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Comments 121701 to 121750:

  1. Is the science settled?
    shawnhet at 06:42 AM on 28 March, 2010 My point was directed to folks who might think that WV feedback on the forcing we've already added was yet to happen. That's not quite right. As you indicate we've had the water vapour feedback on the warming that's occurred so far. However since we haven't yet had all the warming that will eventually result from the forcing we've already added, there is still some water vapour feedback to accrue as a reult of the current forcing.
  2. Is the science settled?
    shawnhet, if you hold the temperature fixed there's no way to vary WV. In all practical purposes we can safely assume that it is in equilibrium at the given temperature. If you let the temperature increase, instead, you'll get increasing concentration at constant relative humidity.
  3. Is the science settled?
    Riccardo:it's not concentration that matters for your argument, it's relative humidity. Also consider that precipitations counteract, or limit, cloudiness increase; the water in the rain drops must come from somewhere after all. Well, obviously, the RH and the concentration of WV are inseparable at a given temperature, but IAC, it is the concentration that matters. It takes a certain number of water molecules to make a raindrop or a cloud. Thus, if everything else is equal we would expect more raindrops and clouds to form when air @ (for example) 15C cools by 1C, than if air @ 14C cools by 1C. Your second sentence is possibly true, but I was going for the least possible assumptions in my "model" namely that everything stayed *proportionally* the same when WV went up. It is possible that increasing WV will cause precipitation to take place quicker which could potentially reduce the amount of clouds. This issue is too complicated for me to get into right now, but it is interesting. Ned:That's right; if we eliminated all other forcings then the water vapor feedback would settle at its new equilibrium level very rapidly. However, it seems likely that we'll keep emitting CO2 for some time now. The water vapor feedback will continue to increase as long as CO2 continues to increase, and it will persist as long as CO2-induced warming persists (i.e., thousands of years). I don't really disagree here, except maybe about the thousands of years. My point was directed to folks who might think that WV feedback on the forcing we've already added was yet to happen. Cheers, :)
  4. How we know global warming is happening, Part 2
    TH, Hansen's reference is a generic assesment: "We conclude that there has been no reduction in the global warming trend of 0.15-0.20°C/decade that began in the late 1970s.". I'd suggest to quantify the "divergence" you keep linking from woodfortrees if you do not trust my number for GISS and their own number for UAH.
  5. What CO2 level would cause the Greenland ice sheet to collapse?
    and i would add that accelerated ice loss appears to be spreading throughout northwest Greenland as a whole.
  6. How we know global warming is happening, Part 2
    Hansen is currently quoting 0.15-0.20 http://data.giss.nasa.gov/gistemp/paper/gistemp2010_draft0319.pdf The graph I linked shows the divergence between GISS and UAH.
  7. Is the science settled?
    fydijkstra at 23:02 PM on 27 March, 2010 Setting aside the “hot spot” point that has already been addressed ( Riccardo and Tom Dayton), there are a couple more points that could be addressed in your post fydijkstra: There is no high confidence that the warming in the last 30 years is exceptional, nor that anything in the pattern of warming in the last 200 years is closely related to the concentration of CO2. Since paleoanalysis indicates that the warming of the last 30 years is exceptional at least in the context of the last millennium and likely last two millennia, I don’t think your statement is supported by the science (see e.g. overlay of paleotemp reconstructions, and more recent paleoanalysis). Likewise, the pattern of warming is entirely consistent with the expected effects of enhanced [CO2], both in degree (see chris) and its nature (polar amplification; tropospheric warming associated with stratospheric cooling etc.). The relationship of the global temperature with patterns of ocean circulation is much better than the relationship with the CO2 concentration. That’s certainly incorrect. Analysis of ocean current contributions to 20th century warming indicates that these have made close to zero net contribution to warming over the last 100 years, and in fact reinforce the dominant role of enhanced greenhouse gas contributions ( Swanson et al (2009)[*] There is a lot of evidence, that the climate is much more complicated than could follow from the high understanding of heat trapping by CO2 alone. I don’t think anyone would say otherwise. That doesn’t negate the fact that we have rather high scientific certainty that raised greenhouse gas levels have dominated the Earth’s surface temperature rise during the last 100-150 years. [*]K.L. Swanson et al. (2009) Long term natural variability and 20th century climate change Proc. Natl. Acad. Sci. USA 106, 16120-16130
    (from the conclusions): This analysis indicates that natural contributions (largely ocean circulation variability) have had a significant effect on 20th century temperature variability. However the nett contribution to overall 20th century warming is close to zero. Essentially ocean circulation variability made a positive contribution to early (1900-1940) 20th century warming, a negative contribution to mid 20th century warming and a positive contribution to late 20th century warming. Once the natural variability is removed the externally forced (greenhouse) contribution is manifest as a continuous accelerating warming.
