sunny starry skies

Hi Jethro, I'll have one last 'go' at your question. How much ice should be up there without AGW? It's a hypothetical question, as we don't have a world without AGW to experiment on, but here's my shot. My guess is as I put in my last reply, a bit more than was observed in the 1950s/1960s/1970s, and a good healthy dose of thick perennial ice that keeps the overall area of pack ice stable (by virtue of not allowing large amounts of open water to appear and trigger the dark water positive feedback). G-W's last post was an excellent description of that. My basis for that assessment - the forcing attribution studies would have a contribution of something like 0.2/0.3C to early 20th Century warming from solar activity. We should assume ENSO (as directionless) and volcanic to be as they were, and so the 0.2/0.3C forcing is all we'd have without AGW. Solar activity stabilised from the 1950s and has slightly declined towards present, but assume it's approximately where it was. There's no historical/empirical evidence of any internal oscillation large enough to remove the old perennial ice and therefore destabilise the multiyear pack. And so my guess is that to determine how much Arctic ice there should be without AGW, take the mid-20th Century values, and maybe add a small amount. That's essentially the whole Arctic basin covered with a decent proportion of thick multiyear ice. Ice outside the basin is easily prone to large fluctuations as it is much more mobile. How's that for my best guess, J? Hiya - I'm not sure of the numbers off the top of my head, but I think you're looking at as much as 50m in some of the fjords - enough to eliminate some very low coastal sites. There'll be papers around somewhere, and I may be well off with my estimate. Though my feeling is that there would be few settlements right at the coastline due to the mini-tsunami risk from passing icebergs. See this: http://www.geus.dk/publications/bull/nr14/nr14_p26-49_A1b.pdf - p46 for sea level near Disko Bay (north of the settlements). Also interesting to show ice advances since the MWP - much as in Iceland and Norway, you're generally looking at most at 1-2km laterally. G-W and Dev - for boats, they could go to 'Markland' (Labrador) for boat-building-sized trees, as well as having some supply from driftwood, and until near the end there were strong trade links with the rest of Europe (walrus ivory). In that way it's not like Easter Island at all. One bad winter doesn't wipe out a settlement - remember where these people came from (Iceland and Norway), and they have shown remarkable ability to adapt. Were one (or a few) bad winters enough to wipe them out they would certainly not have lasted 450 years. That's nearly as long as the time since Columbus! Longer/colder winters quite probably drove them to more heavily utilise the more secure food source of seals, but there's little reason to suggest it killed them (Diamond was speculating on old research). There's other reasons at least as plausible, and we know they were adaptable people. sss

YS, NSSC and Dev, I've worked with the original researchers on this one (Greenland), and there is no evidence to demonstrate (a) significant environmental degradation (in fact there is evidence for the opposite), or ( elimination due purely to climate. That was an out-dated idea which Diamond included in his book. More recent research shows this not to be the case. For example, homefields in Greenland were manured (improved) so as to be more productive - they are still visible, and some are used today. The land did not become "inhospitable" in the LIA - less productive may be a better phrase, with the adaptation being to take more seals, but the diet was not exclusively marine even at the end. There is no historical evidence to show "no ice" like you suggest Y.S. (if there is, I'd love to see it, as would many of my colleagues!). The diet of the Norse had little fish (you're right Dev), and had progressively more and more seals into the early LIA. Many of the seals were the Harp seals, which follow the drift ice in early summer. Oddly enough, Harp seals made up 40% of the seal catch as recorded in middens in the earliest pahse from Brattahlid, and >30% of seal bones in all sites in all periods since 1000 AD, indicating that far from there being "no ice" there was indeed sea ice present. This is one of many lines of evidence to show that ice conditions in the MWP in Greenland were likely to be at least comparable to today, and my guess based on the Eastern Settlement data is probably with more ice. Here's a sample reference on seals: http://www.nabohome.org/publications/labreports/Norsec34BrattahlidGreenland05.pdf Y.S., exactly what areas (settlements??) are covered by ice now that weren't in the MWP? If you can't provide some hard evidence I don't believe you. You do also appreciate that the MWP is very pronounced in Greenland and NW Europe, but that Greenland/NW Europe is not the world (Jean Grove's "The Little Ice Age" is an excellent book BTW)? And what does a warm MWP in Greenland/NW Europe tell you about conditions in Asia, Africa, the Pacific, America? Not much... Just like a cold winter in Europe, USA doesn't cover the fact that it was the warmest winter globally... Jethro, why don't you ask the original authors if you're that concerned? [and in case you think otherwise, I'm not suggesting you have strong opinions on their conclusions BTW] I think it's an irrelevant point, as Arctic sea ice change is merely seen as a response to greenhouse forcing, and therefore certainly is not a fundamental pillar of the science. The retreat was predicted and is one of many predictions to come true, as shown by 30 years of detailed data and scattered older data. It is doing exactly as predicted. It may have retreated at some stage in the distant past, but so far as modern Arctic exploration and monitoring goes, the retreat is unprecedented. Graphs reconstructed back to early this century show only a little more ice than in the 1970s/80s, and so if you want my guess, then that should be your non-AGW baseline. But whether it is unprecedented or not, does not matter (not to me, anyway). NSSC, your post is pure speculation, at odds with the physics of CO2 and our observations of the atmosphere (you do know the greenhouse effect has been observed?). As for water vapour, I'd like to know how you think there wouldn't be more water vapour in a warmer atmosphere! http://www.skepticalscience.com/water-vapor-greenhouse-gas.htm sss

