Mike, Douglas thinks: "it is possible that neither of those options would arrest mass loss without cooling beyond preindustrial, and that over the ensuing millennium we would eventually lose our coastal cities no matter what we do, "
But it is curious how may former seaports have ended up stranded inland by sediment transport- Troy and Pisa fpr instance.We need to consider how many of "our" major coastal cities existed in recognizable form a hundred, let alone a thousand years ago? Modern demographics have driven the rise of skyscrapers out of former swamps from Miami to Singapore, and experience architectural rollover on a time scale reckoned in generations, not centuries. Coastal plains may be doomed, but San Francisco and Hong Kong are a ar cry from Houston and Lagos. Has the IPCC mapped and counted the fraction of current coastal city populations that can gain a meter of elevation by walking a kilometer inland from the neighborhoods in which they presently reside? There's more at issue than urban islands like Venice. Cities have a life of their own , and wherever waterfronts can migrate inland, waterfront properties will continue to be built behind them On Saturday, August 15, 2020 at 12:54:14 PM UTC-4 Mike MacCracken wrote: > Hi Doug et al.--I'm a bit late to this particular conversation, but I am > astonished by the suggestion that Greenland can only cause such a small > potential rate of rise in sea level. There was just a kerfuffle with the > IPCC authors on their draft projections of rates (see attached letter). > While surface melt rate may be relatively slow as often calculated, it is > not the main loss of mass process--ice stream flow is very likely the major > loss rate once it gets going and the calculations that are done in most > models do not include this term, nor do they include the effects of ice > shelf thinning that is going on. From the peak of the last interglacial to > 8 ka, sea level rose at an average rate of a meter per century while global > average temperature rose at an average rate of a degree C per 2000 years, > and the CO2 concentration was less than 300 ppm. The documentary "Chasing > Ice" shows how fast ice can disappear, and not just in the ice stream > calving that is the most amazing aspect of that film. And paleo evidence > also makes very clear that ice sheets go away much faster than they build > up. > > And the question is not so much when the cities will be under water as > when it will become inevitable that they will be under water--given that > consideration and the paleo sensitivity being something like 15-20 meters > per degree C warming (and this is not just me saying this, but see Eric > Rignot talk to the NAS last year--see https://vimeo.com/332486918 ). > > Based on this sensitivity, we're already past the point where it would be > good to have climate intervention underway if we want to avoid significant > and early risk to our cities with a very high likelihood (and this is the > criterion that is often used in building infrastructure--avoiding 1 in 100 > year events or even rarer ones--consider the Dutch for their levees--1 in > 10,000 year storms). > > Mike MacCracken > > > > > > > On 8/15/20 7:03 AM, Douglas MacMartin wrote: > > What is not correct in the media report is this sentence: “This process, > however, would take decades.” Well, I guess arguably that’s true, it’s > just it would take a LOT of decades. Melt rate is currently of order > 1-2mm/yr equivalent SLR, so to get the 6m from melting all of Greenland > would take a few thousand years. Obviously it can speed up a lot, but > “hey, it’s losing mass” does not remotely imply “therefore we only have a > few decades before we lose our coastal cities”. So no, you can’t use this > study to claim that geoengineering is required to keep our coastal cities. > The problem with relying on mitigation+CDR is time-scale, but this study > doesn’t prove that our response time-scale needs to be faster than what CDR > can (at least hypothetically) provide. > > d > > *From:* geoengi...@googlegroups.com <geoengi...@googlegroups.com> *On > Behalf Of *Andrew Lockley > *Sent:* Saturday, August 15, 2020 3:40 AM > *To:* geoengineering <geoengi...@googlegroups.com> > *Subject:* [geo] Background-Greenland collapse > > > > If this study is correct https://www.nature.com/articles/s43247-020-0001-2 > > And is correctly reported here > https://mobile.reuters.com/article/amp/idUSKCN25A2X3 > > Then it appears to back up a point that I have been making for a long > time: geoengineering is required, if we are to keep our coastal cities. I > do not see economic or political feasibility for large scale CDR to tackle > historic emissions, and thus the task must fall to SRM. > > > > Nobody has managed to rause an objection to this argument to date. I'd be > grateful if those who might disagree were to raise counter arguments now. > > > > If the situation is as I understand it, prevarication has no clear > benefits, and we should thus move quickly to readiness for deployment. > > > > Andrew > > > > > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to geoengineerin...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/geoengineering/CAJ3C-07%2BJc0dmp26W2_H08Rsrs1V_sjEs1pkG6xuZZ75OcTa%2Bw%40mail.gmail.com > > <https://groups.google.com/d/msgid/geoengineering/CAJ3C-07%2BJc0dmp26W2_H08Rsrs1V_sjEs1pkG6xuZZ75OcTa%2Bw%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to geoengineerin...@googlegroups.com. > > To view this discussion on the web visit > https://groups.google.com/d/msgid/geoengineering/CH2PR04MB6936220B9B7203A2CB55EA4B8F410%40CH2PR04MB6936.namprd04.prod.outlook.com > > <https://groups.google.com/d/msgid/geoengineering/CH2PR04MB6936220B9B7203A2CB55EA4B8F410%40CH2PR04MB6936.namprd04.prod.outlook.com?utm_medium=email&utm_source=footer> > . > > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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