  8. How we know global warming is happening, Part 2
    TH, you quote strange number. UAH offically quote 0.132 °C/decade while from GISS annual averages I get 0.16 °C/decade. And UAH is only one of the two satelite datasets, RSS giving 0.15 °C/decade. I do not see much of a difference considering that they do not even measure the same thing.
  9. Is the science settled?
    Whoops….two of my links don’t work. They should be: R. Knutti and G. C. Hegerl (2008) The equilibrium sensitivity of the Earth's temperature to radiation changes Nature Geoscience 1, 735-743 Knutti and Hegerl (2008) and: Murphy DM et al. (2009) An observationally based energy balance for the Earth since 1950 J. Geophys. Res.114 art. #D17107 Murphy et al. (2009)
  10. How we know global warming is happening, Part 2
    Riccardo, GISS (1.7) does show a steeper trend than UAH (1.2) since 1979.
  11. How we know global warming is happening, Part 2
    TH, so you should deduce that my comment did not refer to your latest but to the second latest comment. More explicitly, i find a bit weird that "none of the mainstream skeptic sites dispute the satellite lower troposphere record" while questioning surface temperature datasets.
  12. Philippe Chantreau at 03:37 AM on 28 March 2010
    Guest post: scrutinising the 31,000 scientists in the OISM Petition Project
    The "guesses" of the modelers are educated by the underlying physics, chemistry etc. There is not that much variation among these guesses. Parameterizations are bounded and so are the changes resulting from different parameterizations. There is indeed a variety of GCMs, that's why IPCC takes into consideration the results of many runs for many models. However, GCMs do not show wildly different results and indeed allow to form projections within reasonable limits, so the end result is usable. It seems you're trying the tired old "skeptic" argument "we don't know for sure so we don't know at all," or something in that same vein. Disappointing from someone better informed and better reasoning than the run of the Watts' mill type of "skeptic."