Blimey, what a mess. P.P. - you're obfuscating big-time when you suggest there's no good data on Arctic sea ice. We have dramatic reductions in extent and volume. As G-W has pointed out, there's no indication that such reductions have happened in the last several thousand years. Here, I think, evidence such as small Canadian Arctic ice caps that are exposing rock only last uncovered thousands of years ago helps. Y.S., you've banged on about Greenland too much for me. There is absolutely no evidence that ice covers what were occupied settlements in Norse Greenland. If you think that, you're sorely deluded. The settlements remain, often with upstanding remains of walls and field systems. The climate back in Norse times, as now, was sufficiently good for them to keep cows and grow enough fodder for the winter. The Little Ice Age did not have the power expand the glaciers and ice sheet outlets into areas where people lived. Climate, contrary to popular belief, but not contrary to the latest science, may not have been the thing that wiped out the Norse - other reasonable explanations include the changing economy of the time and invasion of territory by Thule Inuit. The only destruction of settlements since then is likely to be from sea level rise, which has been considerable in this area. So Jethro, You've laid your argument out bare - yet there are still flaws in it. You're still after numbers which are not necessary. The article quotes, correctly, a volume of decline since the 1970s. This is based on whole-basin data and is reliable. The next statement saying this cannot be natural variation is what you don't like. High-lattude insolation should be driving to more extensive sea ice (if imperceptibly gradually at the present). Solar variations have flatlined (and recently declined) since the 1970s. Internal variations may contribute some of the change (such as winds helping the 2007 minimum be even lower than it would have been), but not a progressive collapse in thickness and extent. If they could do that, we'd expect to see evidence of such large variations within the age of exploration of the Arctic. We don't. Additionally, there's an excellent correlation between Arctic air temperature and sea ice loss - suggesting the driver is in the air, not the sea (my apologies - I looked at the graphs yesterday, but can't find wher they are). Air temperature rise in the Arctic is attributed to humans, and so sea ice loss is most likely driven by the same cause. The article is saying that there is no driver of Arctic sea ice that can be driving the progressive decline in area and volume. Oh, C-Bob, you can add Richard Alley (among hundreds of others) to your list of people that disagree with you on orbital forcing. And one paper suggesting an alternative is not exactly upsetting the applecart on that, rather irrelevant, score. Interesting graph this - shows how we have 20 yeas of relative stability with perhaps a slight decline, followed by a rapid decline in this decade, and the emergence in the last few years of an annual signal in the ice anomaly. This being anomaly and not extent, indicates that the winter allows a refreeze that is comparable in most years (anomaly closer to 0), then a summer collapse that is dramatically lower than previous years as the ice is so thin that it is easily melted out. Ice volume, just in case anyone's in any doubt, or has had the misfortune to read (yet) another cooked post at WUWT, is on a steep progressive downward slide. sss Pete, yup, that was as usual, supposition!

Hmmm, C-Bob, do I detect that you somehow don't believe that orbital forcing indicators would have us gradually heading towards the next ice age, without human intervention? That's a very bold statement and contrary to most of what we understand of past climate. Jethro, I do understand that you are after understanding where the current Arctic sea ice fits within past variation, but it's a very similar argument to the question on where global temperature fits within past variations. The premise seems to go like this: "X change must be beyond the bounds of natural variation before we attribute it to AGW." Yet it's a lame argument to make, as it gives no indication as to the cause of the variation, and ignore the valuable insight that palaeoclimate gives us, which is a measure of the sensitivity of the system. Global temperatures may have had some wiggles up/down with the MWP/LIA, and indeed were rather warmer ~6000 years ago. Does that mean we should take no notice of temperatures until they have surpassed the values of the mid-Holocene? Or the Eemian? Or the Pliocene?? No, of course not! The cause of temperature rise now is not the same as it was 1000 or 6000 years ago, and we know this because we can see the forcing happening, and we understand the cause now. We don't wait until the temperature change has passed some threshold, because we are not relying on some correlation, or identification of unusual temperature. We observe the greenhouse effect from the ground and from satellites, we observe the spatial pattern that tells us it's not the Sun (warm troposphere, cool stratosphere; day/night warming), we understand the radiative properties of the CO2 molecule and its effect on the absorbtion of IR radiation - this is enough to tell us that the cause is different and we should act now to slow our emissions. Same goes for sea ice. You want to know if the dramatic reduction in area and volume we are observing this decade is unprecedented, but it does not matter, so long as we understand the cause of the change. Arctic ice is behaving exactly as expected under present atmospheric conditions, that is, that it is trending to ever smaller areas and volumes throughout the period of full-coverage observations) hence adding some weight to the AGW theory. Whether it did a similar thing under a different set of past atmospheric conditions (or, say, high-latitude insolation) is irrelevant, as different causes can lead to the same result. It does not change the fact that the Arctic warming, ice sheet melt and sea ice loss supports the fact that the Arctic is warming faster than the rest of the globe, in line with what we expect with increased GHGs. If a palaeo record shows that the Arctic sea ice loss is unprecedented, or that seasonal ice has been observed before, what does that tell us? It tells us something about sensitivity of the Arctic sea ice, in the way that the MWP tells us about the sensitivity of global temperature change to forcing. We ought to hope that the present ice loss is unprecedented in the same way that we should hope that the many 'hockey sticks' of temperature are right.... it argues for a lower sensitivity, and less future warming/melting with the observed GHG forcing. But many "skeptics" would use high sea ice sensitivity/high past temperatures in completely the wrong way, not realising their folly! sss

I'm not quite sure what you're driving at there Jethro, and I'm not sure an answer exists that would satisfy you! We only have a few decades of sea ice extent data for the whole basin. There are longer historical records from specific locations (Newfoundland, Iceland etc), but not within the ocean itself. Your question relies heavily on what you term 'natural variation', and how long you are considering. Additionally, the long-term timeseies from sediment cores are most likely (I've not checked this btw) to record presence/absence of ice, and not thickness, probably due to variations in planktic foraminifera? If that's the case we'll never know what the palaeo-record of Arctic sea ice thickness is, though we might find more about the extent. So far, the reductions in both volume and extent are clearly unprecedented and have a direction (they are not apparently random variations, and not clearly tied to any other mechanism than AGW). Had, a mechanism such as the PDO been dominant, we should have seen at least one, probably two similar minima in thickness/extent in the last 100-150 years. We haven't. The decline of Arctic sea ice is one of the predictions of our theory of climate, but does not, by itself, confirm warming due to anthropogenic GHGs. When taken with the other evidence - direct observations of the enhanced greenhouse effect, specific spatial and temporal patterns of warming that confirm it's the GHGs doing it and not anything else, then the fact that we observe polar amplification as predicted means it's (in true IPCC-speak) very likely that the sea ice reduction is a consequence of AGW. In fact, it would be very remarkable if sea ice reduction was not occurring! sss

