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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.

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Comments 127051 to 127100:

  1. Comparing CO2 emissions to CO2 levels
    You DO need to include deforestation and other "land use" emissions, which are clearly not present in your dataset. Note that your curve shows some rise of atmospheric CO2 in the 18th-19th century before industrial emissions became strong. This is due to the deforestation of North America and other regions. All this is well covered by the work of William Ruddiman (for references, look him up in Wikipedia). By the way, Ruddiman's work is even more important for cumulative methane emissions.
  2. How do we know CO2 is causing warming?
    @Henry Pool I'm a little bit confused by what you call the cooling effect of CO2. Do you refer to the part of the radiation that is re-emitted toward space after absorption? If this is what you mean, the point is that the process of absorption and re-emission happens through the whole atmosphere, true, but at very different temperatures and pressures going from the surface up. At some point (altitude), the radiation will escape to space and it's the temperature and pressure at this point that matters for the energy balance.
  3. What does past climate change tell us?
    @RSVP "What I dont understand is how the "non-skeptics" somehow think it is possible to lower CO2 contamination without addressing population growth and the other sources of global warming?" If i get your thoght right, i think you should focus a little bit more. Given that poor people emit enormously less CO2 than rich, the question should be how can they improve their condition without a catastrophic increase of GHGs? This point is made clear and addressed in the UNDP Human Development Report 2008. This little step will change the view that the problem is population by itself, the raw number. And also again underline that the problem is global as global has to be the solution.
  4. What does past climate change tell us?
    Reply to HumanityRules I am in agreement with you, which I will explain, however, you have confused my point with content added by "Response". In fact it was "cbrock" who originally cites Monbiot. I agree with you in that I do not see Monbiot as being correct in, as you imply, holding up some of the worst living conditions as the way forward. On the contrary, my assessment is that the only viable solution is to work on curbing population. What I dont understand is how the "non-skeptics" somehow think it is possible to lower CO2 contamination without addressing population growth and the other sources of global warming?? What do they think got the CO2 contamination to these levels in the first place? And to be quibbling about who exactly is responsible is hypocritical when you consider the extended influence of the globalized economy. Aside from CO2, isnt it clear that there is no energy delivery system that does not pollute heat directly in some form or another, starting with nuclear energy??? Example http://en.wikipedia.org/wiki/Heat_engine And getting real... behind every solar cell, there is a automobile in a chip plant parking lot used everyday for a 25 mile commute. Behind every wind farm, there are trucks (as you read this) used in transport and maintenance burning diesel. ETC. Getting back to my original point. I wasnt addressing man-made global warming. I was referring to the historical data that indicates potential for global warming or cooling whether man-made or not. And the fact that so many people live on the fringes of habitable terrain. ------------------------ By the way, in the news yesterday, an AP article terms greenhouse gasses as "global-warming gases"... fait accompli. http://www.google.com/hostednews/ap/article/ALeqM5jZFyOvC-Hn8ZRKlbw2eJKukIRmHAD9BFKLT00
  5. What does past climate change tell us?
    @ RSVP You include this "Monbiot: "A paper published yesterday in the journal Environment and Urbanization shows that the places where population has been growing fastest are those in which carbon dioxide has been growing most slowly, and vice versa. Between 1980 and 2005, for example, Sub-Saharan Africa produced 18.5% of the world’s population growth and just 2.4% of the growth in CO2. North America turned out 4% of the extra people, but 14% of the extra emissions." I'm not sure what point you are trying to make. That population can expand ith limited impact on CO2 levels? Sub-Saharan Africa has just about the worst living condition for human being than any place on earth. Life expectancy, child mortality, education, infrastructure I could go on and on and on. It seems you (or more accurately Monbiot) are holding these people up as examples to us all. You want all of us to have quality of life similar to sub-saharan africans? I'd prefer to fight for an improvement in their quality of life and the inevitable increase in their carbon footprint than champion extreme poverty as some way forward. Unpleasant decadence from privileged western liberals
    Response: The point is to address the argument that it's increasing population that is causing increasing CO2 emissions. On the contrary, the cause is over-consumption more than over-population. If we're going to hit CO2 emissions, best to be pointing in the right direction.
  6. What does past climate change tell us?
    There seems to be a leap in this article that is unexplained and leaving me confused. Many things can absorb the suns energy and many things can reflect the suns energy and maybe the amount of energy from the sun can vary. And maybe the way processes (currents, continents, winds) move that energy around the global alters things. You show an equation, very sciencey. Then make the comment "The most common way of describing climate sensitivity is how much global temperature would change if CO2 is doubled." and from then on it seems everything is explainable by CO2 levels. I don't get that last jump. Just because some people simplify the process down to CO2 levels doesn't mean that CO2 is the main cause. Or have other factors been corrected for? How would you know albedo, volcanic activity, cloud cover, ocean currents etc for this whole period? Few other things. 1) So there was a Medieval Warm Period? Because I thought this was expunged from history by Mann as an inconvinient truth. 2) "Hegerl 2006 looks at global temperatures spanning both periods, using 4 different temperature reconstructions." Isn't it northern semishpere temperature not global temperature in that publication?
    Response: In its most fundamental terms, climate sensitivity means "if climate experienced a radiative forcing of 3.7 Wm-2, global temperatures would rise 3°C". This is the case whether the radiative forcing came from CO2, methane, solar variations, changes in albedo, etc. Or more accurately, all those factors added together.

    CO2 is not the only driver of climate. When you add them all together, then you have the net radiative forcing that is driving climate. I've gone back and tweaked the wording of that paragraph, hopefully clarifying the language somewhat. In fact, I'm currently working on a post coincidentally titled "CO2 is not the only driver of climate" :-)

    The main controversy with the Medieval Warming Period is whether it was global or a regional phenomenon. However, bickering over how widespread the MWP was underlies the irony of arguing about past climate change. If, as skeptics say, the MWP was a global phenomenon and temperature change was greater than currently thought, that would mean climate is more sensitive than previously thought. Hence the climate reaction to current CO2 radiative forcing would be even larger.

    Re Hergerl 2006, you're right, it did use NH reconstructions, not global. Thanks for spotting that, I've updated the post.
  7. Alberta Clipper at 15:22 PM on 22 October 2009
    How do we know CO2 is causing warming?
    Co2 is not CO2. Co2 is molecular cobalt (Co). Why didn't the moderator pick up on that?
  8. How do we know CO2 is causing warming?
    It appears no one ever seemed to have come up with the thought that carbon dioxide also causes cooling. I did not receive an answer to my question at post 67.perhaps I still get an answer. But I doubt it. It seems everyone forgot to look at the cooling aspect. In my view, especially with CO2, the way for radiation from the top to the bottom is the same as for the bottom to the top because the CO2 is almost 100%diffused into the air, so this question is and must be relevant. Why did no one ask it before? The cooling does not happen just in the upper air, it happens anywhere. I am busy carefully analyzing the graphs that I posted at 67, and all in all, it looks to me pretty much evens up, In other words: the cooling effect might in fact be just as much as the warming effect. If you enlarge it big enough you will notice that there are a few small gaps caused in the sun’s radiation which is due in part to the two absorptions of carbon dioxide between 2 and 3 um. It seems to me that the spectral intensity at the 4-5 um absorption is pretty much the same for both the sun and earth, although it is probably not on the same scale. But let us say this cancels each other out, more or less. It seems there is a small corner of radiation not being emitted by earth due to the CO2 absorption, at 14 um. (note that water is also absorbing here). This is the warming effect. Without someone doing some experimental testing, I think it will be difficult to quantify which is the biggest: the cooling or the warming. But if you ask me, it looks to me that the nett effect is or will be close to zero
  9. Philippe Chantreau at 11:04 AM on 22 October 2009
    How do we know CO2 is causing warming?
