Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.

Settings

Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup

Settings

All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Support

Bluesky Facebook LinkedIn Mastodon MeWe

Twitter YouTube RSS Posts RSS Comments Email Subscribe


Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...



Username
Password
New? Register here
Forgot your password?

Latest Posts

Archives

Recent Comments

Prev  2525  2526  2527  2528  2529  2530  2531  2532  2533  2534  2535  2536  2537  2538  2539  2540  Next

Comments 126601 to 126650:

  1. An overview of Greenland ice trends
    chris, I take it you didnt like the fact that the exact same data leads to two completely different predictions, (i.e., 436 years and 11,400 years). All I did in the first case was to use the acceleration derived from the data, and in the second case ignored the acceleration completely, but used the overall slope. In this sense, whatever information my calculations could possibly convey are equivalent to the graph,.. except that I was also considering the overall mass, which I assume is significant. So you may not find any of this helpful, but there is a certain usefulness in knowing what you cant know.
  2. An overview of Greenland ice trends
    "A recent study by Peter Chylek et al. (2006) put all of these Greenland temperature records together in one place (Figure 8 ), and commented: Although there has been a considerable temperature increase during the last decade (1995 to 2005) a similar increase and at a faster rate occurred during the early part of the 20th century (1920 to 1930) when carbon dioxide or other greenhouse gases could not be a cause. The Greenland warming of 1920 to 1930 demonstrates that a high concentration of carbon dioxide and other greenhouse gases is not a necessary condition for period of warming to arise. The observed 1995–2005 temperature increase seems to be within a natural variability of Greenland climate" http://www.worldclimatereport.com/index.php/2007/10/16/greenland-climate-now-vs-then-part-i-temperatures/ The GISS temperature graphs on this site ( covering coastal stations..the warmest bits) show annual means which rarely go above 0C. Given that the average height of the ice sheet is, as Chris points out, over 2000m, and add a lapse rate of 6C/km the annual avergae temp inland is not going to be far off -10 to -12C. Not much melt there I think. Also we do not know how much of that 300m depression was there before the ice (if any) so it is not possible to attribute all of it to the weight of the ice.
  3. There is no consensus
    The important question here is, how important is concensus to science. Lets face facts, a huge portion of people holding any type of degree will simply parrot back what thier professors taught them. This is understandable as they trust their professors and paid a high price for thier education. However, this does not reduce the need to point out that a very small minority actually go beyond their classroom assignments and validate for themselves what they learned. In summary, as long as man made GW is taught in our schools from elementary through college, few should expect any different result than what was pointed out here; concensus only proves what is being taught and can not be used as scientific proof of any theory. Science is proved by evidence not by degrees. Those on both sides of the debate should focus on the scientific evidence so the general public can have a reason to believe/not believe besides "those smart people say its so". Here's my part: http://earthobservatory.nasa.gov/Features/SORCE/sorce_05.php There is a 5% error in our knowledge of the absorption of solar radiation and a 1% error would throw off all the climate models. So how sound is the evidence for the present consensus?
  4. An overview of glacier trends
    From WGMS: In 2005 there were 442 glaciers examined, 26 advancing, 18 stationary and 398 retreating. 90% of worldwide glaciers are retreating. In 2005, for the first time ever, no observed Swiss glaciers advanced. Of the 26 advancing glaciers, 15 were in New Zealand. Overall there has been a substantial volume loss of 11% of New Zealand glaciers from 1975-2005, but the number of advancing glacier is still significant. Tamino also has a very good image that shows the absurdity of the cliams that galciers are advancing: http://tamino.files.wordpress.com/2009/08/glaciers.jpg?w=500&h=295
  5. The albedo effect
    Steve L, you might have given up on that long prior discussion with Henry Pool before I threw in my two cents about his CO2 reflection assertion. I don't know how else to explain it to him.
  6. An overview of glacier trends
    John, A few more good images include: http://www.wgms.ch/mbb/mbb10/Abb1.pdf (This is just a bar chart of the same image you showed in comment #1) http://www2.sunysuffolk.edu/mandias/global_warming... Source: http://www.grid.unep.ch/glaciers/graphics.php
  7. An overview of Greenland ice trends
    #14 i)I think that was my point that the review looked at multiple points not just the salt marsh data which you originally quoted. I don't know where you get smallish (generally 1-10 cm per century) rates for natural sea level change from. Table two shows max rates for some of the more recent measurements (last 10,000years) at 0.1-0.2metres/century. Am I mis=understanding that table? The historical data is by it's nature local and for that matter sporadic. But it remains the best data we have i)If you take the 3 more accurate measurements for the past decade the review suggests between 1-3mm/year (thats 10-30cm/century if you extrapolate) see this long quote from Milne. Yhat is what I understand from this long quote from Milne "After applying corrections for these biases, several studies14-16 have shown greatly improved consistency, in one case14 finding a tightly-closed sea-level budget for interannual and seasonal cycles, but a significant imbalance of over 3 mm/yr in the trend. In the second case15, a smaller net imbalance of about 1 mm/yr was found (this is within the estimated error bars). In the third study16 GRACE data were used in two different ways, in one case using a larger geodetic correction over the oceans than in other studies, and in the other using it only to estimate Antarctic and Greenland mass loss, and combining with other datasets to estimate the total mass entering the ocean. These two methods both result in a balance to within a small fraction of one mm/yr." ii) a) I'm not sure which is correct. The Netherlands data could be correct for the local changes while the Grinsted paper could be accurate on a wider level so both figures could be right. Without accepting Grinsted's figure there does seem to be an error in your interrution of it. Grinsted is a simplified model which identifies a trend based on a relationship between temperature, ice melt and sea levels. There are other processes which cause short term speeding up and slowing down of the ice melt. I'd suggest you're wrong to try to give an averaged rate for the MWP. Similarly it would be wrong to give an average rate between two widely spaced data points as you have no way of knowing if the rate of sea level change remained constant over that time period. Especially when you are comparing it to a decade of detailed global data which by it's nature contains all that detail. I'm starting to think the whole process is invalid. b)Back to the Milne paper. If you take my answer to i) that puts the most recent decades increase well within historical changes or at worst twice historical rates, I don't see where you get the 50x value. iii) I'm pleased to here that graph wasn't lonely but I did find that article lacked logic.
  8. An overview of glacier trends
    Here's an interesting graphic from the IPCC: http://www.grida.no/publications/other/ipcc_tar/?src=/climate/ipcc_tar/wg1/fig2-18.htm
    Response: That is an interesting graphic. Note that the New Zealand glacier Franz Joseph is included at the bottom:

