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chris at 08:24 AM on 29 May 2010Working out climate sensitivity from satellite measurements
shawnhet at 08:04 AM on 29 May, 2010 It's really uninteresting to conjecture upon ill-defined observations of unknown significance shawnhet. If Spencer and Braswell don't know what their linear striations relate to, I'm not very interested in speculating. You'd really have to know what the relationship actually is before considering what it might mean if it was "robust"! There is lots of interesting science on the relationships between TOA radiation variation and surface temperature luctuatins (see the papers cited in my post just above), and I've found this really interesting to read. Spencer and Braswell not so much... What processes do (I) think governs the climate *on the timeframe* Spencer is dealing with? Noise, surely. What else governs climate on the monthly timescale (other than massive volcanic eruptions and extraterrestrial impacts). That's leaving aside seasonal influences on local climate obviously... What predictions can be made about the short term effects of forcing? Well I would say that there is good evidence that the water vapour responds in the direction of a positive feedback as has been determined empirically in several studies, on both short and long time scales. Of course it depends on the strength of the change in forcing. A large volcanic eruption or an extraterrestrial impact can have a dramatic short term effect! It also depends on what you mean by "short term". -
daisym at 08:17 AM on 29 May 2010Latest GRACE data on Greenland ice mass
It has been said that, as Greenland ice melts, the landmass (relieved of this weight) will rise. If this is so, it should have an offsetting effect to the rising sea levels due to ice melt. If this is so, will the effect largely offset sea level rise from the melt water, or will it be insignificant?Response: The rising land is sharpest in regions where ice sheets are melting and yes, will offset sea level rise to some degree (perhaps even exceed it in some places). The effect is much less in other parts of the world. So as I explain in Greenland rising faster as ice loss accelerates, unless you have a huge melting ice sheet in your neighbourhood, you're unlikely to see uplift rates like those seen in Greenland. -
FerdiEgb at 08:09 AM on 29 May 2010On temperature and CO2 in the past
I would post a similar comment as CoalGeologist: The influence of temperature on CO2 levels is quite linear: about 8 ppmv/K over the 420 kyr Vostok ice core period. The opposite is more problematic: neither in recent times (Law Dome, Mauna Loa), neither in long past times (previous interglacials) there is much influence of CO2 on temperature visible. In the previous interglacial (the Eemian), there was a huge overlap between temperature increase and CO2 increase, which makes it near impossible to know the two-way influences. But the end of the Eemian is quite interesting: the temperature (and CH4 levels) were decreasing until a new minimum, while CO2 levels remained high (for unknown reasons). After that, CO2 started to drop about 40 ppmv, but that had no measurable influence on temperature, nor ice sheet formation. Which points to a low influence of CO2 (including fast and slow feedbacks) on temperature. See here -
shawnhet at 08:04 AM on 29 May 2010Working out climate sensitivity from satellite measurements
Chris, you did not really address my point above so to reiterate, Spencer and Braswell have detected (in their opinion) a short-term relationship btw changes in forcing and changes in temperature. If that relationship turns out to be robust, then the climate sensitivity will be less than, for instance, a system where the short-term response is governed by some other process. What processes do you think governs the climate *on the timeframe* Spencer is dealing with? What predictions can be made about the short term effects of changes in forcing? Cheers, :) -
johnd at 07:47 AM on 29 May 2010Working out climate sensitivity from satellite measurements
regarding the comment in the OP on the ability to tweak results by choosing starting and finishing points, just by eyeballing the graph in the lead post, at least the points used by Lindzen et al 2009 (solid circles) start and finish at points that are close to the same value of SST anomaly, whereas Trenberth et al 2010 (open circles) do not. However as the period covered by both studies cover virtually one whole positive phase of the IPO just how relevant are either of them? Any such study should cover at least one full cycle of both phases, especially given the acknowledgement given to the ENSO influence, but unfortunately we will possibly have to wait a couple of decades at least before the next IPO negative phase passes under the watchful eye of the satellites. -
CoalGeologist at 07:46 AM on 29 May 2010On temperature and CO2 in the past
My immediate impression looking at your top graph was that the residuals are not normally distributed around the regression line, especially at high values, and that a linear model might not be appropriate. Then, scrolling down, I saw the quadratic fit to similar data applied by Masson-Delmotte et al. 2010. I've posted previously about the potential risks of using past behavior as an analog for the present. I think it's worth noting that all the previous data points in your graph represent responses of the system interpreted to have been initiated by subtle changes in incoming solar radiation, related to Milankovitch cycles, which set off a complex sequence of feedbacks, partially involving CO2. In the present circumstance, warming is being initiated by increasing CO2, so it's not evident that the same feedback mechanism will prevail. Note that I'm not "saying", I'm asking, because I don't understand the behavior of the system sufficiently well to 'know' anything. Nevertheless, the non-linear trend of the data, together with the extreme departure from "natural" levels of CO2, and the potential for slow feedback mechanism(s) that are not yet fully understood, could pose potentially serious consequences for future warming. -
