In terms of Ken's first comment, perhaps this is a bit aside the point, but I'm not sure it's just rate or rate plus amount of change: if you look at the (admittedly awfully rough) Phanerozoic climate reconstruction, and look at where the 5 big extinctions took place, it's noteworthy that there seems to have been a spike that was both much bigger & faster at the end of the Carboniferous, without any mass extinction, than at the end Devonian, where there was. All five occurred, on the other hand, when temps seem to have been a couple of degrees warmer. So maybe it's the absolute temperature, plus rate & change: it would seem like once it gets above ~60F, then perturbations upwards seem to easily lead to die offs.....
Nathan On Jan 27, 8:31 pm, Mike MacCracken <mmacc...@comcast.net> wrote: > The Greenland ice sheet is very likely a good example of where hysteresis > would apply. Once gone, or mostly gone, it is not at all clear it would come > back if temperatures were returned to 1950 level, for example. > > I sent in a lot of comments on the first draft and look forward to seeing if > they paid attention. From at least some of the comments so far, it appears > that the some of the same problems still exist. > > Mike > > On 1/27/12 7:49 PM, "Gregory Benford" <xbenf...@gmail.com> wrote: > > > > > I like both Ken's and Andrew's comments (especially Ken on their assumption > > that a CROPS strategy will definitely cause damage at depth). > > > Another point often elided in such reports is hysteresis--an effect at best > > buried in the geoengineering literature. This is the dependence of a system > > not only on its current environment but also on its past environment. This > > dependence arises because the system can be in more than one internal state. > > To predict its future evolution, either its internal state -- essentially > > impossible to know for our climate drivers -- or its history (ditto, at > > least > > in detail) must be known. We physicists see this in ferromagnetic materials. > > Increase an electric field and the system attains a certain internal field; > > reverse the electric field and you don't just go back to the prior internal > > field state. Many physical systems show this, and so does climate, > > apparently, > > at least for scales of centuries. > > > This is often invoked by "tipping point" but a full report should show some > > knowledge of the larger truth: beyond some point we may not be able to get > > back to the past state for very long times. That's why you should have > > several > > "knobs" you can turn for a given system, to work the complexities, knowing > > that perhaps no complete solution exists. (Control Theory 101) > > > Gregory Benford > > UC Irvine > > > On Fri, Jan 27, 2012 at 4:28 PM, Andrew Lockley <andrew.lock...@gmail.com> > > wrote: > > >> My personal views on the report's exec summary. Please excuse any > >> instances > >> of going beyond the literature, or errors generally. I've not > >> reference-checked any of this (due to considerations of time management and > >> general laziness): > > >> Lose the hypen! It's geoengineering :-) > >> Geoeng proposals aren't limited to SRM and CDR. There's also heat > >> transport, > >> cirrus stripping, etc. > >> SRM - worth pointing out the tension between SRM for temp and for MSL > >> control. You need it colder to get MSL under control. > >> AFAIK, surface albedo modification is now considered to be a bit of a 'lame > >> duck' technology, as recent studies have shown large and dangerous impacts. > >> Methane hacking techniques have already been developed. Zhou, Stolaroff, > >> Gauci, etc. have all published or are publishing on this, and I've > >> presented > >> but not yet published. > >> It is worth mentioning black carbon and trop. sulfur aerosols in the same > >> breath as SRM. It's virtually the same concept. > >> BECCS/BECS merits a mention in the lead section, esp due to relevance to > >> CBD > >> Retained LGM refugia, especially in TRFs, merit a mention - many are > >> especially vulnerable at present, and this issue needs consideration > >> specifically in the context of the CBD generally. > >> The point needs to be made that bifurcations in the climate system are not > >> necessarily detectable as you pass them (e.g. creating taliks in permafrost > >> overlying free gas reservoirs). A simple analogy is crossing the event > >> horizon of a large black hole. You don't necessarily realise you're doing > >> it, but you're doomed regardless. > >> Any assumption that 450 is a safe target is pure speculation. We're > >> already > >> seeing globally dangerous changes in the Arctic, and that's with trop. > >> sulfur > >> masking current warming. > >> Rise in MSL is a specific biodiversity threat which needs to be discussed. > >> Loss of entire islands, plus rapid retreat and salination of wetlands, > >> mangroves, etc. cannot be ignored. The tipping element of this shift is > >> critical. We're perhaps decades away from losing