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Climate Hustle

Watts Up With That concludes Greenland is not melting without looking at any actual ice mass data

Posted on 13 July 2010 by John Cook

To properly understand what's happening with our climate, it's imperative we consider the full body of evidence. Unfortunately, much confusion is sowed by those who cherrypick select pieces of data while neglecting the full picture. A good example is a blog post at Watts Up With That by Steve Goddard, titled Greenland Hype Meltdown. Goddard characterises the reports that Greenland is losing ice as a "continuous stream of gross misinformation". Curiously, he provides no actual data on Greenland's ice mass to expose this gross misinformation. Instead, he cites temperature from a single weather station and some photos he took while flying over the ice sheet.

Let's look at actual measurements of what's happening to the Greenland ice sheet. The change in ice mass has been measured using a variety of methods. Satellites use radar interferometry to measure the speed of the glaciers as they slide into the ocean. What they find is the glaciers have been sliding faster downhill and dumping more ice into the ocean. Satellite radar altimetry and airborne laser altimetry have also been used to measure the thickness of the ice sheets - they both find the ice sheet is thinning.

GPS receivers have been placed at selected locations around Greenland to measure how much the bedrock is lifting in response to thinning ice sheets. These find the land is now rising up at an accelerating rate. An overall picture is obtained by satellites measuring the change in gravity around the ice sheet. As the ice sheet loses mass, the gravity around Greenland changes, as measured by the GRACE satellites. These measurements find accelerating ice loss.

Net accumulation and loss of ice mass from Greenland are calculated using measurements of precipitation, snow accumulation and the discharge of glaciers into the ocean. The net accumulation/loss measurements find the same rate of ice loss as the GRACE gravity data. When all these independent lines of evidence are compared, we find a consistent picture of accelerating ice loss over the last decade and a half.

Greenland ice loss  measured by net accumulation/loss, altimetry and  GRACE gravity  observations
Figure 1:  Rate of ice loss from Greenland. Vertical lines indicate uncertainty, horizontal lines indicate averaging time. Blue circles are from altimetry, red squares are from net accumulation/loss and green triangles are from GRACE. The black line is a straight-line (constant acceleration) fit through the mass balance data for the period 1996–2008 with a slope of 21 gigatonnes/yr2 (Jiang 2010).

Is there any evidence that this ice loss has stopped recently? The latest gravity data, released just over a month ago, shows continued accelerating ice loss from the Greenland ice sheet. This is because ice loss has spread from southern Greenland to the northwest, confirmed by gravity measurements and GPS data. Currently, Greenland is losing ice mass at a rate of around 286 billion tonnes per year.

Change in Greenland ice mass, 2002 to 2010
Figure 2: Greenland ice mass anomaly (black). Orange line is quadratic fit (John Wahr).

The full body of evidence gives us a variety of direct measurements, using independent techniques, all arriving at the same answer. When Naomi Oreskes refered to "multiple, independent lines of evidence converging on a single coherent account", she may as well have been talking about Greenland ice loss.

Steve Goddard is correct when he says there's a "continuous stream of gross misinformation" about Greenland ice loss but it's not coming from the peer-reviewed research which paints a remarkably consistent picture. Instead, the misinformation comes from those who ignore the full body of evidence and cherrypick bits and pieces to paint a misleading picture.

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Comments 1 to 50 out of 65:

  1. It would be helpful to know what the TOTAL mass of the Greenland ice sheet is, to put it into perspective.
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    Response: This is examined in why Greenland's ice loss matters.
  2. It is particularly good timing, with the Jakobshavn Glacier losing a a substantial chunk in a major calving event July 6-7. This is also a summer where the melt season has gotten off to a fast start on the ice sheet.
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  3. The problems that efforts to deny real world observation lead to is shown by the relationships between polar and mountain glacier land ice melt and sea level rise.

    Despite a short period (2006-2008ish) when sea level rise slowed down a bit probably due to a la Nina event, the rate of increase has "recovered" and the current sea level is pretty much smack on its long term trend rising by somewhere upwards of 3 mm.yr-1. That sea level rise must have come from somewhere. Elsewhere on these boards strenuous efforts are being made to insinuate that the thermosteric (water volume expansion due to enhanced heat absorption) contribution to sea level rise is negligible since 2003.