  9. The albedo effect
    Steve, maybe you must attempt to answer the question I asked in 127 of "How do we know CO2 is causing warming?" You can also check any good solar radiation spectrum graph. It will tell you that ozone, water vapor and CO2 cause reflection of sunlight. It seems pretty obvious to me that that nobody did the right testing that would prove that CO2 causes warming, i.e. how much warming (by trapping earth's radiation) and how much cooling (by reflecting sunlight) is caused by CO2, i.e. what is the net effect? http://www.telegraph.co.uk/earth/earthnews/6553592/Climate-change-scep. Look at my comment at 3:43 pm on 13/11/09. I am (still) not convinced that CO2 causes global warming. But if you have the proof from actual measurements made during actual tests I am (still) willing to be convinced. (I am a believer turned skeptic - I am not saying global warming is not happening, I am saying that I do not know if CO2 is the cause). In any case, it looks to me now that ozone is increasing and if this trend continues this will/could wipe out a lot of the sun's energy coming to earth.
  10. An overview of glacier trends
    Great work as always John, clear and succinct. Are there no NZ glaciers included? I don't see Franz Joseph there which is the one Australian denialists always like to mention. And Steve at #2 - yes, that would be interesting, but you may find that the ones they cherry picked are still gaining. My understanding is that glaciers (the vast majority) are shrinking because of rising temperatures at their site. On the other hand in some situations, particularly (solely?) those near coasts, rising water temperatures may result in increased snow fall which will counteract the melting. Franz Joseph is a case in point. The same thing applies, on a much larger scale, to Antarctica.
  11. An overview of glacier trends
    The first thing I noticed from this post was the small number of glaciers that have a long term record. I was sure we had longer term data on more glaciers. But I guess mass balance is more difficult to estimate than some other metrics regarding recession. So I wonder if data from these photo projects (eg: http://www.nrmsc.usgs.gov/repeatphoto ) can be compiled into something useful for quantitative analysis. I visited the Burgess Shale (Canadian Rockies) about a decade ago and saw two glaciers across a valley and could make a comparison to photos taken from the same spot approximately 80 years earlier. Surely there are many such instances around the world.
  12. An overview of Greenland ice trends
    The notion that future melt can be assessed/dismissed by back of the envelope numerology and false arguments, isn’t very helpful. There has actually been substantial recent investigation of this problem: (i) Recent analysis indicates that 21st century sea level rise is likely to be well in advance of the IPCC estimate. Projected 21st sea level seems to be closer towards the 1 metre level and this requires “non-linear” effects on ice sheet dynamics that are consistent with elements of “collapse”. HumanityRules brought a recent paper on sea levels to our attention. This projects a 1 metre 21st century rise based on an analysis of temperature-dependence of past sea level rise [1]. A recent analysis of the contributions of ice sheet dynamics to sea level rise supports a projection of 0.8-2.0 metres of 21st century sea level increase [2], although rises towards the lower end of the range are considered more likely. These all support very substantial attenuation of the Greenland ice sheet in the 100’s of years timescale. [1] A. Grinsted et al. (2009) Reconstructing sea level from paleo and projected temperatures 200 to 2100 AD Climate Dynamics; in press [2] W. T. Pfeffer et al. (2008) Kinematic Constraints on Glacier Contributions to 21st-Century Sea-Level Rise. Science 321, 1340-1343 (ii) Mizimi suggests that the 300 metre depression of the central Greenland ice sheet resulting from isostatic depression precludes ice sheet collapse. However the average height of the Greenland ice sheet is over 2100 metres, and there is obviously plenty of scope for major Greenland collapse yielding substantial (several metres) contributions to sea level rise. Analysis of the Greenland bedrock topography identifies multiple outlet channels (460 of these), of which only around 36% have been activated up to the year 2000 [3]. These potentially allow increasingly rapid rate of outlet flow from the ice sheet. Likewise an analysis of rapid retreat of the Sam Ford Fjord glacier during the last glacial to Holocene transition 9500 years ago suggest that glaciers with very similar topologies in Greenland and West Antarctica can undergo rapid retreat (10’s to 100’s of kilometers in the coming centuries) [4]. [3] Lewis S. M. et al. (2009) Hydrologic drainage of the Greenland Ice Sheet Hydrol. Process. 