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Comments 121651 to 121700:

121651. Tom Dayton at 11:55 AM on 29 March 2010
        The human fingerprint in global warming
        Bob Close wrote "However, this does not explain multi-decadal warming and cooling cycles evident in the historical data that appear on lack of other convincing evidence to be solar related." So what, Bob? Obviously a cross-decadal upward trend in CO2 or anything else cannot explain variations counter to that trend. Who is claiming it should? (Certainly not Trenberth!) CO2 would have to explain (track/predict/correlate with) all variations in temperature only if CO2 were the only cause of temperature. But a fundamental basis of climatology is that CO2 is not the only driver of climate. Therefore the correlation between CO2 and temperature will not (cannot, must not) be anywhere close to perfect unless the time span is long enough for other forcing and feedbacks both positive and negative to wash each other out. Even then, the correlation with CO2 will be much less than perfect, because other, non-washed-out forcings and feedbacks will interfere. But those effects can be subtracted from the correlation, leaving us with a much closer to pure correlation with CO2--which is much greater than zero. For example, the effects of the Sun's 11-year up and down cycles can be removed most simply by plotting the 11-year running average of temperature. More sophisticated analyses yield estimates of the proportion of temperature increase that is explained by (correlated with, predicted/postdicted by) various aspects of the Sun's activity. For example, solar radiance accounts for a substantial portion of warming for the first half of the 20th century, but not since then (see It’s the sun). A purer measure of the CO2 correlation also can be gotten by looking at total energy rather than only at air temperature, as Glenn Tamblyn explained well. Finally, as chris explained, the causal attribution of CO2 to temperature most certainly is not based only on correlation! The theory was started in the early 1800s and continued to be developed based on formal experiments on fundamental physics, for many decades before measures of the Earth's temperature were sufficient to even begin to look for observational correlations as empirical support for the theory's predictions. I suggest you get an overview by reading the free online book The Global Warming Debate.
121652. ProfMandia at 11:32 AM on 29 March 2010
        The human fingerprint in global warming
        John, I took a whack at explaining stratospheric cooling and I have to say it is difficult to get a handle on and to explain. The link below is my effort: Stratospheric Cooling The key points I took from this: 1) Ozone loss has contirubuted to about 50% of the cooling, CO2 the other 50%. 2) Ozone has begun to increase since 1993 which will offset some of the GHG-caused cooling, especially in the lower stratosphere. 3) The greatest cooling appears in the upper stratosphere near 40–50 km. Ozone concentration above 35 km is minimal so ozone depletion is much less a factor at these levels than cooling due to CO2.
        Response: "I took a whack at explaining stratospheric cooling and I have to say it is difficult to get a handle on and to explain."
        
        Why do you think I spent one sentence on it then hurried on?
        
        That's a great resource you've got there on stratospheric cooling. I've added a new Further Reading section to the "It's Not Us" page linking to your resource. I've also added it as a resource in the Global Warming Links page on "It's Not Us". Thanks for the link!
121653. Leo G at 11:06 AM on 29 March 2010
        The human fingerprint in global warming
        Chris, whole heartedly agree. And it would be interesting to see VS continue on and start inputting all of the factors you state. There has already been corraboration from the likes of Tamino, Bart, Eduardo, etc. Not that they have sat around with a few beers and politely discussed it, there has been some hammering, but all have looked at the issue through the others eyes. What I find interesting about the VS thing, is that there is finally a dialogue happening. Over 700 posts, which 6 months ago, would more then likely have been shut down quite quickly. On Lucia's blog, Zeke, Carrott Eater, Nick Stokes not only post their views and results, but again, a dialogue. Here at John's, since I've been visiting, there has always been this courteous back and forth between disparate views. I just sense that there has been a "step change" in relationships between the pro and cons. Of course, like everything in this world, there will be a lag, before it manifests at the very top! Call me an optimist. It really does bother me to see all of the intelligence wasted by tribalism. I guess you could say that I am finding myself firmly planted in Judith Currie's camp. As Picard would say, "Engage!"
121654. Bob Close at 11:06 AM on 29 March 2010
        The human fingerprint in global warming
        OK, as an Earth scientist and skeptic with no climate science background but an understanding of long term natural changes to the planet and solar system, you have established to my satisfaction that there is CO2 related AGW. However, this does not explain multi-decadal warming and cooling cycles evident in the historical data that appear on lack of other convincing evidence to be solar related. Also on the basis of (Evans 2006) GHG data percentages, water vapour is having a 25x proportionally massive effect compared to CO2 which is directly contributing less than 5% of the total effect. How then is CO2 the main driver of GW? Various authors have argued that the dominant WV effect is a direct result of the expanded evaporation cycle of warmer seawater caused by the CO2 effect, therefore CO2 is the main driver! Where is the verified experimental or actual measurements to support this strange assumption, or its corollary that ongoing atmospheric increases in CO2 above 400-500ppm will automatically create a tip over effect into runaway spiraling catastrophic warming? This critical data is now urgently required because without it one can only conclude that it is wishful thinking or worse to blame fossil fuel generated CO2 for most of the current global warming and its supposed undesirable effects. Lets get the science more exact and in perspective. Until we can clearly see that current climate changes are way outside the normal range over the last millennia, we should only conclude that mankind has (should)or can have a marginal effect on global climate. A possible exception being if we have a massive nuclear exchange creating a radioactive dust blanket thus cooling the planet for a while. This does not mean we should be complacent about the matter and not try to ameliorate our polluting way and thus protect the planet, as we clearly are massively affecting our environment by our burgeoning population increase and industrialization driven by our depleting fossil fuel resources.