    If there is no Greenland contribution to sea level rise and no thermosteric contribution then what is causing the sea levels to rise!? Are we therefore getting 3 mm.yr-1 from mountain glaciers and Antarctic melt? The evidence simply doesn't support such a conclusion. More likely the sea level rise is a combination of Greenland and Antarctic melt contributions, mountain glacier melt contributions and thermosteric (enhanced ocean heat absorption) much as the science indicates.

    The real world does make sense and our interpretations should reflect that!
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  4. I submit that WUWT didn't mention actual ice mass data because it didn't give them the right answer.
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  5. Doesn't it ever bother 'skeptics' to discover that the 'leading lights' of their movement are lying to them? I mean, you'd think that would be a clue.
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  6. I think an upcoming post on glaciology should help with some of this stuff.
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  7. chris at 21:11pm - there's one other source of extra water in the oceans worth mentioning: emptying of underground reservoirs. As I, somewhat unreliably, remember it it's a measurable contribution but not huge.
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  8. How many times does Goddard have to be shown to be just plain wrong by physical reality for the WUWT gang to realise he doesn't have a clue what he's talking about?

    Probably a very large number.
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  9. Icarus at 22:43 PM on 13 July, 2010:

    Well, they don't need ice mass data, since ice mass has nothing to do with anything, not even ice mass itself!

    According to eyewitnessesses, McIntyre has recently acquired a cow, which had tripped and fallen into the water, causing sea levels to rise. Esiwyks and Krad (2010) do not agree with this, since average single cow volume doesn't match any recent sea or ice volume increase or decrease, although Hennub (2010) couldn't rule out the possibility completely, because the cow was rather large.

    Golly wiz, them there science guy persons would claim anything these days. :P
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  10. Ed Davies at 23:29 PM on 13 July, 2010

    Thanks for that Ed. In fact if you look on page 156 of the paper I linked too above (click on "the science indicates" in third paragraph of my post), it discusses the positive contribution to sea level rise from aquifer and ground water depletion and the negative contribution from building dams and impounding water. Over the last several decades these apparently account for around +0.5 mm per year and -0.5 mm.yr-1, respectively, and so the net anthropogenic effect from these is near zero.

    I expect that the negative contribution from dam buildng has or will start to diminish since much of the potentially dammable rivers have been dammed by now, whereas groundwater depletion may continue apace...
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  11. @Jim Eager #7

    Bill Keller, former Managing Editor of the New York Times, observed that a substantial proportion of the [American] public does not look to the [news] media to provide them with a factual accounting of the news, but rather to confirm the beliefs they already hold. WUWT fulfills this function quite well for many of its readership.

    When you consider some of the things that people choose to believe, the present example is not particularly surprising.
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  12. "Cherry picking" is different - simply: incomplete information. To post J.C. was full - not "cherry picking" - like now - I am please let me know: whether the whole area of the Greenland ice mass is decreasing? If not, why? Perhaps the close vicinity of the mass of Greenland's glaciers are growing somewhere? Is solely responsible for changing our warming, or as we wanted in 1978 Stone (always quoted when it comes to oceanic transport of energy) - are the most important cyclical changes in Earth's rotation and ocean circulation?
    I advise you also read "whole" last SG - there is much more "one knows why" the arguments skipped by JC (for example, Greenland ice in 1920 -30 years).
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  13. Wikipedia says that Greenland contains 2,850,000 cubic kilometers of ice. Since one cubic kilometer of ice is nearly 1 gigaton, the current loss rate is 0.05%/year. It doesn't seem like a lot. The acceleration apparent in Figure 2 ought to be a concern, however.

    @Arkadiusz, I'd like to understand what you are saying, but the abbreviations and hyphenations make it difficult.
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    Response: It's not just the acceleration in ice loss that gives us cause for concern. The various lines of evidence that show Greenland is highly sensitive to temperature and expected to contribute significant sea level rise in future decades/centuries are examined in why Greenland's ice loss matters.
  14. Kudos to John for wading into the fray.

    #11:""Cherry picking" is different - simply: incomplete information." More than incomplete, this pejorative suggests that one has actively selected only those data that agrees with his/her POV, as in only those cherries that are ripe.

    Here is one of the graphs posted as a counter-example:

    The author doesn't appear to notice what happened from the early 80's onwards: approx 4 deg in 30ish years, or a resounding 1.3 deg/decade! Alarming trend, no?

