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  2367  2368  2369  2370  2371  2372  2373  2374  2375  2376  2377  2378  2379  2380  2381  2382  Next

Comments 118701 to 118750:

  1. Latest 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.
  2. michael sweet at 01:46 AM on 29 May 2010
    Websites 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.
  3. Why 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.
  4. Why 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.
  5. Why 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.
  6. Has 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:

    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

  7. It'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...
  8. The 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)".
  9. The 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.
  10. The 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.
  11. Johnny Vector at 22:36 PM on 28 May 2010
    Websites 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.
  12. HumanityRules at 21:47 PM on 28 May 2010
    Websites 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.
  13. Latest 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.
  14. The 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?
  15. Tony Noerpel at 20:37 PM on 28 May 2010
    Latest 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 Tony
    Response: It's been a long week
  16. The 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.
  17. Websites 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.
  18. Websites 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
  19. The 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.
  20. Doug Bostrom at 16:21 PM on 28 May 2010
    Websites 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.
  21. Websites 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
  22. Websites 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
  23. Latest 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...
  24. Websites 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.
  25. Jeff Freymueller at 14:41 PM on 28 May 2010
    Latest 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.
  26. Jeff Freymueller at 14:28 PM on 28 May 2010
    Latest 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 :-)
  27. Latest 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.
  28. Jeff Freymueller at 14:25 PM on 28 May 2010
    Why 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.
  29. Jeff Freymueller at 14:20 PM on 28 May 2010
    Why 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.
  30. Why 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?
  31. Greenland 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.
  32. Latest 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.
  33. The 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.
  34. The significance of the CO2 lag
    johnd - the important issue is the sum of all feedbacks. (Yes, I'm opening a Pandora's box here, but...) If the sum of all feedbacks (positive and negative) sums to -1 < x < 0, then you have a reduction or a reduction with damping oscillation after a forcing (depends on time constants). If the sum of all forcings is 0 < x < 1, then you have an amplification. Both sum to 1/(1-x) if I recall correctly, where the sum is rather smaller if x < 0. Feedbacks of the form x < -1 are run-away oscillators - each swing larger. These are sometimes used as frequency generators in electronics, limited by input voltages/energy. Feedbacks x > 1 are run-away growth until some other limit (non-linear limit on available energy?) kicks in. Neither tend to exist in nature. At least, not for long...
  35. Latest GRACE data on Greenland ice mass
    doug_bostrom Yea cause is the Q isnt it... I believe recently that a shift in ocean currents is a contender as one of the major causes http://www.jpl.nasa.gov/news/news.cfm?release=2010-050 Whether this is a result/symptom of anthropogenic co2, or some other cause, i dont know, or pretend to know. But id put money on its the reason for the accelerating mass loss in recent times.
  36. Doug Bostrom at 12:09 PM on 28 May 2010
    Latest GRACE data on Greenland ice mass
    Curving, like Jiang but derived from a different data source. So perhaps we can take it as read that Greenland's got an accelerating mass deficit? That way-- in the upcoming inevitable discussion of why/how this has nothing to do with anthropogenic climate change-- we won't have to sift through a mass of previously failed "it's not shrinking/it's actually growing" hypotheses and stick w/somewhat more plausible alternate mechanisms not involving anthropogenic climate change. And how about those alternate ideas being posted here fully fleshed-out, with details of how they -ought- to work and then some confirmatory observations? Something remotely comparable to what John presents? That would be a really pleasant improvement. (Sorry, somewhat out-of-patience here having listened for the past 24+ hours to BP's rapidly alternating stories about their oil leak while watching the video of the leak itself somehow remaining completely identical in appearance while it supposedly had tens of thousands of barrels of barite mud pumped into it, lost, shut off, then turned on again. I believe the mud's gone in, I guess, maybe, but I don't believe they had the well under control for any period of time.)
  37. Tenney Naumer at 11:55 AM on 28 May 2010
    Latest GRACE data on Greenland ice mass
    I am just really, really grateful that Dr. Wahr did not make us wait for a peer-reviewed publication to come out before making the data public!
  38. HumanityRules at 11:38 AM on 28 May 2010
    Latest GRACE data on Greenland ice mass
    I don't suppose John Wahr wants the bother of monthly updating this data online. Near realtime updates of climate data are exciting. (wait did I say exciting!)
    Response: Then I would be tempted to do regular blog posts on every twist and turn. I've been monitoring Roy Spencer's near-daily satellite data on surface temperature with great interest. To my credit, I've resisted the temptation to blog on it, wary of the fickleness of short-term fluctuations.