121655. Ned at 10:57 AM on 29 March 2010
        The human fingerprint in global warming
        Tom Dayton writes: It is merely a story on the San FranciscoExaminer.com blog by writer Tom Fuller, about scientist Bart Verheggen's suggestions about the statistics. Just to clarify -- As far as I can tell, there's no actual connection between the San Francisco Examiner newspaper and the "Examiner" web portal. Tom Fuller just seems to be a random individual who provides commentary at the latter site. He doesn't seem to be connected with the newspaper, though lots of web postings seem to identify him as "a columnist for the San Francisco Examiner".
121656. Tom Dayton at 10:56 AM on 29 March 2010
        The human fingerprint in global warming
        nerndt, the effects of cosmic rays on cloud cover are discussed in It’s cosmic rays. Be sure to also click on the links in the "Related Links" box at the bottom of that post. Those other threads are the appropriate places if you want to continue discussing that topic. It is off-topic for this thread we are on now. By the way, you can easily find the appropriate threads by using the Search field at the top left of every Skeptical Science page. For example, you can search for "cosmic rays" or "clouds."
121657. Tom Dayton at 10:39 AM on 29 March 2010
        The human fingerprint in global warming
        Leo, I second Chris's reply.
121658. chris at 10:36 AM on 29 March 2010
        The human fingerprint in global warming
        re: Leo G at 09:03 AM on 29 March, 2010 Leo, statistical analyses are meaningless outside of the context of the physics of the system of interest. One can set up false premises, and come up with any conclusions from a bit of statistical numerology. Your example is a case in point: the temperature rise to 1936 certainly wasn't natural (false premise). Atmospheric CO2 levels rose from 286 ppm to 308 ppm in the period from the mid-19th century up to 1936 (high resolution [CO2] record), and inspection of the long term CO2 record, together with understanding of human greenhouse gas emissions, indicates that this rise was not natural. That change in [CO2] should give a global surface temperature rise of ~0.3 oC at equilibrium under the mid range of Earth climate sensitivity to enhanced greenhouse forcing (3 oC rise per doubling of [CO2]). The global surface temperature rise in the period from the mid 19th century to 1936 was around 0.3 oC (e.g. Hadcrut reconstruction ). So it’s very likely that a substantial amount of the warming to 1936 was due to very large anthropogenic enhancement of greenhouse gas concentrations that had accrued already through the first third of the 20th century. Of course if you really want to understand the temperature evolution (over the last 150-ish years say), one needs also to factor in the rest of the known physics – i.e. the known aerosol emissions and their forcings; the known volcanic emissions, and the amplitudes of their negative forcings (these account for the suppressed late 19th-early 20th century temperatures); the solar contributions; the contributions from black carbon and from land use changes etc.; the response times of various elements of the climate system etc. etc…..i.e. the sort of attribution studies done here and here . To throw away all knowledge of the physics of a system, and then attempt to draw conclusions from a statistical analysis of a single parameter is hopeless for scientific understanding. Statistics is an adjunct to physical/empirical analysis. It has no meaning in isolation.
121659. Tom Dayton at 10:17 AM on 29 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        gallopingcamel, the FACE experiment's topic of CO2 being sequestered by CO2-enhanced growth of trees is off-topic for this thread, so I've replied over on the thread CO2 Is Not A Pollutant.