chris at 07:15 AM on 29 May 2010Working out climate sensitivity from satellite measurements
shawnhet at 05:30 AM on 29 May, 2010 If....if...if... I don't think so shawnhet. If you play around with the data sufficiently, eventually you might get something that seems to support the notion that you're trying to advance. Lindzen's conjuring up of a similar conclusion by cherrypicking convenient time points in analyzing TOA radiation in response to surface temperature variation is another example of this sort of numerology. There's a very interesting psychology going on here! The devotion that these celebrity crowdpleasers (e.g. Spencer and Lindzen) have in some circles is rather touching (if also a bit scary). Spencer's paper hasn't been published (I've read the in-press version on the AGU website), but already Berenyi Peter has referred to it twice on this site without having read it, and it's been publicised all over the web. Never mind that the two things that we can be fairly certain of in relation to Spencer's work are (i) there's a high probability that it will be wrong (he has a near 20-year record of getting things hopelessly wrong) and (ii) he will publicise overblown interpretations of his "analyses" on his blog and elsewhere. It can't be about science I think. After all if we want to understand the methodology, analyses, problems and interpretations of estimating fast feedbacks by regressing TOA net radiation variation in response to surface temperature fluctuations, there's quite a rich scientific literature. We can look at Tsushima et al 2005, Foster and Gregory 2006, Gregory and Foster, 2008, Murphy et al, 2010, Chung et al 2010, Trenberth 2010, and so on, to help us understand the science. But all that stuff is like lead balloons to those who need to have the issue filtered through some Lindzen/Spencer hokey. In fact Spencer's paper is not a big deal, and his conclusions are rather divorced from what he says on his website. He's fiddled around and found some linear striations. He doesn't know what they mean but observes that they're different from similar plots of random number series so they might have a physical basis. We can then put in place a train of "if's" as in your post. But it's much more satisfying to address the science rather than build castles in the air (at the top of the atmosphere?) based on conjecture...... ....if we had some ham we could make ham and eggs....if we had some eggs! -
FerdiEgb at 07:00 AM on 29 May 2010Why Greenland's ice loss matters
Chris G at 01:27 AM on 29 May, 2010 About temperature: Besides simple pressure from the huge ice mass (over 3,000 m), air temperature and direct insolation are important, as whithout elevated temperature above freezing point (and summer melt at the ice surface), there wouldn't be any accelerating extra melt and/or smearing by water reaching the glacier bottom via moulins. There is a substantial difference in speed of the largest Greenland glacier between summer and winter (about 20%), but once the meltwater reaches the bottom, it stays there for longer periods, giving a sustained all-year acceleration of the glacier. See RealClimate on that topic. -
FerdiEgb at 06:30 AM on 29 May 2010Why Greenland's ice loss matters
Peter Hogarth at 08:09 AM on 28 May, 2010 Thanks for the graphs! I used the raw (GISS) data, not corrected for anything, but as Greenland is only rural and had very few shifts in position of the thermometers, I didn't expect much difference. See the detailed trends here. The yearly average trends indeed are substantially increasing in the pre-1940 period, but I looked at the summer temperatures, as these are more important for the ice melt and these show hardly any trend. Thus it seems that mainly winters over Greenland (and the rest of the NH?) were colder some 100 years ago. About aerosols, see my previous comment... -
FerdiEgb at 06:10 AM on 29 May 2010Why Greenland's ice loss matters
[That was an interesting post, had some intriguing parts. Why not try it again, without the insinuations such as Rahmstorf being "economical with the truth?"] -
Chris G at 05:43 AM on 29 May 2010Why Greenland's ice loss matters
Thanks Ned, that's interesting stuff. I'm suffering from not wanting to buy a subscription to every worthy source, Science, Nature, AGU, etc., and determining which ones are most useful to me as a non-researcher. But, I'll see if I can't find an adequate way around that problem. I figured sublimation had to be small potatoes. If you are loosing a Lake Erie annually, well, that is a pretty high rate for sublimation to account for above and beyond whatever the historical baseline rate was. Besides, even if it were the primary mechanism for the loss, what would cause it to change that wasn't an effect of climate change? -
shawnhet at 05:30 AM on 29 May 2010Working out climate sensitivity from satellite measurements
Chris, "Eventually they come up with "evidence of linear striations". These have slopes of around 6.2 W.m-2.K. Spencer and Braswell state: "These striations are significantly different from a similar plot of two time series of random numbers, shown in Fig. 3b, suggesting that the striations are due to some underlying physical process." Does that sound like they've "found low sensitivity here"? I don't think so. The paper has some interesting comparisons of a simplified model with GCM's. It's quite good at highlighting the difficulties of identifiying fast feedbacks in the presence of external forcinsg. What it doesn't present evidence of is "low sensitivity". " While S&B doesn't necessarily demonstrate low sensitivity, it is definitely consistent with *lower* sensitivity. If the short-term response to, for example, an increase forcing is a rapid warming followed by a reduction in temperature according to the pattern S&B found, then an increase in forcing will have a much smaller effect than if the response to forcing does not include such a short term response. If one assumes a given set of feedback where the short term response is consistent with Spencer's results one will have a less sensitive climate than if the short term response was consistent with the Stephan-Boltzmann relationship. Cheers, :) -