YS, I've been through the review process myself and so you're teaching a grannie to suck eggs on the review process. And seeing as you were incorrect about the quote, best to check your sources before mocking my reading of the literature! If you're so interested in reviewed literature, why do you spend so much time being concerned about one book by a climate skeptic (Taylor's Chill)? You, I'm sure, are aware that books do not go through the same review process as academic papers and so the information in them reflects the author's personal opinion, whether he believes in aliens, a flat earth, perpetual motion, or CO2 not being an effective greenhouse gas! I'm not interested in Peter Taylor's opinion, but am more interested in the peer-reviewed research. If you follow up the papers I referred to in my last post you'll see that Wild does not agree with your opinion on water vapour or on the climate sensitivity of clouds. It makes a lot more sense that the quote from Wild (which made it sound like he saw a large sensitivity due to clouds, contrary to his other research), was actually taken out of context by Peter Taylor in his book. When you look at the literature you see that the large cloud-induced forcing is not supported by observational evidence, hence why it did not make it into the AR4 summary. Wild states exactly that in the subsequent sentence in his 2005 paper, referring to literature that seriously cast the finding of a large cloud forcing in doubt. Y.S., by all means, defend Wild, research I agree with him, perhaps rather more than you think you do! Read the other references in my last post if you don't believe me. Apologies to others that the references are not, I think, free to view. As always in this debate, the most useful thing is to identify the originl sources, identify clearly the context in which a quote originates, and identify how this has survived in the literature subsequently. It's not an easy job, which is why so many lay climate scientists get it wrong (BTW, I'm not being personal here). sss Edit: SC, why do you always have to believe that data must be 'manipulated'? Implying dishonesty amongst a staggering range of researchers! Do you doubt that the Arctic has rather less ice than in recorded history? And in a related comment to above, if you doubt G-W's information because of the website it was on, then go to the source - find where the data originated, then identify problems with it.

You're confusing water vapour (present in clear air and a powerful greenhouse gas, though a feedback not a forcing) with condensed water droplets (clouds). I'm amused that you give Wild as a reference for water vapour not being a greenhouse gas as the Wild papers deal with global dimming masking the enhanced greenhouse effect until the 1980s. Water vapour is not mentioned in Wild et al 2005, and Wild would certainly disagree with you on the presence of the enhanced greenhouse effect! Wild is talking of how anthropogenic aerosols enhance cloudiness until the 1980s (and reduce transmissivity in clear skies), and the effect reversing after this time. The quote you have is from Wild et al (2005), but referring to data from Palle et al (2004). Palle et al's results are found to be erroneous by Wielicki et al (2005) who use CERES and MODIS results to show that Palle is in error. Consequently the variations seen by Palle are much too large, and in the wrong direction. There is no observed increase in cloudiness to account for the earthshine data used by Palle in the MODIS cloud data. Palle acknowledged that they were lacking alternative data than earthshine data. Wild acknowledges Wielicki's result when stating that the dramatic increase in albedo (the Palle result) is controversial, ie not verified and perhaps wrong. What it goes to show is that you can't rely on a single paper to prove your point, unless that paper has been verified or accepted by subsequent literature. And still no evidence for PDO being effective at producing a secular trend in global climate (as if an internal oscillation could...)! Your quote is from Wild et al (2005), not the IPCC, and does not include the context of Wild (and Wielicki), finding it unsupported by other data. sss

Well done Osmoposm, 0.0003 is 3 parts per 10,000, and I laughed seeing everyone agree on the wrong answer! (happens to us all...) The "there's not much in the atmosphere" fallacy: It's another common fallacy that many people fall into, believing that just because CO2 comprises 0.038% of our atmosphere it couldn't possibly have an effect. I think it comes down to people thinking of the greenhouse like a thick cosy blanket, which of course something so sparse couldn't be, right? But it's not to do with it being a cosy blanket, it's about optical depth, and these are two totally different things. Consider stratospheric ozone and ultraviolet rays - the concentration of stratospheric ozone is measured in parts per billion (~200-400ppb), which on our measure is 0.0000004 as a fraction of 1, or 0.00004%. Fortunately the optical depth of this very sparse gas is sufficient to protect us from UV radiation from the Sun. Is it so crazy to think that a gas that is 3 order of magnitude more prevalent by concentration (and mixed through the troposphere too) might be effective at intercepting radiation of a particular wavelength? http://chriscolose.w...fect-revisited/ The graphs on this page by Chris Colose are very nice at showing what happens to the longwave spectrum of emitted radiation when you add concentrations of CO2. The red curves on the graphs show the emitted spectrum as more and more CO2 is added. You see that the effect of adding just 2ppm to a CO2-free atmosphere is dramatic, and leads immediately to a 1.9C warming. The amount of intercepted radiation is shown by the dent in the red curve, reducing the total outgoing longwave radiation. The logarithmic decrease in the effect is visible as the rate at which the absorption bands saturate and broaden slows down as the concentration increases: No CO2 2ppm CO2 - immediate effect, 1.9C warming. 50ppm CO2, beginning of saturation, but bands still able to broaden so atmosphere not completely saturated. 390ppm CO2, modern concentration. Greenhouse effect slowing down w.r.t. CO2-free atmosphere due to the logarithmic effect, but producing something like ~1C/doubling as in all above cases. Add onto that the water vapour feedback, and the impact of gases with smaller concentration (e.g. CH4 and others) and you understand not only the impact of small concentrations, but why the concentration of CO2 has a lesser effect per tonnage/concentration increase than methane - methane is increasing from much smaller concentrations/less saturation so we can effect a 'doubling' much more easily, and so it is called a 'super-grenhouse gas' even though it is no more effective than CO2 at trapping IR radiation. All above figure created by Chris Colose from his linked page, using the MODTRAN atmospheric model. The last paragraph of his post relating to water vapour is well worth a read too. The enhanced greenhouse effect has been observed both from the ground and from satellites, with the changes occurring in the spectral signature bands of the GHGs, confirming that it is the human-produced greenhouse gases warming the Earth and not anything else. sss