121660. Tom Dayton at 10:14 AM on 29 March 2010
        CO2 is not a pollutant
        This comment is my response to a question by gallopingcamel on another thread. This topic is off-topic for that thread, so I'm responding in this thread. The Duke FACE experiment (Free-Air CO2 Enrichment) of artificially fertilizing trees with CO2 is an important one. Its results are consistent with other experiments on other plants: Plants' growth is limited by whichever nutrient or other condition is in shortest supply or detrimentally high supply, or by inherent physiological limits. A plant whose growth is limited by water supply isn't going to grow more if you give it more CO2, or more sunlight, or more soil nutrients. If initially the CO2 supply is the limiting factor, then giving the plant CO2 will let it grow faster only until some other factor that was sufficient for the previous growth rate becomes the bottleneck for the higher growth rate. Farmers and gardeners know this, which is why they don't waste money by giving plants too much of any one thing. Even greenhouses whose air is spiked with CO2 don't have 100% CO2 atmospheres. "Detrimental conditions" include temperatures that are too high. Even if a plant has sufficient other nutrients and conditions to allow it to take advantage of extra CO2 to grow more, if that CO2 is accompanied by higher temperature, the temperature can slow growth. The net growth then will depend on the balance of the enhancement from CO2 and the detriment from temperature. But even if you keep all the nutrients and conditions in synch, there are inherent physiologic limits to growth rate. All plants in the world today have evolved for, or been bred for, approximately the current CO2 levels. There was no survival advantage of being able to use more CO2 than was available. Not all plants respond the same to increased CO2 levels. For example, the Aspen FACE experiment (different from the Duke pine tree FACE experiment) found that "aspen grow much faster in response to elevated carbon dioxide, [but] similar effects have not been observed in other trees species, notably oak and pine." And aspen in moist soil take advantage of additional CO2 by growing faster, but aspen in dry soil do not. In contrast, loblolly pines react oppositely: They grow more with extra CO2 only during dry years, not during normal or wet years. The bottom line is that

        "Forests will continue to be important to soak up anthropogenic carbon dioxide," says [the aspen FACE experiment's] Waller. "But we can't conclude that aspen forests are going to soak up excess carbon dioxide. This is going to plateau." "Aspens are already doing their best to mitigate our inputs," agrees Cole. "The existing trees are going to max out in a couple of decades."

        The Duke pine FACE experiment's Schlesinger said:

        Based on available evidence from the Duke experiment, “I’d be surprised if the forests of the world will take up more than one-third of the carbon dioxide from fossil fuel emissions in the year 2050, which is what our experiment simulates,” he predicted.

        More information on biologic carbon sequestration, with a number of links to even more info, can be found on an EPA page. Wikipedia has a broader page.
121661. TruthSeeker at 10:07 AM on 29 March 2010
        The human fingerprint in global warming
        Excellent Post, very well written. Perhaps your best one yet. I have some questions that I will post later, but I wanted to first give you kudos.
121662. Leo G at 09:03 AM on 29 March 2010
        The human fingerprint in global warming
        Glen @ 22. VS has just done an analyses of temp rise, comparing up to 1936 (supposedly natarul) to 1936 to 2008 (supposedly more AGW). His result just simply states that the recent temp rise does not fall out of the boundaries of natural causes. He clearly states that this in no way disparages the CO2 hypothesis. He has not looked into that aspect yet. Who knows if he will. Tom - VS has not been debunked by Tamino. Tamino helped to show VS that temp is not a random walk, which he has admitted. What I see coming out of this post @ Bart's, is like here and @ Lucia's, we are starting to see more and more the possibility of "both sides" (Gawd how I hate that term!) starting to work together, putting strengths together to really nail this issue down. Eduardo has said that he would welcome working with a statistician of high calibre. Could the halls of hell be freezing over? Do you think that one day we may see a paper by M & M - Mann and McIntyre??? :)
121663. Glenn Tamblyn at 08:36 AM on 29 March 2010
        The human fingerprint in global warming
        manacker Your observation reflects a common fallacy in how people are looking at Climate Change. We live on the surface of the Earth and to us 'climate' is effectively air temperature. All the different climate models are making predictions about future air temperatures (among other factors) so we are interested in whether they are correct. However, the air isn't the climate. It is one part of it, albeit the part we are interested in. The climate is actually the air, oceans, land surface, ice and some would argue, the biosphere. And the key thing we need to be looking at if we are seeking confirmation of AGW is energy not temperature. Ultimately the theory is that multiple different factors - GH gases, H2O feedback, Aerosols, Clouds, Albedo change, Solar output variations an then the complex interactions of all these in the 3 Dimensional real world will lead to an energy imbalance for the planet - Energy Out being less than Energy In or the so called Radiative ImBalance. So there is a net accumulation of heat within the environment. So the key correlation is between Radiative Balance and Total Heat Content for the planet. And as John has shown well here, this connection is very clear cut. The ext important correlation is Radiative Balance vs the various factors causing it. Again John has higlighted these well here. The largest area of uncertainty is Aerosol/Cloud effects. Next is the break up of where the heat is accumulating. 90% or more is in the oceans with the atmosphere making up around 3%. The atmosphere is small in enegy terms compared to the oceans and various heat transfer mechanisms that operate between air and oceans mean that air temps can be volatile. Small, percentage wise, changes in the oceans can flow through to much larger changes in the air. Also, this combination of a large, slowly accumulating, heat reservoir and a smaller, volatile one also means that there can be significant time lags between an initial heat injection and the consequent temperature change in the air. So attempting to do a statistical correlation of one forcing factor vs one small, time lag dependent and volatile consequence is a rather meaningless exercise. I haven't read the article although I have heard of others like this done by econmists. Either they don't understand enough of the physics to know which correlations to look for, in which case their mistakes are honest ones. Alternatively the act of focusing on a narrow aspect of the science so it can be attacked is a classic strawman argument and a common technique of AGW denialists, in which case my view of them is less charitable. Look at the range of views put forward by denialists. How many of them are loudly trumpeting how radiative balance and Total Heat Content are the smoking gun that AGW is all a fraud. Rather cherry pick and keep the focus on small details. You can always pick the strawman when the real, live, 3 dimensional real man enters the room. Thats why the denialists don't touch this question.
