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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. -
Berényi Péter at 21:34 PM on 27 May 2010Has the greenhouse effect been falsified?
Funny. It looks like absorptivity of CO2 in the 14-16 μm band is so high that in this frequency range air is opaque even at a 20 km altitude. Therefore measurements taken from aircraft around 15 μm only show the temperature of air nearby. This is why tropical Western Pacific (Fig 8.3 c) is warmer than expected there. However, proper high resolution molar absorptivity spectra for carbon dioxide mixed with dry air, measured in a controlled lab environment at different pressures from sea level down to perhaps 10 Pascal in tabular format (no pictures) would be appreciated. With these data at hand carbon dioxide photosphere altitude could be computed as a function of frequency. BTW, I can't believe it is not done already. A pointer, anyone? -
Riccardo at 21:27 PM on 27 May 2010Has the greenhouse effect been falsified?
Berényi Péter, because you used temperature profiles which are not the real ones, let alone the ones in that particular place and particular moment when the measurements were taken. Then even if you reasoning is right i do not expect it can be shown in this way. -
FerdiEgb at 21:01 PM on 27 May 2010Why Greenland's ice loss matters
chris at 20:27 PM on 27 May, 2010 As far as I know, ice melt at the Greenland edges is mostly a matter of (summer) temperatures. It has been warmer in the period 1935-1950 (with a loss of 70 meter ice in height) around the ice sheet edges than in the past 10 years. Several stations in Greenland have data since 1880 and show a periodic behaviour with a length of about 40 years for cold(er) and warm(er) periods. There is no significant trend in the Greenland temperature data over this 130 year period. Thus extrapolating the Greenland ice melt from data over the past 10 years is not warranted. That is also the case for global warming: part of the warming/sea level over the period 1970-2000 is certainly from natural variability (PDO, NAO, AO,...), which have some similar periodicity, while all warming of that period is attributed to CO2 by the models. But no model shows the influence of any known natural cycle with a periodicity between 1 and 100 years. This makes that all models overestimate the effect of CO2 and can't explain the halt in warming over the past decade. The current global temperature is already at the lower end of all projections (except for the brief El Niño period, which is at its end now). -
chris at 20:52 PM on 27 May 2010Why Greenland's ice loss matters
Arjan at 20:33 PM on 27 May, 2010 I think that's a reasonable point Arjan. There is still lots of uncertainty about ice sheet dynamics, the factors involve in acceleration of glacier outflow to the seas and so on. It is possible that the Greenland ice sheet has several metastable states, the transition from one to another perhaps occurring rather quickly. So we can't rule out the possibility that we're seeing an acceleration of ice loss which will stabilise at some new state of reduced mass (e.g. perhaps when a particular region/volume of vulnerable ice has melted). As far as addressing that specific point I think we probably need to defer to expert knowledge. -
skagedal at 20:33 PM on 27 May 2010Why Greenland's ice loss matters
Just quickly pointing out that his last name is spelled "Eschenbach". Thanks for the post.Response: Fixed, thanks. -
aj1983 at 20:33 PM on 27 May 2010Why Greenland's ice loss matters
I do however agree that, though the increasing rate of mass loss is worrisome, it (the acceleration) is hard to tell if this is temporarily or not because we do not understand the mechanism behind it well, and the measurement series is rather short. -
chris at 20:27 PM on 27 May 2010Why Greenland's ice loss matters
FerdiEgb at 17:38 PM on 27 May, 2010 "Extrapolating a trend from a cyclic behaviour is quite triggy..." No one is "extrapolating a trend from cyclic behaviour". Variation of Greenland temperatures/ice sheet mass balance through the Holocene has no element of "cyclic behaviour" (other than the very long term Milankovitch influences whose high N. hemisphere forcing resulted in high N. hemispheric warming around 9000-7000 years ago - this should be causing the Earth to cool achingly slowly now). The ice sheet varied according to variations in forcings and heat transfer, and the effects can be understood in relation to causes. So we certainly don't look at historical variations of climate phenomena (temperature/ice sheet/heat transport/sea level or whatever) arbitrarily call these "cyclic" and then pretend that that's an "explanation". Variability has accessible explanations in relation to known physics. That's why we can make projections of future behaviour based on empirical observations and theoretical knowledge. It's very difficult to escape the strong evidence that polar ice mass balance and its rate of change, and the resulting effects on sea level variation, are strongly linked to global temperatures (see references cited here here). -
Berényi Péter at 20:23 PM on 27 May 2010Has the greenhouse effect been falsified?