Not sure what you mean about the MWP lacking credibility SC - it's perfectly real in the North Atlantic area, but just not really in a global sense. If it turns out to be real in the global sense, we should all be much more scared about how hot the world will get, as that would imply high climate sensitivity, which we are now forcing with GHGs. As for your accusation about me not reading the literature, maybe I could say the same of you? Point me to unrefuted scientific papers showing that AGW does not exist or is vastly overstated. The ones I've read tend to get little things wrong, like removing trendlines and saying there's no trend, or confusing degrees and radians. Very few "skeptical papers make in into the peer-reviewed literature, and the ones that do tend to be shown to have errors, minor or major, that contradict their findings. The ones that don't (that end up in junk journals like E&E) are even worse! Meanwhile there is a huge coherent body of empirical evidence, supported by physical theory, laboratory experiments and various kinds of modelling, showing that AGW is on perfectly solid ground. You'd be surprised about how it's well worth looking at places like WUWT, Climate Audit or other denier blogs, but only to hone your deductive skills in determining exactly where they've gone wrong with their pseudoscience this time! A recent example on WUWT had Steve Goddard suggesting that atmospheric pressure was proportional to temperature, therefore CO2 was not a greenhouse gas. I hope that on a weather forum you would be aware that the air pressure in Antarctica and Europe is approximately the same! sss

Y.S. The hockey stick has not been discredited (maybe only in your mind), and has been successfully reproduced many times over. Actually, the only value in the 'hockey stick' is to place some limitations on our climate sensitivity - the physics of the atmosphere does the actual 'AGW' bit. http://www.realclima...ck-controversy/ http://www.realclima...ick-were-wrong/ It's well-known that the Sun is the dominant driver over the millennium prior to the Industrial period - find a respectable climate scientist who thinks it isn't! It's just that since industrial times and especially in the last 50 years, GHGs have become dominant. I'm also happy to agree that it may have some particular impact on regional (North Atlantic) climate - a very recent paper whose link I can't find supports this. BTW, Roy Spencer has been debunked more times than a chocolate teapot, so why use him as a data source? http://tamino.wordpr...spencers-folly/ http://www.realclima...e-easy-lessons/ http://www.skeptical...c-consensus.htm among many others. His GRL paper is old hat, and the 2010 papers show him to be wrong. Clouds - apart from having no identifiable link with climate, the projected feedback by the IPCC of clouds is negative, not positive as you state: http://www.realclima...007_radforc.jpg Your graph nicely shows that solar activity and climate have gone their separate ways since 1950 or so, and that divergence is proven by the spatial pattern of warming. The problem here is that there is no rational position to suggest that solar, clouds or a "cycle" dominates recent climate change, far less then how such factors would explain why the physics of the CO2 molecule fails to work under such an hypothesis. And even more how such a process can work, inhibit the radiative properties of CO2 (despite the fact that we observe these properties operating in the real world), and yet produce a spatial pattern of warming that is inconsistent with any process except for greenhouse gases!! sss Edit: Deepsnow Not heard of that argument before - I've heard the old canard about CO2 lagging temperature in the distant past - see this link: http://www.skepticalscience.com/co2-lags-temperature.htm The fallacy is to suggest that because one process drove climate in the past (orbital forcing), another one cannot drive climate now (humans emitting vast amounts of CO2). Much like saying that because ancient forest fires were caused by lightning, no modern forest fire was caused by people...

Y.S., why you feel the need to be so rude to Dev when he is challenging (rightly) what you're posting is a mystery. reminds me why it's rarely worth posting here any more. Some questions, and some data: 1: what is the trendline between 2000 and present on the UAH dataset? What direction is it? You can use woodfortrees to calculate it: http://woodfortrees.org/plot/uah/from:2000/every:1/plot/uah/from:2000/every:1/trend 2: The trendline in (1) is not significant of course, as it is insufficiently long a time period. Is the trend for 15,20 or the commonly-accepted 30 years also positive, and does it differ significantly from any other timeseries (GISS, HADCRUT3 etc)? 3: Climate sensitivity: You deride the Mann 'Hockey stick'. The best datasets show that the MWP and LIA are muted on a global scale, not least because they are not temporally synchronous, unlike modern warming. if the MWP was as pronounced as you seem to wish (say, as warm as present), what is the significance for global climate sensitivity? 4: (related to (3)) Why should you, and all of the rest of us, really hope that hockey sticks are the right shape for global temperature over the last 1000 years? 5: If it's all to do with the Sun, why does the troposphere warm when the stratosphere cools; why is warming observed day and night; why do the poles warm more than the equator; and why does winter warm more than summer? http://www.skepticalscience.com/solar-activity-sunspots-global-warming.htm http://www.youtube.com/user/greenman3610#p/u/34/_Sf_UIQYc20 6: If it's clouds, why is there no observable link between clouds and cosmic rays (the favourite hypothesis)? Calogovic et al. (2010); Kulmala et al. (2010) among others. http://www.skepticalscience.com/cosmic-rays-and-global-warming.htm Here's a good summary of why it's clearly us, and not some mythical 'natural cycle' (a term I've always found amusing as even 'natural cycles' should have an identifiable cause and forcing value): http://www.skepticalscience.com/human-fingerprint-in-global-warming.html For general interest: http://www.aip.org/history/climate/summary.htm http://www.skepticalscience.com/What-happened-to-the-evidence-for-man-made-global-warming.html - loads of good links on research current as of late 2009. Of course the recent remarkable high temperatures and low Arctic sea ice (area and volume) are not shown there. sss

round and round we go SC. I did not state "this shows AGW to be right". I was very specifically pointing out that enhanced warming of the Arctic is but one of many requirements for the AGW theory, and one that is supported by the evidence. Therefore AGW is supported by Arctic observations, not proven by them. Or do you not believe that Arctic sea ice is retreating, that temperatures have risen more in the Arctic than elsewhere, and that the Greenland Ice sheet is melting at an ever-faster rate? These observations are not based on dodgy science. All the studies I're read clearly state that the thinning and reduction in albedo of the sea ice makes it ever more vulnerable to favourable winds or weather patterns. I haven't seen a single recent study suggesting natural variation to be the cause of Arctic warming. Care to enlighten me? I do like your "Absolutely no evidence"! Go have a read of the papers yourself. Restrict yourself to the last 2 years of publications on Greenland and the Arctic ice, and there's plenty to keep you busy. Good posts G-W, but it's clear that some just don't want to understand what is happening. sss