    But the surface temperature data are suspect, the gravity data are immaterial, the satellite temperatures are cooked. And the Greenlanders farming where their grandfathers couldn't are clearly drinking the vodka they can make from their own crops:

    " ... pulled 20 tons of potatoes from the earth last summer, and his harvests have been growing larger each year. "It's already staying warm until November now, ..." says Egede. And if this is what faraway scientists call the greenhouse effect, it's certainly a welcome phenomenon ...."

    Who knows, maybe they'll be planting cherries in Greenland one of these days?
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  15. CoalGeologist, hence the very large number.
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  16. Arkadiusz @ 11

    Message garbled, please resend.
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  17. #15

    Message garbled, please resend.

    I had to stop reading Arkadiusz some time ago, because the stylistic quirks and lack of formatting produce instant eyestrain.

    I'd prefer to read all the comments here, even the ones I almost invariably disagree with, so I hope Arkadiusz will make an effort to present his opinions in a format that's a little easier to decipher.
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  18. I take your point John but The WUWT article mainly focuses on the temperature record with a few spurious comments on mass balance while you seem to focus on mass balance. The WUWT temp stuff seems fairly accurate, there is plenty of science that suggests the 1940's and the recent period temperature records are not too dis-similar.

    I think figure 10 from this CRU paper is essentially showing what WUWT are arguing with regard to the Greenland temperatures.

    It peeves me that we don't have accurate mass balance data for 1930-1940.
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  19. Sea level change doesn't appear to be reflecting the melt...

    During the period of time (2002-2009) when GRACE gravitational anomalies implied a doubling of ice mass loss the global average sea level went steadily down.

    Can anyone here explain that?
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  20. Didn't mean to say sea level went steadily down. Meant to say the annual rate of sea level rise went steadily down. If rate of meltwater pouring into the ocean doubled one wouldn't reasonably expect that the rate the oceans are rising would decline during the same period.
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  21. Muoncounter (#13),

    That graph also appears to be just the raw data, lacking the homogeneity adjustment.


    Most of Greenland was indeed on par with today temperature-wise, as was east of the Rockies in the CONUS. That's about the extent of it. Nearly everywhere else (Arctic included) it was consirably warmer.

    recent decade vs 1930's

    The double-whammy of greenhouse gases and black carbon is overwhelming a robust natural variation in the Arctic.
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  22. I think maybe you missed a trick here John: several papers have used altimetry JUST of the interior and there has been good evidence of thickening in the interior (e.g. Johannesen iirc?). Altimeter data has regularly had problems at getting low elevation (e.g. coastal) ice.

    This is expected with increased snowfall from greater water vapour content - but it's confusing when you first hear about it and the likes of Monckton and WUWT prey on that.
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  23. Dave Springer, re the short term negative acceleration in sea level rise, I wonder if the increase in atmospheric water vapour can account for at least part of this.
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  24. For the record, not to nitpick. But Altimetry is not used to measure glacier speeds. Radar interferometry is...
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    Response: Nitpick away! Have updated the post, thanks for the correction.
  25. Dave @18,

    Not sure which data you are looking at. One should look at the data calculated after applying the inverse barometer correction and removing the seasonal signal. Then one gets this.

    Looking at those U of Colorado data, I cannot see any significant change in the rate of increase over the 2002-2009 period. There was a slow down in 2007-2008, but that may have been associated with the La Nina event. Which goes to illustrate that loss of terrestrial land ice is not the only contributing factor to sea levels.
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  26. Dave Springer at 02:24 AM on 14 July, 2010

    I’m not sure that the sea level data merits such detailed analysis. Regression of the satellite data indicates that the sea level rise "flattened" for a period especially between 2006-2008, but has “recovered” such that the current sea level is pretty much smack on the longish term trend.

    Sea level can vary in the short term by quite large amounts especially during La Nina’s and El Nino’s partly due to water volume expansion changes from changes in shallow water heat content but mostly from changes in surface evaporation and enhanced rainfall on land during La Nina’s (and vice versa for El Nino’s; see for example the top of the left hand column of page 25 of a recent review). That’s likely the cause of the anomalous temporary slow down in sea level during 2006-2008.

