpret the significance of observations.
Instead of that, the story makes an incredible claim:
The scientific data he and a team of six other researchers collect here could yield groundbreaking information on the rate at which the melting of the Greenland ice sheet, one of the biggest and fastest-melting chunks of ice on Earth, will drive up sea levels in the coming decades. The full melting of Greenland’s ice sheet could increase sea levels by about 20 feet.
Not only is there no evidence presented, the article is silent about the contextual facts that contradict that claim.
Here is what you need to know, and what they should be telling you:
1.The Greenland ice sheet is massive and has persisted for millennia.
Doing the numbers: Greenland area 2.1 10^6 km2 80% ice cover, 1500 m thick in average- That is 2.5 Million Gton. Simplified to 1 km3 = 1 Gton
200 Gton is 0.008 % of that mass.
Annual snowfall: From the Lost Squadron, we know at that particular spot, the ice increase since 1942 – 1990 was 1.5 m/year ( Planes were found 75 m below surface)
Assume that yearly precipitation is 100 mm / year over the entire surface.
That is 168000 Gton. Yes, Greenland is Big!
Inflow = 168,000Gton. Outflow is 168,200 Gton.
So if that 200 Gton rate continued, an assumption not warranted by observations below, that ice loss would result in a 1% loss of Greenland ice in 800 years. (H/t Bengt Abelsson)
2. The melting and refreezing depend on multiple factors, principally the runoff rate (which these scientists are studying) and the snow accumulation which is poorly understood and not yet predictable.
That’s not surprising since the ice sheet rebuilds during wintertime, the harshest time of year. Because of the difficulty of doing polar research, the emphasis is understandably on the summer observations. But we should also not make the mistake of the drunk looking for his lost car keys under the street lamp because the light is better.
For an ice sheet that neither grows or shrinks, there is at all points averaged over the year a balance between
the amount of snow that falls and is compressed to ice
the amount of snow and ice that melts or evaporates (sublimates) and
the amount of ice that flows away due to the ice motion
The two first contributions make up the surface mass balance. For the ice sheet as a whole, there is a balance between the surface mass balance and the amount of ice that calves into the ocean as icebergs.
3.Greenland ice is the most stable land ice in the world despite its location in the lower latitudes. Greenland ice sits in a bowl with a ring of mountainous edges constraining the runoff and is unlikely to ever completely melt. That is why it is preferred as a site for ice core sampling to study paleoclimates.
Topographic map of Greenland bedrock
4.The changing of Greenland ice mass waxes and wanes over years, decades and centuries. The fastest rates of melting recently were in the 1930s and 40s. Discoveries were made of Medieval Viking settlements showing when it was much warmer than now.
The resumption of melting recently is reported by GRACE, a new technology that is promising, but researchers caution against trusting it until calibrations are completed and the longer record is built.
DMI has been studying Greenland for a long time and they report this:
Greenland’s ice sheet has seen more growth so far this year than in the last four years. Greenland’s ice sheet growth in 2015 is also higher than the mean growth for 1990 to 2011.
5. Sea levels do rise from melting ice in warm periods such as the Roman era, but this comes mostly from land glaciers not the polar ice caps. For example, Ephesus was a port on the Aegean Sea in biblical times, but is now several kms inland. Many other such examples exist in times when it was much warmer than now and when Greenland ice was still massive.
6.The Danes know and care the most about the Greenland ice sheet, and they are not alarmed.
The Danes originally colonized the place and still subsidize the national government there. Their scientists have studied the issue and have this to say:
Scientists have long believed that Greenland’s ice sheet is melting with increasing speed and that this will result in considerable rises in water levels in the world’s oceans over the next 100 years.
But the foundation for this view now appears to be completely wrong.
Greenland’s ice mass shrinks periodically. The ice mass around and on Greenland shrinks because of two effects: Ice melting and the amount of precipitation – these two factors give a negative net result which means Greenland’s ice mass shrinks.
Ice that flows out to sea and calving – ice that breaks off from glaciers. This form of loss of ice mass is called ‘dynamic ice-mass loss’ and it can be many times higher than the loss of ice due to melting.
Until now, researchers have believed that the dynamic ice-mass loss accelerated constantly. Most climate models are based on this belief.
We can see that the dynamic ice-mass loss is not accelerating constantly, as we had believed,” says Shfaqat Abbas Khan, a senior researcher at DTU Space – the National Space Institute.
“It is only periodically that the ice disappears as rapidly as is happening today. We expect that the reduction in Greenland’s ice mass due to the dynamic ice-mass loss will ease over the next couple of years and will reach zero again.”
Is Greenland ice melting? Maybe. . . Probably a little.
It has melted a lot faster in the past, and only restarted recently, while the ice sheet has persisted over many millennia. No one knows how long it will melt and when it will reverse. Some Greenland ice loss is a good thing, since it means we are still in a warm period and not yet sliding into the next Ice Age.
So it is something interesting to watch, but not a reason to lose sleep. And it is nothing that we can fix.
Additional informative discussion is here: