Arguments
Recent Comments
Prev 2365 2366 2367 2368 2369 2370 2371 2372 2373 2374 2375 2376 2377 2378 2379 2380 Next
Comments 118601 to 118650:
-
KR at 12:32 PM on 28 May 2010The significance of the CO2 lag
johnd - the important issue is the sum of all feedbacks. (Yes, I'm opening a Pandora's box here, but...) If the sum of all feedbacks (positive and negative) sums to -1 < x < 0, then you have a reduction or a reduction with damping oscillation after a forcing (depends on time constants). If the sum of all forcings is 0 < x < 1, then you have an amplification. Both sum to 1/(1-x) if I recall correctly, where the sum is rather smaller if x < 0. Feedbacks of the form x < -1 are run-away oscillators - each swing larger. These are sometimes used as frequency generators in electronics, limited by input voltages/energy. Feedbacks x > 1 are run-away growth until some other limit (non-linear limit on available energy?) kicks in. Neither tend to exist in nature. At least, not for long... -
Joe Blog at 12:19 PM on 28 May 2010Latest GRACE data on Greenland ice mass
doug_bostrom Yea cause is the Q isnt it... I believe recently that a shift in ocean currents is a contender as one of the major causes http://www.jpl.nasa.gov/news/news.cfm?release=2010-050 Whether this is a result/symptom of anthropogenic co2, or some other cause, i dont know, or pretend to know. But id put money on its the reason for the accelerating mass loss in recent times. -
Doug Bostrom at 12:09 PM on 28 May 2010Latest GRACE data on Greenland ice mass
Curving, like Jiang but derived from a different data source. So perhaps we can take it as read that Greenland's got an accelerating mass deficit? That way-- in the upcoming inevitable discussion of why/how this has nothing to do with anthropogenic climate change-- we won't have to sift through a mass of previously failed "it's not shrinking/it's actually growing" hypotheses and stick w/somewhat more plausible alternate mechanisms not involving anthropogenic climate change. And how about those alternate ideas being posted here fully fleshed-out, with details of how they -ought- to work and then some confirmatory observations? Something remotely comparable to what John presents? That would be a really pleasant improvement. (Sorry, somewhat out-of-patience here having listened for the past 24+ hours to BP's rapidly alternating stories about their oil leak while watching the video of the leak itself somehow remaining completely identical in appearance while it supposedly had tens of thousands of barrels of barite mud pumped into it, lost, shut off, then turned on again. I believe the mud's gone in, I guess, maybe, but I don't believe they had the well under control for any period of time.) -
Tenney Naumer at 11:55 AM on 28 May 2010Latest GRACE data on Greenland ice mass
I am just really, really grateful that Dr. Wahr did not make us wait for a peer-reviewed publication to come out before making the data public! -
HumanityRules at 11:38 AM on 28 May 2010Latest GRACE data on Greenland ice mass
I don't suppose John Wahr wants the bother of monthly updating this data online. Near realtime updates of climate data are exciting. (wait did I say exciting!)Response: Then I would be tempted to do regular blog posts on every twist and turn. I've been monitoring Roy Spencer's near-daily satellite data on surface temperature with great interest. To my credit, I've resisted the temptation to blog on it, wary of the fickleness of short-term fluctuations. -
The significance of the CO2 lag
johnd, you're confusing net temperature gain with the feedback factor (aka ratio or percentage). In your example, the feedback factor is: 1-(1/1.23)= 0.187, which is a positive number < 1.0. That's what KR was referring to. If the feedback factor is positive but < 1.0, then each successive feedback is smaller than the previous by a constant factor. This geometric series converges to a finite number, hence the warming is not runaway. If the feedback factor is >= 1.0, then yes, you would have a runaway warming. -
CoalGeologist at 09:37 AM on 28 May 2010Why Greenland's ice loss matters
Sorry, Berényi Péter @26, but I will be stubborn and hold to my "Something is new under the sun" argument. Kaufman, et al., “Recent Warming Reverses Long-Term Arctic Cooling,” Science, 4 September 2009: 1236-1239, DOI: 10.1126/science.1173983 concluded that 20th Century Arctic warming reversed a trend of Arctic cooling that had persisted for some 2000 years prior to that. Such (it would seem) is the power of AGHGs (although the warming apparently got started rather early, it would appear), as shown below.
