Followup to "Global Warming Adventure"

A while back, we explored some criticisms of the ideas espoused in An Inconvenient Truth. (If you haven't already, you can read the original "Global Warming Adventure" post here.) Most notably, we looked at an ad aired by the CEI discrediting the claim that polar glaciers are melting. At the time I wrote an email to an author of one of the scientific papers cited by the ad. The author I wrote, Ola, did not reply, but another co-author, Kirill, did. Below is a transcript of the email conversation we had. For context, I will start with my initial message to Ola:

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Dear Ola Johannessen:
Thank you for your research and publication on www.sciencemag.org, regarding the Greenland ice. Below is a link to the publication:

http://www.sciencemag.org/cgi/content/abstract/1115356v1

I have some questions I'd like to ask to help understand this publication better.

Your paper says that that the average measured altitude of certain "already high" regions of Greenland is increasing, while the average measured altitude of certain "already lower" regions is decreasing, but not by so much. The "spatially averaged increase" is positive, which to many readers of your report indicates that Greenland is growing and not shrinking.

My understanding of the alleged melting of Greenland is as follows: Pools of meltwater are appearing in many areas of Greenland. These pools have a tendency to "burrow" to the bottom of the ice, but the presence of a given pool of melt water should not affect your average measured altitude until it has burrowed all the way through to the bottom, allowing melted ice a way to run off of the glacier. Avalanches are occuring, especially near the shores of Greenland; ice is running off of Greenland and into the ocean. This decreases the mass of Greenland, but does not decrease your average measured altitude of your "low" (below 1500 m) region of Greenland, since the "lower" avalanched ice is not measured after the avalanche due to being in the ocean. In fact, since the lowest regions are the ones that tend to slide off into the ocean and cease to be measured, I would expect said average altitude of the REMAINING region below 1500 m to INCREASE as a result of avalanche.

Is my understanding sound? To me this means that, even as you make these truthful observations about measurements, Greenland may still be losing mass at an arbitrarily high rate. Do you think Greenland is losing mass?

Thank you for your considerate and speedy response.
Ryan Murphy

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Dear Ryan Murphy,

Thank you for your attention to our paper.
However your understanding of ice sheet processes is not sound. The lowest regions are NOT the ones that tend to slide off into the ocean. Actually WHOLE ice sheet is flowing to their margins. This is the main process, which result in ice loosing through iceberg calving. Therefore both ice mass and ice elevation are depends on several factors: 1) ice flow velocity, 2) surface ice melting and water runoff over ice sheet margins, and 3) snow accumulation (precipitation).

Best regards,
Kirill.

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Thank you for your reply! Would you tell me please if Greenland is losing or gaining mass from year to year?

Ryan

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Yes. There are interannual variations of mass resulted from changes in precipitation and summer melting on the surface.

Kirill.

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So is it clear to scientists that Greenland is specifically LOSING mass over the years?

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It is clear that Greenland loosing mass over the ice sheet margins and growing in interior regions during the last decades. But there are different estimates of the overall change obtained using different methods and datasets.

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Ok, thanks. That makes sense. Thank you for your patience with me! I have just a few more questions.

1. Your report's abstract talks about altitude measurements, but never about mass. In your studies, did you learn anything about the mass gained from precipitation versus the mass lost from melting and iceberg formation? Are you familiar with the scientific community's work in determining whether Greenland has a net loss in mass? The following 2 sources suggest the net change in Greenland's mass is negative. Do you and/or your team think these sources' findings are correct?

"Climate Change, the Scientific Basis." Intergovernmental Panel on Climate Change (IPCC), 2001

"News: Greenland Ice Loss Doubles in Past Decade, Raising Sea Level Faster." Jet Propulsion Laboratory news release, Thursday, 16 February 2006.

2. Your findings are the result of analyzed data from 1992 to 2003. Have you or your team analyzed similar data from years after 2003? If so, what are your findings?

Thank you so much!
Ryan

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We reported only assessment of elevation change, but not mass change. It may be estimated by calculating the product of thickness change, area and snow density. However there are debates concerning the value of snow density that should be selected for mass balance assessment (from 0.3g/m3 to 0.9 g/m3). (See for example, Zwally, et. al, 2005. Mass change of the Greenland and Antarctic ice sheets and shelves and contributions to sea-level rise: 1992-2002. J. of Glac., 51(175), 509-527.)

