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Comments 14851 to 14900:

14851. Bob Loblaw at 11:27 AM on 17 April 2018
       Sea level rise predictions are exaggerated
       

       Tamino has a new post out on recent sea level changes. It focuses on the US, but has a discussion of why rates vary locally and over time. He is less than charitable on the idea that sea level has been changing at a constant rate - and that extrapolating a linear fit is appropriate.

14852. scaddenp at 07:41 AM on 17 April 2018
       Climate's changed before
       

       Bearling, where do you get the idea that mass extinctions are caused by cooling not warming? That doesnt match the published science. The critical thing affecting extinctions is rate of change (because organisms need time to adapt/migrate) not the direction of the swing. Also the Pliestocene ice age cycle is rather slow and not notably associated with extinctions (except where low sea level allowed humans to migrate into new areas where they wiped out the local megafauna), unlike the current rate of change caused largely by our emissions.

       If humans werent around then next peak age would be about 80,000 years. There is more info on this here.

14853. michael sweet at 07:39 AM on 17 April 2018
       American conservatives are still clueless about the 97% expert climate consensus
       

       Norrism:

       The scale is largest around 2100 on graph C so it is the easiest to read.  I note that your estimate of 0.4 m of sea level rise is well below the 68% range, nowhere near a midpoint value.  This paper is used a lot by deniers because it is at the very lowest range of peer reviewed papers.  The IPCC has relied on low papers a lot in the past and increases its projections every report because the low estimates are incorrect.

       This paper by Hansen, Rignot and 17 other top scientists in 2016 (already cited by 196 others!!!) give projections of up to 17 feet of sea level rise by 2100.  They discuss ice sheet disintegration.  I could not immediately find again the paper by Rignot that describes the mechanism of ice sheet disintegration.  He may not be the lead author.  It is cited in the Hansen paper or you could go to his website and look at his list of publications for the years 2014-2016.  The 19 authors of the Hansen paper have much more experience and past successes than Rohling and his coauthors.

       Rignot had a youtube video previously linked for you that described the process.  Search youtube.

       I use GOOGLE or GOOGLE SCHOLAR to find free papers.

       The central, consensus estimate of the IPCC is that humans were responsible for 110% of the warming since 1950.  Your lawerly review of the terms does not appear  to recognise that this is the central, consensus number.  I cannot understand how you discount the central, consensus number.  Gavin Schmitt at RealClimate calculated that there was only a 0.5% chance of humans causing less than 66% of the warming (Curry was unable to do the calculation and said scientists did not know how to either.  She was wrong.)

       The average sea level rise since 1900 is about 1.7 mm/yr according to you (I cannot find your post since it is not on the sea level rise thread).  For the past 30 years sea level rise has been 3.4 mm/yr according to satalite measurements.  Sea level rise must be accelerating since the most recent 30 year rise is double the average over the past century, no analysis is needed. 

       You think sea level rise will immediately slow down to 1.7 mm/yr again??  What is the physical mechanism for the decrease in sea level rise?  Your suggestion of a decline in sea level rise appears unphysical (a very strong term in science) to me.

       Scientists have predicted for over 100 years that sea level rise would accelerate due to AGW and that prediction has come true.  Why could we possibly think that sea level rise will slow down to half of the current rate when peer reviewed papers measure more acceleration?  As temperature increases the forcing for sea level rise increases and we would expect acceleration.

14854. NorrisM at 01:09 AM on 17 April 2018
       American conservatives are still clueless about the 97% expert climate consensus
       

       michael sweet @ 24

       Are you saying that graph d is incorrect?  Graph c is hard to read the measurements for 2100.  I understood that Rohling in graph d was simply expanding the size so that you could better read the measurements.

       I have no recollection of any reference by you to a Ringot paper but in any event, could you provide me with some access to the paper? I appreciate that I could search it out but you seem to have url's that can get past paywalls.

14855. Alexandre at 00:25 AM on 17 April 2018
       2018 SkS Weekly Climate Change & Global Warming Digest #15
       

       The IPCC was created in the 80s and it stands for Intergovernmental Panel on Climate Change. That's the name that was already used back then. They pick on any argument they can make up.

14856. bearling at 20:04 PM on 16 April 2018
       Climate's changed before
       

                 Before humans have existed, the big climate changed has happened before and it leads to cause major extinctions naturally. Scientists believe that, over time, changes in the amount of CO2 in the atmosphere have altered the climate of the planet. The proportion of CO2 that is dissolved in the ocean, as opposed to the CO2 that is present in the atmosphere, also varies over time. When more CO2 is trapped in the oceans, the planet cools. By contrast, when atmospheric levels are high, the planet warms. Carbon dioxide is considered to be the most important greenhouse gas involved in global warming. (from http://www.arctic.uoguelph.ca/cpe/environments/climate/climate_past/ice_cause.htm)
                 So after humans have existed, people are putting CO2 more and more into the atmosphere. But cause minor extinctions because climate changes cause major extinctions from cooling not warming.
                 If humans are not the factor that causes big climate changes and let the world run naturally, will the next major climate changes be like ice age?

14857. MA Rodger at 19:21 PM on 16 April 2018
       2018 SkS Weekly Climate Change & Global Warming News Roundup #15
       

       bozzza @3,

       The two studies that kicked-off this AMOC discussion are Caesar et al (2018) and Thornalley et al (2018). Neither are directly measuring the flow but use either SST data & modelling (there is an illustrative animation of their modelling in this RC post) or proxy paleo-data to infer the past strength of the AMOC. Caeser et al (2018) conclude the AMOC has weakened by around 3 Sv (Sv=milllion cu m/sec). The AMOC is measured today at 17 Sv, so that's a drop of 15%  since the mid-20th century. Thornalley et al also put it as approximately 15% but relative to the preceeding 1,500 years, with their proxy data showing a transition occuring by 1900, that is a big big wobble down that has remained down and not wobbled back up.