  13. Is the science settled?
    Ken Lambert at 14:39 PM on 27 March, 2010 Yes O.K. Ken, but you’re really addressing a quantitative accounting that (a) we’re yet not in a position to determine (see discussion by Trenberth in the article under discussion), and (b) doesn’t really add or subtract from our present understanding of the Earth’s surface temperature sensitivity to enhanced radiative forcing. Of course, we could come up with some numbers that would accommodate a 3oC surface temperature rise (say) in response to a radiative forcing from doubling atmospheric [CO2] . But that wouldn’t take us any further than our present understanding of climate sensitivity which comes from many analyses of paleotemp/CO2 relationships (in which equilibrium responses are more likely to apply), and analyses of transient responses (e.g. to volcanic forcing). These indicate an Earth surface temperature response near 3 oC, with a range of 2-6 oC that is reasonably well-bounded at the low end and poorly bounded at the top end (see Knutti and Hegerl (2008) , for a review). On long timescales that allow slow ocean/ice sheet feedbacks the climate sensitivity might be larger than this (e.g. Lunt DJ et al. (2010)). Inspection of the temperature evolution/atmospheric CO2 levels during the last 150-odd years helps us quite a bit but also illustrates the nature of the uncertainty. So since the mid-19th century we’ve had around 0.8-0.9 oC of surface temperature rise, and [CO2] levels have gone up from around 286 ppm to 386 ppm. How might this translate into a climate sensitivity? Detailed quantitition is problematic since (i) the aerosol forcing which has certainly opposed some of the greenhouse-induced warming is poorly defined, and (ii) the climate-response time, particularly the very slow equilibration of the oceans to enhanced forcing, is not known with certainty. So we don’t know (i) if that 0.85 oC of warming (1850ish to now) would by 1 oC or 1.2oC or what, if we were to remove our atmospheric aerosols, and (ii) whether the current level of forcing will give us another 0.3 oC or 0.6 oC or what, of warming once the climate system has re-equilibrated with the forcing at some time in the future (multi-decadal timescale). We also have to account for non-greenhouse gas contributions to warming (v. likely these are small), and the fact that non-CO2 greenhouse contributions (methane, tropospheric ozone, N2O) need to be factored in. Can we say anything helpful? Well yes, we can look at the expected warming from various climate sensitivities [***] to determine the surface temperature rise expected from the enhanced [CO2]. For a climate sensitivity of 2oC (of surface warming per doubling of atmospheric [CO2]) this is around 0.85 oC at equilibrium (for a [CO2] increase from 286-386 ppm), and for a 3 oC sensitivity, ~1.25 oC of surface warming. Since we’ve already had 0.85 oC of warming without taking account the aerosol effect and the climate response time), it’s very unlikely that the climate sensitivity can be lower than 2 oC of warming per doubling of atmospheric CO2. A similar conclusion was recently obtained from an obviously (!) much more detailed analysis of the Earth’s energy balance since 1950 (Murphy et al. (2010) -------------------------------------------- [***] delta T = (ln([CO2]final/[CO2]start))*s/ln(2) where deltaT is the surface temperature change expected from a change in [CO2] from [CO2]start to [CO2]final in ppm, and s is the climate sensitivity in oC.
  14. How we know global warming is happening, Part 2
    Riccardo, I was referring to GISS and you responded with a comment that skeptics don't trust ground based measurements - when obviously I do.
  15. How we know global warming is happening, Part 2
    TH, there are not that many temperature datasets, you can take for granted that we all know them. P.S. a secular linear trend can be acceptable only when there's nothing more we can say on the parameter under study. This is definitely not the case for temperature and related forcings.
  16. Is the science settled?
    fydijkstra, regarding the "hot spot", see the Skeptical Science argument "There’s no tropospheric hot spot." Be sure to read the comment by jshore.
  17. What CO2 level would cause the Greenland ice sheet to collapse?
    It is worth noting the sensitivity of northern Greenland to the 400 ppm scenario. Think about the Petermann Glacier as an indicator of this. http://glacierchange.wordpress.com/2010/03/27/petermann-glacier/
  18. Antarctica is gaining ice
    I find it interesting too that as the land ice moves toward the sea, not only will there be less land ice, but it occurs to me that there is likely to be much more sea ice as well. Rather like a migration. Moves from here to there. At some point as that nasty green line becomes vertical, there is going to be a whole grunch of sea ice as no land ice remains to jump in.
  19. How we know global warming is happening, Part 2
    Riccardo, GISS is the surface record from Dr. Hansen. It shows 0.8C warming for the last 130 years, or 0.6C per century. http://www.woodfortrees.org/plot/gistemp/from:1880/plot/gistemp/from:1880/trend
  20. Is the science settled?
    shawnhet writes: WV feedback(whatever its magnitude or sign for all but the very recent *atmospheric* temperature changes has *already happened*. There may be some other temperature changes coming along "in the pipeline", but WV adjusts to a temperature change in a period of months or so. That's right; if we eliminated all other forcings then the water vapor feedback would settle at its new equilibrium level very rapidly. However, it seems likely that we'll keep emitting CO2 for some time now. The water vapor feedback will continue to increase as long as CO2 continues to increase, and it will persist as long as CO2-induced warming persists (i.e., thousands of years).