    Otherwise in the period of your graph, the mass volume contribution (from glacier melt) seemingly went up a bit while the thermosteric contribution apparently went down a bit (either due to reduced absorption of heat into the ocean or a redistribution of heat to somewhat deeper levels where the thermosteric contribution is suppressed). That’s the interpretation from direct analyses of mass and heat contributions to sea level rise as described by Cazenve and Llovel earlier this year.

    I do agree with you that once this internal variability is “averaged out”, one would expect the rate of sea level rise to increase a little if polar ice melt continues to be enhanced. Time will tell….
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  27. Re: 19, Dave Springer...

    Careful not to fall into the trap of viewing sea level as a 1-parameter system. Greenland icemelt is not the only contributing factor to sea level rise. In particular, thermal expansion is the single largest influence. I'm not an expert in the field and I imagine the dynamics are complicated. Nevertheless, I think I can say with confidence that the rate of thermal expansion is tied to where the heat is being transported in the ocean -- tropical vs. polar; surface vs. deep. So just because the Greenland icemelt has increased, other influences -- most likely thermal expansion -- are also playing a significant role.

    It's like cranking up the furnace in winter and wondering why the house isn't warming as fast as before, without also noting that you also opened a few windows. :)
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  28. On sea level rise... if we assume that the influx of water and/or thermal expansion are constant then would we not perforce have to expect the rate of sea level rise to decline over time? After all, when sea level goes up X amount it then covers a larger surface area of the planet... which means a greater volume of water will be required to go up X again.

    So, in order for the rate of sea level rise to increase we'd have to see melt / thermal expansion increasing fast enough to exceed this 'diminishing returns' factor.
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  29. CBDunkerson at 04:14 AM on 14 July, 2010

    hmmm....I hadn't thought of that. The answer must be known, but a simple consideration of geometry would tend to support your point. I wonder how significant it is...
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  30. #25 chris at 04:00 AM on 14 July, 2010
    the thermosteric contribution apparently went down a bit (either due to reduced absorption of heat into the ocean or a redistribution of heat to somewhat deeper levels where the thermosteric contribution is suppressed)

    What do you mean by "to somewhat deeper levels where the thermosteric contribution is suppressed"? In fact at constant temperature volumetric thermal expansion coefficient of seawater increases steadily with pressure. It also increases with pressure if kept at constant potential temperature (when sinking adiabatically).

    It means if you succeed to push down a body of water with a slightly higher temperature, the deeper it goes the higher its heat content anomaly pushes sea level. Therefore thermosteric contribution is not suppressed by redistribution of heat to somewhat deeper levels, just the opposite. You can check it yourself with this Sea Water Equation of State Calculator tool.
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  31. I am about to make my second trip to Greenland. This time to visit the NEEM ice core site. I can tell you there are very few people in Greenland (Scientist or not) who will tell you that Greenland is NOT melting.

    Dan S
    Huntsville AL
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  32. NewYorkJ #21:

    Your map compares the 2000 decade with the 1930s; there's not much difference between those two decades on the graph I snipped from the WUWT article. It would be more informative to map the comparison between the 1980s and the current decade.
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  33. For those who could use a few laughs please link up to WUWT where Steven Goddard is getting pummeled by several posters on that issue. I provide an example below.

    stevengoddard says:
    July 13, 2010 at 11:52 am

    Jeff P

    I am talking about rates of sea level rise. If the rate of ice loss has doubled, then sea level rise would also have to double.


    Jeff P says:
    July 13, 2010 at 12:36 pm

    “I am talking about rates of sea level rise. If the rate of ice loss has doubled, then sea level rise would also have to double.”
    This is false.

    This would only be true if the cause of sea level rise was ONLY from ice loss. Clearly this is not the case.

    If ice loss has gone from something like 50 Gt a year to 100 Gt it has doubled but the impact on sea level rise would be tiny and far below the margin of error for the measurement of sea level rise. A 50 Gt increase in Ice loss would be less than 0.1 mm increase.

    If you’re saying that ice loss could not have possibly doubled (or even increased) because we aren’t seeing a 3+mm increase in the rate of sea level rise you’re way off base.

    stevengoddard says:
    July 13, 2010 at 1:25 pm

    Jeff P

    Uhhmm… You might want to think your sea level argument through a little more carefully. Increasing ocean heat content will also tend to raise sea levels, and makes the the ice melting argument even less tenable.

    villabolo says:
    July 13, 2010 at 1:32 pm

    Ahhhh . . . Steve, with all due respect. Thermal increase would simply be a CO-FACTOR with ice melt. And where would both come from?
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  34. Berényi Péter at 05:05 AM on 14 July, 2010

    No, that's not correct Peter. Remember that the thermal expansion coefficient of water has a strong temperature dependence, and temperature obviously isn't constant as in your statement. The thermal expansion coefficient is larger for warmer waters than cooler waters.