    TS, all the science used by the IPCC is done "outside" of the organization. You say you like the science papers presented in this site. Did it occur to you that most of them are part of the body of science used by the IPCC in its work?
  10. How we know global warming is still happening
    Chris, are you really unaware that there is substantial debate in how much natural contribution there has been to warming over the last century? What was the temperature increase from 1800-1900? IAC, I'll give a very simple argument here. The PDO shift which happens every 30 or so years has been claimed by many people to be able to cancel out the current rate of global warming, which means that the current rate of GW should be approx. equal to the cooling rate of a negative PDO(and, by extension the warming rate of a positive PDO). From that logic, we had two warming PDOs and one cooling one btw 1900-2000, we end up with PDO shift accounting for btw 0.2-0.25 C of your 0.8-0.9C in the last hundred years. If you then add your **separate** heating of 0.1C you reference above, you end up reasonably close to my 0.5C. Cheers, :)
  11. How we know global warming is still happening
    Not really Shawnhet. You can't just make things up according to your preference. The attribution of natural contributions to 20th century warming has been addressed empirically and analytically and simply doesn't accord with your unattributed assertions. You really need to address the science; we do notice when you try to sneak completely unfounded assertions into your messages! So for example the most recent analyses of natural and anthropogenic contributions to 20th century warming indicate that very little was from natural variation. J. L. Lean and D. H. Rind (2008) How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006 Geophys. Res. Lett. 35, L18701 Which indicates that the natural contribution to warming in the period 1889-2006 was around 0.12 oC (0.002oC per decade ENSO; -0.001 pd volcanic; 0.007 pd solar). Nothing like your hopeful guess of 50%! A similar conclusion results from the recent analysis of Schmidt and Benestad: Benestad RE and Schmidt GA (2009) Solar trends and global warming J. Geophys. Res. 114, D14101 who determine a solar contribution of 7% for 20th century warming with a slight cooling contribution since 1980, in line with quite a bit of other research on this subject. And while natural variations resulted in significant modulation of 20th century warming its nett contribution was near zero (around 0.1 oC or less): Swanson KL, Sugihara G, Tsonis AA (2009) Long-term natural variability and 20th century climate change Proc. Natl. Acad. Sci. USA 106, 16120-16123 And so on. The science simply doesn’t support your assertions shawnhet, and so your arguments about climate sensitivity are based on a false premise (or wishful thinking perhaps). Notice that your comment about where we are with respect to forcing from doubling of CO2 is not relevant without considering the inertias in the climate system that delay the full temperature response to that forcing. The abundant data on climate sensitivity that indicates a sensitivity near 3 oC per doubling is consistent with the major anthropogenic warming of the 20th century, as indicated by attribution studies as I’ve just indicated, and with modelling which has been rather successful in predicting the greenhouse-induced warming since the mid-1980’s. In fact the modelling is actually consistent with a climate sensitivity somewhat higher than 3 oC. J. Hansen et al. (2006) Global temperature change Proc. Natl. Acad. Sci. USA 103, 14288-14293 If the science from a number of different methodologies indicates that the climate sensitivity is near 3 oC, I don’t think one can gainsay this by unattributed assertions and argumentation that is demonstrably incorrect. It’s best to address the science on these issues. R. Knutti and G. C. Hegerl (2008) The equilibrium sensitivity of the Earth's temperature to radiation changes Nature Geoscience 1, 735-743
  12. The growing divide between climate scientists and public opinion
    The most convincing book i've read is 'without the hot air' by david j mackay. its on line free http://www.withouthotair.com/ but i bought it after reading one chapter. it focuses on how much energy everyone uses (rather than climate change) and how much energy is available renewables / nuclear / fossil fuels, it really focus's the mind on the reality of humankind's predicament whether forced by climate change or declining fossil fuels. it is an example of how to make something huge and complicated understandable. no surprise david mackay has recently been appointed as chief scientist at the (British) department of Energy and Climate Change (http://news.bbc.co.uk/1/hi/sci/tech/8283909.stm). Politicians must be relieved to have a scientist able to summarise the reality of what is going on. brilliant. puts other scientists, journalists and politicians to shame. i'm not saying the content is not to be challenged - it is the method of delivery. numbers not adjectives!
  13. What does past climate change tell us?
    Chris:"1. The sub-set of tide guage measurements he used show a marked modulation with the solar cycle that isn't seen in the globally averaged sea level analysis. The fact that the satellite measure is short doesn’t discount the fact that it doesn’t show the marked solar cycle modulation; after all one only needs the satellite measures through one solar cycle to assess whether the globally averaged sea level shows the marked solar cycle modulation seen in the sub-set of continental margin-biased records…it doesn’t. The data is in the Church et al. reference I cited above – see their Figure 3." Ok, well I haven't read the original Douglas paper, so I can't really comment here at the moment, perhaps you are right and they are improperly chosen for the purpose. As to the Church paper and the lack of solar cycle trend: Are you just eyeballing it and guess-timating or do you have an actual reference here? I think drawing this conclusion is much more complicated than that. 3. The third problem also relates to the OHC (ocean heat content) measures. Shaviv has to apply a number of corrections to remove “noise” like ENSO modulation of upper OHC, and after all of the corrections are made the correlation with the solar cycle is low as he states (see (2) above). What Shaviv doesn’t seem to have done is to remove the influence of volcanic eruptions, which is important in analyzing solar cycle related effects on OHC since for two of the 5 cycles (or 6; it’s not clear from Shaviv’s paper) analyzed, the volcanic forcing happens to be in phase with the solar cycle. This will produce a spurious “amplification” of any apparent solar effects that is not, in fact, related to solar effects. This has been pointed out by Lean and Rind in their recent analysis of attributions to 20th century warming (see section 4 on page 4 of their paper): Thanks for this. It does appear to be a flaw in Shaviv's paper. It would be interesting to see it redone with volcanic corrections made(if in fact they weren't done). IAC, I still tend to think that the amplification factor will still be there when appropriate adjustments were made. It is pretty clear the solar signal has been much more strongly evident in its climate effects than its raw forcing value might suggest. It is pretty hard to imagine Herschel in 1801 being able to detect 0.1% change in solar radiation if that's all there was to it. Cheers, :)
  14. How do we know CO2 is causing warming?
    Philippe Chantreau, "This statement by Truth Seeker: "I have found the UN to be a horribly corrupt organization" is totally meaningless and bad rethoric ... How relevant is it?" It is relevant in that I don't accept IPCC (UN) as being an organization of Scientist, rather they are a political organization (and a relatively corrupt one at that) with policy agenda. Their call for action has my highest suspicions, and I look to real science (done outside of this organization) for evidence of the truth. The thing I like about this site is that most of the arguments and evidence I find here meet that qualification.
    Response: If you read the IPCC reports, you'll see they're basically just a summary of all the peer reviewed scientific literature. It reads like a science textbook (a rather dry one) and its conclusions are conservative. I often use the AR4 as a starting point to lead me to what papers are out there. I strongly recommend reading the IPCC Fourth Assessment Report - you will learn a lot about all the research that's out there.
  15. How do we know CO2 is causing warming?
    Steve L, you made the comment "but for one theory to supplant another, it must explain/predict more than the incumbent theory." This is true, however usually theory's have a basic ability to predict. I have seen much with regards to the correlation between Temperature and CO2, but the predictions on how temperature will change with increasing CO2 concentrations have been horribly in accurate. So, until the temperature / co2 models get some degree of credibility, it's difficult to accept the premises that CO2 is the culprit for the increase in temps.