Moreover, the unusual Arctic warming described by the estimable Sir Joseph Banks, actually seems to show up during the mid-teens on the proxy-temperature trends of Kaufman et al., yet it is barely a 'blip'. In fact, the entire proxy temperature curve reminds me of a hockey stick, that is in the process of being lowered to the ice by a sharp-eyed goalie, in the hopes of blocking an oncoming slapshot! (Where is the Medieval Warm Period, when Vikings apparently basked in the warmth of sunny Greenland?!)
I was, however, very pleased to see in the Summary, and on p. 288 of the proceedings, that the Royal Society saw fit to honor Sir Humphrey Davy, who, among his other important scientific contributions, designed a lamp that could safely illuminate underground coal workings, while not causing them to explode. There are current efforts underway to attempt to capture 'coal mine methane' before it escapes into the atmosphere.
-
hadfield at 09:19 AM on 28 May 2010Why Greenland's ice loss matters
My comment was not intended to express an opinion either about the validity of any criticisms of Velicogna (2009)'s statistical method, nor about how well we understand the processes. On the former, I was hoping to get a few more eyeballs on the issue. As you say, Doug, Tamino could offer an informed opinion. He could probably sort this out before breakfast, and then get to his day job. On the latter, I was pointing out the instability and ill-foundedness of purely mathematical extrapolations. A pretty obvious point, I admit. And now I must get back to my day job. -
johnd at 09:19 AM on 28 May 2010The significance of the CO2 lag
e at 08:31 AM on 28 May, 2010, perhaps you can show a simple equation to demonstrate. Using the example by Chris above, an initial forcing of 1oC results in a additional temperature rise of 0.23oC giving a total rise of 1.23oC. That is positive feedback. If the temperature only responded to the initial 1oC forcing and the total rise including feedbacks remained at 1oC, that is neutral feedback. If the initial forcing is 1oC and the total rise is less than 1oC, that would be negative feedback. -
The significance of the CO2 lag
johnd > "Perhaps one reason being is that it is negative feedback" This shouldn't need to be said, but a positive feedback < 1.0 is not negative. A negative feedback would be a factor < 0.0 of the forcing. -
chris at 08:31 AM on 28 May 2010Why Greenland's ice loss matters
hadfield at 07:55 AM on 28 May, 2010 "Extrapolating an accelerating curve into the future is always problematic." Or into the past, I might add. We need understanding of the processes. We understand the processes pretty well hadfield. If the Earth temperature stabilises, land ice volume (and sea level) will eventually settle around an equilibrium state. Raise the temperature and the ice will melt, and sea levels will rise towards a new (reduced land ice volume) equilibrium state. If the temperature is higher, then the rates of land ice melt and sea level rise will be faster. It's pretty simple physics. At a given temperature above the equilibrium temperature there will be a fairly constant rate of melt on the decadal timescale. As temperatures rise, so the rate of melt accelerates. Extrapolating this into the near future is likely to be pretty reliable. The simple physics of this phenomenon and its agreement with empirical observations, has been recently reiterated here -
Doug Bostrom at 08:09 AM on 28 May 2010Why Greenland's ice loss matters
Hadfield, just a suggestion, or a demonstration? Tobis runs a pretty tight shop, surely this is not simply speculation? Tamino at OpenMind would be -ideal- for this work but surely he has a day job, might not be able to take it up. -
Peter Hogarth at 08:09 AM on 28 May 2010Why Greenland's ice loss matters
FerdiEgb at 21:01 PM on 27 May, 2010 I’m a little doubtful of your statement “There is no significant trend in the Greenland temperature data over this 130 year period” I’ve looked at the records, but they are visually summarized nicely by the DMI:
The overall Greenland (and global) temperature trends are strongly positive over 130 years. There does indeed appear to be anomalous Greenland warming between 1920s and 1940s. This is strongest at these NH latitudes, there is some debate as to why. Recent work on aerosols is interesting as the US has been a major industrial source of sulphates and the concentrations extracted from Greenland ice cores (which give high resolution records covering this period, I think it’s in McConnell et al., 2007) mirror the variations, even if they do not mirror the overall rising trend. Perhaps the “natural variations” aren’t so natural.
-
chris at 08:06 AM on 28 May 2010Why Greenland's ice loss matters
FerdiEgb at 21:01 PM on 27 May, 2010 Not sure that I agree with too much of that Ferdi. There is certainly a trend in Arctic temperatures with a reversal of a long-term very slow cooling, starting in the mid-late 19th century, to yield a rather dramatic warming especially over the last 100-plus years [*]. Greenland itself is more difficult to assess. However it seems also to have warmed considerably since the mid-19th century. The temporal variation in warming is more complex, but recent analysis indicates that this is likely to have been strongly influenced by atmospheric aerosols (volcanic and anthropogenic) to which the Greenland ice sheet is especially susceptible (i.e. to cooling effects) [**]. So the suppression of Greenland temperatures in the late 19th century and the rapid warming especially from around 1910 has likely got a strong contribution from the high volcanic activity in the late 19th/early 20th century, and then a rapid recovery from this aerosol-induced cooling to "catch up" with the enhanced greenhouse-induced forcing. The same likely applies to the cooling in the middle of the 20th century. So there’s nothing necessarily “cyclic” about these contributions. Rather they’re likely to have been stochastic. A concern raised by Box et al (see [**]) is that Greenland temperature anomalies should rise above N. hemisphere anomalies, and they haven’t got there yet. So it seems we have a bit of extra Greenland warming still to come irrespective of present and future enhanced greenhouse forcing (see [**] for a discussion of this). As for polar ice melt, there’s no evidence from the trajectory of 20th century sea level rise that early 20th century warming of Greenland was associated with ice melt to the extent that we’ve seen in the last decade. Of course that's not really surprising since globally-averaged temperatures were quite a bit lower then than now. Clearly in a world with globally enhanced temperatures, the rate of ice melt will be greater. That seems to be pretty well established (see papers cited here). It’s all very well to talk about “natural variability (PDO, NAO, AO,...)” but that doesn’t have much meaning without a quantitative analysis. Swanson et al (2009) have done this and find that while natural variability relating to ocean circulation likely made contributions to early-mid 20th century temperature progression, its contribution to the warming since the early 1970’s has been small (~ 0.1 oC) [***]. And any putative absence of natural cycles from models doesn’t “overestimate the effects of CO2” since natural cycles don’t contribute to long term forcing (they just introduce "noise” around any trend). So Swanson et al. (2009) conclude that natural climate variability (including ocean circulation variability) has made close to zero contribution to the warming since the start of the 20th century. And it’s very difficult to sell the notion that there has been a “halt in warming over the last decade” when every year of the past decade has been warmer than every year of the previous one bar the highly anomalous 1998 (not to mention that we’ve just had the warmest Dec-Feb quarter on record; NASA Giss). And I don’t think it makes sense to say that the current temperature is at the low end of all projections when at least through 2006, the temperature trend was near the top end of the IPCC projections [****]. There's no question that Greenland melt is now faster than any previous record of Greenland melt outside glacial-interglacial transitions, and it's rather certain that Greenland melt and its contribution to sea level rise, is going to increase in the coming decades. There is some very fundamental physics involved in these phenomena, and vague reference to ill-defined "cycles" isn't going to alter those facts! [*] Kaufman, D. S. et al. (2009) Recent Warming Reverses Long-Term Arctic Cooling Science 325, 1236 – 1239 abstract [**] Box, J. E. et al. (2009) Greenland Ice Sheet Surface Air Temperature Variability: 1840-2007 J. Climate 22, 4029-4049. abstract [***] Swanson, K. L. et al. (2009) Long-term natural variability and 20th century climate change Proc. Natl. Acad. Sci. USA 106, 16120-16123. abstrsct [****] Rahmstorf, S. et al. (2007) Recent Climate Observations Compared to Projections Science 316, 709. abstract -
scaddenp at 07:58 AM on 28 May 2010Why Greenland's ice loss matters
Geo Guy - volcanoes at least occur in predictable places - Greenland not among them. I, like angliss, would like to see your reference for a volcano in Greenland. My thermal modelling depends pretty much on predictable, steady crustal heat flow and this backed by a lot of empirical data. Even the effects of a volcano are quick localized. -
Doug Bostrom at 07:56 AM on 28 May 2010Has the greenhouse effect been falsified?
