By Steve Goddard, as a follow up to this story
‘http://en.wikipedia.org/wiki/File:Jakobshavn_retreat-1851-2006.jpg
The press has been getting worked up about a 7 km² chunk of ice which broke off the Jakobshavn (Greenland) glacier on July 6. Is this an unusual event?
Since 1831, the glacier has retreated about 60km, as seen in the image above. About half of that occurred in the first 80 years (prior to 1931) and the other half has occurred in the last 80 years. The long term rate has not changed. As you can see, the retreat occurs in spurts, with quiesced periods in between.
We keep hearing over and over again theories about huge recent increases in melt from Greenland and Antarctica, supposedly based on GRACE gravity anomaly data. If this were actually happening, sea level rise would absolutely have to accelerate to match. Where else can the melted ice go, but to the sea?
But sea level rise rates have generally declined since 2006, with the exception of the El Niño spike.
http://sealevel.colorado.edu/current/sl_noib_global_sm.jpg
The sea level data unequivocally shows that accelerated melt is not happening.
Now, let’s look at the size of the chunk which broke off from Jakobshavn – in green.
That represents 0.0003% of the Greenland ice sheet in area, and a much smaller percentage of the volume, which is 2,800,000,000,000 cubic metres.
A huge chunk of glacial ice sunk the Titanic almost 100 years ago. Where did that chunk come from? Enough alarmism, please.
In order to interpret gravity data, you need to have bedrock reference points below the ice. This is an impossible task for several reasons.
1. Any place where the ice is deep is, by definition, buried in ice.
2. There is almost no bedrock exposed in the interior of Greenland, as seen in the satellite image below. The few places where you can find bedrock are mountain tops, which exhibit very different isostatic behaviour than the valleys which are – buried in ice.
Conclusion – the interpretations of gravity anomaly data are flawed.
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Let’s take a look at Ohmura et al. 1999 which is so important to your argument that the GIS is “gaining substantial mass”. I’d recommend reading it, except that it is in a fairly obscure journal that doesn’t even have the abstracts online. Fortunately, it was cited by the third IPCC report, and therein is sufficient information to understand something about the paper.
First, its over a decade old, and based on older data. Is it still a valid description of the mass balance?
Second, melt ablation is given, but not iceberg discharge. Since iceberg discharge is similar in magnitude to ablation, this creates a slight problem when attributing the difference between accumulation and ablation to mass gain.
Third, these figures are based on a GCM. Most skeptics abhor these models, but I’m so glad that you trust them.
++++
Please read an undergraduate text on ice sheet flow.
More later.
This article is steeped in ignorance. No, this article is the archetype of ignorance. The fundamental usage of GRACE is to examine time-variable signals in the Earth’s gravity field- an incredibly important detail that Mr Watt chooses to overlook in his unshakable analysis of the validity of NASA’s project. Because these gravity signals vary on the time scale of months, seasons or years, they are known not to be due to the long-standing features of our planet. When was the last time you saw a mountain change dramatically in a month? The bedrock under the Greenland Ice Sheet is not changing significantly on an annual time scale and thus is not one of the signals interpreted by GRACE scientists. So, WATT might change that fast? Ice and water. Greenland has a great amount of seasonal surface melt water than can be seen on any satellite photos beginning in June of each summer. Certainly, water is one aspect that can change. And that water is really just melted snow from the surface of the Ice Sheet so, obviously the surface elevation of the Ice Sheet can change in that time. In the deep interior, people track the ablation of ice from the surface and this is known to occur on a relatively short time scale. The bedrock underneath Greenland is not changing. It is Archean cratonic blocks that have been wedged together for the last 1800 million years. If you want to attribute seasonal GRACE gravity changes to something in the bedrock underneath the GIS, you might want to propose a means of altering a 1.8 billion year old mass of metamorphic rock that has survived 3 million years of Northern hemisphere glacial cycles on an annual time scale.
There is so much more to say but, judging by what you absorbed on the GRACE project before writing this egregious article, you’ll only half-read my response anyway.