  16. How we know global warming is still happening
    Chris, sure if you only look at things from your POV, then they will appear to line up, the way you have outlined them. However, there are other ways of analyzing the evidence, I don't really like addressing the same points on two different threads so I will leave most of your post there. "(iii) we've had around 0.8-0.9 oC of warming during the last 100 years. That's entirely consistent with a climate sensitivity near 3 oC of warming per doubling of atmospheric CO2, and it's rather difficult to take seriously your notion that we might have "only ~0.5C of anthropogenic warming over the next century" with a negative cloud feedback. After all where has this supposed "negative cloud feedback" been for the last 100 years?" We may have had 0.8-0.9C of warming over the last 100 years, but some of that has probably been due to natural fluctuations. The increase up to 1940 is pretty close to the increase since 1940. It is therefore pretty reasonable to say that somewhere around 1/2 of the total increase was natural. That brings the amount of anthropogenic increase up around the 0.5C mark which is pretty much consistent with a no net feedback response to CO2 forcing, which is basically my opinion. "(iv) We've already seen that we don't need a positive cloud feedback to give us well over 2 oC of warming during rhe next 100 years, and that there isn't any evidence of a negative cloud feedback." In fact, I think that if most GCMs included negative cloud feedback the sensitivity to a CO2 doubling would be under the 2.0C mark. see here. (Don't forget that we are already ~ halfway to a forcing from double CO2). ftp://eos.atmos.washington.edu/pub/breth/papers/2006/SPGRL.pdf For the record, I haven't been able to get past the paywall on the Clements paper. It looks interesting, but I have a suspicion that it treats all variation to clouds as a feedback and doesn't allow for the possibility that cloudiness can be independently forced(which would obviously have temperature effects). Cheers, :)
  17. How do we know CO2 is causing warming?
    John, I still have some questions regarding you response to TP100 [ Response: Theory says more CO2 will trap more heat leading to global warming. Now we have observations that quantitatively confirm this. I think you have done a good job of this, but I haven't seen solid indication of the magnitude of impact (how much temperature increase can we expect with the next incremental increase in ppm concentration.) This is important to the debate, because policy is being decided based on very "scary" scenarios that this magnitude is great, but I haven't seen any science on this.
  18. What does past climate change tell us?
    Yes there's a number of reasons for being skeptical of Shaviv's study that you cite, shawnet: 1. The sub-set of tide guage measurements he used show a marked modulation with the solar cycle that isn't seen in the globally averaged sea level analysis. The fact that the satellite measure is short doesn’t discount the fact that it doesn’t show the marked solar cycle modulation; after all one only needs the satellite measures through one solar cycle to assess whether the globally averaged sea level shows the marked solar cycle modulation seen in the sub-set of continental margin-biased records…it doesn’t. The data is in the Church et al. reference I cited above – see their Figure 3. 2. This obviously leads to a problem with this measure of apparent “amplification”, and has a knock on effect with the rest of the analyses, since if this part of the analysis is likely wrong due to the bias described in (1), the agreement with the other analyses suggests that the others might also be spurious. This is particularly the case considering the fact that Shaviv’s apparent “correlations” between ocean heat content (OHC) and solar cycle is poor. So in fact the tide guage analysis actually plays a dominant role in Shaviv’s paper. As Shaviv states (see section 3.2): “Given the relatively small correlation coefficient and modest significance, it is worthwhile to corroborate the existence of the large heat flux variations using an independent data set. We thus turn to analyze tide gauge data measuring sea-level variations.” And: “Note that the relatively low correlation coefficient between the OHC and solar signals may seem somewhat suspicious” (page 10) 3. The third problem also relates to the OHC (ocean heat content) measures. Shaviv has to apply a number of corrections to remove “noise” like ENSO modulation of upper OHC, and after all of the corrections are made the correlation with the solar cycle is low as he states (see (2) above). What Shaviv doesn’t seem to have done is to remove the influence of volcanic eruptions, which is important in analyzing solar cycle related effects on OHC since for two of the 5 cycles (or 6; it’s not clear from Shaviv’s paper) analyzed, the volcanic forcing happens to be in phase with the solar cycle. This will produce a spurious “amplification” of any apparent solar effects that is not, in fact, related to solar effects. This has been pointed out by Lean and Rind in their recent analysis of attributions to 20th century warming (see section 4 on page 4 of their paper): J. L. Lean and D. H. Rind (2008) How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006 Geophys. Res. Lett. 35, L18701
  19. What does past climate change tell us?
    Chris:"Whether or not the warming effect of solar activity is "amplified" or is "increased by a positive feedback" is immaterial to the question of climate sensitivity, unless one considers that there is something "special" about the forcing from solar activity that doesn't apply to other forcings." Well, clearly there is a lot different about solar activity than other sorts of forcings. Solar energy heats the oceans directly, it is composed of many different wavelengths of energy and it is correlated with other phenomena. IAC, in this context an amplification means an increased forcing. "And one has to be a little careful in taking Shaviv's analysis at face value, due, amongst other things, to his selection of data sets. For example much of his analysis is based on a set of tide guage records of Douglas (1997), which shows a marked cyclic variation of local sea level that matches the solar cycle. However, this doesn't match the globally averaged sea level variation, especially the satellite-derived record which doesn’t show a marked variation with the solar cycle" Well, given that the tide guage data set is only one of three that demonstrate the same basic magnitude of solar cycle response, the totality of the date is fairly suggestive. IAC, do you have a reference for your claim that the satellite measurements don't show a marked solar cycle response? It does not appear to be the Church reference. and regardless, satellite measurements of sea level seem much too short to reach such a conclusion(less than two complete solar cycles along with a likely PDO regime shift since satellite measurement began). You potentially make a good point about placement of the tide guages though. Cheers, :)
  20. Philippe Chantreau at 03:19 AM on 22 October 2009
    How do we know CO2 is causing warming?
    Henry pool, from the way you wprd it, I can't be sure, but I believe that what you're describing is mainly seen in the stratosphere. I recall that the Iacono and Clough (1995) paper is considered a seminal paper on the subject.
  21. What does past climate change tell us?
    cbrock I just read Monbiot's essay. It is a bit off topic because I was not focussing on CO2. I was implying that the negative effects of Global Warming or and Ice Age (whether man-made or not, and whether the time scale for disaster is 100, 1000, or 10,000 years) seem to indicate that there is less habitable space than one might initially suppose. In other words, even if mankind were able to supress absolutely all forms of pollution (which is nearly impossible), the natural fluctuations of global temperatures would at some point catch up with us and eat away many of the areas of the Earth that are now inhabited. It is easier to imagine (although maybe I am too optimistic here) human migrations on a less populated planet than one that is maxed-out as is the current situation. Please see: http://en.wikipedia.org/wiki/Waterworld for further reference.
  22. dopeydoctorjohn at 01:51 AM on 22 October 2009
    The growing divide between climate scientists and public opinion
    I discussed on the "there is no consensus" debate that the Doran paper comes to an invalid conclusion comparing the earth scientists views to that of the general public because the question asked of the earth scientists in the Doran survey was substantially different to the question asked of the general public in the Gallup poll. Undoubtedly most scientists in the field agree with the current dominant paradigm. Undoubtedly some do not. Sometimes the majority are wrong; but usually not. However, the Doran study is seriously flawed and tries to exaggerate the degree of consensus that exists. Because it does this clumsily and amateurishly, and is easily exposed with a little further research and thought, it actually undermines (rather than firms) belief in the consensus. There must be better "consensus" papers around than this. Regarding the extent to which there is a cultural dimension to science, I believe Kuhn's work was highly influential and some of the posters might like to have a look at it http://en.wikipedia.org/wiki/The_Structure_of_Scientific_Revolutions
  23. What does past climate change tell us?
    At the risk of moving a bit off-topic, I'll respond to RSVP: I think you are right that in the long term, human population is a huge concern regarding all sorts of environmental abuse and resource consumption. But for now, let's put the blame firmly where it belongs: in the hands of the industrialized societies, whose extreme per capita consumption has led to the current situation with greenhouse gases and the measured temperature increases to date and the potential increases to come. An interesting, if perhaps overwrought, discussion of this issue can be found on George Monbiot's site at http://www.monbiot.com/archives/2009/09/29/the-population-myth/. While most population increases are occurring in the less-developed nations, it is the industrialized nations, and the growth-at-all-costs economic model that we have espoused, that have led to the current levels of greenhouse gases in the atmosphere.