23, 2004-2011 [4] Briner J. P. et al. (2009) Rapid early Holocene retreat of a Laurentide outlet glacier through an Arctic fjord Nature Geosci. 2, 496-499 (iii) While Mizimi suggests that the central regions of the ice sheet “has not changed for over 100,000 years” we know that isn’t true since the deepest (3000 metres) central Greenland cores reach bedrock at a bit over 100,000 years ago. So a large proportion of the central parts of the Greenland ice sheet have only been deposited during the last 100,000 years. As we know, during the last interglacial 125,000 years ago when Arctic temperatures were ~2 oC warmer than now, sea levels were 4-6 metres higher [5]. Much of this was from massive Greenland melt. [5] Allison I. et al. (2009) Ice sheet mass balance and sea level Antarctic Sci. 21, 413-426 (iv) Analysis of rates of sea level rise in the past are instructive about how ice sheets might respond to forcing from very fast temperature rise. During the transition to the present interglacial there was a period of very rapid sea level rise (meltwater pulse 1A, 14,600 years ago) when sea levels rose 20 metres in 500 years [6]. During the last interglacial 125,000 years ago when the situation was more comparable to the present, the transition to sea level highstands that were 4-6 metres above current sea level, occurred at rates of 1.6 metres per century [7]. These rapid large melts occurred during climate transitions with overall warming that was slower than current warming. [6] A. J. Weaver (2003) Meltwater Pulse 1A from Antarctica as a Trigger of the Bølling-Allerød Warm Interval Science 299, 1709-1713 [7] Rohling, E. J. et al. (2008) High rates of sea level rise during the last interglacial period. Nature Geoscience, 1, 38–42 (v) The Greenland ice sheet is pretty much committed to major melt already at current greenhouse gas levels. We know that ice sheet disintegration/melt in a warming world generally occurs much faster than ice sheet growth in a cooling world, since disintegration/melt can occur through dynamic processes, whereas growth is limited by the rate of precipitation. The evidence suggests that dynamic processes (flow transition from ice sheet to floating ice shelf; the dynamics of rapidly flowing ice streams and outlet glaciers; the effect of basal melt water on ice dynamic processes [5]), are likely to cause Greenland (and the West Antarctic ice sheet) to melt much more quickly than “back of the envelope” guesswork might imply…
  13. Are humans too insignificant to affect global climate?
    Re. #31, Now a new paper in GRL claims that the ariborne fraction has stayed constant since 1850: Knorr 2009
  14. An overview of glacier trends
    pdt, the World Glacier Monitoring Service seems to do periodic updates and are currently collating data for the next update incorporating the period 2007-2008: http://www.geo.unizh.ch/wgms/datasub.html We spent some time in Switzerland this summer, and visited some glaciers. We found this site covering Swiss Alpine data through 2008 pretty interesting: http://glaciology.ethz.ch/messnetz/ While worldwide updated mountain glacier data might not be available through 2008, the increasing rates of polar ice sheet mass loss supports the expectation that mountain glacier retreat is continuing through the last couple of years (as it is in the Swiss Alps): Velicogna, I. (2009), Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE Geophys. Res. Lett. in press http://www.agu.org/pubs/crossref/2009/2009GL040222.shtml abstract: “We find that during this time period [April 2002 and February 2009] the mass loss of ice sheets is not constant, but accelerating with time, i.e. that the GRACE observations are better represented by a quadratic trend rather than a linear one, implying that the ice sheets contribution to sea level becomes larger with time. In Greenland, the mass loss increased from 137 Gt (gigatonnes)/yr in 2002-2003 to 286 Gt/yr in 2007-2009, i.e. an acceleration of -30 +/- 11 Gt/yr^2 in 2002-2009. In Antarctica the mass loss increased from 104 Gt/yr in 2002-2006 to 246 Gt/yr in 2006-2009, i.e. an acceleration of -26 +/- 14 Gt/yr^2 in 2002-2009."
  15. An overview of glacier trends
    I think Fred Singer and others have been doing this cherry-picking for years. I wonder if it would be a worthwhile project to go back and find the glaciers they were identifying, say, 6 or more years ago and see how those glaciers have fared since.
  16. An overview of glacier trends
    Is there data available for 2006 - 2008?
    Response: Not quite but I dug a little deeper on the WGMS website and found data through to 2007:

