Greenland is one of the “hot” button topics in the AGW debate. When the Arctic Report Card (ARC) was released in September, many of the AGW sites were quick to jump on it saying that the current behavior was so far beyond the normal behavior that it was absolute proof that global warming was real. Of course, such claims are pretty normal.
So I looked at the two of the papers that were cited which showed such dramatic proof that Greenland has never before behaved in the way that it is now. One was the SMB by Wake and the other was the 2010 ARC update. The reports do differ from each other so a direct comparison isn’t really possible. At the same time I did not choose these reports. Here is the article with the links to the papers at SkS.
Since direct comparison of the reports isn’t possible and the ARC is the one with the most recent data, I will cover that one first. The ARC provides the Surface Mass Balance (SMB) from 1958-2010. Not a long period, but more than enough for what I needed. The other slightly misleading aspect for 2010 is that the SMB includes a large chunk that broke off. They refer to this as dynamic ice loss. That chunk of ice off the Petermann Glacier is still there, it just isn’t attached anymore. It could be decades before it works it’s way out to the ocean.
The standard deviation for SMB change over the period is 124 GT (gigaton) per year. That does not include the dynamic ice loss. If the glacier break-off is included, it changes to 129 GT/yr. Not much of a difference, so I will use the lower value. In the period of time, there are only 4 years that are outside of 2 sigma. They are listed as follows:
In 1992 and 1997 the SMB was positive outside of 2 sigma. In 2007 and 2010 it was negative, but the 2010 includes the glacier break. If that is removed, it is only -190 GT and is well within the 2 sigma. So in the period from 1958-2010, there are only 3 years that are outside of 2 sigma, and two of them are years of positive growth in the Greenland’s mass. Suddenly it is difficult to call the loss of mass in Greenland unprecedented, even over the past 52 years.
This is shown in the accumulated mass of Greenland in the ARC report. The accumulation of mass shows a decrease from 1958-1971. Then the mass steadily increases from 1971-1997. It then started to decrease again starting in 1999. Here is the total accumulated change in mass over the last 52 years.
If only the last 8 years are looked at (like SkS) it appears that the recent behavior is abnormal. If a longer period is looked at it is clear that such behavior appears to happen in cycles.
That takes us to the next study. The Wake paper is the longest paper covering the SMB of Greenland. The absolute values differ for each year so I cannot directly compare them to each other. The Wake paper shows less overall variation than the ARC. The standard deviation is 78 GT/yr. The last year covered by the paper is 2005 so the lowest years of the ARC are not covered.
It does cover a period that is about 3 times longer than ARC, covering 1866-2005. Surprisingly enough the 5 year period with the largest drop in SMB is 1965-1969. That period showed 28% more mass loss than the period from 2001-2005. It is certainly likely that if the Wake paper extended to 2010 it would beat 1965-1969, but probably not by much, especially if the Petermann glacier break is excluded. The overall accumulation for the Wake paper tells a similar story. Greenland is always changing by hundreds of gigatons per year.
I admit that Greenland is losing mass, but statistically it is not significant rate of loss, even over a 50 year period, or a 150 year period. The mass of Greenland over the past 150 years has varied by large amounts. The longest period of mass loss was from 1923-1962. In that 40 year period it lost mass every year but 2 of them. According to the Wake paper Greenland lost 63% more mass from 1923-1962 than it did in the period from from 1963-2005.
Greenland is losing mass. Nothing in the total amount of loss or the rate of loss indicates anything unusual is going on. The claim that what is happening now is absolute proof of global warming is simply not supported by the data. Only by focusing on short and recent periods of time can such a conclusion be reached.
In addition is is well supported that the period from 1400-1866 was colder than the period from 1866-1900. The rate of accumulation in that period averaged 52 GT/yr. If that low estimate is used for the 466 year prior, then the total accumulation would have been 24,232 GT. That actual accumulation could easily be more than double. That begs the question, what is better for mankind, a growing or shrinking ice sheet. The one thing it has never done is stayed constant.