  24. What does past climate change tell us?
    I am dizzy. So the logic goes that since climate is demonstrably susceptible to change, it is easy for humans to affect change. Furthermore, by correlating the recent temperature rise with a doubling of CO2, it is possible to deduce the leverage and scale of this influence. '''''''''''''''''''''' Getting practical How productive is it to be focussing on a symptom, when the real cause and problem is overpopulation? You wouldnt have as much CO2 to begin with if there were simply less people around. Anyone bother to correlate CO2 with population growth? Curbing population will not only lower CO2 emissions, it will also give people a chance for surviving (and with less pain) the fall out of global warming. I'm sure the CO2 proponents admit that CO2 is not the only man-made factor that is contributing to global warming. And again, even if GW were completely caused by nature, the remedy for humans would be the same. Decrease population.
    Response: To answer your first section:
    1. "since climate is demonstrably susceptible to change, it is easy for humans to affect change" - well, I don't know if it's easy, we have to work pretty hard to send 29 gigatonnes of CO2 into the atmosphere every year. But the basic point is true - past climate change shows how sensitive climate is to radiative forcing - therefore it will be sensitive to the radiative forcing from CO2
    2. "by correlating the recent temperature rise with a doubling of CO2, it is possible to deduce the leverage and scale of this influence" - no, not the case. We deduce the scale of CO2 influence by calculating the radiative forcing from CO2. This is worked out using line-by-line radiative transfer codes. This result is then verified by direct observations of satellites and surface measurements which quantify the amount of longwave radiation that CO2 has sent back to the Earth's surface.
    "Has anyone bothered to correlate CO2 with population growth?" Yes, in fact, to quote Monbiot: "A paper published yesterday in the journal Environment and Urbanization shows that the places where population has been growing fastest are those in which carbon dioxide has been growing most slowly, and vice versa. Between 1980 and 2005, for example, Sub-Saharan Africa produced 18.5% of the world’s population growth and just 2.4% of the growth in CO2. North America turned out 4% of the extra people, but 14% of the extra emissions."
  25. Antarctica is gaining ice
    Seriously? A graph from 2002? That's just silly. By moving the range a couple points in either direction you could get a trend going any way you want. Meanwhile, there's a 20-year graph that confirms Antarctica appears to be gaining mass: http://www.gsfc.nasa.gov/topstory/20020820southseaice.html
    Response: Note: the rebuttal above has been updated since this comment was posted, incorporating later references and clarifying that sea ice and land ice are two separate phenomena. Antarctica is losing land ice at an accelerating rate. Sea ice around Antarctica is increasing. The reasons for sea ice increasing in a warming Southern Ocean are complex and described in detail above.
  26. How we know global warming is still happening
    re #73 That doesn't accord with the evidence Shawnwt, in at least four different ways: (i) Remember that most of the estimates of climate sensitivity are empirical, based on phenomenological analysis of climate responses in the past (e.g. during ice age cycles or from paleoCO2/climate responses duing the deeper past). Thus any cloud response is implicitly included in the analysis. The best estimate of a climate sensitivity near 3 oC (plus/minus a bit) incorporates all feedbacks/amplifications (except very slow ice sheet responses and methane release feedbacks). R. Knutti and G. C. Hegerl The equilibrium sensitivity of the Earth's temperature to radiation changes Nature Geoscience 1, 735-743 (ii) The evidence is reasonably good that the direct resonse to a doubling of CO2 (around 1 oC) is amplified to around 2 oC by the water vapour feedback, and therefore the "neutral" situation without extra amplifications would give us more than 2 oC of warming over preindistrial levels during the next century at current rates of CO2 emissions. With albedo feedbacks that will be larger still (let alone any large feedbacks from greatly accelerated release of methane from clathrates or tundra). (iii) we've had around 0.8-0.9 oC of warming during the last 100 years. That's entirely consistent with a climate sensitivity near 3 oC of warming per doubling of atmospheric CO2, and it's rather difficult to take seriously your notion that we might have "only ~0.5C of anthropogenic warming over the next century" with a negative cloud feedback. After all where has this supposed "negative cloud feedback" been for the last 100 years? (iv) We've already seen that we don't need a positive cloud feedback to give us well over 2 oC of warming during rhe next 100 years, and that there isn't any evidence of a negative cloud feedback. Is there evidence of a positive cloud feedback? yes: A. C. Clement et al. (2009) Observational and Model Evidence for Positive Low-Level Cloud Feedback Science 325, 460 – 464
  27. What does past climate change tell us?
    re #4 Whether or not the warming effect of solar activity is "amplified" or is "increased by a positive feedback" is immaterial to the question of climate sensitivity, unless one considers that there is something "special" about the forcing from solar activity that doesn't apply to other forcings. We’ve already seen, for example, that there is evidence for a positive cloud feedback (call it an “amplification” if you like!) as a result of radiative-forcing-induced ocean warming: A. C. Clement et al. (2009) Observational and Model Evidence for Positive Low-Level Cloud Feedback Science 325, 460 – 464 And one has to be a little careful in taking Shaviv's analysis at face value, due, amongst other things, to his selection of data sets. For example much of his analysis is based on a set of tide guage records of Douglas (1997), which shows a marked cyclic variation of local sea level that matches the solar cycle. However, this doesn't match the globally averaged sea level variation, especially the satellite-derived record which doesn’t show a marked variation with the solar cycle; e.g.: Church JA, White NJ, Aarup T, et al. (2008) Understanding global sea levels: past, present and future Sustainability Sci. 3, 9-22. It’s proposed that the tide guage measures, many of which are close to continental margins, have solar forcings magnified by more rapid warming/cooling in shallow waters, and that this amplifies the amplitudes of responses to forcings by a factor of 2-3 relative to the globally averaged response. So Shaviv’s use of this data to determine a radiative forcing from sea level response may well be erroneous (greatly overestimated) by that sort of factor. Whatever the origin of the discrepancy between tide guage measures and satellite measures with respect to amplitudes of response to solar cycles, I suspect that Shaviv’s analysis will be found to be a rather marked overestimation of the solar cycle response and his required “amplification”.
  28. What does past climate change tell us?
    The climate sensitivity has been introduced to allow comparison between different forcing. Given a starting condition, it can be considered the same for all forcings essentially because you average both anomaly and forcing over space and time. The only exception i'm aware of is the Galactic Cosmic Rays feedback that works only for the sun forcing. (Incidentally, this explains why many sceptics are stuck to the beloved GCR). The logical consequence is that if you try to explain the trend with just one forcing you need a larger sensitivity (amplification factor). But if you put back all the forcings, everything's screwed up; this last step is too often missing.