#59 Riccardo at 17:22 PM on 27 May, 2010 for good reasons Specify those reasons, please. -
CoalGeologist at 20:19 PM on 27 May 2010Why Greenland's ice loss matters
Berényi Péter @7: One thing new "under the sun" (unfortunately) is another 100+ ppm CO2.... (and by "new" I mean post-Ecclesiastes!). -
aj1983 at 20:13 PM on 27 May 2010Why Greenland's ice loss matters
@B. Peter: And how does the total area compare to today? What about other glaciers? -
CoalGeologist at 20:06 PM on 27 May 2010Why Greenland's ice loss matters
Peter Sinclair's Climate Denial Crock of the Week for April 11 includes an informative discussion of the mass loss of the Greenland ice sheet vis-a-vis "skeptical" arguments (in "Debunking Lord Monckton, Part One"). Discussion of Greenland begins at 5:50. The power of any scientific theory is to explain what we observe, and to predict what we have not yet observed. Climate scientists are making their best effort to anticipate future trends, but there will always be uncertainty. Thingamadonta @3 & FerdiEgb @2, the term "Climate Optimum" is value laden. It may have been optimal for some species, but surely not for woolly mammoths (among others). In any case, circumstances were quite different then, with continental glaciers still receding, sea levels considerably lower (stablizing at near current levels ~4,000 B.P.), Venice and New Orleans still in the planning stages, etc. In any case, warming at that time was apparently confined mostly to Arctic regions. Global temperatures are interpreted to have been cooler. We can't assume that contemporary warming will lead to "optimal" conditions. -
Berényi Péter at 19:54 PM on 27 May 2010Why Greenland's ice loss matters
#2 FerdiEgb at 17:38 PM on 27 May, 2010 In the period 1935-1950, the break-up point of the largest glacier was moving upward as fast as today From the 1920s on. Indeed.
The thing that hath been, it is that which shall be; and that which is done is that which shall be done: and there is no new thing under the sun. Is there any thing whereof it may be said, See, this is new? it hath been already of old time, which was before us. There is no remembrance of former things; neither shall there be any remembrance of things that are to come with those that shall come after.
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Riccardo at 19:44 PM on 27 May 2010Why Greenland's ice loss matters
crhiscanaris, immagine to have a pot of water sitting in equilibrium on a spring on a slowly subsiding land; the pot will go down with the land. Then you start draining water from the pot, the spring pushes the pot up and the result will be that the pot will slower motion downward or even reverse direction if you drain fast enough. Not sure if this analogy makes it clearer. -
Riccardo at 19:31 PM on 27 May 2010Why Greenland's ice loss matters
thingadonta, models do not extrapolate current behaviour. They project on the basis of scenarios, not extrapolations. -
chris1204 at 19:21 PM on 27 May 2010Why Greenland's ice loss matters
Returning to an earlier post, I still haven't got a good sense of why Greenland seemed to be in a state of decelerating rebound (sinking?) around 2003 if ice was melting at an accelerating rate. Apologies if an answer has been posted which I've overlooked. -
thingadonta at 18:21 PM on 27 May 2010Why Greenland's ice loss matters
You mention that "Extrapolating an accelerating curve into the future is always problematic." But isn't this what all the IPCC future climate projections do? These very 'problems' are what skeptics are concerned about. Another point, wasn't the early Holocene also 1-2 degrees C warmer than now? I think Eschenback is making a point that minute Greenland ice losses are sometimes reported as something large and worrisome right now, rather than if they continue to accelerate. It's ony going to be a major problem if the 'extrapolated acceleration curves' of the IPCC turn out to be correct. -
Riccardo at 17:59 PM on 27 May 2010There's no empirical evidence
PaulK, the process you describe is just an integration, which we already know. In some cases, like for example the linear forcing, we have the analytic solution. For a more general forcing we need to do it numerically. And we agree on this. But then you confuse the forcing with the OLR and never in you analysis does the net balance appear. Indeed you write dH/dt=-f(t); here f(t) should be the net energy (im)balance but then it cannot be equal to the OLR. You need to have both the forcing and the thermal radiation. I'd suggest to first write and solve the heat balance equation for ΔT (sorry if i keep using variations, why bother with the equilibrium values?). After that we can try to see who's that guy we call OLR.
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