  17. ACRIM vs PMOD, the rematch
    Clayco, look at the cites in that paper. It's speculative. It ends with a supposition, a what-if. What remains is for someone to find a way to establish the existence (measure, identify, show, detect) of those supposed effects. Show they happen, measure them. Remember, for a "god-in-the-gaps" explanation, you need two of them, you need _both_ 1) show the hidden cause working, and 2) find an explanation that counteracts the known causes already accounted for. You need to subtract the known causes with some unknown force taking them out, then replace them with the same amount of effect from the newly revealed cause. ----excerpt----- ... Its effect on climate is supposed to be through modulation of the cosmic rays flux which affects stratospheric ozone and small constituents (Veretenenko S.V., Pudovkin M.I., J. Atm. Solar-Terr. Phys., 61, 521, 1999), and/or aerosol ionization (Marsh N., Svensmark H., Space Sci. Rev., 107 (1), 317, 2003), and/or the global electric circuit (Tinsley B.A. et al., Adv. Space Res., 40 (7), 1126, 2007), and finally the transparency of the atmosphere. However, the mechanism is not quite clear, and is not included in any climate simulation model ...." If you go and look at each of those papers, follow the "citing papers" forward in time. The supposed mechanisms are less than "not quite clear" in each case. The unstated supposed mechanism that counteracts the known forcings is also not discussed at all.
  18. An overview of Greenland ice trends
    John, Sorry if I came across that way. My comment was only in reference to the math error, and I appreciated Mizimi's pointing it out. By the way, he also says something later that seems reasonable, implying that the ice mass acceleration is not necessarily a constant, and would tend to diminish as soon as the bulk of the peripheral ice fields disappear. I am sure the problem is much more complex, and even the simplest models would depend on a series of functions that reflect the dynamics of various stages. Personally, I dont think it is at all realistic to extrapolate to 436 based on a second derivative extracted from the fuzz of nine samples. It is however useful to give some feel of a worst case scenario and perhaps what is possible. However, another very simple calculation with the same data leads to very different conclusion. That is to assume acceleration is zero or neutral, but that the ice loss rate (slope) is constant at the current rate. From the curve, we see about 1500 x 10e9 T/year over a 6 year period, which equals 250x10e9 T/year. Using the same value for total ice... 2.85 x 10e15 T / 250 x 10e9 T/y = 11,400 years.
  19. Philippe Chantreau at 18:56 PM on 14 November 2009
    An overview of Greenland ice trends
    Mizimi, as ice is shed, isostatic rebound could bring the underlying land quite a bit higher, so all that ice might not be as safely land locked as you say.
  20. An overview of Greenland ice trends
    RSVP, i didn't want to say that the GIS might collapse altogether. There might be partial collapse along the slopes at the edges. How comes that GIS cannot release all of it's ice? Given that we are heading toward temperatures never seen in the last several hundreds thousands years (not just 100,000), the GIS is definitely capable of releasing all of its ice and allow a 7 m sea level rise. It's just a matter of how much warming and how much time it takes.
  21. An overview of Greenland ice trends
    The Greenland ice sheet cannot 'collapse'. The ice sheet sits in a basin around 300m below sea level surrounded by mountains...whether the basin is due to the weight of the ice or was there originally is not clear. What is clear from core samples is that the central and most massive portion of the ice sheet has not changed for over 100,000 years. What we are seeing now is increased melt and ablation at the edges of the ice sheet which ,if it continues, will diminish as the central sheet becomes unable to sustain the flow outwards. So there cannot be a collapse and no 7m rise in sea level.
  22. The albedo effect
    At the risk of encouraging nonsense, Henry Pool (#20) -- where do you find CO2 reflecting a lot of sunlight? My understanding is that it is mostly invisible to visible light but opaque to infra-red.
  23. An overview of Greenland ice trends
    RSVP, i've never thought of doing this rough calculations. This means that assuming not even partial rapid collapse of the ice sheet we'd get 16 mm/yr, 1.6 m in a century, from Greenland alone. Pretty scaring, indeed; let's hope it will slow down. Take it easy Greenland!! :)
  24. An overview of Greenland ice trends
    To Mizimi Thank you for pointing out my error. You are right about the exponent, which was also missing in the denominator. Plugging new values in gives us... years = sqr(2 x 2.85 x 10e15/30 x 10e9) = 436 years hmmmm... how long do you have to boil a hat to optimize digestion?
    Response: You're remarkably blase about the potential 7 metres sea level rise from the collapse of the Greenland ice sheet not to mention a similar contribution from the Antarctic ice sheet. Surely you realise the impact of such a sea level rise on humanity.
  25. An overview of Greenland ice trends
    today's Science has a relevant paper: M. van den Broeke et al. (2009) Partitioning Recent Greenland Mass Loss Science 326, 984-986 (November 13, 2009) http://www.sciencemag.org/cgi/content/abstract/326/5955/984 abstract: Mass budget calculations, validated with satellite gravity observations [from the Gravity Recovery and Climate Experiment (GRACE) satellites], enable us to quantify the individual components of recent Greenland mass loss. 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. Without the moderating effects of increased snowfall and refreezing, post-1996 Greenland ice sheet mass losses would have been 100% higher. Since 2006, high summer melt rates have increased Greenland ice sheet mass loss to 273 gigatons per year (0.75 millimeters per year of equivalent sea level rise). The seasonal cycle in surface mass balance fully accounts for detrended GRACE mass variations, confirming insignificant subannual variation in ice sheet discharge.
  26. An overview of Greenland ice trends
    re #10 (i) Your first point is incorrect HumanityRules on two levels (I think you've misread Milne et al.) Firstly the data isn't from one type of measure, from one locality. Milne is using the Maine salt marsh data as a detailed illustration of local relative sea level variability. However their paper is a review, and their conclusions come also from other papers cited(specifically, as they indicate, from coral microattols from the Cook Islands; foraminifera from peat deposits on the Connecticut coast; salt marshes on the coast of Denmark). And there are many other examples including the papers I cited on relative sea level variation in NW Europe in post #9. The bigger error, is to mistake local relative sea level for global eustatic sea level. Milne et al present the evidence that even considering local variation in sea level (that may have post glacal isostatic and land subsidence contributions etc.), this is smallish (generally 1-10 cm per century). (ii) Let's look at global eustatic sea level. You've linked to another unattributed picture in your post. This turns out to be a model of past and projected sea level rise from this paper [*]. Presumably you want us to take it at face value, so let's do so: (a) Grinsted et al use historical temperature data to estimate possible sea level variation during the last 2000 years. For example, they suggest that during the period from around 600 AD to 1150 AD in the Medieval Warm period), sea levels might have risen by around 25 cm. This is about 15% of the sea level rise during the same period in the earlier picture you linked to in your post #3 (which presumably you now