       Of course, such findings don't of themselves say a lot but require comparing firstly with what is expected of the AMOC under AGW (IPCC AR5 put it as 1-24% drop by 2100 under RCP2.6 and 12-54% under RCP8.6, all with the 'low confidence' sticker) and secondly what would be the resulting impact on global climate which is a bit of a big ask as it would all be wrapped up with other AGW impacts. As an example, while Hansen et al (2016) present a dramatic scenario with the AMOC switching off, this is the result of other major climatologial change.

14858. bozzza at 16:52 PM on 16 April 2018
       2018 SkS Weekly Climate Change & Global Warming News Roundup #15
       

       Is there a rate of change measurement at hand?

14859. Riduna at 16:39 PM on 16 April 2018
       Sea Level Rise: Some Reason for Hope?
       

       In this video Dr Grinsted expresses the view that a rise of 1.6°C will be a tipping point for eventual loss of the Greenland Ice Sheet.
       We are already less than 0.2°C below that point and will likely exceed it in less than a decade.

       Dr Ramstorf says that we risk SLR of as much as 2 metres by 2100 but suggests that discharge of cold water from ice sheets may be a mitigating factor, slowing mass loss.
       Rignot, Hansen and others argue that discharge of fresh water on the ocean surface will result in formation of warm bottom water hastening, not slowing polar ice mass loss, particularly in West Antarctica where the ice sheet rests on the seabed.

       Dr Hansen has predicted multi-metre median SLR by 2100 as the likely outcome, driven primarily by the rate of mass loss from the polar ice sheets. If decadal doubling of that rate continues to occur – at present it is accelerating – SLR in excess of 3 metres by 2100 seems a more likely outcome.

14860. DPiepgrass at 16:24 PM on 16 April 2018
       Climate Science Denial Explained
       

       Unfortunately greenhouses (or hot cars) aren't ideal examples of the greenhouse effect, because a greenhouse works in part by trapping air so that it can't rise (and be replaced by cooler air that used to be higher in the atmosphere). The glass of a greenhouses also, incidentally, traps infrared radiation the same way greenhouse gases do, but it's easy for a pseudo-skeptic to point to the lack of convection and say "that's how a greenhouse really works - so the planetary greenhouse effect is a hoax."

       If I catch someone denying the greenhouse effect, I just point out that most contrarian climate scientists (e.g. Roy Spencer, John Christy, Judith Curry) agree that the greenhouse effect exists. More learned pseudo-skeptics have all kinds of other arguments.

14861. scaddenp at 14:18 PM on 16 April 2018
       Sea level rise predictions are exaggerated
       

       NorrisM, if you believe that climate models are faulty, then why do you believe they will err low rather than err high?  Surely you dont think government policy should be guided by such biases?

14862. michael sweet at 10:24 AM on 16 April 2018
       Sea level rise predictions are exaggerated
       

       Free copy of "Testing the robustness of semi-empirical sea level projections",

14863. Bob Loblaw at 06:23 AM on 16 April 2018
       Sea level rise predictions are exaggerated
       

       Returning to NorrisM's arguments about the unreliability of sea level rise predictions, in comment #58 and follow-ups. NorrisM has argued that there is uncertainty in the predictions, and closes comment #58 with a justification of using a linear extrapolation with the following sentence:

       "For me, I would go back to the observations and look at where the sea level has moved since 1900 and assume that it will follow along the same largely linear path that it has pretty well followed since we have kept records in tide gauges.

       NorrisM also makes the statement:

       "We cannot base our rational responses to AGW based upon theories which have not been supported with observational evidence.

       Let us examine the uncertainty issue, with particular reference to observations, and whether a linear extrapolation is justified.

       In comment 63, I linked to a RealClimate graph (linked again below) that shows historic sea level estimates from several sources. It is obvious that the different sources provide different curves, which indicates uncertainty even in the historical record. Why is there this uncertainty? Well, observing global sea level isn't as easy or obvious as one might think. We need to do a bit of digging to understand why.

       The RealClimate post linked to earlier about the IPCC Fifth Assessment results  includes a link to another RealClimate post. Both posts include a reference to the following paper (which unfortunately is paywalled):

       S. Rahmstorf, M. Perrette, and M. Vermeer, "Testing the robustness of semi-empirical sea level projections", Climate Dynamics, vol. 39, pp. 861-875, 2011. http://dx.doi.org/10.1007/s00382-011-1226-7.

       That paper incudes a good summary paragraph (p862) about some of the adjustments that need to be made:

       "The various tide-gauge based global sea-level reconstructions differ with respect to the selection of gauges, the correction for glacial isotatic adjustment (GIA), the correction for changes in atmospheric pressure ("inverse barometer") and. most importantly, the method for aggregating worldwide tide-gauges into a synthetic global mean sea-level curve.

       The Rahmstorf et al paper also gives additional details on methodology. The second RealClimate post linked above talks specifically about the odd Jevrejeva method of weighting the tide-gauge data. I mentioned this in comment 63, quoting from the first RealClimate post. In the second RealClimate link, you can see more about why this method is odd. Note that RealClimate does not just say it's odd, they make the effort to understand the method and do some calculations to understand the impact of the methodology. In that post, they also challenge the readers to find the problem (and they do).

       This is what scientists do when faced with uncertainty: they look in detail at the different sources of information and try to determine why they are different. They don't just throw up their hands and say "I don't know". Uncertainty due to different assumptions and availability of data helps us know what we need to do better, but it does not justify ignoring everything that we do know.

       So, in spite of NorrisM's argument that we should use "observational evidence", he is basing his simple linear extrapolation on data values that represent a significant amount of theoretical understanding, analysis, and interpretation of raw tide-gauge data. So much for his rejection of the danger of sea level rise because it is "theoretical".