  21. Is the science settled?
    fydijkstra, I think a frequent logical misconception is to somehow separate a natural greenhouse warming from AGW (although this manoeuvre may well be justified or even indispensable in a political debate). Just consider a noisy recorder output from any experimental measurement. If you take the baseline for granted, you can of zoom into the graph, focus on the noisy ups and downs and complain that nobody will ever be able to predict the future. Zoom out to get the whole picture. The more GHGs, the warmer. That's it. BTW, Ned, chris, the discussion on WV, feedbacks that run away and those that won't was highly instructive.
  22. It warmed before 1940 when CO2 was low
    "Also, after a burst of volcanic activity in the late 18th century, there was a relative quiet volcanic period in the early 20th century." Did you mean 19th century for the former period?
    Response: Sorry, it's taken 11 months, several comments and an email before I got around to changing a single digit in the article above :-(
  23. Is the science settled?
    fydijkstra, when i see comments with kind of "randomly distributed" claims plus a few references i usually check. For example, Santer et al. 2008 do not say what you claim, just the opposite. Anyway, it's quite strange that the story of the so (inappropiately) called hot spot keeps flowing around us while a dusty shelf would be more appropiate. It's indeed a basic physical response of our atmosphere not GCM or AGW, not even a skeptic argument. Other claims are inconsistent as well, e.g. warming is not exceptional or no warming pattern related to CO2. Your comment looks more like a piece of propaganda than of climate science.
  24. Is the science settled?
    You are quite right, John! The science is settled, but some pieces of science are more settled than others. There is only one problem: the combination of all these relative uncertainties is unknown. The heat trapping effect of carbon dioxide is well understood, at least for a hypothetical planet without water and aerosols. The saturation of the heat trapping by CO2 at sea level is also well understood. The increased heat trapping by CO2 in the higher troposphere as predicted by the models, is well understood, but not empirically verified. Santer et al (Int. J. Clim. 28(2008), 1703-1722), could not find the hot spot, nor could Douglass et al, (Int J. Clim (2007) DOI: 10.1002/joc.1651) prove that the hot spot does not exist. The effect of heat trapping by CO2 on water vapour and clouds is poorly understood. The only possible conclusion is that the total effect of all these factors is not well understood. That question is settled, as long as no better understanding is available. There is high confidence that the global climate has been warming since about 1800, although the datasets (GISS, HadCRU) cannot be verified independently. There is no high confidence that the warming in the last 30 years is exceptional, nor that anything in the pattern of warming in the last 200 years is closely related to the concentration of CO2. The relationship of the global temperature with patterns of ocean circulation is much better than the relationship with the CO2 concentration. There is a lot of evidence, that the climate is much more complicated than could follow from the high understanding of heat trapping by CO2 alone. So we can try to cut CO2-emissions, but whether that has any effect on the global climate is fully unknown. Some pieces of science are less settled than others!
  25. Is the science settled?
    shawnhet, it's not concentration that matters for your argument, it's relative humidity. Also consider that precipitations counteract, or limit, cloudiness increase; the water in the rain drops must come from somewhere after all.
  26. How we know global warming is happening, Part 2
    Skeptics appears to believe in satellite data but do not draw the obvious conclusion. Surface stations are essentially in agreement with satellites so not so much "contaminations" can be present in the former, unless you accept that the surface has not warmed while the lower troposphere did.
  27. Is the science settled?
    Well, not the "entire" mechanism of course. Albedo changes scale the entire spectra relative to the S-B spectra, and any change in solar input dictates what "equilibrium" means. But right now greenhouse gasses are the dominant mechanism.
