tag:blogger.com,1999:blog-7612793.post314848747280220929..comments2024-03-27T23:59:49.801+00:00Comments on Stoat: Sea level rise in picturesWilliam M. Connolleyhttp://www.blogger.com/profile/05836299130680534926noreply@blogger.comBlogger7125tag:blogger.com,1999:blog-7612793.post-22236420221955326602018-05-23T18:55:26.071+00:002018-05-23T18:55:26.071+00:00Also relevant is this discussion paper:
https://ww...Also relevant is this discussion paper:<br />https://www.earth-syst-sci-data-discuss.net/essd-2018-53/essd-2018-53.pdf<br /><br />Figure 3 shows the rate of SLR over the satellite period, and I think one conclusion of the paper is that observed acceleration has been about 0.1 mm/year/year, roughly consistent with the Nerem paper that ATTP references. The paper also does a nice job of attributing SLR to various components (thermal, ice sheets, glaciers, impoundment, etc.)... though, in a major oversight, they leave out the Cliffs of Dover.<br /><br /><br />Regarding 20th century SLR: I generally prefer the Hay/Kopp approach (https://www.nature.com/articles/nature14093.pdf). I will note that as far as I understand it, the tide gauge approach and the satellite approach actually agree reasonably well in terms of post-1990 sea level rise: I think the apparent rate change there is a visual illusion resulting from the two linear fits. In any case, Figure 4 of Hay et al. 2015 is the most useful for understanding how the rate of sea level rise has changed over time. The peak in the 1940s is what confuses some contrarians, as they seem to be under the impression that if the climate has ever changed naturally, then we can't attribute modern changes to anthropogenic influences. Hay et al. found a smaller 1940 peak than some other papers - these other papers (in particular, Jevrejeva et al., whose methodology was critiqued by RC) were what led the IPCC to (erroneously, IMO) state that the 1920-1950 rate of SLR was likely as large as present-day (I think it was likely less, though maybe not "very likely"). <br /><br />It sounds like you are also be interested in the "expected" SLR question: Kopp et al (http://www.pnas.org/content/pnas/113/11/E1434.full.pdf) gets a bit at this, finding that at least 40 percent, and possibly more than 100 percent, of the 20th century sea level rise is due to anthropogenic factors.<br /><br />-MMM<br />Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-7612793.post-2020763901638878772018-05-23T15:54:41.653+00:002018-05-23T15:54:41.653+00:00> reveal a substantial increase in the rate
Ah...> reveal a substantial increase in the rate<br /><br />Ah. You actually read the paper. I only ctrl-f'd for "acceleration".<br /><br />I find myself uninterested in the acceleration. I'm inclined to think it is there, but not to care very much. ATTP's paper reffed does indeed make a better case. But somewhat missing is what acceleration you'd actually expect. It makes some vague comparison to GCM results, but it's rather half-hearted.William M. Connolleyhttps://www.blogger.com/profile/05836299130680534926noreply@blogger.comtag:blogger.com,1999:blog-7612793.post-29421390340065515492018-05-23T15:47:44.500+00:002018-05-23T15:47:44.500+00:00>"In Figure 29 of that paper, Hansen claim...>"In Figure 29 of that paper, Hansen claims to show that sea level rise has been accelerating" is, AFAIK, wrong. That's how ATTP used it, but Hansen doesn't.<br /><br />It's kind of ambiguously non-committal about the graph, but the text referencing it does say the rate of sea level has increased:<br /><br /><i>We do not argue for the details in Fig. 29 or suggest any change points for the rate of sea level rise, but the data do reveal a substantial increase in the rate of sea level rise</i><br /><br />Though, as you say, if they were particularly interested in emphasising acceleration, they could have done a much better job.<br /><br />---------------------------<br /><br />>But that only makes sense if H is looking for acceleration. If he isn't, then it also has the effect - which WE strangely neglects to mention - of reducing prior SLR.<br /><br />Maybe you didn't get the memo? "Skeptics" don't care about the magnitude of 20th Century SLR anymore. In fact, the more the merrier. Everything is now about acceleration.