       Now, using those global sea level reconstructions is not necessarily bad - indeed, it is a useful exercise. But is it appropriate to use a linear extrapolation? In a word, no. I will repeat the figure that I included in comment 63:

       

       A linear extrapolation would be appropriate if the slope of these curves were approximately linear. They are not. Another RealClimate post  talks about acceleration in sea level rise, and points out that even fitting a quadratic is problematic. Tamino has also posted on this  and includes the following graph that shows how the slope of sea level varies with time:

       

       If sea level rise were linear, the slope would be constant. It is not. If it were quadratic (constant acceleration), the slope versus time would be linear. It is not.

       When deciding to use a particular statistic fit, the first step is to graph the data and see if the preferred equation actually resembles the data. For linear fits, I have always like the illustration given by Anscombe's Quartet. It presents four small data sets that have nearly identical simple descriptive statistics (mean X and Y, standard deviations, linear regression results), but only one of the four is suitable for linearization:

       

       Naive statistical extrapolation of the different global sea level reconstructions is not appropriate. The reconstructions already have "theoretical" knowledge in them, deriving a global value from scattered tide-gauge data. Extrapolating those curves into the future also requires strong theoretical understanding of how the factors that have affected historical sea level will play out in a warming world.

       The scientific literature that provides the basis for the IPCC projections has done this analysis. NorrisM has not.

14864. Charliec71 at 04:24 AM on 16 April 2018
       2018 SkS Weekly Climate Change & Global Warming News Roundup #15
       

       This is a telling event and cool story, which seems to have drawn little attention in the media or community given all the competing events.  Anybody that has followed this story for the past decade will have an idea of the potential consequences of a slowdown in the AMOC, and they are significant. The prospects for world seems dismal at this point. I think we're at a low point with lots of competing events drawning our attention.

14865. scaddenp at 19:42 PM on 15 April 2018
       New research, April 2-8, 2018
       

       Bilb, I inadvertently deleted a second comment from you this morning while trying to add to a moderation comment in a rush before leaving. The reason your first comment was deleted was because you were posting a gish-gallop of nonsense and long debunked myths, which simply violates the comments policy here.

       However, this obviously impressed you. If you came here to investigate the truth, then pick the argument that you found convincing, use the Search function on the top left to find a suitable topic; read the article; and then tell us why you found your video more compelling than the science. I also suggest you spend some time making your yourself aware of the comments policy at this site. It is designed to encourage meaningful debate about the science rather than flame wars. If you just want to vent at warmists, this is not the site for you.

       Moderator Response:

       [JH] You actually deleted Bilb's third comment. I deleted his second one because it was a moderation complaint. DB deleted his first.

14866. ancient_nerd at 09:29 AM on 15 April 2018
       Climate Science Denial Explained
       

       When someone you know comments that it is hot in his car after it has been sitting in the sun, point out that this is the greenhouse effect and that global warming is happening for a similar reason.  Showing the mathematics behind a gallon of gasoline producing 19.5 pounds of CO2 can get people intrigued.

       People who are not into science do not know the basics,  They have no real reason to.

14867. michael sweet at 08:54 AM on 15 April 2018
       American conservatives are still clueless about the 97% expert climate consensus
       

       I am sorry, the range of 0.4-1.8 meters is the 90% interval.  The 68% interval is 0.5-1.2 meters.

14868. michael sweet at 08:45 AM on 15 April 2018
       American conservatives are still clueless about the 97% expert climate consensus
       

       Norrism:

       According to the graph in Rohling you must look at graph C and not graph D (the scale is incorrect for the purpose in graph D) source:

       

        

       I see that in graph C that the 95% range in 2100 is 0.3 m to 2.3 meters.  Your claim that 0.4 meters is midrange appears to be deliberately incorrect.  The 68% range is 0.4 to 1.8 meters, 0.4 meters is the absolute bottom of the range.  Everyone knows that there is much more chance of sea level rise being higher than expected than it being lower.

       Since Rohling was published Ringot has published data showing that Rohlings assumption that the maximum rate of sea level rise would be 2.0 meters/century is incorrect and the actual maximum rate is much higher.  I have given you the reference previously but you ignored it.

       Rohling points out that the current rate is at the very top of the 68% curve or 1.8 meters of sea level rise.   You must provide justification why you think the rate will decrease to less than half the current rate for the rest of the century.   Data shows that the rate is accelerating, not slowing down.

       You are either incapable of reading a graph or deliberately being deceptive.    When you are incapable of reading a simple graph it makes me wonder if you are really capable of calculating expected sea level rise yourself (the answer is no).  People on this website check your references and know when you are misleading them. 

       It is sloganeering to repeatedly give incorrect information.  You are very well informed about the low end of the data but seem completely ignorant of the upper end. You are misdefining the IPCC information.

14869. nigelj at 08:11 AM on 15 April 2018
       2018 SkS Weekly Climate Change & Global Warming News Roundup #15
       

       The weakening of the Gulf stream / AMOC is a very concerning development. However some people probably won't be worried, because they simply can't seem to compute that small global temperature changes over time can have severe impacts like this that could reshape climate systems. You see evidence of this in blog commentary.

       Perhaps they see large swings of temperature seasonally or diurnally that don't cause problems, and reason form there. Remember Senator Inhofe dumping a snowball on the floor, and proclaiming "theres no global warming" in either an astonishing display of ignorance, or cynical and deliberate avoidance of the issue.

       One thing blocking awareness of the severity climate problem is therefore possibly psychological perception of this sort, as well as political ideologies, and vested interests. They probably mutually reinforce each other. I can't think of many other issues in society with so many things blocking understanding and action.

       Perhaps if humanity could just focus on a sustainable future and set of related values this would help.

       The gulf stream and AMOC is really part of the global thermohaline circulation system as follows.

       en.wikipedia.org/wiki/Thermohaline_circulation

14870. NorrisM at 06:10 AM on 15 April 2018
       American conservatives are still clueless about the 97% expert climate consensus
       

       nigelj @ 20

       "I don't see how you can get from high confidence in 100% human attribution of warming, to a medium consensus." 