    The consequence is that the deposition of 1 kcal (say) of thermal energy in the warmer upper mixed-layer of the ocean will cause a larger volume expansion than if the same quantity of heat is deposited in the cold deeper ocean (say below the thermocline).

    This effect of depth (temperature)-dependent thermosteric contributions to sea level rise have been described in early studies of sea level responses to warming:

    e.g. Wigley, TML and Raper SCB (1987) Thermal-expansion of sea-water associated with global warming Nature 330, 127-131.

    and you can find it stated rather explicitly in Trenberth's review that I linked to in a post above.

    e.g. see bottom of page 21 to top page 22:
    "Sea level rise from thermal expansion depends greatly on where the heat is deposited as the coefficient of thermal expansion varies with temperature and pressure. The warming required to produce 1 mm SLR if the heat is deposited in the top 700 m of the ocean can take from 50 to 75 x 10^20 J, or ~ 110 x 10^20 J if deposited below 700 m depth [14]."

    In other words, some of the apparent shortfall in the thermosteric (ocean heat absorption) contribution to sea level rise during the period ~ 2003/4-2007/8 may be due to a larger than "average" transfer of heat to the somewhat deeper layers of the ocean.
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  35. CBDunkerson @ #27: I would have thought that such an effect would be very minor - if you consider that oceans already cover ~70% of the Earth's surface, the maximum impact of the increasing area would be around 43% (1/0.7). But that would be the point at which *all* landmass was covered by water. I think, when we're still talking tens of millimetres, that the increased ocean area would be very, very small.

    A quick search didn't turn up any numbers for inundation areas with various sea level rises, I'm sure the numbers are out there, though.
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  36. Bern: IPCC AR4 WG2 would be good place to start, specifically here.
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  37. #33 chris at 08:08 AM on 14 July, 2010
    you can find it stated rather explicitly in Trenberth's review

    Yes. But he also says in his review:

    "A 1 mm eustatic rise in sea level requires melting of 360 Gt of ice that takes 1.2×1022 J. Because the ice is cold, warming of the melted waters to ambient temperatures can account for perhaps another 12.5% of the energy (total 1.35×1020 J)."

    That must be a misprint. 360 Gt of ice is 3.6×1014 kg. Heat of fusion for (freshwater) ice is 3.3355×105 J/kg. Therefore the energy required to melt that much ice at 0°C and atmospheric pressure is 1.2008×1020 J, which is a hundred times smaller than Trenberth's figure (his total of 1.35×1020 J seems to be correct, at least as an order of magnitude estimate).

    What do reviewers do?
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  38. Can anyone explain Figure 2 to me?

    First, it shows a very short timeframe - the sort of thing I would expect from denialists, not here.

    Second, it seems to show that up to mid 2006, the ice mass was actually growing. It cannot have done that forever, and the quadratic fit looks nice by I do not expect that will hold forever, either.

    As I see it, this picture could just be a small section in a process of random fluctuation. Any thoughts?
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    Response: Figure 2 is a short time frame because that's as long as the GRACE satellites have been measuring the gravity around the Greenland ice sheet. Would be lovely to have more data but that's the hand we've been dealt. In fact, we're lucky that the latest data through to early 2010 fell into our hands in May, giving us an even longer data series than was publicly available until then.

    That's why Figure 1 is so important - it shows other estimates of Greenland mass balance back to 1960. The fact that the other estimates are consistent with the gravity data gives us confidence in the estimated rate of ice loss.

    I don't expect the quadratic fit to hold forever either. The ice melt has continued to accelerate because the ice loss has spread to the northwest but I expect the rate of ice loss will eventually reach a peak. So how do we know the current ice loss isn't just a random fluctuation and things will bounce back to mass balance?