<br /><br />---------------------------<br /><br />I think part of the issue is a confusion over what is meant by acceleration. Some of that is because "skeptics" generally want to be confused. But also many of the early mainstream assessments (such as the infamous Munk's enigma) tended to focus only on GHG forcing, with the result of a very clear expected acceleration during the 20th Century, and more recent assessments (e.g. AR5) have continued to imply importance of 20th Century acceleration.<br /><br />The thing is though, when you simply add in natural forcings - in particular the shift from very strong 19th Century volcanic forcing to a quiet period up to 1960, increased solar forcing in the early 20th Century, then resumption of volcanic forcing in the late 20th Century - the result is a much weaker expectation of only slight acceleration. When you further add in uncertainty over anthropogenic aerosol forcing, it's quite plausible that we would expect to see deceleration over the 20th Century.<br /><br />Acceleration during the 20th Century simply isn't a robust expectation of current climate science, yet that's what many seem to want to test. As far as I can see the two main robust expectations are:<br /><br />1) Faster 20th Century rate than the average of the past millennium or so<br /><br />2) A faster rate over the past 30-odd years than the 20th Century average<br /><br />Both these check out as far as the available evidence goes.PaulSnoreply@blogger.comtag:blogger.com,1999:blog-7612793.post-84887407455017651972018-05-23T15:24:29.963+00:002018-05-23T15:24:29.963+00:00There also appears to be a recent paper suggesting...There also appears to be a recent <a href="http://www.pnas.org/content/early/2018/02/06/1717312115.short" rel="nofollow">paper</a> suggesting that sea level is accelerating at 0.084 +- 0.035mm/y^2. This also appears to be based only on the satellite data, which is somewhat different to what I was suggesting (it appears to be faster now than it was before).Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-7612793.post-69049087592101272722018-05-23T15:06:19.355+00:002018-05-23T15:06:19.355+00:00Maybe I should have been more careful and said som...Maybe I should have been more careful and said something like "probably" but unless I'm missing something, it's seems reasonable to interpret that graph as suggesting that sea level is rising faster today than it did earlier this century (and faster than the 20th century average). The claim being made in the article was that it hasn't changed. I guess one could test the null hypothesis of "there has been no change in the rate of sea level rise", which I think one would reject (although, admittedly, I haven't done the formal statistical analysis). I believe there are also other indicators that sea level rise is accelerating (<a href="http://www.realclimate.org/index.php/archives/2011/07/is-sea-level-rise-accelerating/" rel="nofollow">here</a>, for example, but maybe a bit old).Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-7612793.post-29466329977619043462018-05-23T14:30:30.366+00:002018-05-23T14:30:30.366+00:00Oh noes, I knew I should have written faster. Neve...Oh noes, I knew I should have written faster. Never mind. While WE points out some things, as usual he gets others wrong. "In Figure 29 of that paper, Hansen claims to show that sea level rise has been accelerating" is, AFAIK, wrong. That's how ATTP used it, but Hansen doesn't. He also claims Hansen is "flattening the record and thus reducing the prior sea level trends … which of course makes it seem like there is more acceleration than might actually exist". But that only makes sense if H is looking for acceleration. If he isn't, then it also has the effect - which WE strangely neglects to mention - of reducing prior SLR.William M. Connolleyhttps://www.blogger.com/profile/05836299130680534926noreply@blogger.comtag:blogger.com,1999:blog-7612793.post-16089914205323610632018-05-23T14:13:13.984+00:002018-05-23T14:13:13.984+00:00Sorry, you got beaten to it by your old friends.Sorry, <a href="https://wattsupwiththat.com/2018/05/22/changes-in-the-rate-of-sea-level-rise/" rel="nofollow">you got beaten to it by your old friends</a>.PaulSnoreply@blogger.com