  39. The significance of the CO2 lag
    johnd, you're confusing net temperature gain with the feedback factor (aka ratio or percentage). In your example, the feedback factor is: 1-(1/1.23)= 0.187, which is a positive number < 1.0. That's what KR was referring to. If the feedback factor is positive but < 1.0, then each successive feedback is smaller than the previous by a constant factor. This geometric series converges to a finite number, hence the warming is not runaway. If the feedback factor is >= 1.0, then yes, you would have a runaway warming.
  40. CoalGeologist at 09:37 AM on 28 May 2010
    Why Greenland's ice loss matters
    Sorry, Berényi Péter @26, but I will be stubborn and hold to my "Something is new under the sun" argument. Kaufman, et al., “Recent Warming Reverses Long-Term Arctic Cooling,” Science, 4 September 2009: 1236-1239, DOI: 10.1126/science.1173983 concluded that 20th Century Arctic warming reversed a trend of Arctic cooling that had persisted for some 2000 years prior to that. Such (it would seem) is the power of AGHGs (although the warming apparently got started rather early, it would appear), as shown below. Moreover, the unusual Arctic warming described by the estimable Sir Joseph Banks, actually seems to show up during the mid-teens on the proxy-temperature trends of Kaufman et al., yet it is barely a 'blip'. In fact, the entire proxy temperature curve reminds me of a hockey stick, that is in the process of being lowered to the ice by a sharp-eyed goalie, in the hopes of blocking an oncoming slapshot! (Where is the Medieval Warm Period, when Vikings apparently basked in the warmth of sunny Greenland?!) I was, however, very pleased to see in the Summary, and on p. 288 of the proceedings, that the Royal Society saw fit to honor Sir Humphrey Davy, who, among his other important scientific contributions, designed a lamp that could safely illuminate underground coal workings, while not causing them to explode. There are current efforts underway to attempt to capture 'coal mine methane' before it escapes into the atmosphere.
  41. Why Greenland's ice loss matters
    My comment was not intended to express an opinion either about the validity of any criticisms of Velicogna (2009)'s statistical method, nor about how well we understand the processes. On the former, I was hoping to get a few more eyeballs on the issue. As you say, Doug, Tamino could offer an informed opinion. He could probably sort this out before breakfast, and then get to his day job. On the latter, I was pointing out the instability and ill-foundedness of purely mathematical extrapolations. A pretty obvious point, I admit. And now I must get back to my day job.
  42. The significance of the CO2 lag
    e at 08:31 AM on 28 May, 2010, perhaps you can show a simple equation to demonstrate. Using the example by Chris above, an initial forcing of 1oC results in a additional temperature rise of 0.23oC giving a total rise of 1.23oC. That is positive feedback. If the temperature only responded to the initial 1oC forcing and the total rise including feedbacks remained at 1oC, that is neutral feedback. If the initial forcing is 1oC and the total rise is less than 1oC, that would be negative feedback.
  43. The significance of the CO2 lag
    johnd > "Perhaps one reason being is that it is negative feedback" This shouldn't need to be said, but a positive feedback < 1.0 is not negative. A negative feedback would be a factor < 0.0 of the forcing.
  44. Why Greenland's ice loss matters
    hadfield at 07:55 AM on 28 May, 2010 "Extrapolating an accelerating curve into the future is always problematic." Or into the past, I might add. We need understanding of the processes. We understand the processes pretty well hadfield. If the Earth temperature stabilises, land ice volume (and sea level) will eventually settle around an equilibrium state. Raise the temperature and the ice will melt, and sea levels will rise towards a new (reduced land ice volume) equilibrium state. If the temperature is higher, then the rates of land ice melt and sea level rise will be faster. It's pretty simple physics. At a given temperature above the equilibrium temperature there will be a fairly constant rate of melt on the decadal timescale. As temperatures rise, so the rate of melt accelerates. Extrapolating this into the near future is likely to be pretty reliable. The simple physics of this phenomenon and its agreement with empirical observations, has been recently reiterated here
  45. Doug Bostrom at 08:09 AM on 28 May 2010
    Why Greenland's ice loss matters
    Hadfield, just a suggestion, or a demonstration? Tobis runs a pretty tight shop, surely this is not simply speculation? Tamino at OpenMind would be -ideal- for this work but surely he has a day job, might not be able to take it up.
  46. Peter Hogarth at 08:09 AM on 28 May 2010
    Why Greenland's ice loss matters
    FerdiEgb at 21:01 PM on 27 May, 2010 I’m a little doubtful of your statement “There is no significant trend in the Greenland temperature data over this 130 year period” I’ve looked at the records, but they are visually summarized nicely by the DMI: The overall Greenland (and global) temperature trends are strongly positive over 130 years. There does indeed appear to be anomalous Greenland warming between 1920s and 1940s. This is strongest at these NH latitudes, there is some debate as to why. Recent work on aerosols is interesting as the US has been a major industrial source of sulphates and the concentrations extracted from Greenland ice cores (which give high resolution records covering this period, I think it’s in McConnell et al., 2007) mirror the variations, even if they do not mirror the overall rising trend. Perhaps the “natural variations” aren’t so natural.
  47. Why Greenland's ice loss matters