reject; they can’t both be correct). It corresponds to a bit over 2 cm per century. If one takes the Grinsted analysis at face value we may well expect around 1 metre of sea level rise during the 21st century. (b) So the data you’ve presented to us indicates the sea level rise of the 21st century may occur at close to 50 times the rate of sea level rise associated with what is considered to be the transition to the warmest period in the previous 2000 years before the middle of the 20th century (sea levels are already rising around 15 times more quickly than during the period pictured in the graph you linked to). If you were to put the projected 21st century rise on the same horizontal time scale as the previous 2000 years in your picture, it would be near vertical. Isn't this all pretty consistent with Milne et al.? They review data that shows rather little preindustrial variation in eustatic sea level; that current measurements show sea levels are already rising much faster (by more than 10-fold) that even during the rise to the MWP; and that we are pretty certain to get significantly increased rates during the current century. It's certainly inconsistent with the old graph you linked to from that dodgy web site (your post #3). (iii) In a previous post (#8) you asked the question "Would you put 100% of the sea level rise this century down to AGW?". If you look more widely at the NERC Planet Earth site from which you cut and pasted that lonely figure from Grinsted et al (2009) you would have found an analysis that addresses your question: http://planetearth.nerc.ac.uk/news/story.aspx?id=551 Jevrejeva et al determine that almost 80% of sea level rise during the 20th century is as a result of anthropogenic greenhouse forcing. In fact they point out that the anthropogenic contribution to sea level rise was likely suppressed somewhat by volcanic eruptions: "If no volcanic eruptions had happened since 1880, then sea-level rise over the last century would've been seven centimetres higher than it was," explains Jevrejeva. [*]A. Grinsted et al. (2009) Reconstructing sea level from paleo and projected temperatures 200 to 2100 AD Climate Dynamics; in press. [**] Jevrejeva, S et al (2009) Anthropogenic forcing dominates sea level rise since 1850 Geophys. Res. Lett., doi:10.1029/2009GL040216, in press.
  27. An overview of Greenland ice trends
    RSVP: your sums are a bit out I think.... A km3 of ice is 10E9 tonnes ( roughly),so 2.85 x 10E6km3 is 2.85 x 10E15 tonnes. Since 2002 the loss is 1100 x 10E9 tonnes, or 157 x 10E9 T/yr as an average - so if the rate continues in a linear fashion it would take around 10,000 years to melt all the ice ( which cannot happen). But the rate is accelerating at around 30Gt/yr so in 5 yrs the loss will be around 300Gt/yr.
  28. An overview of Greenland ice trends
    Sorry. Looking at the units, I see I forgot to add another assumption. That 1 m3 of ice weighs one ton, which it does not. At any rate, it is probably close enough to give an idea of the general order of magnitude in years. Should anyone really be concerned even if it were 10,000 or 5,000 years?
  29. An overview of Greenland ice trends
    I was going to ask what the total amount of ice there was in Greenland, but then realized this was a dumb question when I could just look it up. So I did. http://en.wikipedia.org/wiki/Greenland_ice_sheet says it is 2.85 x 10e6 km3, or 2.85 x 10e9 m3 . Sounds like a lot of ice. Then taking your acceleration of 30 x 10e9 tons/yr2, (if we ignore the initial condition) this equates to solving this as a falling body at rest d=(1/2)gt2. Solving for t, leads to years = sqr(2 x 2.85 x 10e9/30) = 13,784 years. Sounds like a lot of ice up there.
  30. 1934 - hottest year on record
    Will Nitschke, you asked for an explanation as to why the "2% land mass of the United States has only an 'infinitesimal effect on global trends' yet the 3% land area of the Arctic is apparently significant 'concrete' proof?". Your argument is a strawman. No one is claiming that what is happening in the Arctic alone is "significant 'concrete' proof". Your comparison would be fair only if those arguing that GW is happening are basing their arguments entirely on what is happening in the Arctic and no where else, but this is absolutely not true. What is happening in the Arctic, along with what is happening elsewhere around the globe is what is considered.
  31. An overview of Greenland ice trends
    I've only had time to read the Milne paper. Here's the PDF for those interested. 'These data indicate that local rates were generally at the 1–10 cm per century level" As you know this data is from one type of measure, salt-marsh stratigraphy, that work was done in one local (East Maine) so as you pointed out to me one localality shouldn't be used to represent global averages. The papers presentation of a much wider selection of data is informative That paper is eye openning in its honesty about the number of variables and inherent difficulties associated with these sort of measurements. I read Milne and took from that not that we could give definitive numbers to the last 2000years of sea level and beyond but that the science still has a long way to go. I still don't think anything presented in that paper says stasis for 2000years followed by rises in the industrial age. From what I read the rise in the 20th century was between 10-30cm depending on which data set you use. In table one Milne says the salt marsh data covers the last 500years and the maximum sea level change within that period is 20cm/century Also this graph is useful, try to ignore the pending apocalypse portrayed for the future and focus on the little hill around 1200AD (the Medieval Warm Period???) when sea levels were higher than today. Back to Greenland by way of North America There is something that caught my attention a while back and which was briefly mentioned in the Milne paper, the Laurentide ice sheet. This was a huge ice sheet that cover North america down to New York and slow melted over the past 20000 years. You could see the Greenland ice sheet as the remmnents of it. There is a cartoon of it's historical retreat here. I was wondering how that fits in with long term story of the Greenland ice sheet? It should be noted that the retreat hasn't been an even process and at times it's even grown. I wonder whether we should expect anything other than a retreating Greenland ice sheet?
  32. An overview of Greenland ice trends
    re #8 It's worth pursuing this point, since Greenland ice melt, past, present and future, is quite relevant for sea-level change past, present and future (so necessarily off-topic!). The Dutch data you linked to is difficult to assess since none of the links to the data on that web site are live. So we can’t tell what the Dutch data is, where it was taken, and whether it refers to local relative sea level (I suspect it does) or global eustatic sea level (very likely not). However we can look at data published in recent years that bear specifically on mid-late Holocene sea level variation in the coastal regions near and around Holland, and more generally at papers that assess late Holocene variation in global eustatic sea level, in other words the absolute change in sea level arising from warming/cooling and mass influx (ice sheet melting) and decrease (ice sheet expansion), that is independent of the local post-glacial isostatic effects, land subsidence, and so on, that can give rise to spurious interpretations. So on local (Dutch and environs) late Holocene sea levels, an analysis of sea levels from a region less than 100 miles to the NE of N Holland doesn’t show any up-down variation in regional sea level during the Holocene, although there has been a step-wise increase in relative sea level during the mid-late Holocene, largely due to post-glacial subsidence: Bungenstock F, Schafer A (2009) Holocene relative sea-level curve for the tidal basin of the barrier island Langeoog, German Bight, Southern North Sea, Global Planet. Change 66, 34-51 Likewise, a very comprehensive analysis of Holocene sea level data that covers a large chunk of the NW European coast (the coasts of Germany, Belgium, Holland) indicates very little upwards and downwards variation in sea level. There is a general rapid rise to around 6000 years ago with much slower subsequent sea level rise, and the data fit well to eustatic sea level analyses indicating rather little rise or fluctuations during the last 2000 years: Vink A et al (2007) Holocene relative sea-level change, isostatic subsidence and the radial viscosity structure of the mantle of northwest Europe (Belgium, the Netherlands, Germany, southern North Sea) Quatern. Sci. Rev. 26, 25-28 More generally a recent review of sea level change indicates that sea level variations have been of low amplitude throughout the couple of millennia before the industrial age: G.A. Milne et al (2009) Identifying the causes of sea-level change Nature Geosci. 2, 471-478