    We get a good sense of Greenland's trajectory by considering all the evidence. We see accelerating ice loss from both Greenland and Antarctica - similar patterns from opposite sides of the globe. We look at past sea level and see it closely copuled to changes in temperature. Looking at the Earth's past, we see that the last time temperatures were 1 to 2 degrees warmer than now, sea levels were at least 6 metres higher than present levels. This tells us that the Greenland and Antarctic ice sheets are highly sensitive to sustained warmer temperatures.

    You're correct in identifying the dangers of looking at narrow pieces of data. You need to take in the full body of evidence to get an accurate picture. All this evidence taken together indicates Greenland will contribute sea level rise in the order of metres over the next few centuries.
  39. Chris#33, BP#36

    "In other words, some of the apparent shortfall in the thermosteric (ocean heat absorption) contribution to sea level rise during the period ~ 2003/4-2007/8 may be due to a larger than "average" transfer of heat to the somewhat deeper layers of the ocean"

    "May be due" is sheer speculation. At the time the paper was written (Aug-09), Dr Trenberth was not aware of the Von Schukmann paper which claimed to find a large chunk of the 'missing' heat down to 2000m.

    In fact I drew the Von Schukmann paper to Dr Trenberth's attention in February this year, and he has since used it in a banter with Dr Pielke in April - calling it a 'nice analysis'.

    Well, BP produced a pretty convincing demolition of the Von Schukmann paper and its 'bumpy' OHC chart elsewhere in this blog.

    Willis subsequently came up with a 'small' number for deep OHC of about 0.1 W/sq.m which is only about 16E20 Joules/year.

    The 1.22E22 Joules in the Trenberth paper is a typo - not a serious one - but I read this some time ago and could not make out the following 1.35E20 as a 12.5% increase on the former number.

    Who said this stuff was 'peer reviewed?

    Anyway, the essential point is that the SLR budget and the energy budget do not come close to consistency, and more ice melt component for a given SLR worsens the shortfall in the energy budget.

    In reality you can't have more ice melt and more steric rise at the same time for a given SLR.
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  40. I published a paper back in 1990 called the Equilibrium balance of the Jakobshavn Glacier. This paper looked at the consistent velocity data from 1950-1986, the consistent terminus position and field measurements of snow depth and snow melt, all lines of data suggested a near equilibrium balance for this system, which now is anything but. That is the long range evidence we actually have. That study was undertaken by the U of Maine partly because we saw the Jakobshavn as an analog for other glaciers particularly Pine Island which might accelerate in a similar fashion.
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  41. Ken Lambert at 22:52 PM on 14 July, 2010

    Not really Ken. There is certainly evidence for an increase in heat content in the deeper oceans as described at great length previously. There's nothing surprising in that; in a world warming under enhanced radiative imbalance, we expect the oceans to absorb heat and some of this will find its way to depths.

    Peter has attempted to discount the possibility of reduced thermosteric contribution through deeper ocean heat sequestration by reinventing the laws of physics on thermal expansion of water! It's worth pointing out that he's got that fundamentally wrong. Might Peter's "demolition" of von Schuckmann et al. be of a similar nature?

    The increased rate of Greenland ice melt apparent in Figure 2 above (say comparing 2002-2004 to 2008-2010) amounts to a few tenths of a millimetre of eustatic sea level rise per year. Since sea level measurements are a little noisy, that may simply not be apparent in the data yet, and of course this small rise (around 10% of the absolute yearly sea level rise) may have been countered by a shortfall elsewhere (e.g. mountain glacier contributions); it's pretty difficult to do this "acounting" on very short time periods.

    And while you're right that "you can't have more ice melt and more steric rise at the same time for a given SLR" (assuming your measurements are sufficiently precise), you can have a little more ice melt contribution with a similar or even enhanced ocean heat content, if some of the latter has found its way to somewhat deeper parts of the ocean. That might have looked a little unlikely 2-4 years ago when SLR seemed to have slowed down somewhat. However that slow down was likely due to a La Nina period and the SLR is pretty much back on its longish term trend. I guess we'll have a better idea as things develop over the next couple of years....
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  42. Sense Seeker at 22:08 PM on 14 July, 2010

    "Second, it seems to show that up to mid 2006, the ice mass was actually growing. It cannot have done that forever, and the quadratic fit looks nice by I do not expect that will hold forever, either.

    As I see it, this picture could just be a small section in a process of random fluctuation. Any thoughts?"

    The Y axis is an "anomaly" Sense Seeker, and I don't think the "zero" represents a point where Greenland ice mass in balance between mass increase and loss. So the ice sheet wasn't growing up to 2006 as one might infer from the figure.