Afraid I won't be at the office for quite a while to check the Myhre paper. Dickinson, 1982; WMO, 1986; Cess et al., 1993 are what the TAR refers to in relation to the second equation, so you could look there. Dickinson, R.E., 1982: In: Carbon Dioxide Review [Clark, W.C. (ed.)]. Clarendon, New York, NY, USA, pp. 101-133. WMO, 1986: Atmospheric Ozone: 1985, Global Ozone Research and Monitoring Project, World Meteorological Organization, Report No. 16, Chapter 15, Geneva, Switzerland. Cess, R.D., M.-H. Zhang, G.L. Potter, H.W. Barker, R.A. Colman, D.A. Dazlich, A.D. Del Genio, M. Esch, J.R. Fraser, V. Galin, W.L. Gates, J.J. Hack, W.J. Ingram, J.T. Kiehl, A.A. Lacis, H. Le Treut, Z.-X. Li, X.Z. Liang, J.-F. Mahfouf, B.J. McAvaney, K.P. Meleshko, J.-J. Morcrette, D.A. Randall, E. Roeckner, J.-F. Royer, A.P. Sokolov, P.V. Sporyshev, K.E. Taylor, W.-C. Wang, and R.T. Wetherald, 1993: Uncertainties in CO2 radiative forcing in atmospheric general circulation models. Science, 262, 1252-1255.

VP asked where on the log curve we were: If ΔF = 5.35 * ln(C/Cbase) ΔT = ΔF * λ. where ΔF is radiative forcing relative to pre-industrial, C is desired CO2 concentration and Cbase is preindustrial (278ppm), then the forcing can be calculated. This gives us our 3.7W/sq m for a doubling, and a 1.7W/sq m for present concentrations, compared to preindustrial levels. The equation is from the IPCC AR3 and AR4, derived from Myhre et al (1998). This is directly based on the radiative forcing driven by absorbtion of longwave radiation as described in links I've put up elsewhere (Jethro doesn't like linking to blogs in the technical thread but the relevant blogs are duly referencing the literature on radiative transfer). The relationship is logarithmic because of the gradual saturation of the CO2 absorbtion band. Temperature change (ΔT) is related to forcing by the variable λ, which is very close to a constant of 0.5. So to answer VP's question, x = 387ppm, y = 1.77W/sq m. Add another 100ppm and we get to 3W/sq m, demonstrating the logarithmic effect. sss

But surely the point is that enhanced warming in the Arctic was one of the predictions of AGW theory, therefore observation of it, as predicted, is in support of the theory. It does not, on its own, tell us that humans are warming the planet, but if the Arctic were not observed to be warmer, then the mechanisms (in relation to the Arctic) by which AGW theory operates would be suspect. However, we observe a reducing trend in Arctic sea ice (most prominent in September minima, but also present in March maxima), and we observe acceleration of and negactive mass balance in high latitude glaciers and ice sheets. Hence the theory is supported by the evidence. Temperature data conclusively shows polar amplification. A great deal of other evidence from other sources demonstrates the link to humans, and observed effects in different layers of the atmosphere. sss

I still don't really believe your lag would work on a physical basis - why would temperature differences of ~1K out of ~288K result in a substantially different lag? An example from something I know well - the response rate of a valley glacier is dependent upon it's size and the magnitude of the forcing (e.g. change in temperature, precipitation), excluding dynamic and hypsometric factors. If this valley glacier is 28.8km long, the response rate to a forcing (be it to trigger retreat or advance) will be indistinguishable from that if the glacier was 28.7km long. The point of the blog posts (particularly the Chris Colose one and the RC radiation ones) was to show that the radiative forcing as measured at the top of the atmosphere is eminently quantifiable, and that in knowing that, you also know just where you are on the logarithmic forcing curve. I don't see how this is in very much question, as given the spectrum of radiation leaving the Earth, you can quantify exactly how much the OLR has changed by, and what that means in terms of radiative forcing by analysing the spectrum. Y.S: sunspot cycle length does not correlate with climate. Friis-Christensen and Lassen were wrong on that point (and have been shown to be so) - try plotting it yourself. Nor does cosmic ray flux - another proposed mechanism. Climate and attribution - read the relevant material and you'll understand where the 1940s to 1960s dip comes from. Cloud cover: is a feedback not a forcing - so what's the forcing? For example, if it increased in the above period the is it not likely related to the aerosol forcing that also causes the temperature dip? You need a mechanism by which to explain why you get an increase in cloud cover. Additionally, you need to explain why it is a particular type of cloud - some produce net warming, some net cooling. CB - seen that one before, and, apart from the obvious agenda, the author clearly does not understand feedbacks as well as they think they do. The author has no clue that, despite his fancy equations, we know for a fact that the CO2 released does not come from the oceans, as it has the wrong 13C/12C ratio. Given these rather basic 'errors', I am unconvinced by the application of Beer's law - the structure of the atmosphere is misinterpreted, saturation does not occur at the layers where the radiation is emitted. The spatial distribution argument is totally fallacious, as it ignores horizontal redistribution of heat in the atmosphere by weather! And he does not seem to generally understand the 'saturation' issue as it applies to spectra of radiation. ah well... SC: The reason it is more powerful than any other theory is that is is based on the physics of absorption of radiation. Theories of a solar or cosmic ray influence are so far only (at best) based on correlation, and most of these correlations have been shown to break down in recent years, be very weak or be plain incorrect. So we have on one side, a sound physically-based theory which is verified by observations, which fits predictions on intesity, and importantly on spatial distribution... and on the other side we have hypotheses based on correlation with no supporting physical process. Which one would you bet your grandchildren on? Good to hear that Phil Jones has been exonerated of any wrongdoing by Parliament, despite the best effort of deniers like Lawson, Macintyre and the like. As was pointed out immediately by the scientists themselves, and was visible to anyone who looked at the emails with an appraising eye, there was nothing in the emails to indicate scientific wrongdoing or manipulation of data. I actually support the full release of code etc (which is already done by many, contrary to practically any other science), just so that everyone can see the steps taken... even though it is an unscientific measure - if a scientific finding is to be verified, then it should be independently replicated - you do not achieve this with identical data and code, you achieve this by creating your own model and code. Ask yourself why skeptics have not done this normal scientific procedure? I'm sure Exxon would have funded such a project sss