121664. nerndt at 08:18 AM on 29 March 2010
        The human fingerprint in global warming
        I found a link to effects on solar bursts to cloud cover Precipitation, cloud cover and Forbush decreases in galactic cosmic rays References and further reading may be available for this article. To view references and further reading you must purchase this article. D. R. Kniveton School of Chemistry, Physics and Environmental Science, University of Sussex, Falmer, Brighton, BN1 9QJ, UK Available online 6 August 2004. Abstract The results of a study to explore variations in cloud cover, over regions that are minimally affected by rainfall and heavy rainfall, and that are coincident with variations in the galactic cosmic ray flux, are presented. Using an extensive record of global satellite derived cloud and rainfall products from the International Satellite Cloud Climatology Project D1 data series and Xie and Arkin (J. Climate 9 (1996) 840), epoch superposition analysis of a sample of events of short term decreases in the galactic cosmic ray flux, is conducted. Analysis of data that is largely free from the influence of rainfall and heavy rainfall, averaged over 10-degree geomagnetic latitude () bands reveals that cloud cover is reduced at high latitudes, and at middle and lower (including equatorial) latitudes over regions of relatively higher cloud cover, over both land and ocean surfaces, while increasing over ocean surfaces at middle and lower latitudes in regions of thinner cloud. Author Keywords: Cosmic rays; Clouds; Precipitation; Climate; ISCCP; Forbush decrease; Solar variability Article Outline 1. Introduction 2. Method 3. Results 4. Discussion and conclusion Acknowledgements References
121665. nerndt at 08:14 AM on 29 March 2010
        The human fingerprint in global warming
        Tom - thanks for your previous response to my question. Another question relavant to this debate: Does cloud cover change from daytime to nighttime? If so, by what amount? If for example cloud cover decreases 10% (SWAG - truly random numbers to give an example) when the sun hits the earth and increases 10% (SWAG 2) on the shaded side of the earth, wouldn't troposphere and stratosphere readings vary heavily based on cloud conditions? Clouds form the largest thermal blanket of the troposhere, followed by water moisture and then other gases. On a separate issue, I once heard (I'm afraid it was a while ago and I do not remember the source or time period for the events) that large solar wind bursts can send up to 10% of earth's cloud cover out into space. This could cause quick fluctuations in earth's temperature swings that would take years to recover. I once thought if we drastically expanded the Ozone hole we could quickly cool down the earth. Is this so? It would not be safe, allowing dangerous rays to hit the earth where the hole was made, but sure could cool things down quickly.
121666. michael sweet at 07:51 AM on 29 March 2010
        The human fingerprint in global warming
        Max, As others have mentioned there are other forcings besides CO2. Aersol forcings can account for much of the departure from CO2 increasing. John has another thread that discusses this. Where do you get your data for your claim of golbal cooling? What time period do you claim for this cooling? GISS shows continued increase, as does the NCDC data. Michael Sweet
121667. Riccardo at 07:46 AM on 29 March 2010
        The human fingerprint in global warming
        johnd, do you have any reference to data showing a trend in cloud cover coherent with your claim? Or you are just throwing a hypothesis?
121668. gallopingcamel at 07:41 AM on 29 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        Ned (#64) and JMurphy (#65), You say that NOAA is not throwing away station data. There is a simple way to test this statement. I have emailed the Canada Weather Office to ask them what station data they are currently providing to NOAA, NASA and UEA/CRU. If it turns out that they are sending data on more than one station (Eureka) above 65N and three stations between 60N and 65N (WITHEHORSE, DAWSON and CORAL HARBOUR) I hope you guys will be gracious enough to apologise.
121669. Riccardo at 07:40 AM on 29 March 2010
        The human fingerprint in global warming
        Well, Fuller article is just another example of people jumping to (wrong) conclusions after reading something the do not understand. We're getting used to this. The statistical debate is interesting and worth reading but it's a highly specialized field and not so easy to fully understand. In the meanwhile, better stick to good old (and rock solid) physics that tells us that surface temperature cannot be a random walk.
121670. grypo at 07:34 AM on 29 March 2010
        The human fingerprint in global warming
        shargash said "isn't the greater warming at the poles than the equator also a fingerprint of the greenhouse effect?" Polar amplification can result from any positive forcing, although there is less known about past Arctic Oscillation. See Moritz, R.E., C.M. Bitz, and E.J. Steig, 2002: "Paleo-data show that Arctic SAT in the 20th century was exceptionally high compared with the previous 300 years and that this was likely caused by GHG forcing, although there is no consensus on the cause of the Arctic cooling during 1940 – 60. In the past 30 years, the AO has played a key role in Arctic climate change. It is not clear whether the AO has been as important before this period or how it will contribute to the future. Most GCMs underestimate the magnitude of the trend in the AO when forced with 20th-century radiative forcing and continue to simulate weak trends under future forcing scenarios. In addition, these models tend to produce a tremendous spread in their predicted future warming in the Arctic. Clearly, the spread in warming cannot be attributed to their simulation of the AO. It is more likely that the disagreement stems from the parameterizations of surface albedo, cloud processes, and other feedback mechanisms in the high latitudes."