    Sea-level observations for the mid- to late Holocene provide constraints on the natural variability of sea-level change immediately preceding the industrial revolution. These data indicate that local rates were generally at the 1–10 cm per century level (see Table 1).
    So considering the relevant global parameter of eustatic sea level variation resulting from ice sheet/glacier mass balance and ocean temperature variations, there doesn’t seem to be much evidence for very significant fluctuations in global sea level, at least in the couple of millenia before the industrial age. Even if we consider local relative sea level where postglacial isostatic effects, land subsidence, tidal range variations and so on influence the local sea level, I can't find anything that shows the variability in the unattributed data set you linked to, and that includes data in papers that cover the equivalent coastal region (see papers cited above). If you could find the source of the data you linked to I'm mildly curious to see what it actually is... I don't think this is at all straightforward, and there is still uncertainty in mid-late Holocene sea level variation. However there just doesn't seem to be any evidence for the large scale fluctuations that your link might imply, and the recent papers/reviews on this support the opposite interpretation. I'm afraid I haven't found downloadable versions of the papers cited...
  33. The albedo effect
    re #20 That simply doesn't accord with the evidence Henry. Analysis of earth surface temperature data indicates that apart from the hugely transiently amplified 1998 temperature (largest El Nino of the last century), surface temperatures maxed around 2005. All of the years of the current decade are warmer (by around 0.2 oC on average) than all of the years of the 1990's apart from the anomalous 1998: NASA GISS: http://data.giss.nasa.gov/gistemp/tabledata/GLB.Ts+dSST.txt UK HADCRUT: http://www.cru.uea.ac.uk/cru/data/temperature/hadcrut3vgl.txt One could say that temperatures haven't risen since around 2005, but you simply can't make that sort of interpretation from a few years worth of data that incorporates large interannual variability. What do we expect the earth's surface temperature to have done during the last several years? We know categorically that the sun has dropped from the top to the bottom of its solar cycle from around 2002 to now (it's just starting on its upturn). There's pretty good evidence that the solar cycle contribution is around 0.1 oC of cooling, max to min (and obviously 0.1 oC of warming min to max). So we expect all of the greenhouse warming contribution since around 2003 (~ 0.15-0.2 oC per decade) to be negated by the small solar cycle cooling between around 2003 and now. It's therefore not surprising that surface temperatures haven't yet gone above the 2005 levels in the last few years. That's pretty much what we expect. This leads to a serious problem with those attempts to assign a cooling trend (for which there isn't any evidence in the surface temperature records) to albedo, or ocean regimes, or amplified solar effects or whatever, namely that these effects should have caused the earths surface to cool significantly during the last decade if they existed. Either that or the earth's surface temperature is much more sensitive to greenhouse warming that the science indicates. I suspect we'll find (as Palle et al. 2009 state quite explicitly), that there hasn't been a significant increase in albedo since 2000, and in any case (as Palle et al, 2006 state quite explicitly), an albedo change due to secular cloud variation doesn't necessarily inply a surface temperature response since clouds have warming ("heat trapping") as well as cooling (albedo) effects. E. Pallé et al (2006) Can Earth's Albedo and Surface Temperatures Increase Together? Eos Trans. AGU, 87(4), doi:10.1029/2006EO040002 Palle et al. (2009) Inter-annual variations in Earth's reflectance, 1999-2007 J. Geophys. Res. 114, D00D03
  34. The albedo effect
    if I look carefully at our World Climate Widget, (watts up with that) it looks to me that since about 2001 we have a slight decline in global warming, or shall we say: global cooling has started. This seems to coincide with the increase in earth’s albedo, http://wattsupwiththat.com/2007/10/17/earths-albedo-tells-a-interesting-story/ although I think this graph may need some updating (look Palle et al 2008) As I suspected, I found that at the same time ozone has begun increasing. http://atmoz.org/blog/2007/09/05/ozone-hole-update/ I also note that CO2 is increasing (it seems there is no doubt about that). CO2 also reflects sunlight. We also note that water vapor is increasing, due to human activities, mostly shallow water (dams for consumption and irrigation). So all in all, I think the increase in earth’s albedo will hold, and it wipes out the effect normally attributed greenhouse gases
    Response: This theory is invalidated by the fact that our climate is still accumulating heat. It's still in positive energy imbalance. From 2003 to 2008, the world's oceans have been absorbing heat at a rate of 0.77Wm-2.
  35. An overview of Greenland ice trends
    Response and #5 I take your points but teh climateaudit graph shows rises and falls over the last 2000years with no real nett change. I'm aware that misleading data supporting sea level rises has been used in the past. From memory, data from around Hong Kong and a Pacific Island (i think Tuvalu). So certainly making the correct measurements is important. No nett change can still mean ups and downs in the intervening time. And the recent up needs to be put into that context. I guess the point I'm making is that to argue absolutely no change over the last 2000years followed by sudden rise during the industrial age would be extremely damming. But putting the recent change into the context of a naturally dynamic system, which is undoubtedly the case, requires a little more sophisication. Would you put 100% of the sea level rise this century down to AGW? Sorry this has strayed off topic from Greenland
  36. An overview of Greenland ice trends
    As the authors themselves say, it is "the classic pattern expected in a warming climate, with increased snowfall in the interior and enhanced runoff from the marginal ablation zone." Also noteworthy is that they date the onset of significant response of the ice sheet to 1990.
  37. An overview of Antarctic ice trends
    there is an antarctic post on realclimate too.
    Response: I've updated your URL to directly link to the Antarctic post - it won't be on the RC homepage forever.
  38. An overview of Greenland ice trends