  29. Comparing CO2 emissions to CO2 levels
    Alexandre, during a rather obsessive period a couple of years ago, I investigated some of Jaworowski's claims concerning ice core CO2 measures, and wrote the following in another cotext, which I've re-edited in response to your question (apols for the long post): I’m looking at his piece written supposedly for a US Senate Committee hearing (you can probably find this, but I don’t like linking to this sort of rubbish). Here’s a summary of the essential points that Jaworowski makes with respect to ice-core data: 1.Physical processes and technical problems mean that the data is incorrect as a representation of true CO2 levels 2.ice core records show an inverse correlation between load pressure (ice weight) and CO2 levels (his Fig 1a) (in other words deeper ice has CO2 "squeezed” out of it by the ice load above and this is reflected in the ice-core record) 3. ad hoc assumptions are used to “normalize” trapped gas age with the direct atmospheric CO2 measurement (his Fig 1b) 4. stomata frequency of fossil leaves indicate CO2 levels significantly higher than direct measurement of trapped CO2 in ice cores 1. Physical processes/technical problems These are (according to Jaworowski): -the presence of liquid water in the ice -the formation of gas hydrates (or clathrates) -drilling contaminates these with drilling fluid -drilling decompression causes cracks through which gas escapes Notice that these are generalized problems; Jaworowski, doesn’t indicate that any particular studies have any particular problems but infers that these in general negate the validity of ice core data. Notice also that Jaworowski refers to rather old data (the Siple core is from 1980). So let’s have a look at something a bit more modern and see how Jaworowski’s problems are dealt with: Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn; DM Etheridge et al J. Geophys. Res. 101, 4115-4128 (1996) These authors drilled three cores at Law Dome Antarctica to obtain a 1000 year record of CO2 (this is the data in Figure 1 (green line) of John Cook's top article): ice melt: Etheridge et al show that regions of ice melt are readily identified in the cores. They say “At most five melt layers, less than 1 cm thick, were identified in each of the DE08 cores, and even fewer in DSS” [n.b. the DE08 core was 234 metres deep; the DE08-2 243 metres; the DSS 1200 metres]. clathrates: Etheridge et al say “no clathrates were observed in any of the cores, which is consistent with the dissociation relation with temperature and pressure [Miller 1969]” drilling problems: Etheridge specifically take note of the potential problems of stress cracks caused by certain drilling methods and of fluid contamination, by drilling each of the three cores using a separate coring method: they say: “The drilling methods used were thermal, electrochemical and fluid-immersed electrochemical for DE08, DE-082 and DSS, respectively. This allowed a useful confirmation that the ice core CO2 was not influenced by effects such as ice heating during thermal drilling or the presence of drill fluid or stress cracks (occasionally caused by thermal or electrochemical coring and subsequent pressure release after removal from the ice sheet).” Since the data from the three cores overlap and the equivalent data match, the problems that Jaworowski highlight simply don’t apply. He's insinuated problems that don't, in reality, exist. 2. Ice core data show an inverse correlation. Jaworowski is looking at very early ice core data (like that from Siple in his Figure 1A) and saying “hey, the deeper you go, the lower the CO2 levels. It must just be an effect of pressure." This is foolishly false, especially in light of the 100,000’s of year ice core record where the trapped CO2 levels range up and down in cycles that match the glacial cycle, with CO2 levels around 280 ppm in interglacial periods and 180 ppm in interglacials. Even looking at the CO2 record from Etheridge et al shows that this inverse correlation is fictitious (Figure 1 in John Cook's top summary). Going back in history the CO2 concentration levels off to a steadyish level between the late 1700’s back to around 1600, when it rises again. The period from around 1600 forward to around 1800 is the period known as “The Little Ice Age” with quite a lot of independent evidence for a coldish period certainly in the N. Hemisphere. 3. Ad hoc asumptions are used to normalize the ice core gas “age” with respect to the real age. This is completely false. Going back to Etheridge et al, their normalization of gas age with respect to ice age was determined analytically. Notice that this normalization is necessary, since there is a significant period where air diffuses through the unpacked snow layer before the latter converts to ice and seals off the trapped gas. Thus the trapped gas is not only younger than the ice within which it is trapped, but pre-freezing diffusion averages out the atmospheric CO2 concentrations over a number of years (which can be very large in extremely deep ice cores). Without going into detail, it is known from previous work that a density of 0.8 gm per cubic cm is sufficient to effectively stop diffusion. This density was found at 72 metres in DE08; 72 metres in DE08-2 and 66 metres in DSS. Dating of the ice (by counting annual layers for several proxies like hydrogen peroxide that dispay clear seasonal cycles) indicates that these depths correspond to 40 years old, 40 years and 68 years. Measuring known diffusion rates indicates that the mean age of CO2 in the air at the sealing depths was 10 years in each case. Thus the air trapped in the ice was 30 years (DE08; DE08-2) or 58 years (DSS) younger than the ice age. 4. Stomatal frequency measures of ancient CO2. This is a fascinating insight into Jaworowski’s methods of misrepresenting the science in this area. Notice that his article goes to great lengths to insinuate problems associated with ice core data. He then says: “A study of stomatal frequency in fossil leaves from Holocene lake deposits in Denmark, showing that 9400 years ago CO2 atmospheric level was 333 ppmv, and 9600 years ago 348 ppmv, falsify the concept of stabilized and low CO2 air concentration until the advent of industrial revolution.” The assumption being, I’m sure you will agree, that stomatal frequency measures of CO2 in ancient times is a well-established, foolproof method. After all he’s stating that the measures of CO2 from stomatal frequency “trump” anything from ice-core data. That turns out to be an awesomely dishonest misrepresentation. Notice by the way, that there is nothing wrong with the science on stomatal frequency as a proxy for CO2 levels. It’s a science in relative infancy, and one that may make a very interesting contribution to the field. But the notion that this provides a valid measure of ancient CO2 levels has yet to be established. That’s clear from looking at the papers published within this specific field itself. The method relates to the way that plants respond to changing CO2 levels. It turns out that when CO2 levels go down they increase the stomatal aperature and increase the number of stomatal cells (and vice versa). These cells contain the pores that allow exchange of gases with the atmosphere. If you can calibrate some stomatal index (SI) with respect to CO2 levels then you might be able to use this as an indirect measure of CO2 levels. The procedure is complicated by the fact that the SI is species specific and assumptions have to be made about moisture levels and other factors that can indpendently affect SI. There seem to be two major groups doing these analyses. That of Visscher (Jaworowski’s stomatal index comments refer to his measures) and Rundgren and Beerling. The latter published a brief overview a few years ago: Fossil leaves: effective biomarkers of ancient CO2 levels? Rundgren M and Beerling D Geochem. [Geophys. Geosys. 4, 1-5 (2003)... in which they showed that their reconstruction of ancient CO2 levels tracked the ice core data very reliably during the entire last 6000 years. There was more variation during the previous years (back to 12,500 years ago) but CO2 levels from their SI measure never went above 290 ppm. They comment on ice-core data and Visscher’s data: “Other early Holocene and Lateglacial records [Wagner et al, 1999; McElain et al. 2002] have reproduced similar CO2 patterns, indicating self-consistency in the approach both between species and sites. Some stomatal-based records however have reconstructed atmospheric CO2 values higher (maximum 40 ppmv) than those obtained in ice core studies [Wagner et al 1999, McElwain et al, 2002; Wagner et al, 2002]. The overestimation in these studies may relate to the use of fossil leaf assemblages containing a mixture of closely-related species. Leaf SI responds to CO2 in a strongly species-specific manner [Royer et al, 2001; even closely-related species capable of hybridising with each other differ in their CO2 responsiveness[Rundgren and Bjork, 2003]. Additionally, studies involving fossil betula leaves may be compromised by developing calibration functions with trees of very restricted genotype diversity [Birks et al, 1999]” Likewise in another paper from the SI community: On the relationship between stomatal characters and atmospheric CO2, CD Reid et al Geophys Res Lett 30, 2003... ...the authors explore the SI index in relation to plants response times: they say: “We examined the phenotypic response of stomatal index (SI), density (SD) and aperature (AP) to rising atmospheric CO2 gradient (200 to 500 micromol per litre atmospheric CO2) at three Free Air CO2 Enrichment (FACE) sites. Along the CO2 gradient SI and SD showed no evidence of a decline to increasing CO2 while AP decreased slightly. ..Without evolutionary changes, SI and SD may not respond to atmospheric CO2 in the field and are unlikely to decrease in a future high [CO2] world.” So what does all this mean? It means that stomatal analysis of ancient fossil plants is a fascinating research area. But it surely also means that taking the results from one or two SI studies and suggesting that these completely negate the observations from ice-core data is a wilful bit of cheating, especially without stating that (i) much of the SI data actually matches the ice-core data and (ii) that even within the SI community it is clear that the issues of methodologies and analyses haven’t yet been normalized such that consistency in data can be achieved. After all if you're going to throw the book at ice-core methods with a vast list of problems (that in fact turn out to be generally overcome in modern studies), one might expect a critical approach to the SI data. SUMMARY: Jaworowski makes a negation of the ice-core data with a blanket dismissal based on every possible technical problem he can think of. He ignores the fact that these factors are considered carefully and overcome in modern coring studies. He misrepresents the methods of data analysis. And he then completely uncritically accepts the results from one or two studies from a field of indirect measures of CO2 levels based on stomatal indices in fossil plants, that is still sufficiently underdeveloped that the proponents themselves haven’t yet agreed on reliable methodologies.