But CB, I've shown you examples of our direct measurement of the causation, namely reduction of outgoing longwave radiation at CO2 and methane-specific wavelengths, and a similar increase in downward longwave radiation measured at the surface. The decrease in OLR is of the magnitude expected for our increase in GHGs. (Harries et al, 2001 Nature and other refs - the Skeptical Science link has them I think). This is direct observation that CO2 is the cause. The basic fact that adding CO2 to the atmosphere causes warming is not really up for discussion in the sense that it's science as old as the Theory of Evolution, and older than quantum mechanics. The physics says so, the effects were first predicted, and now they are observed, directly. That Richard Alley doesn't feel the need to explain that adding CO2 to the atmosphere causes warming is merely an extension of the fundamental nature of that property of the gas. What he is concentrating on is the sensitivity, as recorded in palaeoclimate records. The magnitude is up for discussion, yes, but sensibly it should reside somewhere between 2C and 4.5C as judged by many studies, be they experimental, modelling or palaeoclimate. So yes, (as Alley says) the fact we can't explain it any other way is not causation in itself, but it is powerful evidence in favour of CO2 being as important as he says it is. That aligned with our direct observations of the CO2 warming effect in the atmosphere, and the spatial pattern of effects that is distinct from other possible causes, shows that CO2 is the driver of warming, and not solar, clouds, ENSO or anything else. YS: some RC links: http://www.realclima...climate-change/ (earlier Scafetta paper) http://www.realclima...climate-models/ (summary of global dimming including Wild) http://www.realclima...logical-sequel/ (2007 scafetta paper you quote - very poor science!) http://www.realclima...e-easy-lessons/ (clouds, weather and bad science!) As I've said before, just because it is peer-reviewed (eg Scafetta and West 2007, McLean et al 2009) does not make it 'right'. Consider the data in the paper, and consider others' replies to the data. I've a suspicion you're misinterpreting Wild et al 2005, and your assertions are far too simplistic. I don't think Wild would say what you have said (re relative influence of solar vs CO2), so who did, or was it your interpretation? sss Edit: basics of CO2 properties from two sources, both with lots of technical info, and the second a 7-part series (removed from my posting on the technical discussion as it wasn't peer-reviewed): http://chriscolose.w...fect-revisited/ http://scienceofdoom...e-gas-part-one/ And from RC, another really good description of why a little extra CO2 means a lot, and why we are not near saturation of CO2: http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument/ http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument-part-ii/

Comments like this are unhelpful. I don't suppose you have any evidence to back up your claims that we won't be ice-free in 50 years? The real state of the data on extent is that sea ice extent values are retreating much faster than predicted, therefore, as in the following link, seasonally ice-free Arctic is perfectly plausible before 2050: http://nsidc.org/news/press/20070430_StroeveGRL.html The other issue is of course that areas are misleading on many counts. As Stewfox puts very well, "give me its thickness any day above its area." a wide area of thin ice is far more susceptible to melting out than a smaller area of thicker ice. Monitor the melt on a pond or some such - the ice will gradually thin, and then rapidly disappear - if your eyes only saw the area of ice you'd see not much change for a while, then a very rapid transition from 'ice' to 'no ice'. In the Arctic, thickness studies (such as Barber's) are telling us that we've done most of the melting of volume, and so therefore we are heading into the phase where loss in area becomes more important. An increase in area (such as we've seen over the past month) is misleading if it is not accompanied by a concurrent increase in volume. And given that the trend in sea ice areas is downward and accelerating, 2007-scale extents are not only probable, but very likely within a small number of years, quite possibly this year if the pack is in as poor a state as observations suggest. sss

Messy debate ver the past few days! Anyway, just here to post a couple of links... First of all, another good summary on the reason why we think that humans are the dominant cause of global warming: http://www.skepticalscience.com/human-fingerprint-in-global-warming.html Yes, it's a blog post, but there are plenty of references to the peer-reviewed literature therein. The crucial point is that the spatial/temporal nature of the warming is that which is expected from CO2 and not from other sources, such as the Sun. Doubling CO2 - too many posters are perhaps not aware of the literature on climate sensitivity: Knutti and Hegerl 2008 is a good reference for that: http://www.nature.com/ngeo/journal/v1/n11/abs/ngeo337.html Full text at: http://www.iac.ethz.ch/people/knuttir/papers/knutti08natgeo.pdf and discussed at the ever-excellent Skeptical Science: http://www.skepticalscience.com/Working-out-climate-sensitivity.html Something for VP (maybe for discussion in the technical thread?) - To my knowledge, the logarithmic effect of CO2 is the consequence of the saturation and broadening of the CO2 absorption line in the IR spectrum of heat leaving the Earth. This is understood and quantified, and therefore the logarithmic effect is accounted for when calculating sensitivity. So (as you know), for example if somebody predicts a 2C rise for a doubling of CO2, the next doubling will cause a further 1C rise (ignoring other feedbacks). But the position we are on the logarithmic curve is not open to question, as we understand the spectrum of radiation leaving the Earth? http://chriscolose.wordpress.com/2010/02/18/greenhouse-effect-revisited/ For those who still believe the foolish fallacy that CO2 followed climate in the past therefore can't be leading it now, how about a lecture by Richard Alley at AGU: http://www.agu.org/meetings/fm09/lectures/lecture_videos/A23A.shtml sss