John Cross at 03:48 AM on 29 May 2010Websites to monitor the Arctic Sea Ice
Great place to have all the links together. I can offer a little first hand knowledge on this topic since I was a navigation officer on ships that travelled in the Canadian arctic in the late 1970's and early 1980's. We always went about midway through July since the ice was thin enough to make it through then. Later on I will pull out some pictures of what the ice looked like in Hudson Straight and we can compare that to what it looks like this year. Best, John Cross -
Ned at 03:10 AM on 29 May 2010Latest GRACE data on Greenland ice mass
Arjan writes: Though this graph looks worrisome, the grand question remains if the rate will continue (to accelerate). It's not well understood how ice sheets loose mass, and what mechanism has caused the more rapid mass loss. Over in one of the other Greenland threads I show some figures that break down the "Greenland ice loss" budget into its various components. The figures are from van den Broeke et al. 2009. And Doug is right that it's not really useful to say "Well, it would take a long time for the entire Greenland ice sheet to disappear." A loss of 10% of the ice would leave Greenland looking superficially more or less similar to its present appearance -- but it would add 65 cm to sea levels worldwide, which, combined with thermal expansion and contributions from Antarctica and mountain glaciers, would probably mean more than a meter of sea level rise. That's very problematic. You're right that the real question is if (or, more realistically, how much) the current loss of ice will accelerate over the next few decades. If global warming stopped now and the rate of loss stayed at a constant 200-300 GT/year, it would take a very long time to send 10% of that ice into the ocean. In the more probable case where the planet continues to warm and the rate of ice loss continues to accelerate, this could happen at the century time scale. -
Ned at 02:51 AM on 29 May 2010Why Greenland's ice loss matters
Chris G writes: Thinking more about the rate of loss, it comes to mind that loss takes place through two mechanisms, flow of ice into the sea, and melting of ice and water flow into the sea. [...] The ice mass loss of Greenland is a total of these (and I suppose some evaporation/sublimation), and I don't think there are measurements that help attribute how the mass is being lost. Actually, people are starting to work on partitioning these. There's a 2009 Science paper by van den Broeke et al. that gets into this in some detail. The bottom line is, as they say "The total 2000–2008 mass loss of ~1500 gigatons, equivalent to 0.46 millimeters per year of global sea level rise, is equally split between surface processes (runoff and precipitation) and ice dynamics. " More detail can be seen in some of the figures. The first figure shows a comparison of actual mass balance measurements from GRACE with their modeled ice budget (SMB - D, where SMB is modeled surface mass balance from a regional climate model, and D is measured discharge from marine-terminating outlet glaciers):
The next figure from the paper breaks down the budget into surface mass balance and discharge:
Clearly, discharge is increasing, and surface mass balance (precip minus runoff) is also increasingly negative, so both contribute to the overall negative mass balance.
When this was all discussed a while ago, someone (Geo Guy?) was suggesting that sublimation could account for the loss of ice mass measured by GRACE. Here's a breakdown of the components of surface mass balance, including sublimation:
Check out the paper if you're interested.
Response: While you're at it, check out my blog post on this paper :-) -
Doug Bostrom at 02:25 AM on 29 May 2010Latest GRACE data on Greenland ice mass
Arjan, though others seem fixated on the idea, the issue is not about whether or when Greenland's ice sheet will vanish. -
The significance of the CO2 lag
johnd, Yeah I think I was using the terms a little differently. In my usage and the equation quoted by others x was the feedback factor and f is the sum of all temperature changes and feedbacks. I'll try it with completely different terminology so it doesn't get confused with the others: In a geometric series, the sum (s) of infinite terms with a ratio (r) between successive terms and r < 1 can be calculated as follows: s = a / (1-r) Where a is the value of the first term (the initial forcing in our examples). This is where the 1/(1-x) equation comes from when we have an initial forcing of 1 degree. It calculates the net temperature change in the system after an initial forcing. In your example the final temperature was 1.23, so s=1.23. From the above equation, we can solve for r with: r = 1 - a/s, which is where I got 1-(1/1.23)=.187, which in your example is the ratio (r) between successive feedbacks in the system. This is the number that needs to be < 1 in order to have a finite net feedback. The point is to show that even if you have an infinite series of feedbacks on feedbacks, as long as the ratio of one feedback to the next is < 1, the net temperature change will not be infinite or "runaway". -
aj1983 at 01:48 AM on 29 May 2010Latest GRACE data on Greenland ice mass
Though this graph looks worrisome, the grand question remains if the rate will continue (to accelerate). It's not well understood how ice sheets loose mass, and what mechanism has caused the more rapid mass loss. Glaciers have rapid advancements and retreats, and it might be that ice sheets have somewhat identical melting patterns. I wouldn't count on it though. Still, I believe currently it is thought that it will take thousands of years before (if) the Greenland ice sheet melts completely.Response: We don't need to depend on guess work on whether Greenland is going to continue to lose ice or whether its part of a natural cycle. A variety of studies based on empirical data show us that Greenland is highly sensitive to sustained warmer temperatures and hence we can expect sea level rise in the order of metres over the next few centuries.