For more on saturation effects, also see the wonderfully titled A Saturated Gassy Argument, at RealClimate. -
hadfield at 07:55 AM on 28 May 2010Why Greenland's ice loss matters
On a post at Michael Tobis's blog: http://initforthegold.blogspot.com/2010/05/eschenbach-has-half-point.html Willis Eschenbach, MT and others are expressing doubt about Velicogna's 2009 finding of accelerating mass loss from Greenland and Antarctica in the period 2002-2009. The suggestion is that she has neglected (or otherwise failed to account properly for) the effect of smoothing on the number of degrees of freedom in the data. My suggestion is that this criticism, if it's well-founded, needs to be conveyed in a comment to GRL. Does anyone else more statistically competent than me want to venture an opinion? By the way, Ned (#16), on MT's blog I asked "Why would anyone extrapolate a quadratic fit based on a sample of 7 years of data out to 91 years beyond the sample end-points? In either direction?!". You have gone one better by converting it to an exponential before extrapolating. I can only admire your boldness, sir! But seriously I think we all can agree that "Extrapolating an accelerating curve into the future is always problematic." Or into the past, I might add. We need understanding of the processes. -
KR at 07:51 AM on 28 May 2010Has the greenhouse effect been falsified?
Note that even if the peak absorption is extremely high, the absorption spectra shows a set of approximately Gaussian peaks. Increasing amounts of GHG's will therefore raise the edge effects, increasing the bandwidth of blocked radiation, even if the center of the band is saturated - as discussed here to some extent. -
chris at 07:45 AM on 28 May 2010Working out climate sensitivity from satellite measurements
HumanityRules at 14:14 PM on 27 May, 2010 The relationship is: Del(Teq) = Q/Y where Del(Teq) is the equilibrium climate sensitivity [note that this relates to the fast (water vapour/cloud) feedback. The real (Charney) sensitivity incorporating albedo feedbacks, for example, should be somewhat larger]. Q is the radiative forcing due to doubled [CO2] which is normally taken to be 3.7 W.m^-2 (not sure why 3.3 was chosen in your example). Y is the feedback parameter (in your example 1.25 - 2.0 W.m^-2.K-1) so putting in your values, the fast component of the climate sensitivity is ~ 1.9 - 3 oC at equilibrium per doubling [CO2] -
KR at 07:43 AM on 28 May 2010Has the greenhouse effect been falsified?
Berenyi, the absorptivity spectra will be dependent on the partial pressure of CO2, not the pressure of other gasses - in other words, you can simply adjust partial pressure of CO2 based on total pressure at different altitudes to calculate total absorption/re-emission for CO2. There's an application here for calculating spectra for various gasses, in graphic and tabular forms - that might be of some help... -
johnd at 07:30 AM on 28 May 2010The significance of the CO2 lag
KR at 07:03 AM on 28 May, 2010,"positive feedback <1.0 of the forcing will NOT be runaway" Perhaps one reason being is that it is negative feedback, but then perhaps that can also runaway. -
KR at 07:03 AM on 28 May 2010The significance of the CO2 lag
RSVP, positive feedback <1.0 of the forcing will NOT be runaway. For each forcing, a feedback of 0 -
Doug Bostrom at 06:56 AM on 28 May 2010Why Greenland's ice loss matters
Geo Guy, indeed I think because this climate change matter is so controversial, in collision with some hefty interests including both commerce and our own habits and proclivities, it's probably going to stand for a long time as an extraordinary example of careful attributions. The IPCC reports are an outcome of that, the recent NRC review, even the GRL letter and especially accompanying press release you cited are evidence of this. Think about it for a moment and you might agree, this is a case of science going to extraordinary lengths to get it just as right as possible. No choice, really; look at what's happened to researchers producing climate science findings causing them to collide with public policy and our habits. Spotlights, accusations, recalculations, reobservations, reconfirmations, gaps identified, leading ever more researchers to pile on. I don't think it's paradoxical to say it's all been an ironically extraordinary boon to our understanding of climate. I do however hate to see people tortured because their curiosity leads them in the "wrong" direction. Outrage over silly accusations of fraud is what led me to bother participating on places such as SkS. -
angliss at 06:36 AM on 28 May 2010Why Greenland's ice loss matters