    Analysis of surface mass balance "Results from the high-resolution run with RACMO2.1/GRN are shown in Figure 1. It is found that total annual precipitation on the Greenland ice sheet for 1958-2007 is up to 24% and surface mass balance up to 63% higher than previously thought." and.. "RACMO2.1/GRN is able to simulate a realistic spatial and temporal SMB for the Greenland ice sheet for present-day climate conditions. Our findings show that considerably more mass accumulates on the GrIS than previously thought. The higher resolution, the used ice sheet mask and the redundant need for post-calibration could be a cause for disagreement between models." The combined graph of precip./melt/runoff/mass balance shows the beginning (maybe?) of a recovery from 2007.
    Response: Thanks for the link, I've turned it into a hyperlink as the URL was quite long. That data is a little older than the GRACE data which shows that ice mass loss has continued past 2007 - see Figure 2 above.
  39. It's ozone
    Nice. I asked everyone to give me the latest ozone graph and nobody says anything. Then I find it here on same site! Did you notice the upward trend since 1998? We or on the road back up the hill - but true - it is going slowly.Unfortunately the damage done by the CFC's must not be underestimated. But we are going up. I am confident that this will result in more of the sun's radiation being blocked. The CO2 going up will also help!~
  40. High CO2 in the past, Part 2
    re your points, HumanityRules: (i)& (ii) best to read the paper (click on the link in John Cook’s summary), and be careful in reading posts! Then it's obvious that: a. Figure 2 above from Royer 2006 is an "extremely low resolution" analysis (highly smoothed proxy record and a very coarsely-time resolved model) to assess the broad evolution of forcing from the slow solar constant increase in the light of a highly smoothed CO2 record/model b. the rest of the data in Royer 2006 presents data at "a much tighter time resolution". That's what I said in my post and that's quite obvious from Royer's review. Royer is addressing one point in his Figure 2, and another point in the rest of his article. (iii) good! (iv) That’s not right I think in two respects. First Royer shows the variations in CO2 and temperature/climate regimes throughout the Mesozoic (see Royer’s Figures 3 and 4). That's the relevant data. I don’t think there’s much evidence for significant Mesozoic glaciations, although there is evidence for cool spells in the Mesozoic (generally associated with low CO2 where contemporaneous proxies are available), with some warmer/hot periods associated with higher CO2. According to Retallack (2009) (the paper you cited, and many thanks for that), “The Mesozoic greenhouse was not hot with cool spells (Royer, 2006), but warm with hot flashes”, the hot flashes associated with raised CO2. An essential point though (and one that Retallack addresses) is that one can only make infererences about the relationships between temperature/climate regimes and CO2 levels where there are contemporaneous temp and CO2 proxies. So we should be careful not to assume that if temp (or CO2) was high at some point in time where we have a proxy, and high at some other time, that all the intermediate periods are defined. That’s likely to be wrong. I think in general we agree that the temperature/climate and CO2 records are bound to be spiky. That’s the conclusion to be drawn from the data in Royer 2006 and Retallack 2009. The other conclusion is that generally where there are contemporaneous CO2 and climate/temperature proxies the two are associated (high CO2 warm/low CO2 cold). That’s also the conclusion that Retallack (2009) draws. Here’s the abstract of Retallack, GJ (2009) cited in post #15: http://gsabulletin.gsapubs.org/content/121/9-10/1441.abstract
  41. An overview of Greenland ice trends
    re #3 The point refers to the effects of polar and land ice melt on sea levels as a result of the Glacial to Holocene transition. The evidence indicates that the bulk of this was realised by around 6000 years ago, and that for the last 2000 years, the nett change in sea level before around the last 100ish years was negligible (they may have actually gone down a tad in the period from the Roman era to the mid 19th century); so at the very least, any residual post-glacial melt has been balanced by snow deposition. Sea levels likely went up and down a bit during that period, but the modern increase in sea levels as a result of ocean warming and mountain and polar ice retreat is resulting in a nett rise in sea level (that is expected to accelerate as temperatures continue to rise). As pointed out already, the metric of interest is the eustatic sea level rise, which is the mean sea level. Obviously the effects of post glacial rebound and depression and local tectonic effects means that extreme care must be taken to assess eustatic sea leels and their changes that are independent of land surface changes. So in general eustatic sea levels are determined in the mid-latitude (Carribean/Meditteranean) far from direct effects of post-glacial rebound. Care must still be taken to assess other tectonic effects (e.g. the Greek mainland is sinking towards the SW as a result of collapse around the edges of the Tibetan plateau which has been pushed up (against its will!) by the Indian sub-continent. So eustatic sea level change is not a straightforward measure...
  42. An overview of Greenland ice trends
    John, the Netherland and Denmark are on the same tectonic plate as the Scandinavian peninsula. As a boat that rise on one side and sink on the other when put away some weight from just one side, the plate is rising on the scandinavian side and sinking on the other side because there was much more ice on the scadinavian side of the plate.
  43. An overview of Greenland ice trends
    #2 "....analysis of sea levels in the late Holocene support the conclusion that ice sheet melt contributions to sea level rise had more or less come to equilibrium by around 3000 years ago (some evidence supports a lack of polar ice sheet contributions to sea level change by 6000 years ago). So although it’s not a straightforward analysis, the evidence indicates that sea levels have been pretty static at least for the 1000-2000 years before the mid-18th century, and the modern period of accelerating sea level rise encompasses only the last around 100-odd years" Have sea levels been unchanged for the past 1000-2000years? That is no change at all!! I realise this is from a skeptics website but the graph seems to tell a different story http://www.climateaudit.org/?p=61 . Can't confirm this Dutch finding but I'm prepared to believe in some variation in every natural process and not complete stasis until you hit the industrial age. Actually you would get what you describe if you put a trend line in that graph i.e. levelling out about 3000years ago but you would lose the detail that puts the recent sea level changes in perspective. In terms of the above article I still think you don't give full justice even to the data you present. In summary 1960s ~100 gigatonne loss 1970s-1980s no change 1990 rising to ~100 2007 347 gigatonne loss you suggest at the start of the article that data from 1958 will show accelerating ice loss. Half way thourgh you abandon the first section of the data to state "So we see a long term trend of accelerating ice mass loss since the 1970s". When in reality the data from 1958 to 1996 says steady or no loss. It still looks to me like you're relying on the last 6-7 years of GRACE data to cocclude accelerating ice loss.
    Response: Note that the climateaudit post you link to is talking about sea levels at one particular location in the Netherlands. The post also notes that "the part of the Netherlands which is below sea-level is sinking as a result of post-glacial rebound" (although I would've thought post-glacial rebound causes the land to rise - perhaps a mistype).