  28. Is the science settled?
    Ken L. What you're missing is that the way greenhouse gasses work is to "take a chunk out" of the S-B emission curve. The OLR at two different temperatures can only be related by (T1/T2)^4 if both emission spectra have the same shape relative to the ideal S-B spectrum. In this case, the entire mechanism by which the temperature is changed is a widening and deepening of the absorption lines so that, in equilibrium the OLR at the higher temperature but with more absorption lines is actually the same as it would be at the lower temperature and a pre-industrial atmosphere.
  29. What CO2 level would cause the Greenland ice sheet to collapse?
    My my... I find this site quite disturbing. I have been watching the ice move since 1999, when I first located information of its acceleration. I have been dismayed since that day to see all forecasts of ice ignore the acceleration factors and end up giving linear conclusions which do not fit the trend lines curving motions. However this is the first time I have seen evidence of the Eastern Ice Sheet becoming unstable. A fact I find unsettling. Likewise I find the curve posted. The green line does not appear to be interested in hanging around until the year 2100 from its appearance, but looks more interested in becoming vertical long before then. I am sorry to ask so simple a question, but I am a laymans layman, and your graphs beg the question: How long before the land ice becomes zero density and speed becomes maximum? To the eye it appears about 2022 to 2025 or so(ish). Its not just an issue of sea level rise at that point... but of splash as well. Information which should be understood and shared I would think.
  30. We're heading into an ice age
    Im glad you brought this up. I have heard argument in the area of the 'mini ice age'. The melting of the northern ice cap along with the melting of ice in Greenland to flood the northern sea with fresh water. The fresh water from the melting ice is lighter, and so tends to hug the surface, forcing the Gulf Stream lower and in the end, further east sooner. The bulk of heat from the Gulf Stream is left to transfer toward Europe then, as Canada finds itself cooling... and entering a miniature ice age whose duration is limited to centuries at most. Your comments on this general theory would be considered a rare light in an area I consider shadowed, and confusing at best. Im sorry for the lack of references. It has been many many years since I read of this odd theory and references are lost to time.
  31. gallopingcamel at 17:21 PM on 27 March 2010
    What CO2 level would cause the Greenland ice sheet to collapse?
    Tom Dayton (#68), The paper you referenced is new to me. The idea that the present inter glacial could extend for another 130,000 years is exciting to say the least (British understatement). If the paper is well founded there will be a sudden temperature rise of about six degrees Celsius. Such a rise would melt all the remaining major ice sheets in a century or two, increasing the planet's albedo and raising sea levels by 75 meters. As there will be no ice at either pole we will have emerged from the present Ice Age. Is that how you see it? Am I missing something?
  32. gallopingcamel at 16:57 PM on 27 March 2010
    What CO2 level would cause the Greenland ice sheet to collapse?
    Philippe Chantreau, (#67), Thanks. This is really good news. Let's hope they are right!
  33. How we know global warming is happening, Part 2
    GISS shows 0.8C warming since 1880. Not very scary, is it. http://www.woodfortrees.org/plot/gistemp/from:1880/plot/gistemp/from:1880/trend
  34. How we know global warming is happening, Part 2
    Tom, A lot of Cook's links are bogus. For example, the National Post article was just quoting Josh Willis at NASA who said ocean temperatures are declining. Take it up with NASA if you disagree. Once again, none of the mainstream skeptic sites dispute the satellite lower troposphere record. In fact Christy and Spencer are considered trusted sources there.
    Response: Here are a few links from Watts Up With That, which I believe you would characterise as a mainstream skeptic site, that we're now experiencing global cooling: The point here is that while the more credible global warming skeptics such as Lindzen or Spencer (eg - publishers of peer-reviewed research) don't deny global warming is happening, there are many skeptics who do. Just a few weeks ago at a family get-together, an uncle said to me "I hear a few scientists are saying it's been global cooling over the last few years". This is not restricted to crank uncles either. Several Australian federal politicians have been heard to express similar views that global cooling is now happening.