121671. gallopingcamel at 07:33 AM on 29 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        Tom (#75), I was hoping for a comment on the FACE experiment or even on the idea that mankind has the power to defer the next Ice Age. My take on the latter point is that it can't be that easy. Imagine driving around in your SUV or Gulfstream IV (if you are Al Gore) because it is your duty to save the planet from the big freeze?
121672. johnd at 07:30 AM on 29 March 2010
        The human fingerprint in global warming
        The frequency of cold and warm days and nights will be a function of cloud cover as much as anything, especially cold or warm nights.
121673. Tom Dayton at 07:21 AM on 29 March 2010
        The human fingerprint in global warming
        If anyone wants more details on Martin Hedberg's comment that the relationship between CO2 and temperature is indeed robust, see the Skeptical Science argument There’s no correlation between CO2 and temperature.
121674. Martin Hedberg at 07:05 AM on 29 March 2010
        The human fingerprint in global warming
        manacker (max) notes that temperature does not always increase as CO2 increases. He concludes therefore that the relationship between CO2 and temperature "is not so robust". Well, CO2 is not the only thing affecting planetary radiative balance and hence air temperature. Worth mentioning is for example other greenhouse gases, the albedo and that energy is absorbed by oceans as well as ice and land (not only the air gets warmer). You also have to include feedbacks and complexity. Neither this nor variations in temperature diminishes the impact CO2 has upon the greenhouse effect, radiative balance and temperature. The link he refers to analyses part of the climate with statistics, not physics. The author asks for more investigations, but he does not bother to read/understand even part of all the information at hand. No scientist of today claims that CO2 is the only thing affecting temperature, yet a lot of people believe scientist think so. Why? /Martin
121675. Tom Dayton at 07:03 AM on 29 March 2010
        The human fingerprint in global warming
        Anyone reading the blog post that manacker linked to should be careful not take it at face value. It is merely a story on the San FranciscoExaminer.com blog by writer Tom Fuller, about scientist Bart Verheggen's suggestions about the statistics. The scientist Verheggen himself vigorously objected to Fuller's interpretation of his work, in a comment on Fuller's comments thread:

        Tom, Thanks for highlighting the discussion at my blog. However, I think you’re overstating the significance. I replied to the quote you cited from whbabcock: “No, that’s not what this thread is about. It’s about a few things: Whether the temperature data contain a unit root, and what the consequences would be for how to analyze the time series. You would be correct with your inference if AGW was only based on (perhaps spurious?) correlation, but it’s not. It’s based on physics and a myriad of observations.” VS’ argument does not contradict “the theory” (of radiative transfer; or of AGW for that matter). It may mean that statistical significance in one (!) part of the observations is not as easily established as I’ve thought in my (admitted) statistical naievity. It has no bearing on physics based GCM studies about expected future climate changes. See also ourchangingclimate.wordpress.com/2010/03/18/the-relevance-of-rooting-for-a-unit-root/

        That last link is to a page where the scientist Verheggen further debunks the overinterpretation and incorrect interpretation by commenter VS and by the San Francisco Examiner's Tom Fuller. Commenter VS's incorrect interpretation has been further debunked in extreme detail by the professional time-series statistician specialist Tamino in his post Not a Random Walk.
121676. shargash at 06:50 AM on 29 March 2010
        The human fingerprint in global warming
        John, isn't the greater warming at the poles than the equator also a fingerprint of the greenhouse effect?
121677. shargash at 06:49 AM on 29 March 2010
        The human fingerprint in global warming
        manacker @9 said, "The observed multi-decadal warming and cooling cycles cannot be explained by the gradually and smoothly increasing CO2 levels" That is true of atmospheric temperatures. However, the heat content of the oceans is much great than the atmosphere. We can see the effect in El Nino/La Nina years, but much of the ocean still cannot be measured directly. For that reason, the satellite measurements are much more reliable than atmospheric temperatures.
121678. manacker at 06:28 AM on 29 March 2010
        The human fingerprint in global warming
        Atmospheric CO2 increase since the 19th century is likely to be at least partly a result of increased human CO2 emissions, as this article concludes. However, the correlation between atmospheric CO2 and “global temperature” is not so robust. The observed multi-decadal warming and cooling cycles cannot be explained by the gradually and smoothly increasing CO2 levels; the current global cooling despite record increase in CO2 is also hard to explain. A robust statistical analysis of the CO2 / temperature correlation, as proposed by pro-AGW scientists, Bart Verheggen, may shed more light on this apparent dilemma. http://www.examiner.com/x-9111-Environmental-Policy-Examiner~y2010m3d24-Global-warming-Bigger-than-Climategate-more-important-than-Copenhagenits-statistical-analysis Max
121679. Tom Dayton at 05:23 AM on 29 March 2010
        We're heading into an ice age
        Scinan, I should clarify that the risk of a shutdown of the North Atlantic Current (thereby causing a Northern Hemisphere ice age) is not an ice age threat that is reduced by increased CO2. To the contrary, the threat is increased by increased CO2. The point of my previous comment was that the probability of it happening is very small.