The main uncertainty to be resolved is time frame. The latest research indicates roughly 1 to 2 metres sea level rise by 2100 but it's difficult to say how quickly sea level rise will evolve after that. However, this uncertainty does not serve as a basis for inaction - quite the contrary. -
michael sweet at 01:46 AM on 29 May 2010Websites to monitor the Arctic Sea Ice
Ned, I tried to keep a neutral tone when I wrote the post. The sea ice area has recovered a little from its 2007 low, but the ice volume has not come up at all. As you point out, both continue their long term declines. Of course, a reasonable person would not expect a monotonic decline for a parameter as complex as sea ice that depends on the weather. -
Chris G at 01:27 AM on 29 May 2010Why Greenland's ice loss matters
I wouldn't think too much on temperature records over Greenland in determining melt rate. There is an awful lot of energy difference between water at 0C and ice at 0C; there's no difference in temperature. -
Chris G at 01:24 AM on 29 May 2010Why Greenland's ice loss matters
Thinking more about the rate of loss, it comes to mind that loss takes place through two mechanisms, flow of ice into the sea, and melting of ice and water flow into the sea. The viscosity of ice and the topography of the land place some upper bounds on the rate of loss that way. I'm going to assume that the rate of melting places a lower bound on the loss than does the rate of flow of water. The ice mass loss of Greenland is a total of these (and I suppose some evaporation/sublimation), and I don't think there are measurements that help attribute how the mass is being lost. Just diving a little more into the potential problems of extrapolating the curve. -
Chris G at 01:13 AM on 29 May 2010Why Greenland's ice loss matters
#46 Nichol, This factor is a subject of some arguments amongst the professionals. I've come across some articles on the subject; the ones I remember were looking more at Antarctic Peninsula glaciers and shelves rather than Greenland glaciers. Pine Island Glacier comes to mind. The impression I left with was that tides and storm surges were much larger effects, but every little bit adds up, and, as the ice thins through increased outflow, eventually a balance point is reached where small changes can matter. However, obviously, a spring tide in combination with a storm surge would dwarf any sea rise that is expected any time soon. Jeff F., I'm not sure that uplift will play much around the coast. I'm thinking that uplift will be greater where the mass loss is greater. Since the edges of the ice are inherently thinner than the interior, I'd suspect that there is greater potential for uplift in the interior. In the larger picture, I consider sea level rise to come in third, in terms of threat level, behind reductions in agricultural production as a result of changing patterns of temperature and precipitation, and behind problems associated the ocean acidification. Problems associated with sea level rise involve relocating people and the buildings they live and work in; the others lead to problems feeding all the people. -
sylas at 00:44 AM on 29 May 2010Has the greenhouse effect been falsified?
Sorry I am a bit slow answering at present, I am not getting a lot of net time. Brényi Péter says:If you want to explain "greenhouse effect" anomaly due to changing carbon dioxide levels, you should provide some more details. Thanks.
Actually, I do not want to explain the anomaly in the greenhouse effect, and I say so in the final paragraph of this blog post. This essay aims at a much more basic level: does the greenhouse effect exist at all? Most people do understand that there is a greenhouse effect. However, some people are skeptical even of this. The aim of this blog and this answer is to help people understand, at a very basic level and using direct observational data, simply that there really is an atmospheric greenhouse effect and that it really does give warmer temperatures at the surface than if the atmosphere did not have the greenhouse gases. All the diagrams shown, and your own comments, continue to confirm this basic point, so I presume we don't have a disagreement on this. The distinct question of the impact of changes in atmospheric composition on the magnitude of the greenhouse effect is dealt with as a separate issue in another page, which I have linked previously. However, I will just quickly respond to your comment about the effects of changing concentrations of carbon dioxide, since you may have missed the most important consequence, which is change to the width of the stopband. You say:
It is easy to see that radiation temperature in CO2 stopband (between 14 and 16 μm) is about as cold as it can get. It means that photosphere (the region from where photons have a reasonable chance to escape to space) in this frequency band is above the troposphere. Below that line atmosphere is opaque (optically thick) in stopband. Now. In that region (lower stratosphere) temperature does not decrease with height anymore. If you put more carbon dioxide into air, photosphere will ascend, but its temperature may even increase slightly. Therefore OLR (Outgoing Longwave Radiation) should not diminish in this range with increasing CO2.
The basic theory involved for calculating OLR is covered in some of the more technically detailed textbooks. In particular, Principles of Planetary Climate by Ray Pierrehumbert, due to be published by Cambridge Uni Press in Dec 2010 is excellent and designed to give the student all the tools to do the calculations themselves. This requires a computer to do a large numeric integration through all different frequencies and up a series of graduated steps in altitude of the atmosphere. But in the end you can calculate OLR for a given atmospheric profile. A major primary reference used for the effects of changing CO2 concentration is:
- Myhre et al., (1998) New estimates of radiative forcing due to well mixed greenhouse gases, Geophysical Research Letters, Vol 25, No. 14, pp 2715-2718.