       Nigel, how I get from "high confidence" to "medium consensus" is that this is exactly what the term "High Confidence" means when used by the IPCC and the US Climate Report.  I think this term is rather misleading but here is the definition of "High Confidence" right out of the US Climate Report (see my long sea level rise post where I listed these definitions):

       "High Confidence means moderate evidence (some sources, some consistency) medium consensus."

       As for Rohling's midpoint estimate for 2100 of a .4M rise since 1700, please refer to Figure 3(d) in the paper which shows a range for 2100 of .2M to .9M with .4M as the mid range value.   I think Rohling's reference to .8M is stating that it is near the upper bound of his 68% probability interval of natural change.  

       Rohling makes it clear that his projections following LIg values (previous interglacial) are based upon extrapolation of "well-constrained processes for Greenland" and that "proportionally greater contributions might be possible for Antarctica".

       You asked me why I am always at the low estimates.  My underlying reason for looking at the lower end is my underlying distrust of whether the GCMs are accurately predicting the amount of temperature rise we will actually have from now until 2100 and therefore the impact it will have on sea level rise both from a thermal steric standpoint as well as a mass increase from melting ice sheets.  It comes from a general philosophical view that Hume is right that as soon as we move from empirical analysis we get into dangerous waters. 

       I know this is not the place to get into a discussion of GCMs but you asked me why I am always on the low end.  I have a general distrust of the ability of the GCMs to replicate our complicated climate system especially with the admitted problems with properly inputting the impacts of clouds owing  to a combination of not fully understanding their impact and not having the computing power to build them into the models.   You then add to this serious questions as to whether RCP 8.5 is a realistic scenario given the move to alternative sources of energy in the world.  I think China has realized that it cannot continue to use coal in an unlimited manner.  

       PS Presently reading a book which somewhat explains the "Age of Trump" by Kurt Andersen titled "Fantasyland - How America Went Haywire".  It is a 400 year history of "delusion and make-believe in the US" since the first settlement of Jamestown, Virginia. 

       Moderator Response:

       [DB] Off-topic snipped.  I'd warn you about the repercussions for such continued violations of this venue's Comments Policy, but I know you'd just continue to ignore such.

14871. John Hartz at 12:59 PM on 14 April 2018
       They changed the name from 'global warming' to 'climate change'
       

       Recommended supplemental reading:

       Climate Change Or Global Warming? Three Reasons Not To Be Distracted By The Name Game by Marshall Shepherd, Science, Forbes, Apr 13, 2018

14872. Eclectic at 11:17 AM on 14 April 2018
       American conservatives are still clueless about the 97% expert climate consensus
       

       NorrisM @19 , allow me to unruffle your feathers.  Yes, I was making a cheap shot in suggesting your posting activity outweighed your breadth of non-partisan reading.   I am half-ashamed of my rudeness in attempting a witticism, there.

       Still, you yourself know how strenuous is your advocacy for minimizing the appreciation of the adverse effects of AGW (and especially, regarding sea level rise).   You appear to lean towards the cherrypicking of any studies/opinions hovering at the extreme-low end of the likely range of MSL rise for the next 80 years.

       I won't insult you by quoting others who pointed out the need for prudent risk-management wrt AGW and MSL rise.

       Yes, reading the [2013] 5th IPCC's Summary For Policymakers . . . is educational, but we must recognize that the whole IPCC output is toned down towards the "Lowest Common Denominator" (both in politically-acceptable terms and in terms of defending a smaller scientific position).   And it is footling to attempt to "reverse engineer" a realistic scientific risk-assessment by shuffling phrases such a ">66%" , "highly likely" , "moderate confidence" , and so on.

       Hence the unwisdom of viewing the real world entirely through a prism which (a) is 5 years out of date, and (b) is inherently tilted towards undue emphasis on The Least.   (Of course, the IPCC reports are still a goldmine of information & references.)

       Already (since 2013) we have seen the spectacular end of the "Hiatus" in surface temperatures, and we have seen evidence that ice-melt is occurring faster than previously thought.   And we are only at the beginning of that 80-year period to Century's end !     Nor should we turn a blind eye to the much larger effects to come, in the centuries beyond 2100.

       NorrisM, you are being irresponsible in wasting your time pointing at the "[merely midpoint] 0.4 by 2100" scenario (one of many scenarios based on information prior to 2013).    Less partisanship and more prudence, please !

14873. Riduna at 11:16 AM on 14 April 2018
       There Will Be Consequences
       

       A recent study, reported here, confirms that slowing of the Gulf Stream and warming of ocean water along the east coast of North America are already happening much faster than expected – and that once again Dr Hansen and his colleagues in their 2016 Paper have been proven right. These findings make a multi-metre sea level rise by 2100 accompanied by increasingly severe storms a likely outcome.

14874. nigelj at 10:43 AM on 14 April 2018
       American conservatives are still clueless about the 97% expert climate consensus
       

       Typo alert. I meant .26M per century. 

14875. nigelj at 10:34 AM on 14 April 2018
       American conservatives are still clueless about the 97% expert climate consensus
       

       NorrisM @19

       If I can add my two cents worth. I don't see how you can get from high confidence in 100% human attribution of warming, to a medium consensus. The IPCC doesn't publish any result unless theres a strong consensus among the review team.

       I look at the basics of the science behind this. There are only so many natural things that can plausibly cause a warming trend, including changes in solar energy output, big sustained changes in volcanic activity, possibly cosmic ray trends (still rather contentious) and longer term ocean cycles. Since the late 1970's the atmosphere has warmed, and theres no evidence these factors are currently causing a warming trend in recent decades. For example solar irradiance has been essentially flat.

       When you eliminate the possible and plausible natural causes, you are left with burning of fossil fuels and the greenhuse effect. Various characteristics of how the atmosphere has warmed since the 1970's also point towards CO2, called greenhouse fingerprints.