    This is apparent if one looks at longer time period analysis of Greenland mass balance. I can't find a linkable version, but a recent paper by Rignot indicates that the Greenland ice sheet grew overall a little between 1957 and 1977, was pretty much in balance between around ~1977 and 1987, started to lose mass slowly between ~1987 and 1997, and that the mass loss has accelerated since then...

    Rignot, E et al (2008), Mass balance of the Greenland ice sheet from 1958 to 2007 Geophys. Res. Lett., 35, L20502
    link to abstract
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  43. Of course, the other salient point to be made here: Steve Goddard chooses to "publish" his analysis on a blog rather than the the scientific literature.

    I'd like to challenge him to submit his analysis for legitimate peer review and publication. I'll even help. Journal of Climate, I should think, would be a good place to start ...
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  44. Sense Seeker writes: Second, it [Figure 2] seems to show that up to mid 2006, the ice mass was actually growing.

    That's a common, and understandable, misconception. The zero line in that figure isn't an equilibrium mass balance. It's an "ice sheet mass anomaly" similar to temperature anomalies that are measured with respect to an arbitrary zero point. In other words, the Y axis is (as stated) gigatons, rather than gigatons per year.

    Any time the line has a negative slope on that graph, it means Greenland is losing mass, regardless of whether the line is currently above or below 0.
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  45. Er, one could also read chris's comment making the same point as mine, but 93 minutes earlier....

    Sorry for the repetitive redundancy.
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  46. So what does figure 2 show? It appears that at the beginning of 2004 the change in Greenland's ice mass was +450 gigatons. At the end of 2004, the change in Greenland's ice mass was +250 gigatons.

    In 2009 it was -600 and -800, respectively. Shouldn't the anomoly be positive if the ice is growing, and negative if the ice is shrinking?
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    Response: The title for the graph is "Change in Greenland ice mass" but really, what I should've called it was "Greenland ice mass anomaly". I went with the more plain English terminology because anomaly is a technical term. But obviously, there is a reason why scientists use technical terms - they're more precise in meaning and less open to misinterpretation.

    Greenland has been losing ice mass every year from 2002 to 2009. So the positive values at the start of the graph don't mean the ice sheet was gaining mass at that point. Those values are just the variation from the average over the whole 2002 to 2009 period. As it's been losing mass over the whole period, that's why the first half of the graph is positive and the second half is negative.

    Am strongly considering going back to "Greenland ice mass anomaly".
  47. No, that's exactly what chris and I are pointing out. A value of +450 GT at the beginning of 2004 just means that there was 450 GT more ice in 2004 than in 2006.

    In other words, in 2006 Greenland had [X] gigatons of ice. In 2004 it had [X+450], and in 2010 it had [X-800]. We don't actually know exactly what [X] is.

    Again, the analogy is to temperature anomalies. If a temperature anomaly is calculated with regard to the period of 1971-2000, then temperature anomalies above zero just mean that the temperature is currently higher than it was in 1971-2000, not that it's necessarily rising right now.
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  48. #40 chris at 01:54 AM on 15 July, 2010
    Peter has attempted to discount the possibility of reduced thermosteric contribution through deeper ocean heat sequestration by reinventing the laws of physics on thermal expansion of water! It's worth pointing out that he's got that fundamentally wrong.

    Come on. There was nothing fundamentally wrong with it. Volumetric thermal expansion coefficient of seawater at constant temperature increases with pressure indeed.

    At 700 m it is 104×10-6 and it gets 50% more at 3200 m (156×10-6). As a water mass sinks, there is not much adiabatic heating. If it started at 2.72°C at the surface, its temperature would be 3°C at 3200 m.

    It is quite possible heat does not actually get to depth this way, but it is not a reinvention of fundamental physics.
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  49. Thanks for the explanations of Fig. 2. It makes perfect sense to me now.
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  50. BP:
    If you read the density/temperature graph in the link you supplied, you will see that the expansion of sea water is temperature dependent. This means that the expansion of surface water at 20C when it absorbs 1E22 joules of energy is greater than the expansion of bottom water at 1C when it absorbs the same amount of energy. This is the basic physics that Chris is referring to. Since deep water is colder then surface water, the graph you copied with constant temperature is not relevant to the discussion.
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