Last one for the day - I think it's looking increasingly likely we can quite safely put the "world hasn't warmed since 1998" rubbish to bed. As I've shown many times (with reference to Tamino's excellent graphs, see his 'riddle-me-this' post), the world has continued to warm exactly as it was predicted to do throughout the 2000s, with ENSO-induced variations about the mean and the decrease in solar activity making the noise in the signal not peak above 1998 (if you use HADCRU). If you use GISS which adds the Arctic, 2005 was unsurprisingly hotter than 1998. 2009 ended and 2010 has begun with a bang as far as high global temperatures are concerned, and exactly as you would expect in a noisy rising trend, a new high global temperature is imminent, when the cyclically-varying factors (ENSO, solar) trend in the right direction. This time, the El Nino isn't even particularly remarkable, solar activity is still pretty low, and yet 1998's record is under threat. Only a dramatic La Nina or a big volcanic eruption can save the day for the "no warming since 1998" loonies... http://climateprogre...satellite-data/ Of course, by 2011 there'll be a "no warming since 2010" crowd too... 1998: close to solar maximum, record El Nino 2010: close to solar minimum, moderate El Nino, yet matching and beating 1998. Looks like some other forcing factor has changed... can it possibly be the AGW effect we have already observed to be occurring? sss Edit: CB, I await your explanations. I absolutely understand that you should always be alive to alternative explanations. But solar activity has a hard time explaining the observed energy balance changes in longwave radiation, as well as the stratospheric effect, hence why GHGs are an easy winner at present.

Can it be that the world is reacting in exactly the way predicted by generations of climate scientists? The first NAS 'consensus' on AGW was in 1979, before the observed effects of the 1980s, 1990s and 2000s, showing that the 'consensus' in climate science is not a new thing. To extend G-W's list, can it be that tropospheric warming, stratospheric cooling, polar amplification, reduction in outgoing longwave radiation, increase in downward longwave radiation, all predicted by AGW and observed to be happening, represent a trend... and one that is only going to be exacerbated by the destabilisation of stores of methane? How else do you explain this pattern if not by anthropogenic GHGs, whose effects were predicted before the subsequent observations? sss

OK, I'll bite, though I suspect we're back to radiators again, and I think your reasoning is incorrect. I'll start with: http://www.skepticalscience.com/solar-activity-sunspots-global-warming.htm and specifically the graph showing TSI from the 19th Century to present. You can see that TSI has dropped off sharply and is back to 19th Century LIA levels at present. This is the equivalent of turning off/down our radiator, or the gas under the pan - whatever you prefer. So if the premise of long-term well above average solar activity is a good one, the heat is 'on' until recently. But now it's not 'on', and irradiance is dropping, the pan must cool immediately. To follow your analogy, the pan is boiling, and continues to boil for a bit after turning the heat down. Is it because it is retaining the heat before cooling? No! It's mean temperature immediately must be dropping as the heat source has been removed. The water remains boiling, because the temperature of the pan itself has risen slightly above 100C (notably the metal at the base of the pan), and takes a small amount of time to cool below 100C. This time will be shorter if you use a thinner pan, compared to a thicker pan, for obvious reasons. Once the temperature of the pan, and consequently the lowest part of the water, slides below 100C boiling ceases. Similarly, if you turn a radiator off, it cools immediately, even if the cooling is slight. And all this does not explain why 50 years of high solar irradiance that has just recently ended should lead to a greater lag in time than the 70 years of the Maunder Minimum, wich coincides with the peak of the LIA in Europe (and does not apparently lead or lag it). Yet in each case we are talking about the energy gain and loss of a degree or so C, in the same world system. Yet temperatures are still rising (March looks like yet another record), and GISS note that the 12-month running all-time record will most likely be broken in the next few months. What is much more plausible is that the solar activity increase in the early 20th Century had a noticeable (if relatively small) impact, but then the effect levelled off, indicating a relatively short lag time. Anthropogenic impacts, already present in the early part of the century, become dominant once they override aerosol effects by the late 1970s. The trend since the 1970s has been approximately linear, as expected from an exponential increase in GHG counterbalancing the logarithmic forcing property of CO2. This sequence of events fits the observations, and a solar-dominated sequence of events does not. And my last point for now - you keep mentioning laboratory CO2 (first sentence of your last-but-one post), but I was talking about real-world observations in the actual atmosphere. Why can we actually observe the CO2 energy imbalance from above and below, in the real world, as predicted by the physical properties of CO2, if it's not supposed to be effective or if there are mitigating factors? The energy imbalance caused by anthropogenic CO2 is as real as the observations of sunspots or the measurement of air pressure. Why try and invoke another mechanism that has been tried and does not fit, when we have one that we can see, have a very sound physical mechanism for, and fits very well? Speaking of which, how do you warm the troposphere and cool the stratosphere by increasing solar activity? sss