       Now nobody will claim 100% certainty, because its impossible to be 100% certain all data sets on these factors are 100% perfect, but when the IPCC says good confidence or high confidence it means the data sets and research are certainly good quality. Putting it another way, when they say high confidence, this is science speak for saying it would be very unwise to ignore what we are saying.

       I don't think its wise to base your information on potential future sea level rise on just one single research paper on the past geological record, actually. You would need to review everything published on the issue, and even then past information is of limited value and so is only part of the picture and needs caution. Having said that it's an interesting paper, so thanks.

       The underlying premise of the Rowling paper is not based on past history where ice volumes were three times presnet day volumes. They mention this in passing, but focus their main attention on the last interglacial (130 - 115 K ago), where ice volumes are similar to today, and note that when temperatures were approximately 1 - 1.5 degree above pre industrial averages, sea level rose about 7 metres total, at between 2.6 - 0.92 M century, (0.7M on average). They say there were probably shorter periods of more rapid sea level rise.

       It needs to be noted we are ar risk of warming the climate more than 1 - 1.5 degree. Unless I'm missing something in the article, we are therefore at risk of more than 7 metres total sea level rise, and probably faster rates per century.

       Their end conclusion is about 0.8 metre of sea level rise is likely by the end of this century, with 2 metres as the upper limit - but less likely. This is presumably assuming a worst case emissions scenario, and this is of course entirely a possible scenario.

       I do not see your 0.4 M number in the study, and it may be assuming slower emissions growth and low sensitivity of how ice sheets respond. Anyway its a middle range estimate of some sort, and personally I wouldn't count on it.

       There's nothing here to cheer about or be complacent about. Plenty of evidence points towards rates of ice loss being likely towards the pessimistic end of this scale such as recent behaviour of the greenland and antarctic ice sheets .

14876. NorrisM at 07:18 AM on 14 April 2018
       American conservatives are still clueless about the 97% expert climate consensus
       

       eclectic @ 13

       I can assure you that I am doing much more reading than blogging.

       But I have to admit that my question regarding the view of the IPCC was somewhat rhetorical because I was pretty sure that the IPCC Fifth Assessment had not made any statements on attribution beyond the following statement from the Executive Summary of Chapter 10:

       "More than half of the observed increase in global mean surfacetemperature (GMST) from 1951 to 2010 is very likely1 due to the observed anthropogenic increase in greenhouse gas (GHG) concentrations.   ...... The Atlantic Multi-decadal Oscillation(AMO) could be a confounding influence but studies that find a significant role for the AMO show that this does not project strongly onto 1951–2010 temperature trends. {10.3.1, Table 10.1}"

       michael sweet has provided a "100%" attribution statement from the US Climate Report but the level of confidence is "High Confidence" which effectively means "medium consensus".  I do not think we need to pursue this further.  I was just responding to michael sweet's bold statement that 100% of AGW can be attributed to AGW since 1950.  If he had said there was a "medium consensus" on this then I would have just kept quiet.

       As to michael sweet's comment that my ballpark estimate of .4 m by 2100 (based upon what I had read up to that time) is just some figure of mine pulled out of the air, here is a paper by Rohling et al (2013) which has as its predicted "mid-point"  for 2100 my same guesstimate of .4 m: 

       www.nature.com/articles/srep03461

       The underlying premise of the Rohling paper is that the predicted rates for the period 2080 to 2100 to get to the higher levels of sea level rise per year relies on information based upon times when the volume of ice at the times of these high 10 mm/yr rates (and occasional 40 mm/yr pulse rates) was when the world had three (3) times the volume of ice we presently have.  As well, much of this ice was sitting at lower latitudes and was therefore very susceptible to high melting rates.

       Any thoughts on this? 

       I think I have said that the DeConto & Pollard (2016) paper referred to me by Glenn Tamblyn certainly raises issues about the WAIS.  Can anyone direct me to where the observational evidence is about retreating ground lines?  I understand there is some discussion somewhere. 

14877. SirCharles at 23:01 PM on 13 April 2018
       Sea Level Rise: Some Reason for Hope?
       

       1.5C is already in the pipeline. 2C would imply to cease fossil fuel burning within the next two decades. I wouldn't call that "some reason for hope".
       https://www.youtube.com/watch?v=VbhlWSxcoYg

14878. Eclectic at 22:46 PM on 13 April 2018
       Murry Salby finds CO2 rise is natural
       

       Sailrick , I must congratulate you on your tenacity against "RealOldOne2" on that Disqus thread.   He certainly is an outstandingly fine example of Dunning-Krugerism.   He's quite impervious to reason, it appears.   Still, your comments won't enlighten such hard-core denialists, who are considerably denser [depleted uranium? . . . or  neutronium?] than the more ordinary type of ideologically-motivated denialist.   Nevertheless, you will also be read by that (narrow?) band of "uncommitted" readers presently situated between the scientific-thinkers and the science-deniers.   (Plus I hope you enjoy the intellectual exercise !! )

       I did enjoy "ROO2" giving a reference to the Rocketscientist blog . . . where Rocketscientist showed a graph with [the Keeling] CO2 change diverging from the O2 change.  Duh.  Perhaps Mr Rocketscientist lives in one of the "flyover states" — where the presence of a planetary ocean is something that rarely impinges on everyday thinking.   Do the thoughts of two different D-K individuals always reinforce . . . or sometimes cancel out ?

       "ROO2" also seems oblivious to his proposed oceanic CO2 outgassing having any relation to ocean acidity changes.   But I reckon such denialists have long accustomed themselves to swimming in a sea of self-contradictions, without noticing a thing !

       I think MA Rodger must be right — "RealOldOne2" must be a Skydragonslayer or very similar.    "ROO2" seems to have almost zero grasp of the physics of the (so-called) Greenhouse Effect.