121680. Tom Dayton at 05:15 AM on 29 March 2010
        We're heading into an ice age
        Scinan, I think you are talking about the North Atlantic Current portion of the thermohaline circulation. It has happened in the distant past, so reasonably it has been speculated to be a risk in the near future. More research has revealed that it is extremely unlikely to happen in the near future. More information can be found by clicking on the links in the "More Information" section at the bottom of the page by climatologist Stefan Rahmstorf, "The Day After Tomorrow: Some Comments on the Movie." (For the quickest route to the information, skip straight to the bottom of that page.)
121681. Tom Dayton at 04:41 AM on 29 March 2010
        The human fingerprint in global warming
        nerndt asked "Wouldn't increased water vapor cause the same effects as warming the troposphere and cooling the stratosphere?" CO2 is well mixed through the atmosphere, so additional CO2 will end up in the stratosphere as well as lower. The extra below the stratosphere prevents infrared radiation from reaching the stratosphere, thereby keeping the stratosphere cooler. You're right that water vapor below the stratosphere has that same insulating effect. But the extra CO2 in the stratosphere radiates more IR out toward space (as well as in all other directions), thereby cooling the stratosphere more. Water vapor, in contrast, is not well mixed in the atmosphere. It is sparse in the stratosphere, so water vapor's increase in the atmosphere as a whole does not cause a proportionately large increase in the stratosphere. So increasing water vapor in the atmosphere as a whole does not increase that stratospheric radiative cooling of the stratosphere that does come from CO2 increase. That's to the best of my knowledge, but somebody please correct me if I'm wrong.
121682. chparadise at 04:31 AM on 29 March 2010
        The human fingerprint in global warming
        GFW beat me to the punch on explaining that the vast excess of oxygen relative to CO2 means that we haven't reduced our oxygen levels dangerously. One of your best posts yet John. The measured carbon isotope ratio graph alone is worth it in debates, and it's a result that makes perfect sense once one thinks of the theory.
121683. at 04:03 AM on 29 March 2010
        We're heading into an ice age
        OK. I have said enough and I still do not know why I am listed as "N/A" But I have one last thought. What are the circumstances that would make more CO2 good? How do we know they arr not in the future? Best to ask many questions and be ready for anything that happens. Have a Swiss army knife of solutions - not one solution for one problem and only that one solution. Warmer will be inconvenient. Ice will kill most of us - if not all. I am gary4books.
        Response: The N/A is a website glitch, still trying to figure it out.
121684. Martin Hedberg at 03:56 AM on 29 March 2010
        The human fingerprint in global warming
        Great post. I'd like to add (Or are they to indirect?): 1. Ocean acidification. 2. Is there a fingerprint of the C13/C12 in biomass? /Martin
121685. nerndt at 03:54 AM on 29 March 2010
        The human fingerprint in global warming
        Good article, but a question: Why was the water vapor filtered out in the "Spectrum of greenhouse radiation" figure 5 when it dwarfs all other gases (95% for H2O versus 5% for all other gases combined)? Also, wouldn't increased water vapor cause the same effects as warming the troposphere and cooling the stratosphere? I always like to look for the obvious reasons for large effects before pursuing minor ones. Am I missing something?
121686. Steve L at 03:48 AM on 29 March 2010
        The human fingerprint in global warming
        Actually, the production of CO2 and consequent reduction of atmospheric oxygen has been balanced a bit by loss of O2 from the oceans into the atmosphere. I typed "per meg" into google and found this website by Michael Bender at Princeton, and here's part of the explanation (scroll down past the nice figures to the bottom): "1 per meg = 0.001‰ using the standard stable isotope terminology. For reference, the amplitude of the annual cycle ranges up to about 80 per meg, and the annual decrease is about 20 per meg /yr. An error of 2.5 per meg in the rate of O2/N2 change translates to an uncertainty of ~ 1 Gt C/yr in the partitioning of CO2 sequestration."
121687. AstroHypercane2010 at 03:03 AM on 29 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        The soot that lands over Greenland from forest fires, industrial activity and burning methane clathrates and methane releases from permafrost fires in peatbogs and fires in tropical rainforests will likely speed up the melting of the ice, along with the melting of the Arctic ice cap which will leave more open ocean in the north of Greenland. When the ice melts, the greatest sea level rise will be seen near Nova Scotia, Boston and New York. At the current rate the sea level rise globally from Greenland will be 0.8 cm by 2020.
121688. shawnhet at 03:00 AM on 29 March 2010
        Is the science settled?