    So regardless of whether mainstream skeptic sites dispute that global warming is happening (and the above links indicate otherwise), the fact remains that many people are being persuaded that global cooling is happening. You haven't been misled by this argument and that's a credit to you. But people less informed than yourself are being misled by these falsehoods. This misconception cannot be left unchallenged.
  35. How we know global warming is happening, Part 2
    TH, see this list of links to blogs claiming either that satellites no warming in the past 30 years, or that any satellite evidence for warming has been faked: Links for 'Satellites show no warming in the troposphere'. I found that list the same way I already explained to you how I found the previous list. By the way, it's not nice to move goalposts. Originally you made the sweeping claim that ""No one doubts that the earth has warmed over the last 30 years." When I pointed you to a handy list of such doubts, you drastically narrowed your claim to only the satellite records.
  36. What CO2 level would cause the Greenland ice sheet to collapse?
    gallopingcamel wrote "Please tell me where you get the idea that we can look forward to '10s of thousands of years' before the next glaciation." Okay: Berger and Loutre (2002) explained why this interglacial could last 50,000 years past today. I found that article's citation easily, by entering "Milankovitch" in the Skeptical Science "Search" field at the top left of every page, which yielded several pages that explain all this.
  37. Philippe Chantreau at 15:46 PM on 27 March 2010
    What CO2 level would cause the Greenland ice sheet to collapse?
    Not really. http://www.nature.com/nature/journal/v429/n6992/full/429611a.html
  38. Is the science settled?
    A couple of points here in re: water vapor and its feedback. The primary thing to keep in mind about WV vis a vis CO2 is that WV condenses and precipitates out of the atmosphere. It is this fact that explains the partitioning of WV and lets us know where negative feedbacks associated with WV might come from. For instance, if we assumed that cloudiness increases proportionally with concentration of WV this would be a negative feedback. Likewise, if precipitation increased in proportion to the conc. of WV. Neither of these propositions is at all unlikely IMO. Finally, one should never forget that WV feedback(whatever its magnitude or sign for all but the very recent *atmospheric* temperature changes has *already happened*. There may be some other temperature changes coming along "in the pipeline", but WV adjusts to a temperature change in a period of months or so. Cheers, :)
  39. gallopingcamel at 15:20 PM on 27 March 2010
    What CO2 level would cause the Greenland ice sheet to collapse?
    Philippe Chantreau (#63), Here is NOAA's view on the last million years: http://www.ncdc.noaa.gov/paleo/ctl/clisci100k.html It looks as if the present warm temperatures are unusual. Much colder temperatures seem to dominate, so please tell me where you get the idea that we can look forward to "10s of thousands of years" before the next glaciation. I really hope you are right but the ice core record from Antarctica suggests that we are still in an Ice Age with short inter glacial periods.
  40. How we know global warming is happening, Part 2
    If you actually read any of the skeptics blogs, WUWT, Climate Audit, etc. you would know that Cook's claims are spurious. None of the writers dispute the 30 year satellite trend of 1.2C/century. http://wattsupwiththat.com/2010/03/05/february-uah-global-temperature-anomaly-little-change/ This argument is a straw man. You are arguing with yourself.
  41. How we know global warming is happening, Part 2
    TH wrote "No one doubts that the earth has warmed over the last 30 years." As Ned replied, in fact lots of people doubt it. You can see a partial list of links to public statements of doubt, on the "Links for 'It's Cooling' argument." You can see links to skeptic statements for all the arguments on this Skeptical Science site, in the "Global Warming Arguments, Sorted by Argument" page. An easy way to get there is to click the "Links" link in the blue horizontal bar at the top of every Skeptical Science page. For example, the "It's Cooling" branch of that tree page has a whole bunch of sub-branches that are more specific skeptic arguments, and each of those (if you click on them) has a similar page of links to pro- and con- public statements.