This paper reports the original calculation of the approximately logarithmic effect of carbon dioxide, at about 5.35 W/m2 per natural log. This is the impact on OLR for a given temperature. Of course, the consequence is that temperatures will increase until OLR again matches the solar absorption. What you are likely to find of particular interest is that this calculation reduced earlier calculations of the effect of increasing CO2 by about 15%, because of more thorough consideration of all effects in particular in the stratosphere. The IPCC 2nd AR used about 6.3 W/m2 per natural log CO2. The IPPC 3rd AR and 4th AR used the improved value of 5.35, and this remains the best estimate for the approximately logarithmic relationship. I do not think there is any credible objection to this relation. If the optical depth at a given frequency is very small, or very large, then there is not much consequence for increasing concentrations for that frequency. Given a frequency in the stopband (with a large optical depth) emissions to space all come from high in the atmosphere, and doubling concentrations doesn't make much difference. Similarly, for a very low optical depth (transparency) the changes at that frequency are comparatively slight. The largest impact by far is for those frequencies where optical depth is close to unity. These are the frequencies for which additional concentrations move the effect of the atmosphere most strongly from being transparent to being opaque. Roughly speaking, higher concentrations mean the stopband is a little bit wider, stopping additional frequencies. This is the most important consequence of higher concentrations. The proof of that can be given in various ways. It can be done theoretically, as in calculations explained in Pierrehumber (2010) or reported in Myhre et al (1998). There are also observational confirmations of the enhanced greenhouse effect described in these pages at How do we know more CO2 is causing warming? I don't propose to go into a long further explanation here. There's ample description of the technical details in various references that have been given for people to chase up themselves if they have an interest, and the impact on OLR (the forcing) is taken for granted by major working scientists who happen to be skeptical of AGW, such as Lindzen or Christy. They tend to focus on the more reasonable question of response to forcings, or "climate sensitivity". Changes to atmospheric composition is, of course, a more technically complex question than I cover in this essay. That is deliberate. But I hope this brief account in the comments may go some way to answering your questions. Cheers -- sylas
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JSFarmer at 00:17 AM on 29 May 2010It's the sun
Basic question- This topic addresses a skeptic's argument that sunspots have been increasing. The scientific rebuttal says the sun is cooling. Does sunspot activity = sun's temperature as the rebuttal implies?Response: "Does sunspot activity = sun's temperature as the rebuttal implies?"
There's more to it than that. Solar activity is measured by more than just sunspots - we directly measure solar output using satellites. When the various satellite records are stitched together, they find a slight cooling trend over the satellite record. However, direct measurements only go back to 1978.
So we use proxies to go further back. Sunspots go back to the early 1600s and are a good proxy for solar output. We can confirm this by comparing them to the direct satellite measurements when the two records overlap.
Here's more info on how we measure solar activity... -
KR at 00:07 AM on 29 May 2010The significance of the CO2 lag
Aaannnd - I write too quickly again. The formula should be Forcing/(1-Feedback). Note that negative feedback also goes into this formula: a negative feedback of 0.5 on a forcing of 1.0 results in a 0.6667 total rise; damping the effect. This is actually a fun exercise in Excel - build a column starting with the forcing and with each following (cell = previous cell * feedback). The sum of the forcing and feedback column gives the total feedback out to whatever number of rows you put in - I would suggest 30-40 or so. You can then compare that to "Forcing/(1-Feedback)". -
KR at 23:20 PM on 28 May 2010The significance of the CO2 lag
johnd - A feedback gain of 'x', for example 0.5, means that a change in temperature of 1 degree C will through some mechanism (such as, say, increased H2O) cause an additional rise of 0.5 degree C. However, now there's an additional temperature change of 0.5, and the feedback on that is * 0.5 = 0.25 additional change, so you have an x^2 term, and so on and so on. Feedback operates on the temp. change, regardless of why it occurs; an initial forcing causes a shift, which causes a feedback, which causes a shift, which causes additional feedback, etc., resulting in the geometric series of 1+x+x^2+x^3+..., which sums to 1/(1-x) as long as -1 < x < 1. That's the stability criteria - each successive feedback is smaller, and there's a finite sum. So the total change from 1.0 degree C forcing, for a feedback of x=0.5, is 1 + 0.5 + 0.25 + 0.125 + 0.0625 + ... = 1/(1-0.5) = 2 degrees C. That's 1.0 in forcing and 1.0 in feedback. For a feedback of 0.25, the total is 1.333..., for a feedback of 0.75, a total of 4.0, and so on. You can Google positive and negative feedback for more details - there's quite a lot of well written stuff out there. -
Riccardo at 22:53 PM on 28 May 2010The significance of the CO2 lag
johnd, 1/(1-x) is the infinite sum of 1+x+x^2+... for x<1 which gives the feedback factor f. Look at chris comments. -