  30. What does past climate change tell us?
    Just for the record, I think here is a contrary view, where solar activity is amplified(it is not increased by a positive feedback). http://www.friendsofscience.org/assets/documents/Shaviv-Ocean%20as%20calorimeter-solar%20forcing.pdf Using the oceans as a calorimeter to quantify the solar radiative forcing Nir J. Shaviv Over the 11-year solar cycle, small changes in the total solar irradiance (TSI) give riseto small variations in the global energy budget. It was suggested, however, that different mechanisms could amplify solar activity variations to give large climatic effects, a possibility which is still a subject of debate. With this in mind, we use the oceans as a calorimeter to measure the radiative forcing variations associated with the solar cycle. This is achieved through the study of three independent records, the net heat flux into the oceans over 5 decades, the sea-level change rate based on tide gauge records over the 20th century, and the sea-surface temperature variations. Each of the records can be used to consistently derive the same oceanic heat flux. We find that the total radiative forcing associated with solar cycles variations is about 5 to 7 times larger than just those associated with the TSI variations, thus implying the necessary existence of an amplification mechanism, although without pointing to which one. Cheers, :)
  31. Comparing CO2 emissions to CO2 levels
    Why might we be skeptical of Beck's weird data with its absolutely massive rapid jumps and falls in CO2? Here's some pretty obvious reasons for skepticism: (i) Beck assures us that the measures were precise (1-3%). But we're really more interested in their ACCURACY with respect to global atmospheric CO2 concentrations. We know that a large proportion of the measurements were made in individual scientists laboratories in cities (Paris, Kew gardens London, Belfast, Clermont Ferrand, Copenhagen, Vienna, Frankfurt, Giessen, Bern, Poona India, Rostock in Denmark, Ames Iowa...etc. etc. etc.). We know that if one goes to a city today and makes CO2 measurements in the air in our city laboratories, large variations in CO2 levels will be recorded, with high values relative to the true atmospheric concentrations. Just as in the 19th and early 20th century, we’re surrounded in cities by CO2 sources (pretty much all transport and heat/cooling generation). See for example point (ii) below. Competent scientists understand the essential difference between PRECISION and ACCURACY. A local CO2 measure may be beautifully precise but wildly inaccurate with respect to the global atmospheric CO2 value. That's where Becks "analysis" is likely to fool the unskeptical. (ii) We can look at this problem of accuracy in more detail by focusing on the individual series of measurements highlighted by Beck. For example, Beck highlights W. Kreutz’s series of very high CO2 measures in 1939/40. These measurements were made just S of the city of Giessen not far from the railway station. Beck fails to point out that Kreutz’s values differ by an astonishing 40 ppm between morning and afternoon (in other words measured atmospheric CO2 values are 40 ppm higher in the afternoons compared to the mornings), that atmospheric CO2 is much lower on windy days compared to windless days and so on. This is all outlined in Kreutz’s paper on the subject (translation available here: http://www.biokurs.de/treibhaus/literatur/kreutz/Kreutz_english.pdf Clearly atmospheric CO2 measurements in, or near, urban centres give massively high CO2 values however precisely they are measured, the CO2 levels will rise dramatically in the afternoons when everyone and their machines are active, and on windless days when generated CO2 isn’t dispersed, measured CO2 levels will be higher still. That’s all pretty obvious. A skeptic might be expected to notice these rather obvious facts…. It's fascinating that Kreutz identified and postulated that some of the high values and extreme variations in atmospheric CO2 levels in his measurements were due to soil sources and industrial sources...sadly, and rather typically, the data of the honest and competent Kreutz has been usurped to support a creepy agenda... (iii) It takes an effort to make truly accurate and unperturbed atmospheric CO2 measurements. Some early practitioners made this effort. Jules Reiset, for example, in the late 19th century, developed a methodology for CO2 measurements taken on the windy Atlantic coast, far from urban centres, and determined values rather similar to those measured in contemporaneous ice cores (around 190-200 ppm in the 1890’s). We can be rather more confident in the ACCURACY of Reiset’s measurements since he (unlike pretty much all other measurers of CO2 in the 19th and early 20th century) identified the clear signature of seasonal variation due to plant growth and decay dominated by the N. hemisphere flora. (iv) We have been observing atmospheric CO2 levels with extraordinary precision and accuracy since the late 1950’s from the Mauna Loa observatory, as well as dozens of other locations around the world. Atmospheric CO2 levels simply do not undergo massive jumps of up to 100 ppm over a few years. It beggers belief that CO2 sources could release and reabsorb extraordinarily massive amounts of CO2 (see (v) just below) during a period when we weren’t actually monitoring CO2 levels very well, and yet just when we started to monitor levels with considerable ACCURACY and PRECISION, atmospheric levels immediately stopped jumping around wildly. A skeptic would be inclined to doubt the accuracy of early measurements from urban centres. (v) According to Beck, atmospheric CO2 rose and fell with massive jumps/falls of around 100 ppm or more during the early and mid 19th century, and the 1930’s-40s’. Since the pre-industrial level of atmospheric CO2 (around 180 ppm) is rather similar to the entire repository of CO2 in terrestrial plantlife, the assumption is that these 100 ppm jumps/falls over a few years are associated with the rapid loss and regrowth of around half the entire plant biomass on earth? Did we really lose terrestrial plant matter equivalent to the entire Amazon and African rainforests and much of Asia during a few short years, and have these regrow again in a few years afterwards? No. We know this can’t have happened during the 1930’s and 40’s since we were monitoring the terrestrial biosphere already during these years. (vi) we have rather abundant ice core measures of atmospheric CO2. Since these measures of atmospheric CO2 locked within ice are in regions far from centres of CO2 sources (urban/plant growth) they are rather reliable measures of unperturbed and well-mixed atmospheric CO2. These show rather constant levels of atmospheric CO2 near 177 (+/- around 6 ppm) during the period from 1000 AD to the mid 19th century, and then slow gradual rises that merge in the late 1950’s with the directly measured Manua Loa and other modern CO2 measures. One can certainly argue that the ice core measures are averaged, since deposited snow in ice sheets doesn’t compact and trap ice for several years after deposition, such that there is exchange with the atmosphere for some time until the atmospheric sample becomes sealed within bubbles in solid ice. However one can’t really postulate massive rise of atmospheric CO2 apparently to value as high as 470 ppm during the late 1930’s and 1940’s, without some rising of ice core CO2 levels that match this time period. Even if the ice core CO2 values are averaged over several years, high CO2 values would have to appear for this period in the ice cores. They don’t. [*] [*] I wrote this last year for another context but it's appropriate in relation to Alexandre's question