Yes, there are different estimates of Greenland mass balance. Each of them has their advantages and disadvantages. These discrepancies imply necessity of further investigations.

ERS satellite altimeter measurements do not available over Greenland after 2003, but data from other sources will be used to prolong time series.

Regards,
Kirill.

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Can you send me a link to a scientific study that concludes that Greenland's net change in mass in recent years has been positive?

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(Sends a scientific paper as an attachment.) They used the same dataset, but with some improvements regarding accounting for snow densification, and including the margin areas in their analysis.

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The paper Kirill sent me is available here.

Ok, so what do we make of this conversation? Well, some might suggest that Kirill was being evasive. He seemed reticent to give direct answers to very direct questions like "Do you think Greenland is losing mass?" and "Do you and/or your team think [the findings from the sources I cited] are correct?" But I don't think that's the conclusion to draw from this. Kirill is a scientist, and scientists are very careful not to claim things that are not carefully and scientifically backed up, so I don't blame him for not giving me his personal opinion on the matter. On the contrary, it was most cooperative of him to continue talking to me for so long, and to send me that paper.

But what to make of the paper! Well, it reported the following:

• From 1992 to 2002, Greenland gained mass at an average rate of 11 billion tons a year. Antarctica lost mass at 31 billion tons a year. Overall, the two polar ice sheets lost mass.
• Both ice sheets gained mass in the middle due to precipitation, and lost mass closer to the outside due to melting and due to icebergs forming and sliding into the ocean. Global warming causes both greater precipitation and greater melting/iceberg formation. The paper's findings were very much in keeping with the idea that the Earth is getting warmer.

Here are some relevant quotes from the paper:

"Expected responses of the ice sheets to climate warming
are both growth in thickness of the inland ice areas, due to
increasing precipitation, and thinning near the margins, due
to increasing surface melting."

"Clearly, [mass gain and loss due to precipitation, melting and iceberg calving] are expected to change, perhaps at a greater rate than has been predicted, as recent measurements of increased outflow and increasing precipitation in Greenland may be indicating."

"Although the finding of near balance in Greenland might be interpreted to mitigate concern about the future contributions of the ice sheets to sea-level rise, the findings indicate that significant climate-induced changes are taking place...The extent to which the competing processes of inland growth will continue to balance coastal shrinkage, until shrinkage under the predicted climate warming becomes dominant, will be seen as observations continue and model predictions are validated or improved."

The paper used data from 1992 to 2002, so it doesn't have anything to say about the record ice meltage that occurred last year. Other papers (see Wikipedia for details) suggest that Greenland has been losing mass since at least 1996. From Wikipeda:

"IPCC [IPCC, 2001] estimates the accumulation to 520 ± 26 Gigatonnes of ice per year, runoff and bottom melting to 297±32 Gt/yr and 32±3 Gt/yr, respectively, and iceberg production to 235±33 Gt/yr. On balance, they estimate -44 ± 53 Gt/yr, which means that on average the ice sheet may currently be melting, though it can't be determined for sure. The most recent research using data from 1996 to 2005 shows that the ice sheet is thinning even faster than supposed in [IPCC, 2001]. According to the study, in 1996 Greenland was losing about 96 km^3 per year in mass from its ice sheet. In 2005, this had increased to about 220 cubic km^3 a year due to rapid thinning near its coasts [JPL, 2006]."

To help make sense of this, let's convert km^3 into gigatons:

Ice has a density of 0.917 g/cm^3 (917 kg/m^3) at 0 degrees Celcius. At Greenland's temperatures it will be denser, so this will be a conservative estimate.

Let's start with 1 km^3 of ice, and try to get gigatons.
1 km^3 = 1,000,000,000 m^3 = 917,000,000,000 kg = 917,000,000 tons = 0.917 gigatons

So JPL suggests that Greenland lost 200 billion tons of its mass last year, while the paper Kirill sent me suggests that Greenland gained 11 billion tons a year from 1992 to 2002.

Ruh roh...