According to the Global Volcanism Project, there were no confirmed eruptions anywhere near Greenland in 2006 (link). Furthermore, if you got the the regional map of volcanoes around the world here, you'll notice that there are a) no confirmed volcanoes pictured in Greenland and b) if you click on Greenland, you get Iceland instead. If you're going to continue saying that there are volcanoes under the ice in Greenland, you'll need some better proof than your say-so. -
angliss at 06:25 AM on 28 May 2010Why Greenland's ice loss matters
Actually, Geo Guy, you asked "what evidence is there to show that the zone of ablation has risen (elevation wise), as opposed to using a 1 degree rise in global temperatures to account for melting." The paper I linked is evidence that the zone of ablation has risen in at least some parts of Greenland, given the fact that glaciers would not be thinning at the headwall if it hadn't. -
Geo Guy at 05:58 AM on 28 May 2010Why Greenland's ice loss matters
Jeff...geothermal activity can extend well beyond the distance between Iceland and Greenland. Magmatic activity is ongoing and its impact on the crust varies widely. There are active volcanoes under the ice in Greenland and the most recent eruption was in 2006 Doug..I don't pretend to say the problem is only the result of one activity but rather the result of multiple events. What I would like to see is a recognition that climate is a very complicated systems and that changes to climate are linked to multiple sources, To point the finger entirely at man made (should I say ground originated?) CO2 emissions without correctly accounting for all of the other sources to me is tunnel vision and not reflective of good science.Response: "What I would like to see is a recognition that climate is a very complicated systems and that changes to climate are linked to multiple sources"
Hopefully this page will satisfy you then: CO2 is not the only driver of climate
No climate scientist would say CO2 is the only driver of climate. The reason we harp on about CO2 emissions is because when you compare CO2 forcing to all the other forcings in climate, it is the dominant forcing and it's also the fastest rising forcing. -
Ron Crouch at 05:55 AM on 28 May 2010Why Greenland's ice loss matters
As far as I am aware Alberto Behar was the first to explore a moulin in 2006. These moulins are connected to the broader plumbing in the Greenland ice sheet and the processes are still poorly understood and difficult to model. As we gain a better understanding of how this plumbing system works we will be able to better estimate total losses from the Greenland ice sheet. This combined with other factors has the potential to place the AR4 projections on the optimistic end of the scale. A further discussion of the AR4 numbers can be found here. -
Geo Guy at 05:33 AM on 28 May 2010Why Greenland's ice loss matters
Jeff...the earth's crust is in a constant state pf flux - as we have seen with recent events in Iceland, volcanic activity (which is magma coming to the surface) can happen unexpectedly at any time. There are numerous studies that identify the role of magma activity to crustal thinning that supports the contention that von Frese arrived at. It is widely known that geothermal activity originating from magmatic activity can extend well into the crust warming the rocks. -
Doug Bostrom at 05:14 AM on 28 May 2010Why Greenland's ice loss matters
Geo Guy you and I won't be able to sort it out here (nor anywhere else, no slight on you, neither of us are capable I'll hazard a guess) but I'll just say I think the probability of a massive change in a hotspot coinciding with what we're doing on the surface in the space of a few picayune human lifespans is rather small. Besides, if that probability was "1" it would just make things worse; the heat flux from a hotspot does not change the underpinning physics of the atmosphere, the two systems are largely oblivious of each other yet would act in concert in the case in question. -
Jeff Freymueller at 05:09 AM on 28 May 2010Why Greenland's ice loss matters
#27 GeoGuy, discussion of magma would be relevant if you were talking about parts of Iceland, but not Greenland. -
Jeff Freymueller at 05:05 AM on 28 May 2010Why Greenland's ice loss matters
The bedrock topography has been pretty much the same for thousands of years or more, and thus its effect on geothermal heat flow has been pretty much the same for thousands of years. The rate of ice loss has accelerated abruptly over the last decade or so. Geothermal heat flux did not change over the last decade or so. It's not responsible for the change. -
