Doug, If it where only the Greenland ice sheet that was suffering catastrophic and irreversible change, we might be able to relax and wait 10 to 15 years, but every part of the world and all it's ecosystems are facing similar destructive change, from the coral reefs to the subsea permafrost. This is happening as the global population is heading towards 10 billion with almost everyone already at each throats.
If we delay SRM then the scale of the necessary intervention will grow with the delay, most likely exponentially, and the risks of unintended consequences or out right failure will grow accordingly. At the same time, society could be at a point of break down making any coordinated plan virtually impossible and debates about agreeing on global governance irrelevant. Maybe some elements of the paper that was posted can be quibbled over, but the need to make an urgent start on SRM can't be. Kevin On Sat, 15 Aug 2020, 22:35 Douglas MacMartin, <dgm...@cornell.edu> wrote: > Hi Mike, > > > > - I don’t know (and I’m not sure anyone really does) how much > Greenland ice sheet mass loss can accelerate, but agree that it won’t stay > at the current rate. > > - Mainly my point was that the media link Andrew sent was silly > by implying that the 6m could happen in decades (even if it didn’t > technically say that), and the paper doesn’t make any claims about how much > the loss rate will accelerate… and to support the claim that geoengineering > is the **ONLY** way to avoid catastrophic sea level rise requires > evidence that we need to intervene now rather than over the rest of the > century. I do agree that there’s good reason to suspect that Andrew’s > claim may be true, but it is certainly not supported by the paper he was > referring to, and I don’t think we can prove that the claim is true. > > - Paleo evidence makes it clear that staying at even the current > CO2 levels for millennia would be catastrophic. It doesn’t do a great job > of constraining how rapidly we need to change, e.g. if CDR over the rest of > the century would also be an adequate alternative to SRM. (And paleo > evidence also shows that it is possible to get ~5m of SLR in a single > century, but that’s coming out of the last glacial when there was a lot > more available to be melted, and that doesn’t say that it is possible to > get anything close to that this century.) > > - Arguably this is simply quibbling over whether we can prove > we’re past the point where even aggressive CDR would work, or whether > there’s simply a risk that we’re past that point, in which case arguing > over whether that is 20% or 50% or 10% might not matter for policy. I do > agree that we are gambling with the climate, and with odds that no-one > would accept in any other circumstance. > > - Personally, given how little research has been done, I don’t > think there’s strong justification for saying that the long-term climate > consequences of waiting another 10-15 years for research (and to develop > governance capacity) will be so bad that we should go ahead and deploy > something now without doing the research (though if we did deploy something > now, I’d worry more about the societal response than the physical issues). > But, just like the US didn’t use the first few months of this year to > prepare for covid when it knew it was coming, it would be truly awful to > not do the research now, leaving us in the same boat yet another decade > later. > > doug > > > > *From:* Michael MacCracken <mmacc...@comcast.net> > *Sent:* Saturday, August 15, 2020 12:54 PM > *To:* Douglas MacMartin <dgm...@cornell.edu>; andrew.lock...@gmail.com; > geoengineering <geoengineering@googlegroups.com> > *Subject:* Re: [geo] Background-Greenland collapse > > > > 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:* geoengineering@googlegroups.com <geoengineering@googlegroups.com> > <geoengineering@googlegroups.com> *On Behalf Of *Andrew Lockley > *Sent:* Saturday, August 15, 2020 3:40 AM > *To:* geoengineering <geoengineering@googlegroups.com> > <geoengineering@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 geoengineering+unsubscr...@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 geoengineering+unsubscr...@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. > To unsubscribe from this group and stop receiving emails from it, send an > email to geoengineering+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/geoengineering/CH2PR04MB69360BBA550F9276C54C33218F410%40CH2PR04MB6936.namprd04.prod.outlook.com > <https://groups.google.com/d/msgid/geoengineering/CH2PR04MB69360BBA550F9276C54C33218F410%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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