14879. MA Rodger at 20:58 PM on 13 April 2018
       Murry Salby finds CO2 rise is natural
       

       sailrick @33/34,

       I notice that the denialist on that Disqus thread was throwing round accusations of insincerity like they were confetti. I have thus responded to the twit direct on that thread. He has the appearance of a SkyDragonSlayer but it is always a bit of a laugh finding out what they do and don't accept/grasp.

       I haven't had a good-old ding-dong on a Disqus thread for some years. I recall one with Peter Lilley MP which would have been a wonderful example of denial in operation. Unfortunately, the interchange was lost as Disqus do not keep the comments for more than a handful of years and I failed to take a copy.

14880. Digby Scorgie at 12:49 PM on 13 April 2018
       Climate Science Denial Explained
       

       I wonder what (some) deniers would think if confronted with evidence that they've been caught for suckers.  Here for example is my paraphrase of a statement by Michael Burger, a law expert at the Sabin Center, in connection with a law suit against fossil-fuel companies:

       These fossil-fuel companies knew.  They knew that climate change was happening.  They knew that continued fossil-fuel production and use was causing it.  They knew that continued fossil-fuel production and use would only make it worse.

       They knew this, but they hid it.  And then they lied about it, and they paid other people to lie about it for them.  All the while they profited from it and plotted to profit more.  Ultimately, their actions caused harm, are continuing to cause harm, and are contributing to future harm.

       Some deniers might change their mind if they knew this history.  Of course, some are beyond persuading.

14881. Eclectic at 23:16 PM on 12 April 2018
       American conservatives are still clueless about the 97% expert climate consensus
       

       Scaddenp @17 , thank you for the link to RealClimate with the 27Aug2014 take-down of Judith Curry's "attribution" of modern sea level rise.   Gavin Schmidt (the article's author) was distinctly more scathing than I have been, about Curry's lack of logical thinking.

       I also read the near-200 comments following the article.  Some amusing stuff there — and with honorable mention of MA Rodger and his [posts #163 and onwards] "analysis" of Curry's golden panacea, the "BNO" [Big Natural Oscillation] which she waves about in all directions.   Actually, it didn't take long to read through the comments — my speed being helped by entirely skipping all posts by "Rob Ellison" (who has a track record of bloviating prolixity & crankdom & ne'er a useful point to make).

       But I regret my curiosity letting me follow the [final] post's link to WUWT  — and an article by [engineer] Matt Skaggs who promised to deliver a rigorous "Root Cause  Analysis of Modern Warming" sort of engineer's approach to things.   Alas, it turned out to be a complete waste of time . . . huge holes in his arguments.   Yes, I should have known better than to think that any WUWT article could deliver enlightenment (rather than just amusement).

       If I may quote from Gavin Schmidt : "In general, the shorter the time period, the greater potential for internal variability, or (equivalently) the larger the forced signal needs to be in order to be detected . . . ~ . . . Thus cutting down the period to ever-shorter periods of years increases the challenges and one can end up simply cherry-picking the noise instead of seeing the signal".      Very fitting — because that is Judith Curry's modus operandi : she cherry-picks a sufficiently-short time period of Mean Sea Level rise . . . where it is just conceivably possible that a fortuitous combination of "BNO" [Big Natural Oscillation, excuse the sarcasm] might explain a substantial minority of recent MSL rise.   But when you stand back and look at the bigger picture, you see that Curry's arguments are twaddle.

14882. scaddenp at 13:40 PM on 12 April 2018
       Climate Science Denial Explained
       

       If you were say a signed-up Democrat, and someone asked "what arguments would convince you to become a Republican", chances are your real answer "nothing could make me become a Republican". That would be partly about identity and partly about values, neither of which change easily. Once a question gets polarized around identity and values, changing a mind becomes impossible. Its vitally important to recognize the difference between questions which are value based ("Should someone who commits a crime be punished for the sake of the victim") and those which are evidence-based. (eg "Is CO2 changing climate"?).

       And dont forget that science is full of debates where people who should have had the critical analysis skills to do better, bitterly fought the evidence. "Science advances one funeral at a time".

14883. nigelj at 12:36 PM on 12 April 2018
       Climate Science Denial Explained
       

       I agree with all comments above that climate denialists score high with confirmation bias, but we are all at risk of confirmation bias to some extent. For example I like coffee and chocolate, so I hunt out research that finds benefits, and it takes me some effort to check research that shows problems, although I'm reasonably objective and disciplined compared to some people I know.

       But why would some people exhibit 1) extreme confirmation bias and 2) only in the direction of climate denialism? Come on think it through.

       The answer is the root cause of the confirmation bias with climate denialists has to be something and its mostly political ideology. Conservatives are more sceptical of the science for a range of reasons related to their deep seated instincts.

       Read this article which sums up the political ideology and confirmation bias and how they relate.

       Conservatives are possibly more susceptible to confirmation bias itself, but thats just a guess on my part. Its certainly not unique to any world view.

       While its natural to look for supportive evidence, its important to try to train yourself out of confirmation bias getting out of control. Because if you get totally wedded to some belief its hard to back down as pointed out above.

       Remember also that acceptance of the science is different from actually supporting changing energy systems to renewables and this is another area of potential scepticism, and while the two go together they dont always do this.

14884. scaddenp at 11:01 AM on 12 April 2018
       Climate Science Denial Explained
       

       Anyone wanting examples of extreme confirmation bias, follow "JeffDylan" (one of many sockpuppets that began as cosmowarrior as far as we know) and following sockpuppets on water vapour as a forcing starting here. You cannot help someone understand what they desparately do not want to understand.

       Climate scientists are pretty upfront about what data would cause them to doubt their theories and change their mind. It would be nice if climate "skeptics" could do the same but either they want something that the science (if they read it) says is impossible (eg "temperatures rise every year because CO2 rises every year")  or simply are so sure they are right, they cannot conceive of any observation that could change their mind.

14885. Lloyd Flack at 10:13 AM on 12 April 2018
       Climate Science Denial Explained
       

       And I mean by indulge that they do not even try to weaken their confirmation bias.