  32. What does past climate change tell us?
    "Ironically, when skeptics cite past climate change, they're in fact invoking evidence for climate sensitivity and net positive feedback. Higher climate sensitivity means a larger climate response to CO2 forcing." In fact, "it's the Sun" skeptics tend to support the idea of a positive climate feedback because it's required to boost the impact of relatively weak solar forcing. Skeptics of the "Hockey Stick", claiming larger variance than all multi-proxy studies indicate, need an even stronger positive feedback to explain such variances with natural factors. Here is an example from Willie Soon, who believes reduced solar output will result in substantial global cooling (which hasn't happened yet despite a decade of solar activity trending down): "1. A reduced energy input from a dimmer sun will result in less heating of the oceans' surface, which would lead to less evaporation from the ocean surface. The result of this would be a decrease in water vapor, which is by far the earth's major greenhouse gas." Positive water vapor feedback - check "2. Less water vapor would result in a decrease in high cirrus clouds, which trap more heat than they reflect." Positive cloud feedback - check "3. A reduced energy input from the sun would equal less energy to bring water vapor high into the atmosphere, so more would end up collecting a few kilometers from the surface, resulting in more low clouds. Low clouds are much more effective at reflecting sunlight, which would produce a net cooling effect." Positive cloud feedback - check http://global-warming.accuweather.com/2009/04/plausible_scenarios_of_a_dimme.html Willie Soon is essentially supporting the idea of not only positive water vapor feedback but positive cloud feedback as well, with negative forcing leading to more reflective low clouds and less heat-trapping high clouds. One has to wonder, then, what Soon's complaint with the scientific consensus is? It seems then that he must then be disputing the direct forcing component of CO2, rather than the feedback that other skeptics generally dispute. Soon and Lindzen should debate the issue, perhaps at the "contrarian-only" Heartland Institute political conference. But that would violate their doctrine "speak no evil of other contrarians". Still, it would be nice to see two contrarians take turns calling each other "alarmists".
  33. What does past climate change tell us?
    The statement you have a problem with is really a no-brainer Mizimi. If the climate didn’t respond historically to changes in forcings it would have a very low sensitivity…..if it changed a lot it would have a high sensitivity. There’s nothing controversial about that. Of course that doesn’t mean that the climate sensitivity is “a fixed multiplier”. It likely varies a bit according to the position of the continents, ocean currents, whether or not the world has significant ice sheets etc. But we expect that the essential factors involving water vapour feedbacks to be rather constant and so don’t expect the climate sensitivity to vary that much between different epochs. The fact that climate sensitivity determined by analysis of temperature changrs involved in ice age cycles of the last several 100s of 1000’s of years, and that determined from analyzing the relationship between paleoCO2 and paleotemp proxies during the last several hundred millions of years, yields a similar climate sensitivity (around 3 oC of temperature rise per doubling of atmospheric CO2), tends towards that conclusion. In fact the long term climate sensitivity in our present world with lots of polar ice is likely somewhat larger (large albedo amplification) than during ice-free periods in the past. Past climate surely “shows” more warmer than colder phases. In any case your statement is a logical non sequitur….and what is a climate sensitivity “historically less than unity”??? The reason that the Earth had cold periods in the past is because the climate has a moderate to high sensitivity to changes in forcings. For example, the extended glacial periods of the Carboniferous were due to the sensitivity of the climate system to drops in atmospheric CO2. Climate sensitivity works in both the warming and cooling directions! A very significant reason why enhanced CO2 levels are particularly problematic now (apart from the fact that they’re racing upwards at a rapid rate), is that solar constant is much greater now than in the past (the sun shines around 4% more strongly now than 400 million years ago). So the absolute surface temperature with CO2 levels now are considerably greater than the surface temperature at the same CO2 levels then.
  34. What does past climate change tell us?
    "The greater climate has changed in the past, the greater the climate sensitivity." I have a problem with this statement. If T is a function of two variables, then a change in either variable causes T to change. Thus T is affected by changes in solar radiation ( from whatever effect) and by the way the planet system as a whole responds to/ influences such changes. In other words, climate sensitivity is never a fixed multiplier, but varies according to various physical, chemical and biological responses. Past climate change shows more colder than warmer phases, indicating climate sensitivity is historically less than unity; so should we not accept this as a reason to maintain ( or even enhance) CO2 levels?
  35. How we know global warming is still happening
    shawnhet, Temperatures will gradually rise in general at a rate of approximately 0.2C/decade, although that growth rate will not be linear just as it has never before been. This expectation DOES NOT include the effects of unleashing a positive feedback with carbon in the form of melting permafrost and methane clathrates which would exacerbate the situation considerably. So we can expect that by the time CO2 has doubled from 280ppm to 560ppm in the atmosphere, world average temperature will have risen by 2C-4.5C over pre-industrial times with the threat of even greater warming if frozen carbon is unleashed.
  36. How do we know CO2 is causing warming?
    I like your explanation but this study did not look at the cooling and weigh the warming and cooling effect of carbon dioxide against one another. Check this http://www.globalwarmingart.com/images/7/7c/Atmospheric_Transmission.png Note that some 30% of the sun's radiation is "absorbed" in the atmosphere, by ozone, oxygen, water and carbon dioxide. Most scientists think that this difference is what heats the atmosphere. I will admit that the aborption of photons may cause some heating but there is a limit to the number of photons that can be absorbed by a substance. The radiation is then re-emitted. I believe the larger amount of this 30% is re-emitted (the same principle as the greenhouse effect) and a large portin is reflected out from the atmosphere back into space. Did anybody of you ever thought of measuring the cooling effect of carbon dioxide? I want to know the nett effect.
  37. How we know global warming is still happening
    WeatherRusty:"If low cloud amount does increase due to a warmer more moist atmosphere so will the greenhouse effect of water vapor be increased. The increased water vapor must be in place first, so at best increased low cloudiness can reduce warming not negate it." The point is how much warming will we end up with? If cloud feedback canceled out other forms of feedback we might end up with only ~0.5C of anthropogenic warming over the next century, OTOH, if cloud feedback is strongly positive, then we might end up with as much as 2C in the next century. Cheers, :)
  38. How we know global warming is still happening
    Even if cloud amount is sensitive to other factors other than temperature variation, what is the point? What matters is if cloud amount is sensitive to a warming climate or changes in temperature since that is the factor humans are altering. Are there studies linking long term changes in cloud amount, both high and low cloudiness, to the warming trend of the past century? If GCR's impact on low cloud amount, we can do nothing about it. If we stick to the physics we know, there is no reason to expect a change in average relative humidity and there are already more than enough nucleation particles in the atmosphere upon which to condense water vapor to form clouds. If low cloud amount does increase due to a warmer more moist atmosphere so will the greenhouse effect of water vapor be increased. The increased water vapor must be in place first, so at best increased low cloudiness can reduce warming not negate it.
  39. It hasn't warmed since 1998
    FYI: the Murphy 2009 link right under the total-heat graph isn't working . . .
  40. It hasn't warmed since 1998
    I suggest that the fill-in color areas under the lines in the total heat-content graph be removed. As experts in the graphic display of quantitative information often point out, such filling-in encourages the reader to compare the magnitudes of the areas under the curves rather than the actual graphed quantities -- giving an impression of a difference between the two quantities (in this case) that is roughly proportional to the square of the actual difference. In other words, the fill-in colors amount to inadvertent exaggeration (technically, they encourage ambiguity about whether one is comparing the curves or their integrals). Why give denialist critics even the slightest toe-hold? Simplify the graph. Trust people to get it without the big splashes of color.
  41. It's cooling
    Thank you for a website that provides information without a political agenda. I would like to understand the global warming debate without feeling like I am being manipulated by someone with a political agenda and most web-sites seem to promote an agenda for one side or the other. Thanks.