Doug Bostrom at 05:00 AM on 28 May 2010Why Greenland's ice loss matters
BP: Told you there was no new thing under the sun. Less important the novelty perhaps and more the particular arrangement. For instance, moving hydrocarbons from entombment to liberation... -
Geo Guy at 04:52 AM on 28 May 2010Why Greenland's ice loss matters
anglis..you missed my point...I wasn't saying the glaciers were not melting..I was simply pointing out that other factors are at play that contribute to the disappearance and that they should be factored in when trying to arrive at any reasonable conclusion. Doug_b..I agree. All I would like to see is a fair assessment of all research before conclusions are arrived at. In the past I have read posts that some scientists believe the rapid movement of the Greenland ice sheet is attributed to surface melt seeping down and lubricating the base of the ice sheet. Now it appears that the water at the base could be attibuted to melting from below..who really knows? As for your comments about the flux, don't assume the heat is constant..magma moves like an ocean only in slow motion. There are hot spots and there are cold (relative) spots as the currents move about. Think of it as a period of warm magma currents that have washed against the overlying crust..eating away at the crust thereby making it thinner - much like a warm current eating away at a layer of ice on a lake or ocean. Just as we see in the air and waters, currents move around and switch from hot to cold etc and we can expect the same characteristics within the earth's magma. As for your comments regarding modeling, it seems the same can be said for many conclusions regarding global warming and climate change which seem to be made based on the output of models. My views regarding models are best suited for another forum -
Berényi Péter at 04:45 AM on 28 May 2010Why Greenland's ice loss matters
It will without doubt have come to your Lordship's knowledge that a considerable change of climate, inexplicable at present to us, must have taken place in the Circumpolar Regions Told you there was no new thing under the sun. -
Doug Bostrom at 04:21 AM on 28 May 2010Why Greenland's ice loss matters
Abstract of paper Geo Guy mentions. Subglacial topography and geothermal heat flux: Potential interactions with drainage of the Greenland ice sheet Many of the outlet glaciers in Greenland overlie deep and narrow trenches cut into the bedrock. It is well known that pronounced topography intensifies the geothermal heat flux in deep valleys and attenuates this flux on mountains. Here we investigate the magnitude of this effect for two subglacial trenches in Greenland. Heat flux variations are estimated for idealized geometries using solutions for plane slopes derived by Lachenbruch (1968). It is found that for channels such as the one under Jakobshavn Isbræ, topographic effects may increase the local geothermal heat flux by as much as 100%. Leaving the question, how did the ice sheet reach the size it did in the presence of this flux, assuming it is relatively constant, and what has changed to cause new behavior in the form of broadly distributed mass loss? By the way, this research was heavily (and appropriately) dependent on modeling combined with observations to produce results. My general point being, let's not disparage some models while highlighting others unless we can offer informative and useful criticism of the model in question. (Geo Guy, I know you did -not- do that here but I think it's a helpful example) -
angliss at 04:06 AM on 28 May 2010Why Greenland's ice loss matters
Geo Guy (3:59 AM/May28 2010): this paper pointed out that many glaciers in Greenland showed thinning all the way up to the headwalls. -
Geo Guy at 03:59 AM on 28 May 2010Why Greenland's ice loss matters
Let's step back and look at the dynamics of a glacier. It melts in the ablation zone and grows in the area above the ablation zone through accumulation of snow. So, when we talk about Greenland, what evidence is there to show that the zone of ablation has risen (elevation wise), as opposed to using a 1 degree rise in global temperatures to account for melting. The second issue to consider is what other factors may be a play here that can contribute to an increase in melting. One possible argument was made in 2007 by a study that identified the warming as a result of a thin section of the earth's crust. "They have found at least one “hotspot” in the northeast corner of Greenland -- just below a site where an ice stream was recently discovered. The researchers don't yet know how warm the hotspot is. But if it is warm enough to melt the ice above it even a little, it could be lubricating the base of the ice sheet and enabling the ice to slide more rapidly out to sea." http://researchnews.osu.edu/archive/hotgreen.htm Sometimes we can't see the forest because of the trees. -