Johnny Vector at 22:36 PM on 28 May 2010Websites to monitor the Arctic Sea Ice
From the Cryosat page, it looks like orbital verification is not complete. They say: With LEOP complete, ground experts will now put CryoSat-2 through an exhaustive commissioning phase lasting several months... LEOP is Launch and Early Orbit Phase, which I assume includes things like deploying solar panels, tuning the attitude control, and turning on and functional checks of all instruments. So they know basically that nothing broke on launch, which is great. But now they have to finish performance checks and on-orbit calibration. For the kind of spacecraft I am familiar with (astronomy satellites), this takes typically 2-6 months. Sounds like it's similar for the down-lookers. So it'll be late summer probably before the normal data products start arriving from Cryosat. -
HumanityRules at 21:47 PM on 28 May 2010Websites to monitor the Arctic Sea Ice
A few other international websites include Norway Denmark Japan This page on the Norwegian Arctic ROOS website has some interesting links including a page on the way the different groups do their extent calculations. As a curiosity I quite like this page on the DMI website which lets you see satellite images around Greenland. You can watch the ice break up and flow out the Nares Strait, if that's your thing. -
seeohtoo at 21:31 PM on 28 May 2010Latest GRACE data on Greenland ice mass
@ #6: the IPCC sea level rise estimates explicitly exclude melting of Greenland, due to their assessment that our current knowledge of ice sheet melting dynamics is insufficient. -
johnd at 21:07 PM on 28 May 2010The significance of the CO2 lag
Riccardo at 19:56 PM on 28 May, 2010, we are both talking about "feedback factor", I think. "f" is feedback factor, but "x" refers to what? The equation you quoted above, "f=1/(1-x)" is different, I think, to the one quoted by e at 09:57 AM i.e "In your example, the feedback factor is: 1-(1/1.23)= 0.187" What is the basis for the equation you quoted, do you have a link to where it is explained? -
Tony Noerpel at 20:37 PM on 28 May 2010Latest GRACE data on Greenland ice mass
Umm, John replace discussion with discussing below But we've been discussion Greenland trends and as it's been over a year since posting regards and thanks TonyResponse: It's been a long week -
Riccardo at 19:56 PM on 28 May 2010The significance of the CO2 lag
I think there's a misunderstanding between you guys. Someone is talking about "f" and other about "x" like in the series 1+x+x^2+... The two are related by f=1/(1-x), as repeatedly stated by others. Beware that this is valid only for x<1. In this notation you have positive feedbacks when f>1 or x>0, negative feedbacks when f<1 or x<0. For x>1 f diverges and you have runaway warming. But being these definitions based on the linearization of the response ΔT to forcing F I think their validity breaks down well before x=1. -
Ned at 19:54 PM on 28 May 2010Websites to monitor the Arctic Sea Ice
Thanks for the post, Michael. It's a nice overview of the resources available. Just one minor suggestion. You write The ice volume has not recovered in the last two years like ice area has. What do you mean by the suggestion that (northern hemisphere) ice area has "recovered"? It's back above the alarmingly steep 2001-2007 trendline, but it's still well below what it was in the early years of the record (early 80s) and is still completely consistent with the long-term downward trend. -
Ian Love at 18:45 PM on 28 May 2010Websites to monitor the Arctic Sea Ice
The Cryostat page Adrianco links to also has a good summary of the prospects and state of the ice in Arctic, Greenland and Antarctica: Earth's changing ice -
johnd at 17:49 PM on 28 May 2010The significance of the CO2 lag
e at 09:57 AM on 28 May, 2010. e, can you clarify something for me as my understanding of the formula to determine the feedback factor is apparently different to yours. It may be just another case of confused terminology. My understanding of the feedback factor is derived from the formula: DTfinal = DTforcing + DTfeedback where DTfinal is the overall change in temperature between the initial and final equilibrium states, DTfeedback is the temperature change resulting from feedback, and DTforcing is the initial change in temperature due to radiative forcing. That equation can also be written as: DTfinal = fDTforcing where f is the feedback factor, thus f=DTfinal/DTforcing. see http://www.global-climate-change.org.uk/2-8.php The formula you have used appears to be: feedback factor = 1-(1/DT forcing + DT feedback). I think. Can you clarify if that is the correct interpretation and from what has the formula been derived. It is obvious that if the same values are plugged into each, the results are totally different, so perhaps there is some fundamental difference in what the term "feedback factor" actually defines in each case. -
Doug Bostrom at 16:21 PM on 28 May 2010Websites to monitor the Arctic Sea Ice
Adrianco thanks for pointing that out. I knew Cryosat had launched but did not know it was done w/engineering checks and the like. So good to see it running; the previous copy ironically ended up splashing down in the Arctic ocean after a launch problem but fortunately was swiftly replaced. -
Neven at 15:15 PM on 28 May 2010Websites to monitor the Arctic Sea Ice
Here's another one I have started watching recently, with Google Maps-like pictures of the Arctic: http://ice-map.appspot.com/ These pictures come from here: http://rapidfire.sci.gsfc.nasa.gov/subsets/?mosaic=Arctic And of course a well-beloved graph for sea ice extent is the one from JAXA, where you see the current trend line compared to those of previous years (from 2002 onwards) and where you can easily download data to play with in Excel: http://www.ijis.iarc.uaf.edu/en/home/seaice_extent.htm -