  42. Empirical evidence that humans are causing global warming
    Robbo, I'm afraid I've let you waste my time (which I assume is your goal -- otherwise, why not link directly to the page you reference instead of to home pages?). You require monthly data to show that multidecadal cycles are responsible for long term trends? You deem my focus on the higher Arctic temperatures after 2000 (in response to your claim that post-1998 should be cooling) as being cherry picking, but you can go back and pick a couple of (less) warm years around 1940 and pretend those provide the proper context for our discussion of your claim? You fib and misrepresent things but say that you are morally constrained from betting? (Good one!) We haven't discussed odds, yet you're already to call it a sucker bet? (Goodbye.)
  43. Robbo the Yobbo at 09:44 AM on 20 October 2009
    Empirical evidence that humans are causing global warming
    Steve, The conclusions depend a great deal on whether you use monthly or annual averages. I always use monthly data because the annual data averages out the interesting peaks. Compare the 2 at Professor Ole Humlum's page. http://www.climate4you.com/ - polar temperature page. So really you are absolutely right about Arctic temperature - but everything needs to be seen in the appropriate context. The difference is a small example of claim and counter claim in a highly polarised debate - or non debate depending on your perspective. Are the differences scientifically meaningful? The answer to that is no. ‘Over most of the past century, the Arctic Oscillation alternated between its positive and negative phases. Starting in the 1970s, however, the oscillation has tended to stay in the positive phase, causing lower than normal arctic air pressure and higher than normal temperatures in much of the United States and northern Eurasia.’ http://nsidc.org/arcticmet/patterns/arctic_oscillation.html Yes I know I said that eyeballing was OK – but you need more context. These are very complex issues - you can’t do a quick Google and cheery pick items that seem to support some sort point or other. But look carefully at your Arctic temperature graph – the peak in the 1940’s is the result of multidecadal modulation of temperature in the Arctic. I am morally constrained from gambling with you on this – I think it is a sucker bet. Cheers Robert
  44. Empirical evidence that humans are causing global warming
    amplificate=amplify :P
  45. Empirical evidence that humans are causing global warming
    RSVP, "Ilustrative example???? Magnetism???? There is no point of any significance." What you do not understand or is poorly explained does not mean it has no significance. First, the electricity and magnetism analogy was not about global warming itself; read the original post on real climate to better understand. Second, i explained why it was an illustrative example. The shift is in 1970 but the fit in the figure starts in 1950; this was clearly done intentionally to amplificate the divergence between the fit and the data in the last decade. Again, look at the post on realclimate and try a fit yourself. The RC analogy is a good one. Although "it does not necessarily mean that the overall heat of the Earth has to increase", this is exactly what is being obeserved. If for example less heat is irradiated to space at night due to CO2 (increase of the RC constant), it certainly will warm. I'll say it explicitly one more time. Nowhere in the AGW theory it is excluded the very existence of fluctuation (more or less or not at all periodic). But they cancel out in the long run leaving a clear, detectable, measurable etc. upward trend.
  46. Empirical evidence that humans are causing global warming
    Riccardo, Since you mentioned electricity, I cant help comparing the idea of greenhouse gas heat capture to a circuit analog. A very simple RC circuit with a pulsed voltage source. That is, a resistor (representing CO2) in parallel with a capacitor (Earth). The voltage, a rounded square wave whose voltage changes on each pulse. The voltage would represent the heat left on the Earth in course of a day. Pulse off means night. Anyway, the output voltage would tend to zero during the off part of the pulse, but if R is too big, the voltage would not reach zero before the next pulse (sunrise). If you simulated Winter as many low voltage pulses, and Summer as many pulses with a higher voltage, you would see periods in which the output voltage would rise as heat is supposedly accumulating on the Earth. The point is to illustrate that just because the extra CO2 heat trapping vector has been added to "the GW mix", it does not necessarily mean that the overall heat of the Earth has to increase. Referring to the circuit model, the condition for this to occur requires that the voltage never gets to zero during the entire year (365 pulses later). In this analog, the values of R and C are critical. In the same way, the concentration of CO2 would also be critical to affect global warming, but up till now the only thing I have heard is that "more" is simply enough to raise the Earths temperature because it is causing an imbalance, when instead there might actually be a real critical value to trigger the real thing.
  47. Empirical evidence that humans are causing global warming
    Robbo (or Robert, if you prefer), re: #37. I note you've taken another step back from the Arctic cooling to a greater extent than the rest of the planet to, now, "My exact position is no warming for 20-30 years from 1998". Uhuh. Why not be more exact right away? I'm going to need you to be more exact if we're to find a bet, but for the purposes of discussion... See here: http://www.arctic.noaa.gov/reportcard/atmosphere.html Sorry for the low resolution Figure A1, but it looks like all years to 2007 (except maybe one) from 1998 have higher Arctic surface air temperatures than 1998. Hmmm. Maybe you define "Arctic" differently, or maybe you define "warming" differently than I do. Perhaps you think that the 10 years since 1998 are just noise. (But if so, then why pick 1998 rather than an average of a range of years?). Or maybe you'd prefer to look at sea ice extent instead of surface air temperatures -- oops, that doesn't support your assertion of cooling (er, not warming) from 1998, either. Well, you can see why your claim doesn't make much sense to me. But if you think that Arctic air temperatures or sea ice will show no evidence of warming relative to 1998, then please put up some money. My wife wants to renovate our apartment. Oh, also note Figure A5 in the above url and read the description: the early 1990s had strongly positive AO. This is incongruent with your claim that it was positive in the late 1970s and peaked in the late 1990s.
  48. CO2 effect is saturated
    GFW, as I understand it, Figure 1 shows outgoing radiation. Therefore, if the Earth has warmed, more radiation remains inside, i.e., less radiation goes out. Therefore, the net outgoing radiation must be below zero (less radiation going out, i.e. radiation that remains inside the atmosphere, in a transient radiative imbalance, until the earth warms enough as to "expel" again the same energy that comes in, going back to equilibrium (at zero) but with a higher temperature given that the greenhouse blanket is now thicker). In this graphic the different wavelengths are differenciated, so we can see which exact wavelengths are being trapped inside (those that are below zero), i.e. the exact wavelengths that are responsible for the warming inside. The rest of wavelengths escape to space the same as before (the components for those wavelengths have not changed, so the same energy goes in and out), and that's why they are at zero level. rlasker3, I think you are perfectly right. If the CO2 saturated, we woudn't see that runaway greenhouse effect in Venus.
  49. Robbo the Yobbo at 06:32 AM on 20 October 2009
    Empirical evidence that humans are causing global warming
    The 0.1 C/decade trend fits any period since the 1800's other than 1976 to 1998. Thompson et al reach the same conclusion on the underlying trend ~0.1 K/decade from 1950. Ilustrative example???? Magnetism???? There is no point of any significance.
  50. Empirical evidence that humans are causing global warming
    RSVP, first of all a quote from Swanson post in realclimate: "Electricity and magnetism are those forces of nature by which people who know nothing about electricity and magnetism can explain everything. Substitute the words “modes of natural climate variability” for “electricity and magnetism,” and well…, hopefully the point is made." That is to say that there are several patterns of roughly decadal climate variability of which we know very little. Their study is in its infancy and very interesting. But one thing can be said, in the long run they average out. Having said this, the shift apparently occured in the '70. If you fit a straight line from 1970 to 1997 you can easily see it nicely fits the last decade too. What Swanson shows is just an illustrative example. As for Thompson paper, they pull out the effect of known varibility (nothing spurious) and see what is left. And yes, as all the scientists do they were looking for something, the temperature trend cleaned up of the known variability. But the good news is that did it using no GCM, filtering, strange smoothing techniques, etc.

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