Doug Bostrom at 03:06 AM on 28 May 2010Why Greenland's ice loss matters
Actually, the thing I find frankly rather annoying about Eschenbach is his redirection of folks' attention from a real problem to an imaginary one. Quite simply, it is not the disappearance of Greenland's ice sheet that is worrisome but instead sufficient shrinkage as to significantly exacerbate sea level rise. When Eschenbach directs his readers to follow calculations leading to the elimination of Greenland's ice sheet he's distracting them in a way that one could reasonably conclude is principally intended to be witty as opposed to genuinely insightful and productive. Greenland could end up looking at a casual glance from space nearly identical to what it does today yet have also bumped up sea level noticeably and indeed even destructively. Why Eschenbach should skip over that point is going to remain an enduring mystery, more so than uncertainties in measuring Greenland's mass balance. -
Doug Bostrom at 02:44 AM on 28 May 2010There's no empirical evidence
PaulK it's even more rare to encounter online folks capable of such contrite speech. Bravo. Not to sink into an opera of tearful counter-apologies but for my part my knee jerk estimation after reading your remark on Tamino was that I was seeing the emergence of another unreasonably intractable person. Sorry about that! -
Doug Bostrom at 02:36 AM on 28 May 2010Robust warming of the global upper ocean
Ken you can check on accuracy and many other fascinating details of the ARGO system and other systemshere (PDF, "World Ocean Database 2009). Also, TOA balance discussions could probably benefit from integration of information found in this article by Trenberth et al, 2009. -
CoalGeologist at 00:46 AM on 28 May 2010Why Greenland's ice loss matters
#9 Arjan at 20:13 PM on 27 May, 2010 What about other glaciers? Or try this.... (from a glacier's perspective.) -
Ken Lambert at 00:07 AM on 28 May 2010Robust warming of the global upper ocean
Chris #62 I checked your sums and they are correct. The next question is what is the accuracy of measurement of water temperature by Argo?? Noting that E22 Joules = 100E20 Joules and Dr Trenberth's 0.9 W/sq.m imbalance at TOA equals 145E20 Joules/year - if all this heat was absorbed in the top 700m of the oceans, then this would equal 0.0145degC temperature rise. Is this rise observed and with what accuracy?? You might explain why there could be a "global short period where there hasn't been a significant radiative imbalance (e.g. due to a particular coincidence of atmospheric effects)". CO2GHG theorizes a relationship of forcing imbalance which is only dependent on log CO2 concentration. Is there any data to suggest a smothering of this CO2GHG forcing by increased cooling effects over a transient period which operates globally? -
Tenney Naumer at 23:42 PM on 27 May 2010Why Greenland's ice loss matters
The mass balance loss curve is very likely to have steps in it from time to time. Recently, data show that melt run off is half of the loss. As the edges of the ice sheet recede, so too will the glaciers, and they will become less of a factor. Have a look at the ancient inlets all around Greenland. They do not taper to points at their ends. It seems to me that their blunt, squared-off, wedge-shaped ends were formed from meltwater pouring down from massive and very high waterfalls in ancient times when the ice sheet was much much larger and higher (I'm going out on a limb with this one). Also, has anyone noticed all the melting going on up and around the ice stream that feeds into the end of the Jakobhavns Glacier? It is so bad that it is creating its own clouds of vapor. Temperatures just to the south have been in the mid 60s. This year, the edge of the ice sheet already appears to be receding fairly rapidly all along the mid-west to north-west coast. -
thpritch at 23:38 PM on 27 May 2010The significance of the CO2 lag