Greenland, even if the > >> changes will take centuries to execute. The MSL benefits of SRM need to be > >> specifically pointed out. It's really the only game in town if you want to > >> slam the brakes on MSL rise. > >> SRM isn't a direct fix for CO2-induced surface temp changes (eg SRM is > >> relatively stronger in the day, CO2 is relatively stronger at night). > >> Diffusion of solar radiation has biodiversity effects on plants, possibly > >> increasing GPP, and may also affect animals (esp birds and insects) which > >> may > >> rely on blue skies and polarized light for navigation, circadian rhythm, > >> etc. This is generally poorly researched at present. Key ecosystem > >> members, > >> e.g. pollinating insects, may be severely affected. > >> CO2 geological storage has non-trivial consequences for lithospheric > >> microbial communities, which are virtually a closed book to current > >> science. > >> Specific mention of the risks of disrupting methane fossilisation through > >> OIF > >> needs to be made - we could end up with less stable methane reservoirs than > >> would otherwise be the case. Currently, it's methane production which is > >> discussed in the report. Again, this area is poorly understood. > >> CROPS ocean storage needs to be explained in the light of poor current > >> knowledge of benthic fauna, flora, bio-geography and various other factors. > >> It's not unlike throwing your bedpan contents into the street without > >> looking > >> what's below first. > >> Moral hazard and reverse moral hazard should be mentioned in the exec - ie > >> the conflicting possibilities that we don't act because geoengineering is > >> being considered, or alternatively that we act more rapidly because > >> geoengineering is a 'big stick' which frightens people into action. Two > >> studies report the latter effect as dominant over the former. > >> Termination shock should be mentioned specifically in the context of a > >> capacity failure, ie that future generations lose the technology or > >> societal > >> capacity to maintain a geoeng programme. This is a major risk to > >> biodiversity. In extremis, we could experience a rise of perhaps 6C in > >> perhaps 3years. That will kick the climate system in the guts, and have > >> potentially devastating effects on slow-growing plants such as > >> cliax-vegetation trees, which cannot change range rapidly. > >> More needs to be made of the potential for changes to precip as a result of > >> SRM, eg considering the work of Vizy et al on Amazon dessication. > >> The synthesis section repeats the tired old mantra of mitigation, namely > >> that > >> it is sufficient alone. There are no credible technological/political > >> paths > >> which could reduce emissions sufficiently to guarantee safety. Indeed, it > >> is > >> no loger certain that even a complete and immediate halt to all emissions > >> can > >> absolutely guarantee a safe future climate (particularly WRT MSL rise, and > >> more speculatively, WRT to methane excursions). The point needs to be made > >> that we can no longer consider geoeng as an 'optional extra'. It may be > >> part > >> of a mix which is essential if the climate system is to be safely > >> stabilised. > >> Legal matters deserve a mention, such as the London convention. The > >> compatibility of geoeng with existing law, and the potential disruption to > >> existing protections, cannot be ignored. > > >> A summary paragraph should be inserted, and I suggest > >> "Geoengineering mave have potential to mitigate some of the biodiversity > >> impacts of climate change, by reducing the temperature rise from a given > >> emissions trajectory. However, a successful geoengineering programme would > >> need to be maintained, and in the case of SRM, any disruption could be more > >> dangerous than a no-intervention scenario. Geoengineering remains an > >> emergent discipline, and key aspects of its effects, including those on > >> biodiversity, remain poorly understood. It must be stressed that > >> geoengineering is a broad pallette of technologies, and generalisations > >> cannot easily be made. There are sociological and political risks to > >> geoengineering technologies, some of which may take substantial effect even > >> before deployment. Consideration of geoengineering technologies must be > >> made > >> against a background where major instabilities or bifurcations in the > >> climate > >> system are poorly understood. This lack of understanding provides both a > >> reason to consider geoengineering technology, and also a risk inherent in > >> its > >> deployment. Generally, it cannot be assumed that emissions cuts can alone > >> guarantee a safe outcome for the biosphere, and thus due consideration of > >> geoengineering technologies is essential.' > > >> On Jan 27, 2012 5:39 PM, "Ken Caldeira" <kcalde...@carnegie.stanford.edu> > >> wrote: -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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