    "you suggest at the start of the article that data from 1958 will show accelerating ice loss"

    To be precise, I said we'll look at "long term trends going back to 1958". And what we find is a "long term trend of accelerating ice mass loss since the 1970s". We've gone from approximate mass balance to gradually increasing ice loss. This is independent of GRACE data.
  44. Ice isn't melting
    In October we hit the all time low for October. http://climateprogress.org/2009/11/08/arctic-multiyear-sea-ice-nsidc-david-barber/ Lynn Shwadchuck
  45. High CO2 in the past, Part 2
    #13 thanks for changing the reference, I realized my mistake after posting. i) and ii) Fig 2 is from Royer 2006 it can't be simultaneously "....at extremely low resolution" (from your point i) and "....a much tighter time resolution" (from your point ii) iii) I'll try to look at them when I have time. iv) Its 'attractive' that the author can fit a couple or three ice ages into drips in the graph but there are also a couple of other ice ages there at periods of positive radiative forcing (not shown in the detailed graphs you talk about here) . The grey vertical lines indicating them are conviniently thin enough to be almost missed. and also high CO2 periods associated with cooler times in the more detailed graphs of fig3. Finally the mesozoic period, touched on in Fig3 and represented with "cooler?" periods has been shown by other authors while being generally a warmer period to also contain significant glaciation periods yet again Royer shows consistent positive radiative forcing. Can I add this to your list of papers Greenhouse crises of the past 300 million years Author(s): Retallack GJ Source: GEOLOGICAL SOCIETY OF AMERICA BULLETIN Volume: 121 Issue: 9-10 Pages: 1441-1455 My point would be that in reality a global temperature graph on that time scale would look more like a seismograph during an earth quake than the generally slow drops and rises shown on the radiative forcing graph above. I accept his attempt to get an overall general feel for climate change but think much, if not all, is lost in throwing away the detail.
  46. dopeydoctorjohn at 11:23 AM on 11 November 2009
    There is no consensus
    This crappy Doran study got a guernsey in the Letters page of the Sydney Morning Herald today, in a boldened piece from a university lecturer who, again, has accepted it without thinking seriously about it. Again, it is touted significant that a group who actively publish in a particular field, surprise, happen to believe in the field in which they are publishing. Again, that is not to deny that most Earth scientists agree with the current dominant paradigm Again, if 20% of Earth scientists can't even agree that humanity is making "a" significant contribution to warming, it would be interesting to hear their reasoning. And again, the only science the Doran paper represents is the science of "tautology".
  47. An overview of Greenland ice trends
    re #1; Yes Bamber’s paper is consistent with the general scientific observations that both Greenland and Antarctic mass balance loss is increasing:
    ”Thus, although there is a lack of consensus about the absolute value for the mass balance of the ice sheets, there is agreement that the trend has become increasingly negative for both Greenland and the WAIS.”
    There seems to be little doubt about that. You’ve selected a quote from Bamber’s article about the ice sheet responses. While it’s true that equilibrium responses are only realised on very long time scales (infinitely long in principle), analysis of sea levels in the late Holocene support the conclusion that ice sheet melt contributions to sea level rise had more or less come to equilibrium by around 3000 years ago (some evidence supports a lack of polar ice sheet contributions to sea level change by 6000 years ago). So although it’s not a straightforward analysis, the evidence indicates that sea levels have been pretty static at least for the 1000-2000 years before the mid-18th century, and the modern period of accelerating sea level rise encompasses only the last around 100-odd years [*]. Those observations are inconsistent with the notion that the polar ice sheets are out of equilibrium with the glacial-interglacial forcing of 12ky ago, to an extent that has real world significance, at last with respect to mass balance and sea level rise. [*] Pirazzoli PA (2005) A review of possible eustatic, isostatic and tectonic contributions in eight late-Holocene relative sea-level histories from the Mediterranean area Quart. Sci. Rev. 24, 1989-2001
    “Finally, several data from tectonic and non-tectonic areas are consistent with nearly stable global eustasy since 6000BP, thus challenging the assertion of significant additional melting of Antarctica after the complete melting of the former Northern Hemisphere ice caps “
    Lambeck K (2005) Sea level in Roman time in the Central Mediterranean and implications for recent change Earth Planet. Sci. Lett. 224, 563-575
    “Part of this change is the result of ongoing glacio-hydro isostatic adjustment of the crust subsequent to the last deglaciation. When corrected for this, using geologically constrained model predictions, the change in eustatic sea level since the Roman Period is -0.13 +/- 0.09 m. A comparison with tide-gauge records from nearby locations and with geologically constrained model predictions of the glacio-isostatic contributions establishes that the onset of modem sea-level rise occurred in recent time at similar to 100 +/- 53 years before present.”
    Church JA et al. (2008) Understanding global sea levels: past, present and future Sustainability Sci. 3, 9-22
    “While sea levels have varied by over 120 m during glacial/interglacial cycles, there has been little net rise over the past several millennia until the 19th century and early 20th century, when geological and tide-gauge data indicate an increase in the rate of sea-level rise.”
    Milne GA (2009) Identifying the causes of sea-level change Nature Geosci. 2, 471-478
    ”The observed fall in sea level following the end of major melting (~7,000 yr bp; Fig. 3b) is due to isostatic processes52. A growing number of high-resolution records (Fig. 3c) detect an acceleration in sea level around AD 1850–1900 (refs 43–45)”
    etc….
  48. CO2 is not the only driver of climate
    Gord, "Your A-B-C left out the only energy source, the SUN. If A, B or C has more energy being radiated than the Sun provides then energy was CREATED....PERIOD." Gord, obviously, the sun is what warms the surface before IR radiation is emitted in A. I have not created energy by adding GH gases, I have changed how and where that energy is emitted to space, that combined with the fact that Earth has a lapse rate is what causes the surface to be warmer, not the creation of energy. IAC, there is no point continuing to argue this point, so I will pose some simple questions here: do you think it is possible to vary the emissivity of the atmosphere by varying GH gases? Assuming arguendo that this can happen, what would be the consequences IYO? Would any part of the atmosphere be heated? If so, which parts? Cheers, :)
  49. Skeptical Science housekeeping: Comments Policy
    Seems like a welcome change, although those likely to break certain rules, such as ranting about one-world government or scientific conspiracy, are the ones likely to view the action of their comments being deleted as supporting their conspiracy theory. Warmists stifle dissent and won't debate!
    Response: To be honest, I've gotten to the point where I don't really care what conspiracy theorists think. You can never have a good faith discussion with them as they will dismiss any data that contradicts their position as the product of conspiracies. Removing that kind of attitude can only improve the signal to noise ratio.
  50. An overview of Greenland ice trends
    "It is important to note, however, that the ice sheets are also still likely to be responding to changes in forcing at the end of the last glacial around 12 ka BP. As a consequence, they will be out of equilibrium with respect to the modern-day climate, and their reaction to external forcing is an integrated response to changes over multiple millennia." http://www.pages.unibe.ch/products/newsletters/2009-2/Special%20section/science%20highlights/Bamber_2009-2(52-54).pdf A balanced 'quick' overview of both N & S ice sheets which is worth reading alongside "Why the Greenland & Antarctic ice sheets are not collapsing" http://icecap.us/images/uploads/OllierPaine-NoIceSheetCollapse-AIGNewsAug.2009.pdf

Prev  2525  2526  2527  2528  2529  2530  2531  2532  2533  2534  2535  2536  2537  2538  2539  2540  Next


The Consensus Project Website

THE ESCALATOR

(free to republish)


© Copyright 2024 John Cook
Home | Translations | About Us | Privacy | Contact Us