adrianco at 15:13 PM on 28 May 2010Websites to monitor the Arctic Sea Ice
For some reason I have seen very little coverage of Cryosat -launched in April and already starting to send back data. Here is a nice explanation with some video animations showing how it works. It should give us much more accurate measurements of sea ice volume. http://www.esa.int/SPECIALS/Cryosat/index.html -
James Wight at 15:06 PM on 28 May 2010Latest GRACE data on Greenland ice mass
This means that your graphic of 2009 ice loss is out of date. According to the abstract of Velicogna 2009, the value of 286 Gt/yr was actually for 2007-2009 (and the data only went up to February 2009). From eyeballing the updated graph above, Greenland actually lost nearly 350 gigatonnes in 2009.Response: You people insist on creating work for me, don't you? I've upgraded the Greenland losing ice graph although now that I look at it, the content on that page needs a dramatic overhaul in light of recent posts. Sigh, damn advancing scientific knowledge... -
jyyh at 14:47 PM on 28 May 2010Websites to monitor the Arctic Sea Ice
Couple more I follow: for ice movement : http://iabp.apl.washington.edu/maps_daily_track-map.html for weather : http://wxmaps.org/pix/hemi.fcst.html the weather maps here are not standard sea level charts, they need somewhat getting used to but fe. the 200mb chart pretty well shows the polar vortex (and its quirks) and the temp charts allows tracking heat movements around the pole. -
Jeff Freymueller at 14:41 PM on 28 May 2010Latest GRACE data on Greenland ice mass
#6 wes george, I can say something about your points. 1. Yes, you are correct about what the IPCC said, but the statement by Kopp is also correct. If I remember their paper, 125,000 years ago temps were sustained at a level 1-2C higher than today, and sea level was about 6 meters higher. 2. "periods as warm as 1-2c greater than today without 6 metre increases in sea levels" First, how long is a "period", because it matters. If you mean years, then very likely there has been a year in the last 3000 years 1-2C warmer than this year. But a year is too short to matter (or measure in the paleo-record). Decade? Also too short to matter as far as sea level goes, and still too short to measure in the paleo-record. Centuries? Now measurable in the paleo-record, and more likely to matter for sea level but less likley to be true. On both 1 and 2, I think the time over which temperatures remain warm clearly matters. 3&4. Good questions, but when you look at where the sea level rise comes from, it takes time unless you are having a massive ice sheet or two collapse. So your comparison is certainly true but not very useful, I think, because the first 10-15,000 years after Last Glacial Maximum were a very different situation than anything since sea level roughly stabilized about 6000 years ago. -
Jeff Freymueller at 14:28 PM on 28 May 2010Latest GRACE data on Greenland ice mass
#5, John's last sentence strikes me as being accurate: "Before then, data is sparse but may have been slightly increasing in mass during the mid-20th century." Well, except for the missing "it" or "ice" before "may", if we're to get really picky (I've been proofreading today, sorry).Response: Thank you, grammar police :-) -
wes george at 14:27 PM on 28 May 2010Latest GRACE data on Greenland ice mass
“What CO2 level would cause the continental ice sheets to collapse”... a topic relevant to the GRACE data: http://www.skepticalscience.com/What-CO2-level-would-cause-Greenland-ice-sheet-collapse.html “Some of the more optimistic emission scenarios from the IPCC predict warming of 1 to 2°C. The last time temperatures were this high were 125,000 years ago. At this time, sea levels were over 6 metres higher than current levels (Kopp 2009).” Four points: 1.... 6 metre sea level rise is way beyond what IPCC scenarios suggest will occur at +1 to 2c temp rise. http://www.grida.no/publications/other/ipcc%5Ftar/?src=/climate/ipcc_tar/wg1/fig11-16.htm 2. It’s highly probably that even during the last 3,000 years there have been periods as warm as 1-2c greater than today without 6 metre increases in sea levels. That’s why it’s called Green Land. Melting around the coast and at low altitude is not unprecedented. Evidence for a Minoan Warm period of 3c warmer than today exists. 3. Even if true, why aren’t sea levels already much higher and rising faster than they are today? After all, it’s already warmed by at least .75c since 1900 that’s almost a third of the way there to 6 metre increases in sea level, but sea levels are only rising at 2-3mm a year. No consilience there. 4. The speed of current warming is also well within Holocene natural amplitudes. Both the Younger Dryas and The Akkadian Collapse occurred at rates that would have reduced modern civilization to rubble in a matter of years. In comparison today’s rate of warming is indeed mild. Although, that GRACE graphic is really scary looking!Response: "6 metre sea level rise is way beyond what IPCC scenarios suggest will occur at +1 to 2c temp rise"
Those IPCC predictions are for sea level rise by 2100. If you look at sea level prediction graphs, you'll note that sea levels are still rising sharply at that point. While you or I will probably not see beyond 2100, our grandchildren probably will. So there will be significant sea level rise beyond 2100 - it's just that the IPCC predictions don't go any further (to my knowledge). The timeframe of Kopp's 6 metre sea level rise is uncertain although other work indicates a timeframe of several centuries.