14886. Lloyd Flack at 09:47 AM on 12 April 2018
       Climate Science Denial Explained
       

       To be a denialist is to indulge in an extreme form of cofirmation bias. But they do not see themselves as doing that. Many times I have seen them claim that they are just askink for empirical evidence that humans are causing dangerous climate changes. They genuinely do see themselves that way and cannot see the special pleading that they indulge in.

       And then there is the claim by many of them that to call them denialists is to try to smear them by associating them with Holocaust denialists. This claim is self pitying and itself an attempt to smear critics of their behaviour. Again they cannot see how they appear to others.

       You have to somehow get them to see what they are actually doing. But you are asking them to not only admit that they were mistaken but that they were doing was improper. And that is hard.

14887. One Planet Only Forever at 08:26 AM on 12 April 2018
       2018 SkS Weekly Climate Change & Global Warming Digest #14
       

       Art Vandelay@11,

       The beneficial advancements for humanity that have been occurring may have occurred during the same time period that burning of fossil fuels was occurring, but that does not prove that the beneficial developments were due to fossil fuel burning. In fact, it is easier to argue that any current day activity that is perceived to be beneficial but relies on fossil fuel burning has no sustainable value, it has to be given up in the near future. Every admired perception that is due to fossil fuel burning is actually of no real value.

       It can also easily be claimed that more beneficial developments would have occurred if there had been an effective global effort to correct the unsustainable and damaging pursuit of benefit from fossil fuel burning. All the talent and effort and investment that was misdirected into fossil fuel burning ventures would have been able to produce sustainable improvements for humanity. Undeniably we could have developed far more renewable energy capability and far less energy intensive ways of living if fossil fuel burning had been curtailed starting in the 1970s and been globally completely banned by now.

       So, it is likely that if fossil fuel burning had been curtailed earlier, and the Sustainable Development Goals had been the objective of all global leaders, the world would currently be a much better place that it is with far less challenge to be dealt with going forward.

       From the perspective of developing a sustainable improved future for all of humanity, the burning of fossil fuels has been Significantly Unhelpful/Harmful. And it is undeniable that the developed popularity and profitability of that activity is continuing to delay the corrections of the understandably harmful and ultimately unsustainable activities that have incorrectly developed.

14888. scaddenp at 07:04 AM on 12 April 2018
       American conservatives are still clueless about the 97% expert climate consensus
       

       Well NorrisM, you could just look up the Ar5 and find it. (ch 10). The attribution statement and pseudo-skeptic responses are discussed here with numerous useful references.

14889. nigelj at 06:55 AM on 12 April 2018
       Climate Science Denial Explained
       

       I think scepticism about new scientific theories among the public forms a continuum from people with a naive and instant acceptance of new theories, to people with mild healthy scepticism, to people with a rigid permanant denial.

       You will convince mild sceptics with education, information, exposing the trikery of lobby groups, and showing that jobs lost in fossil fuels will be replaced with new jobs.

       About 60% of Americans accept climate science. Given acceptance of other scientific theories can get to 90% or more it seems theres room to convince more people.

       You wont change the core group of rigid denialists. Polls show its politically driven and thats hard to change. I would put their number at 10 - 20%. The best outcome would be to pressure the Republicans into accepting policies on renewable energy and revenue neutral carbon taxes.

14890. nigelj at 05:38 AM on 12 April 2018
       2018 SkS Weekly Climate Change & Global Warming Digest #14
       

       Art Vandelay @10

       I understand your ideas and good logic, but even just a temporary geoengineering of the N Hemisphere its still risky. It could still have unintended consequences, and I'm not sure how you would limit solar geoengineering to just the summer months, because particles in the atmosphere normally last a couple of years I think.

       Having said that, Steven Pinker in his book Enlightenment Now does mention the idea of a mild form of solar geoengineering as a temporary thing, until renewable energy is well developed and negative emissions technology sequesters remaining atmospheric carbon.

       Pinker acknowledges we are altering the climate and that geoengineering has risks, hence his idea of a mild, temporary solution. However I'm still sceptical, because once you geoengineer it tends to remove the pressure to reduce emissions.

       However like Pinker I try to keep an open mind on things and the idea needs research. 

14891. michael sweet at 03:51 AM on 12 April 2018
       American conservatives are still clueless about the 97% expert climate consensus
       

       Norrism:

       From Wikipedia":

       "Recently, it has become widely accepted that late Holocene, 3,000 calendar years ago to present, sea level was nearly stable prior to an acceleration of rate of rise that is variously dated between 1850 and 1900 AD. Late Holocene rates of sea level rise have been estimated using evidence from archaeological sites and late Holocene tidal marsh sediments, combined with tide gauge and satellite records and geophysical modeling. For example, this research included studies of Roman wells in Caesarea and of Roman piscinae in Italy. These methods in combination suggest a mean eustatic component of 0.07 mm/yr for the last 2000 years.[15]

       Since 1880, the ocean began to rise briskly, climbing a total of 210 mm (8.3 in) through 2009 causing extensive erosion worldwide and costing billions.[19]"

       They provide a peer reveiwed source.

       We find that sea level was stable for 3000 years until humans began seriously releasing carbon dioxide in 1850.  Then sea level starts to rise.  Scientists predicted that releasing carbon dioxide would cause sea level to rise.  The rise from 1900-1950 was caused by the carbon dioxide released from 1850 to 1950.  All of sea level rise is due to humans. 

       You cannot ignore the measured acceleration since 1900.  Sea level rise is currently about 4 mm/yr and accelerating.

       Curries waves are a figment of deniers imaginations.  They were proved incorrect by the extreme temperatures since she proposed the idea in 2014.  They are falsified by the measured data on sea level rise from 0 AD to 1900 AD.