        Riccardo, I'm not sure what your point is, but obviously it is possible to increase WV in the atmosphere by *evaporation*, even if the temperature stays the same. However, since I am talking about condensation I am not talking about the temperature continually staying the same , but rather what happens when warm air cools. My point, is that when warm air of a given RH *cools* more water vapor is condensed than when cooler air of the same RH cools by the same amount. I will point you to the following page where you can do appropriate calculations to test this out. Relative humidity calculator Cheers, :)
121689. GFW at 02:44 AM on 29 March 2010
        The human fingerprint in global warming
        John R., It's pretty much straight up math for a decent estimate on the O2. We've increased CO2 by ~105ppm. But roughly an equal amount has been taken up by sinks, mostly the ocean. So we've used enough O2 to make ~210ppm CO2. So, one would figure we've decreased the concentration of O2 by ~210 ppm. John's chart shows a decrease of between 300 and 400, so I'm in the ballpark. Maybe John can explain the difference. It could be some other usage of O2, or a difference between ppm (by volume) and ppm (by count). As for how that affects the total amount of O2 available, not much. Air is 21% oxygen, so that's 210,000 ppm (again, not completely sure if that's by volume or count). So decrease relative to original value is 0.1 to 0.2 percent.
121690. Steve L at 02:34 AM on 29 March 2010
        The human fingerprint in global warming
        Agreeing with John Russell, the right axis on Fig 3 could use some explanation. Additionally, Fig 6a has a caption but Fig 6b doesn't (maybe self-explanatory). Your "eg" should be "ie" when explaining isotopes, no? Okay, enough nit-picking. Question: for anticipated solar effects on daytime and nighttime temperatures, are these model-based? I wonder if greater solar heating wouldn't generate more water vapour (greenhouse gas) that might then have the same apparent effect as expected for CO2. Could a similar comparison be done for winter versus summar, and would that also provide a useful fingerprint? Finally, I wonder if solar and CO2 forcings are simply predicted to have different effects spatially rather than temporally. Hmm, I notice that I'm asking questions about what models would predict under various scenarios. I always thought I agreed with your first statements about empirical results!
121691. John Russell at 01:52 AM on 29 March 2010
        The human fingerprint in global warming
        Brilliant post, John. One question from a non-scientist. I always used to worry that burning of all this fossil fuel would reduce the concentration of oxygen in the atmosphere. When I mentioned it to those more knowledgeable than me, they'd give me a metaphorical pat on the head and say, "there, there, don't worry". I'm sure they're right and we shouldn't be concerned -- about this, anyway -- but can you put those falling oxygen levels into context for us, in terms of relative concentrations in the atmosphere? It's the first time I've seen a scientist mention this particular anthropogenic effect.
121692. Riccardo at 19:45 PM on 28 March 2010
        Is the science settled?
        shawnhet, it all started here: "if we assumed that cloudiness increases proportionally with concentration of WV this would be a negative feedback." What i was pointing out is that, as a zeroth order aproximation, if relative humidity is constant on increasing temperature (the only possible way to increase WV concentration) you do not get this feedback, no matter what the actual concentration is. Conversely, it's true that you get an effect on precipitations and, maybe more important, on the energy flow through the system due to the increased latent heat exchange. This is the reason why in a warmer world we expect wet regions to become wetter and dry region dryer, and more frequent extreme events.
121693. shawnhet at 17:33 PM on 28 March 2010
        Is the science settled?
        Riccardo #107, I don't understand what you are trying to say. If we hold the RH constant but increase the temperature, then we have increased the absolute concentration of WV molecules in the air, right? Then, when the water in the air condenses more water molecules are available to form clouds and raindrops etc... than when the air was cooler. There are *not*, for instance, the same amount of water molecules available to form clouds and raindrops when the RH is 60% and temperature is 10C and cools to 9C as when the RH is 60%, temperature is 20C and cools to 19C. Chris, #108 yes, you're right. I mistyped in my previous post. The feedback on the warming has already happened, there may be further warming in the pipeline from the forcing that will then be fed back upon. Cheers, :)
121694. Doug Bostrom at 17:01 PM on 28 March 2010
        It's freaking cold!
        Muoncounter, it's a case of wheels within wheels. Not only are crypto-Communists trying to end our Western lifestyle by confiscating our incandescent lightbulbs, but at the same time the ruthless Canadians are extracting petroleum from tar sands, selling it to us Americans and then tricking us into burning it specifically so more C02 will be released, driving up temperatures, thus pushing the syrup industry north of the Canada-US border. They'll be selling that syrup back to us hungry, desperate pancake eaters later. It's a dastardly plot, one of many.
121695. Doug Bostrom at 16:49 PM on 28 March 2010
        Empirical evidence that humans are causing global warming
        climateresponse at 16:22 PM on 22 March, 2010 Well, here you are, after all, at a site dedicated to explanation of the topic. No need to complain! Your concern has also already been answered by a very excellent writer and scientist by the name of Dr. Spencer Weart. Do take a few hours to read his book The Discovery of Global Warming, published free to read on the Web.