"Why aren’t sea levels already much higher and rising faster than they are today? After all, it’s already warmed by at least .75c since 1900 that’s almost a third of the way there to 6 metre increases in sea level"
The ice sheets have a great inertia - it takes a while for them to respond to the warming temperatures. In that sense, their great inertia is our friend. However, once they start disintegrating, it's not like we can throw a rope around the ice sheets and hold them back. At that point, the inertia becomes our enemy. -
Jeff Freymueller at 14:25 PM on 28 May 2010Why Greenland's ice loss matters
#46 Nichol, for most of the glaciers that terminate in the sea, the glacier bed is hundred of meters below sea level already. So a few more centimeters added to sea level really won't matter. In any case, locally at least the sea level rise is more than canceled out by the uplift of the land from the loss of the ice, so the effect you mention shouldn't have any detectable impact at all on the behavior of the glacier. -
Jeff Freymueller at 14:20 PM on 28 May 2010Why Greenland's ice loss matters
#38 hadfield cites some discussion at Michael Tobis' blog about Velicogna (2009) criticizing the statistics used. I think the most of criticisms there are off-base. There was some complaint about certain corrections not being applied in the figure, but I think those effect either a constant value or trend, not acceleration. I can't access the paper right now (too many of my usernames and passwords are remembered only by my browser, on the computer that is in the shop), but the question about the quadratic fit F-test may be on target (it is if the commenters are right about the smoothed data set being used). However, given that the annual variation has a solid physical basis, the better way to handle it would be to compare a linear + annual period model to a quadratic + annual using the monthly data points (each monthly point is independent). My bet is that the quadratic model fits significantly better. -
Nichol at 13:26 PM on 28 May 2010Why Greenland's ice loss matters
Reading this, I wondered what happens to glaciers ending in the sea, if the sea level rises. For such glaciers, sea level rise should lift floating ice, causing water to enter under the glacier, and melting it from below. So there should be a feedback from sea level rise to melting glaciers. Has this feedback been studied, and is it significant, compared to normal melting? -
wes george at 12:54 PM on 28 May 2010Greenland rising faster as ice loss accelerates
Wait a second. The annual loss of ice off Greenland is about 200-300km^3 per year, but that icecap is big – between 2.4 and 3,400,000 km^3. And old too. Yet you guys keep evincing ridiculously short melting trends then say if these trends not only continue on this very short slope but accelerate exponential then Greenland’s icecap will be gone in 65 years. Oh, then you concede that probably won't happen, it will probably be about 7% melt of total ice in 65 years. Still catastrophic. Yet, the observed data shows 7% of Greenland's ice will take about 1000 years to melt. So you're postulating an exponential rate of acceleration starting today. This should be easy to test. I understand there is a theoretical apparatus behind such claims, but to those of us who are less committed to theory and more to the observed data, it sure looks like Greenland has been melting at a rate of about 0.007% recently. Even if the trend accelerates there seems to be little chance of the Greenland icecap disappearing before the end of the current interglacial. This is because your projections assumes absolutely no interruption in a very short term trend, socially, technologically or climatically (other than accelerated AGW) over the next century. Philia’s comment illustrates that the one truly exponential rate of change that is robust and long observed seems to carry little weight here. That is technological evolution is occurring at a rapidly accelerating rate, rendering any long term forecasts for climate based on today’s level of technology simplistic. Moreover, extrapolating a very short trend forward 10 to 1000 times its length seems to ignore how complex nonlinear systems far from equilibrium evolve. Even if AGW theory is robust, climate is unlikely to respond in a mechanical, direct way to forcing in the same way a steam engine might to a governor adjustment. To those old enough to remember how “futurology” once worked back in the 1960’s and 70’s where someone put a ruler and pencil to a trend of, say, current known global petroleum reserves then drew a line straight into the future arriving at the conclusion that peak oil must occur in 1979…this smells very similar. Doubters back then were told they didn’t understand the confidence levels experts had in total amount of undiscovered reservoirs based on some now long forgotten theories of oil formation and the rate of evolution in extraction technologies.Response: I posted an article on this very line of argument yesterday: Why Greenland's ice loss matters. Please continue any further discussion on this topic over there. -
Nichol at 12:36 PM on 28 May 2010Latest GRACE data on Greenland ice mass
I'm not quite convinced by the last claim that there may have been a slight increase during the mid-20th century. Maybe you'd better say it the data doesn't exclude it? If you like to update such plots with recent historical data.. it would be great to have one collection of important history plots of various quantities, updated whenever new data comes available. You could even try to get the scales to match, so the plots line up so correlations between the histograms can be seen. .. and yes: very nice to get preliminary data plotted here! I guess we should also accept the reality that those preliminary points might still change a bit, e.g. if some calibration of measurement data changes. If the status of the most recent points is as preliminary as I'm guessing.. maybe it is a good idea to give them a different color or symbol. That way, if they change in the future, nobody can blow that up to another pseudo-scandal-gate. -
KR at 12:36 PM on 28 May 2010The significance of the CO2 lag
Ah - a clarification. 0 < x < 1 is a stable positive feedback. -1 < x < 0 is a stable negative feedback. x = 0 is no feedback at all.
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