While CO2 levels may lag temperatures in the Vostok ice core samples, this only indicates the state of the climate in the extreme Southern Hemisphere. Lea's paper in 2003 [1]compares the Vostok CO2 data against proxy data for the Pacific SST. His conclusion - "The strong correspondence of a proxy SST record from the eastern equatorial Pacific and the Vostok CO2 record suggests that varying atmospheric carbon dioxide is the dominant control on tropical climate on orbital time scales. This effect is especially pronounced at the 100 000-yr cycle." This tends to support Caillon's hypothesis (post 33) that the changes in the Earth's orbit relative to the sun initially caused the greatest warming in Antarctica with little to no warming in the tropics and Northern Hemisphere. The warming of Southern Ocean caused the release of CO2 which accelerated the warming of the Southern Ocean and started the warming of the tropics and Northern Hemisphere. -
James Wight at 23:31 PM on 27 May 2010Robust warming of the global upper ocean
John, have you considered updating the ocean cooling page? -
carrot eater at 23:18 PM on 27 May 2010Why Greenland's ice loss matters
When you think about scale, one must consider what is being discussed. If the question is, how long before Greenland has disappeared, or is half missing, then yes, a very very long time. If the question is, is this another line of evidence of warming in that region? Then the topic of lifetime is not so relevant. If the question is, what does this mean for sea level rise in the next 100-200 years? Then the scale here is not negligible. -
Ned at 23:03 PM on 27 May 2010Greenland rising faster as ice loss accelerates
HumanityRules, like the IPCC AR4 sea level rise projections, that paper doesn't attempt to include discharge of ice by marine-terminating glaciers. Its mass balance estimates are based solely on precipitation vs surface melt. This is the same problem that people have been discussing ever since IPCC AR4 came out -- their projections of sea level rise do not include ice discharge and are thus far too low. There are some further issues with the paper HR cites (they don't include several other factors that increase the rate of ice loss, and their model doesn't deal with spatial variability across Greenland -- they themselves point out in the paper's Discussion that this means their estimates of negative mass balance may be too low). So, it's not an uninteresting paper, but its projections of sea level rise are obviously incomplete. I am a bit surprised that they didn't say anything about the fact that their "-300 GT/year mass balance" prediction for 2100 has already come true by 2009-2010. -
Ned at 22:32 PM on 27 May 2010Why Greenland's ice loss matters
Chris's comment above is very insightful. Climate is determined by the earth's radiation balance and the fluxes of energy among components of the climate system. Under some conditions these fluxes create pseudoperiodic "cycles" that we give names like ENSO, PDO, AO, etc. but these are really just manifestations of internal variability within the climate system at particular spatial and temporal scales. Compare the temperatures during recent El Nino episodes. The 1982-1983 and 1997-1998 Ninos were much larger than the 2009-2010 one (both in duration and in magnitude of the peak, e.g. as represented by NINO3.4 anomaly). But 2009-2010 temps are much higher than those in 1982-1983, and rival those of 1997-1998 (slightly lower in the lower troposphere, slightly higher at the surface) despite being a far weaker El Nino. In other words, natural variability such as ENSO is superimposed on a long-term warming trend from greenhouse gases. A small ENSO peak today produces temperatures comparable to a big ENSO peak in the 1990s, and much warmer than a big ENSO peak in the 1980s. -
Berényi Péter at 22:01 PM on 27 May 2010Why Greenland's ice loss matters
#9 Arjan at 20:13 PM on 27 May, 2010 What about other glaciers? Click on image or just here for an overview of ancient literature. -
Ned at 21:36 PM on 27 May 2010Why Greenland's ice loss matters
The recent acceleration of the loss of Greenland's ice mass (increasing at 11% per year, doubling in 7-8 years) is obviously unsustainable. If that continued there would be no ice left in Greenland by 2075. There's no proposed physical mechanism by which that mass of ice could be ablated from that landscape in that time. But even a much smaller loss of ice on the century timescale would be economically and socially problematic. If Greenland lost only 10% of its ice, that translates to 0.6-0.7 m sea level rise on top of the sea level rise from thermal expansion, loss of mountain glaciers, and loss of Antarctic ice (so well over a meter of SLR total). In other words, even a trend much less extreme than that of the past decade would yield much higher rates of SLR than the overly cautious IPCC projections, which don't include dynamical changes to ice sheets.
Prev 2365 2366 2367 2368 2369 2370 2371 2372 2373 2374 2375 2376 2377 2378 2379 2380 Next