    FerdiEgb at 21:01 PM on 27 May, 2010 Not sure that I agree with too much of that Ferdi. There is certainly a trend in Arctic temperatures with a reversal of a long-term very slow cooling, starting in the mid-late 19th century, to yield a rather dramatic warming especially over the last 100-plus years [*]. Greenland itself is more difficult to assess. However it seems also to have warmed considerably since the mid-19th century. The temporal variation in warming is more complex, but recent analysis indicates that this is likely to have been strongly influenced by atmospheric aerosols (volcanic and anthropogenic) to which the Greenland ice sheet is especially susceptible (i.e. to cooling effects) [**]. So the suppression of Greenland temperatures in the late 19th century and the rapid warming especially from around 1910 has likely got a strong contribution from the high volcanic activity in the late 19th/early 20th century, and then a rapid recovery from this aerosol-induced cooling to "catch up" with the enhanced greenhouse-induced forcing. The same likely applies to the cooling in the middle of the 20th century. So there’s nothing necessarily “cyclic” about these contributions. Rather they’re likely to have been stochastic. A concern raised by Box et al (see [**]) is that Greenland temperature anomalies should rise above N. hemisphere anomalies, and they haven’t got there yet. So it seems we have a bit of extra Greenland warming still to come irrespective of present and future enhanced greenhouse forcing (see [**] for a discussion of this). As for polar ice melt, there’s no evidence from the trajectory of 20th century sea level rise that early 20th century warming of Greenland was associated with ice melt to the extent that we’ve seen in the last decade. Of course that's not really surprising since globally-averaged temperatures were quite a bit lower then than now. Clearly in a world with globally enhanced temperatures, the rate of ice melt will be greater. That seems to be pretty well established (see papers cited here). It’s all very well to talk about “natural variability (PDO, NAO, AO,...)” but that doesn’t have much meaning without a quantitative analysis. Swanson et al (2009) have done this and find that while natural variability relating to ocean circulation likely made contributions to early-mid 20th century temperature progression, its contribution to the warming since the early 1970’s has been small (~ 0.1 oC) [***]. And any putative absence of natural cycles from models doesn’t “overestimate the effects of CO2” since natural cycles don’t contribute to long term forcing (they just introduce "noise” around any trend). So Swanson et al. (2009) conclude that natural climate variability (including ocean circulation variability) has made close to zero contribution to the warming since the start of the 20th century. And it’s very difficult to sell the notion that there has been a “halt in warming over the last decade” when every year of the past decade has been warmer than every year of the previous one bar the highly anomalous 1998 (not to mention that we’ve just had the warmest Dec-Feb quarter on record; NASA Giss). And I don’t think it makes sense to say that the current temperature is at the low end of all projections when at least through 2006, the temperature trend was near the top end of the IPCC projections [****]. There's no question that Greenland melt is now faster than any previous record of Greenland melt outside glacial-interglacial transitions, and it's rather certain that Greenland melt and its contribution to sea level rise, is going to increase in the coming decades. There is some very fundamental physics involved in these phenomena, and vague reference to ill-defined "cycles" isn't going to alter those facts! [*] Kaufman, D. S. et al. (2009) Recent Warming Reverses Long-Term Arctic Cooling Science 325, 1236 – 1239 abstract [**] Box, J. E. et al. (2009) Greenland Ice Sheet Surface Air Temperature Variability: 1840-2007 J. Climate 22, 4029-4049. abstract [***] Swanson, K. L. et al. (2009) Long-term natural variability and 20th century climate change Proc. Natl. Acad. Sci. USA 106, 16120-16123. abstrsct [****] Rahmstorf, S. et al. (2007) Recent Climate Observations Compared to Projections Science 316, 709. abstract
  48. Why Greenland's ice loss matters
    Geo Guy - volcanoes at least occur in predictable places - Greenland not among them. I, like angliss, would like to see your reference for a volcano in Greenland. My thermal modelling depends pretty much on predictable, steady crustal heat flow and this backed by a lot of empirical data. Even the effects of a volcano are quick localized.
  49. Doug Bostrom at 07:56 AM on 28 May 2010
    Has the greenhouse effect been falsified?
    For more on saturation effects, also see the wonderfully titled A Saturated Gassy Argument, at RealClimate.
  50. Why Greenland's ice loss matters
    On a post at Michael Tobis's blog: http://initforthegold.blogspot.com/2010/05/eschenbach-has-half-point.html Willis Eschenbach, MT and others are expressing doubt about Velicogna's 2009 finding of accelerating mass loss from Greenland and Antarctica in the period 2002-2009. The suggestion is that she has neglected (or otherwise failed to account properly for) the effect of smoothing on the number of degrees of freedom in the data. My suggestion is that this criticism, if it's well-founded, needs to be conveyed in a comment to GRL. Does anyone else more statistically competent than me want to venture an opinion? By the way, Ned (#16), on MT's blog I asked "Why would anyone extrapolate a quadratic fit based on a sample of 7 years of data out to 91 years beyond the sample end-points? In either direction?!". You have gone one better by converting it to an exponential before extrapolating. I can only admire your boldness, sir! But seriously I think we all can agree that "Extrapolating an accelerating curve into the future is always problematic." Or into the past, I might add. We need understanding of the processes.

Prev  2367  2368  2369  2370  2371  2372  2373  2374  2375  2376  2377  2378  2379  2380  2381  2382  Next


The Consensus Project Website

THE ESCALATOR

(free to republish)


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