Hi sss, where did I say that I could overturn the physics of the CO2 molecule? I said that I could address the issue, not that I could show the science to be wrong. Indeed, I have addessed the issue several times in the past, but for the sake of clarity I shall quickly readdress it here. The physical behaviour of the CO2 molecule in the laboratory is a matter of scientific fact. However, the real world, outside of the laboratory, consists of rather more than a CO2 molecule in a closed system and a heat source. For a start, the Earth is not a closed system. What other factors may counteract the effects of CO2 in the real world is a matter of debate. The physics (and chemistry) of a CO2 molecule are not up for discussion, but the interaction of those physics with all the other physical and chemical effects going on in the Earth climate system is rather more complicated. I have also addressed the issue of how the IPCC have skewed the reporting of the science with the links a few pages back. The omission of studies that "muddy the water" is a deliberate choice to make the science seem more solid than it actually is. Is that not skewing the reporting of science? Further details can be found by clicking on the two links within the link below: http://forum.netweat...ost__p__1796142 I see you're going back to the "to prove AGW wrong you have to present a whole new theory" argument. This is not strictly true, and we have been over this particular point several times in various threads before. AGW theory could well be broadly right (especially the "GW" bit), but with attributions of effects to mankind that seriously overstate our impact on the environment (less of the "A" bit). A complete rewriting of the science is not necessary, but I would suggest that the issue of "how much warming is attributable to man" is rather more than a "fiddly little detail". CB [note to others - I'm just continuing a discussion form the 'consensus' thread that got OT, thought I'd put it in here] Hi CB, I think we can agree that it is a complex system, but I am at a loss to understand how you don't think CO2 would be effective in the real world. There's observational evidence from both above and below the atmosphere that show it is being effective... in the real world. We could have a go around on your snippets from the stolen emails, but rather pointless I think. There's nothing there to suggest improper practice, and your interpretation of individual words is not necessarily the same as mine. For example "some authors argue" to me seems actually weaker than "many authors suggest", as "some authors" may be authors with as much credibility as MacLean, Baliunas or McKitrick, while 'many authors suggest' indicates a much more mainstream opinion... which is what it is. 'A' as opposed to 'the' is also fair enough, unless you think that Milankovitch wasn't also operating on millennial timescales? So I'd suggest you're seeing ghosts where there are none. The papers are out there in the literature, so they're not being hidden. Your second link - alleges that they are ignoring some unknown lagging mechanism, and blocking papers that have suggested such a mechanism. What are those papers? And what is the lagging mechanism? You do agree that solar radiation has been stable or declining over the last 50 years, and that our 'radiator' has just been through a remarkably low point? Now I understand the mechanism you suggest for the LI, but you need to couch it in a physical basis for there being long lags, and why those lags do not appear around other, acknowledged solar-driven changes during the last 1000 years? You didn't answer my previous point that the warming and cooling of one degree is insufficient to account for presence/absence of a long lag. At our temperatures we should see the same lagging around all solar changes. We do not. sss

CB, I really need to enquire on two points from a couple of pages back: First, thi statement: "And why would laws of physics need to be upended? Which laws? Is it a lot of laws, or is it just the one about CO2 being a GHG? If it's just that one then I can address it (as I have several times in the past)." Really? You can overturn the physics of the carbon dioxide molecule that has been understood for 100 years? I await your explanation in the technical discussion thread with some interest. We have emitted more CO2, no problem there. CO2 is a grenhouse gas, absorbing and re-emitting longwave radiation (surely no problem there?!!). We observe both an increase in downward longwave radiation at the surface and a decrease in outgoing longwave radiation from space, showing that the CO2 is blocking more OLR from escaping to space. We know that CO2 has a logarithmic relationship with temperature forcing, due to the nature of the way that the CO2 absorption bands saturate and broaden (the same logic explains why methane is more powerful as a greenhouse gas), and that there is plenty room for more blocking around the relevant spectral lines. This also explains why we have not had a runaway greenhouse in geologic history. We also know, from palaeoclimate and other sensitivity studies, that the sensitivity of the earth to CO2 certainly places us low enough down that logarithmic relationship for a doubling of CO2 to have a considerable effect. This is pretty sound physics you have to overturn, so I'd love to know how you'll do it... The second question relates to quite how you think the IPCC has skewed the reporting of the science. You seem to be suggesting that they have omitted a host of legitimite studies and therefore have artificially created a consensus? Now, I am aware of a number of studies in reputable journals that propose alternative ideas for climate, but the truth of the matter is that most (if not all) of these studies have subsequently been found to contain critical flaws in their understanding. If you are then preparing a paper on the state of the science, you do not then include those studies. The media might like a bit of false 'balance', but in science, if the alternative view has been shown to be garbage, then you safely ignore it. One study confused degrees with radians. Another, recent study (McLean et al in GRL, no less), was not just criticised, but demolished to the core because the authors did not realise (actually they did realise, they just wanted to hide the fact in a figure caption) that their statistical methods had artificially removed the rising trend of temperature. These sorts of studies do exist in the published literature, but it does not make them good science, or worthy as a contribution, let alone a significant thorn in the side of a consensus. So what are these good studies that should have been in AR4, but were not because of an artificial skew? Can you name them so I can read them? The consensus here exists because the science says so, and there is no viable scientific alternative, not because some committee has decided so. I know that every climate or climate-related scientist I have met (and I've met a good few) would dearly love to be wrong about AGW. Or more properly, they would be entirely happy for some upstart to develop a sound theory that explains all our existing evidence while not having CO2 as the culprit. This would give us hope that sea levels will no continue to accelerate their rising trend, and glaciers will not continue to accelerate their flow speed and retreat. There's plenty of evidence out there that junk papers can make it past peer-review (therefore the establishment blocking of contrarian science is a myth), so where's the good ones that would break/supercede the current theory? If they're not being suppressed, then maybe they don't exist? If they don't exist, maybe the consensus, supported by the vast weight of evidence, is a natural one because the prevailing theory is right, or at least right bar the fiddly little details (exactly how much, and how much melting). Now back to much more interesting things happening in Iceland! sss

A quick last one from me before I go away for a bit (some will be happy to hear ). I stumbled across this - it's a 7-part blog, and may be an accessible walkthrough of CO2 science from the bottom upward, called "CO2 - an Insignificant Trace Gas?". Quite involved, lots of maths, and so perhaps VP in particular will be interested in it (notably parts 3 and 4 perhaps), and the references within. Other things of note, and I don't have time to reference them entirely, but two interesting posts at RealClimate, covering recent papers discussing sea level rise (underestimated), solar activity influence (around the 10% level), and the scariest of the lot is: http://www.sciencemag.org/cgi/content/abstract/326/5955/984 Greenland's mass balance looks like it has dropped off a cliff since about 2000, based on GRACE data, and the authors say it would have been 100% worse but for some incresed snowfall. Definitely worrying times. I know some might construe these various papers as 'alarmist', but the data is getting ever more solid, and we are observing the effects all the more each year. I just hope the paper that suggested much higher climate sensitivity was wrong (http://www.sciencemag.org/cgi/content/abstract/1178296)... sss