14892. NorrisM at 02:30 AM on 12 April 2018
       American conservatives are still clueless about the 97% expert climate consensus
       

       michael sweet @ 14

       Thank you for your reference but I did request a comment from the IPCC Fifth Assessment.  Surely, the papers have not changed on this analysis since 2013.

       But even with the US Climate Report, these statements are not at the level of "Very High Confidence" (ie 90%) but rather "High Confidence".  Again, “High Confidence” means moderate evidence (some sources, some consistency) medium consensus.  "Likely" means at least a 66% chance of occurring.  In other words, there is no slam dunk agreement of the experts.  I think the reason why is that there is no clear explanation of what happened in the 1930-1940 period both as to temperatures and the rate of sea level rise at that time.

       As for your statement: "All of sea level rise and all of warming is caused by humans.", how can you say that all sea level rise is caused by humans when everyone agrees that the sea level has been rising at an average rate of 1.1 to 1.7 mm/yr between 1901 and 2010?  

       By the way, I have not really responded to your first reply to my long blog on sea level rise.  I have just been too busy on other things but I promise to get to it at some point.  But I will say that I have zero disagreement with the premise that when it comes to building major infrastructure like a nuclear plant, we probably should use a 1% risk scenario.  This may cut out Florida from a lot of infrastructure but so be it.  

14893. Gooble at 01:54 AM on 12 April 2018
       New resource: The Fact-Myth-Fallacy slide-deck
       

       Dissenting opinions are not allowed in the process of debunking. That makes debunking very effective.

       Moderator Response:

       [DB] This is an evidence-based venue.  While you are welcome to entertain a dissenting opinion, without credible evidence found in relevant scientific (peer-reviewed) sources to support them, you are not welcome to share those dissenting opinions in this forum and represent them as factual.
       
       Please read the Comments Policy for this site, and ensure that future comments are constructed to comply with it, before making further comments on it.

14894. sailrick at 00:47 AM on 12 April 2018
       Murry Salby finds CO2 rise is natural
       

       should read
       In response to one of my comments

14895. sailrick at 00:46 AM on 12 April 2018
       Murry Salby finds CO2 rise is natural
       

       Thanks again.  I posted a comment with the abstract from the Köhler et al (2017) paper that debunks Harde.  Also 10 lines of evidence of Human source added CO2, supplied by Dan Bailey.  
        
       I just noticed that supposed "skeptic" RealOldOne2 posted a comment with half a dozen links to WUWT, in response to one of my articles, while claiming SkS is just propagana.  Not much point in continuing the conversation

14896. MA Rodger at 00:25 AM on 12 April 2018
       Murry Salby finds CO2 rise is natural
       

       Eclectic @30,

       Yes. I was in error using the term "surface albedo" when I was meaning insolation 'absorbed at the surface' of which Hatzianastassiou et al. say "Our computed value of 43.7% for the part of solar radiation that is absorbed by the Earth’s surface, is smaller than the values given in previous studies, which are larger than 46%." And the difference they describe is more to do with atmospheric absorbtion & atmospheric albedo than surface albedo. So "surface albedo" was certainly the wrong term.

       sailrick @31,

       To put that surface radiation budget issue in context, it does suffer from larger levels of uncertainty than other parts of the global energy budget. One of the most active in the field is Martin Wild & if nothing else, the graphics in this Wild et al (2017) show the long-term changes that were being 'wielded' by that denialist.

14897. sauerj at 22:39 PM on 11 April 2018
       EPA’s war with California proves America needs a carbon tax
       

       Good article! A comprehensive, national carbon tax (levied at the source where it enters the economy, mine, well, port) that is also revenue-neutral (money 100% re-distributed) which allows 1) the tax to be significantly high so to have adequate economic "bite" (i.e. at least $100/m-ton CO2, ramped in place), while also 2) assuring its maximum political durability, is an absolute must to achieving any significant & sustained reduction in carbon emissions. Everything else will be futile.

       The hard part is building the political-will to enact such a rev-neutral tax macro-policy. Getting all climate warriors on the 'same page', screaming the same thing 'in unison' is essential to building this political-will. If you want to be a part of the only real solution to achieving carbon emission reductions, then join your local Citizens Climate Lobby chapter, and get involved! CCL is an amazing organization with loads of talent and resources, but to achieve real change requires everyone to get involved!

14898. Art Vandelay at 22:37 PM on 11 April 2018
       2018 SkS Weekly Climate Change & Global Warming Digest #14
       

       One Planet Forever @8, With respect I'm very aware of the downsides of burning fossil fuels but at the same time I also respect the fact that fossil fuels have largely 'fueled' the Industrial and technological revolutions of the 19th and 20th centuries.  For all of the negative health effects, and there are many, it's also impossible to deny the compelling data in areas of infant mortality, adult life expectancy, and global population growth during the fossil fuel epoc.  Of course now is the time to migrate to new energy sources and to walk a path to sustainability, difficult as that may be.   

14899. Art Vandelay at 22:24 PM on 11 April 2018
       2018 SkS Weekly Climate Change & Global Warming Digest #14
       

       nigelj@5, Points taken but I was thinking along the lines of polar regional NH and during the summer months only. Obviously, it would not be necessary to geoengineer all year round, and if isolated to the northern polar region it could help to reduce polar amplification - reduce the rate of sea ice loss and weakening of the NA current etc. 'Whitening' the atmosphere globally as you say would risk undesirable climate change to parts of the world that can least afford it, but if seasonal / regional geoengineering can be done without serious side effects and help to prevent global warming beyond 1.5 degrees K while the globe transitions to clean energy.......we would be crazy not to give it serious consideration.  Another point I would make is that a small amount of geoengineering sooner rather than later would also prevent the possible need to undertake serious global climate experiments if and when global climate change catastrophe becomes a reality.   

14900. CBDunkerson at 21:03 PM on 11 April 2018
       EPA’s war with California proves America needs a carbon tax
       

       bjchip, actually that's fiction.

       Franklin never said it.

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