121696. Tom Dayton at 16:21 PM on 28 March 2010
        Empirical evidence that humans are causing global warming
        gallopingcamel, one reason people get frustrated with you is that you ask questions or (more usually) make strong assertions without bothering to look for the answers with the tools built into this Skeptical Science site. In this case, you could have clicked the "View All Arguments..." link under the thermometer at the top left of every page, or typed "hockey stick" into the Search field. Either method quickly would have led you to the page Hockey stick is broken, where you would find a bunch of hockey stick graphs made from data having nothing to do with tree rings.
121697. Tom Dayton at 16:12 PM on 28 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        gallopingcamel, I'm glad you seem to mostly trust Dr. Archer's judgment about how long it takes for increased CO2 level to fall back to its original value. But note that I did not write "residence time" of CO2, nor "lifetime," because those terms are ambiguous and have been misinterpreted by "skeptics." What matters to climate is how long it takes for the total number of CO2 molecules in the air to drop from its increased value back to its pre-increased value. During that process, some individual molecules that were added by the initial event A (e.g., oil burning) are removed very quickly, but they are immediately replaced by other molecules from sources other than event A (e.g., the ocean). When the latter swap happens, the total number of molecules does not decrease. So the "residence time" or "lifetime" of an individual CO2 molecule is irrelevant. What matters is how long it takes for the total number of molecules to decrease. That was explained briefly by Chemist Dr. Doug Mackie in his Question and Answer 1. More details and references (including links to full text for most of them) are in the caption of the Global Warming Art image Carbon Dioxide Residence Time. What the IPCC "and others" actually wrote is not "35 to 100 years assumed by the IPCC and others" as you asserted. Their actual statements are extracted as snippets, with links to the full texts, by Dr. Lisa Moore in her post Greenhouse Gases: How Long Do They Last?" Additional links to papers by Archer, Solomon, and others are on the Global Warming Links page here on the Skeptical Science site, in the Links for "CO2 Has a Short Residence Time" page. (That skeptic argument does not yet have its own, full page, so it appears only in the Links page, which you can get to via the "Links" link in the blue horizontal bar at the top of every Skeptical Science page.)
121698. gallopingcamel at 16:04 PM on 28 March 2010
        Empirical evidence that humans are causing global warming
        There is little doubt that the burning of fossil fuels by humanity has caused concentrations of CO2 in Earth's atmosphere to rise. The graph of CO2 concentration versus time is a "Hockey Stick". Can anyone show that global temperatures over the last 1,000 years correlate with the CO2 concentrations without using tree ring temperature proxies?
121699. gallopingcamel at 15:08 PM on 28 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        Phillipe (#67) and Tom (#68). Thanks for the links. I have not been able to access the Berger & Loutre paper so I have been reading everything I can find from David Archer and his various collaborators. Considering the huge implications of these papers it is surprising that there has been so little coverage in the media. If these folks are right: 1. It is already too late to prevent the Greenland ice cap from collapsing. 2. Mankind has the power to delay the next Ice Age almost indefinitely. From my perspective this is wonderful news. Maybe that is why it has been ignored by the "Main Stream Media". One of the worst things about being a sceptic is that you distrust the good news as much as the bad news, so I tried to pick holes in Archer's case. Archer's main planks are: A. CO2 is a dominant driver of global temperature. B. CO2 residence time in the atmosphere is orders of magnitude longer than the 35 to 100 years assumed by the IPCC and others. It is not likely that we will agree on point "A" so let's look at the CO2 residence time issue. Archer is a chemist so it was no surprise that I cannot fault his arguments relating to ocean absorption and the weathering of silicate rocks. The complexities of the various models he mentions (CLIMBER etc.) are way beyond my pay grade. Hopefully, Berenyi Peter will be able to comment. There appears to be a carbon sequestration process with a short time constant that Archer & Co may have overlooked. As my lab shares a car park with the folks running the relevant experiment, I forgot about chasing gamma rays for long enough to find out what my tree hugger colleagues have been up to. Take a look at the FACE experiment: http://c-h2oecology.env.duke.edu/site/face.html My hypothesis is that plant growth will accelerate as CO2 concentrations rise, thereby sequestering carbon rapidly (decadal time constant). If true, this effect would overwhelm the longer term processes described by Archer et al. Unfortunately (from my point of view), the FACE experiment is inconclusive. The trees exposed to CO2 at levels predicted for 2050 did grow very rapidly for several years but then slowed down owing to lack of nutrients (primarily nitrogen). Your comments would be appreciated.
121700. muoncounter at 08:19 AM on 28 March 2010
        It's freaking cold!
        On the lighter side: Since we had such a cold winter in North America, there was an uptick in the 'all that snow means global warming doesn't exist' hysteria. Bet we won't here much about this: "It’s on the calendar. It’s widely advertised. This year, everybody knows about it but the trees. And they are the central characters in Vermont’s annual maple syrup open house this weekend, when tourists descend on the state to watch trees being tapped and sap being boiled. Sugaring season ended early for many syrup farmers in southern Vermont, sabotaged by unseasonably warm weather." NY Times, 27 March 2010 (http://www.nytimes.com/2010/03/27/us/27syrup.html)

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