  42. Is the science settled?
    Ken Lambert writes: Let's have a result boys - the answer is the key to the whole AGW CO2 theory. Personally, I'm pretty comfortable with the range of climate sensitivities given in AR4 (2 to 4.5 C, with an expected value somewhere around 3 C). It seems unlikely to be far off in either direction and it's certainly the best estimate we have now.
  43. Is the science settled?
    To illustrate the point about positive feedbacks, here are graphs of two cases, one where f > 1 (resulting in a runaway increase) and one, like the real-world positive water vapor feedback, where 0 < f < 1, so that the temperature increase is bounded (2C in this case):
  44. Is the science settled?
    Chris #89 Obviously a 3degK rise is "the increase in the Earth's.........'equilibrium temperature'. So it's not obvious (to me anyhow!) what your "key" point actually is.... No Chris, a 3degK rise at the surface if it translates directly to the emitting temperature of the atmosphere will increase the OLR using the (Stefan) S-B equation as follows: Current OLR = 238.5W/sq.m, Pre-industrial OLR = 235.7 Current emitting temperature = 255degK Pre-industrial emitting temperature = 254.25 degK For a 3 degK rise in emitting temperature (above pre-industrial levels) the new OLR will be: (257.25/254.25)^4 x 235.7 = 247.0 W/sq.m. Rise in OLR is 247.0 - 235.7 = 11.3W/sq.m (11.3W/sq.m increase in outgoing longwave radiation) The rise in CO2 radiative forcing from doubling of CO2 to 560 ppmv from pre-industrial levels of 280 ppmv will be (using the IPCC Eqan) : 5.35ln(560/280) = 3.7W/sq.m Therefore to balance the CO2 radiative forcing of 3.7W/sq.m, the emitting temperature of the atmosphere only has to rise by (using inverted S-B) : (239.4/235.7)^0.25 x 255 = 255.995 degK - 255 = 1.0 degK You can do the numbers with slightly different OLR (aroung 240) and temperature (around 255) and get a very similar result. So for a 3 degK rise to be the result of CO2 doubling alone, there must be only a 1 degK rise in the emitting temperature of the atmosphere. The extra 2 degK difference in the rises must be in the increased greenhouse effect (complex feedbacks, back radiation etc etc) which is theroized due to increased CO2 and increased water vapour. While brings us to the critical effects of water vapour and CO2 - where BP #84 and Ned #86 are fighting it out. Let's have a result boys - the answer is the key to the whole AGW CO2 theory. (
  45. How you can support Skeptical Science
    Like Zero132132 in the above comment, I also stumbled a bit over the donation process. What sunk my first attempt was that you have to pick an amount (in that funny plastic Ozzie money ;) before the rest of the page will allow you to shift to country specific fields, like U.S. info. (And hey, other then what your bank card might charge for the conversion, it's a deal! An Ozzie $ only costs 0.90 cents U.S.) Thanks for this site, and your hard work, John.
  46. There's no empirical evidence
    kwoods01 writes: The information I would like to address is that greenhouse gases absorb only certain wavelength bands. Hence, there is a maximum amount of energy that can be absorbed out of the electromagnetic spectrum by the greenhouse gases. [...] with respect to CO2, there is a limit to the amount of radiative forcing that can occur. A couple of points. First, we're nowhere near saturation for CO2. Second, even if the atmosphere as a whole were saturated, CO2 would still be low enough in the upper atmosphere for OLR to escape even within the absorption bands. There are references to a number of papers about this on John's page Is the CO2 effect saturated? and much more discussion at RealClimate.
  47. How we know global warming is happening, Part 2
    TH writes: No one doubts that the earth has warmed over the last 30 years It would be nice if no one doubted that, but those of us who spend time browsing through the skeptic blogosphere have seen people make exactly that claim plenty of times. Likewise, people also question whether CO2 is actually increasing, whether humans are responsible for that increase, and whether there's any connection between CO2 and warming. Yes, all of those seem like illogical and easily answered questions, but many people do get confused on these points. Ameliorating that confusion is the reason for this site's existence. TH continues: Six years is not a particularly meaningful trend, and the real question is how much? There is no indication of catastrophic warming in this data. The point of this is not to extrapolate from a six-year trend. The point is to show that even during a period when the surface air temperature has been temporarily more or less flat, ocean heat content has continued to rise. I don't think anyone predicted catastrophe by 2010. Unfortunately the climate system and our economic system both have a great deal of inertia, so it's important to start making changes now so as to prevent catastrophe further down the road. Temperatures are rising slower than any IPCC scenario. The IPCC doesn't make six-year or eight-year predictions, because in any such period the trend will be obscured by normal interannual variability.
  48. There's no empirical evidence
    I'm really glad there is a site like this where we can have civilized discussions about this topic. The information I would like to address is that greenhouse gases absorb only certain wavelength bands. Hence, there is a maximum amount of energy that can be absorbed out of the electromagnetic spectrum by the greenhouse gases. This means that there is a concentration threshold for each gas whereby if the concentration increases, no more radiative forcing is possible for that gas. E.G. If you look at CFC-11 and HNO3 in the figure at the top of the page, their radiances in the bands of 850-900 cm^-1 are near zero. Therefore, increasing the concentration of HNO3 in the atmosphere will not affect radiative forcing anymore because there is no more radiation to absorb. Now don't get me wrong, I'm not saying increasing the concentration of chloroflourocarbons and nitric acid in the atmosphere has no maleffects. Acid rain and ozone depletion are two major problems with those pollutants, that is why they are regulated. But with respect to CO2, there is a limit to the amount of radiative forcing that can occur. Another note is that radiative forcing does not take into account the effects of clouds. If more energy is absorbed, more water will evaporate and convect to the upper atmosphere forming clouds that will reflect radiation. Looking at Ramanathan et al (Science 1989) "Cloud-Radiative Forcing and Climate: Results from the Earth Radiation Budget Experiment," the effect of clouds has a net radiative cooling effect. Hence, the direct correlation between a greenhouse gas increase and an increase in temperature is unfounded due to the radiative cooling of additional cloud cover. About the heat content increase graph, the comparison of 190,000 GW increase should not be compared to nuclear power plant outputs of 1 GW but rather of the amount of insolation hitting the earth from the sun of 160,000,000 GW. That is the correct normalizing parameter. I go into detail about this on the global warming page.
  49. How we know global warming is happening, Part 2
    This is the usual Cook straw man post. No one doubts that the earth has warmed over the last 30 years, and Dr. Roy Spencer has published graphs recently showing that at present the oceans are gaining heat. Six years is not a particularly meaningful trend, and the real question is how much? There is no indication of catastrophic warming in this data. Temperatures are rising slower than any IPCC scenario.
    Response: If only it were a straw man. I'm sure there are many skeptics that would concede that the earth is warming but only dispute that mankind is the cause. Others concede that humans are causing warming but the warming will not be catastrophic. However, there are also many who deny that global warming is happening at all. Thus "it's cooling" is the 4th most popular skeptic argument.

    While I would love to focus my energies on the more reasonable skeptic arguments, practicality dictates I also must pay attention to the most popular ones.
  50. It's not us
    What about stratospheric cooling? An increasing greenhouse effect means the surface and the troposphere should be warming, but the stratosphere should be cooling (because the troposphere is trapping more heat and stopping it from reaching the stratosphere). Satellite and weather balloon measurements indeed show a cooling trend in the stratosphere, the opposite of what would be expected if the Sun was causing global warming. And it looks like it isn’t caused by ozone depletion either.

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