In light of recent modeling results on the lifetime of CO2 in the atmosphere, I am concerned that the current time-integrated (not instantaneous) GWP estimate for CO2 has been underestimated and hence GWP's of other gases (esp short-lived gases) relative to CO2 have been overestimated. E.g., Eby et al., 2009: http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F2008JCLI2554.1 show that 20-30% of excess emissions of CO2 and 60-70% of the subsequent CO2-caused surface air temp anomally exists 10,000 years after emission. Isn't this (or is this?) a far larger total time-integrated GW effect than a mass equivalent emission of CH4? Experts please set me straight. Thanks, Greg
>Agreed, one has to consider a time period, so assume one takes a day >that when injected there is no decay over this period-so it might as >well be a second of time one takes-so virtually instantaneous. And >I'll assume linearity on methane absorption and logarithmic for CO2. > >So, for methane, humans have caused an increase of roughly 1000 ppb >which converts to about 3 GtCH4, and this causes a forcing of about >0.5 W/m**2 (at the tropopause) per IPCC. > >For CO2, we know that a doubling (so we'll say from 300 to 600 ppm >so we are in the range of interest) causes a forcing of about 3.6 >W/m**2 (at the tropopause). So, 300 ppm of CO2 in the atmosphere is >roughly 600 GtC or 2200 GtCO2 (and global warming potential is done >for CO2, I believe. > >So, if we take the ratio of forcing to mass for CH4 divided by the >ratio of forcing to mass for CO2, we get a rough estimate of the >instantaneous GWP, so > >[0.5/3]/[3.6/2200] equals roughly 100 > >for the ratio at t=0 (so allowing for no decay) of the radiative >forcing caused by a unit mass of CH4 added to the atmosphere to a >unit mass of CO2 added to the atmosphere. > >Not exact, but plausible. > >Mike > > > > >On 11/16/09 3:42 AM, "Peter Read" <<>pre...@attglobal.net> wrote: > >John, Andrew >Re "BTW, does anybody know the _immediate_ warming potential of methane?" >Someone will correct me no doubt but my understanding is that >warming is a rate process measured in W/m^2 >So "instantaneous" [[== "immediate"?]] warming is an incorrect concept >Unless it continues for a second, a week, a year, 25 years, for >whatever, no warming takes place. >So it is necessary to multiply by a duration to get joules/m^2 >It's how many joules get into the low albedo meltwater on top of >Greenland's ice that decides how much gets melted each year to fall >down crevasses and lubricate the eventual collapse of large areas of >ice into the oceans. >Meaning that the integral [[roughly]] under the CO2 level curve is >what matters [multiplied by the warming potential over that period] > when it comes to measuring threats of Greenland's collapse >So the key issue is duration - how long elevated greenhouse gas >levels last and how to get them down. >Think that's right >Peter > > >----- Original Message ----- > >From: John Nissen ><<mailto:j...@cloudworld.co.uk>mailto:j...@cloudworld.co.uk> > >To: <>andrew.lock...@gmail.com > >Cc: geoengineering ><<mailto:geoengineering@googlegroups.com>mailto:geoengineering@googlegroups.com> > > > >Sent: Monday, November 16, 2009 6:18 PM > >Subject: Re: [geo] Re: Rejected - a simple argument for SRM geoengineering > > > >Hi Andrew, > >You say: "I don't oppose John's argument, but the evidence on the >severity of the problem is far from conclusive." I disagree. > >The methane presents a very real risk - because of the uncertainty >on timing combined with the potential size of methane discharge - >perhaps even enough to cause thermal runaway due to positive >feedback, as is thought to have happened in the past [1]. Risk >management involves identifying events and assessing them in terms >of their likelihood and magnitude of impact [2]. Thus something > with a small likelihood (such as rapid massive methane excursion) >can have a high risk, if the magnitude of impact is sufficiently >large (and you can't get much larger than thermal runaway). > >It is possible that much or most of the methane trapped in frozen >structures has built up over hundreds of thousands of years. There >is little sign of massive methane discharge in the ice record. In >fact methane seems to track the temperature even better than CO2 >[3]. > >But of course methane discharge is not the only high risk event - >there is also the Greenland ice sheet disintegration. > >BTW, does anybody know the _immediate_ warming potential of methane, > as opposed to the 20 year value (72), 100 years (25) or 500 years >(7.6)? The lifetime is only 12 +/- 3 years. See [4]. > >Cheers, > >John > >[1] ><http://*en.wikipedia.org/wiki/Clathrate_gun_hypothesis>http://*en.wikipedia.org/wiki/Clathrate_gun_hypothesis > >[2] > <http://*en.wikipedia.org/wiki/Enterprise_risk_management>http://*en.wikipedia.org/wiki/Enterprise_risk_management > > > >[3] ><http://*answers.yahoo.com/question/index?qid=20090329215018AAxqYFk>http://*answers.yahoo.com/question/index?qid=20090329215018AAxqYFk > > > >[4] ><http://*en.wikipedia.org/wiki/Greenhouse_gas>http://*en.wikipedia.org/wiki/Greenhouse_gas > > > >--- > >Andrew Lockley wrote: > >At present the likely methane excursion is far from clear. > Further, it is also unclear how quickly the total excursion will > occur. The excursion rate is highly significant due to the short >life of methane in the atmosphere. The methane ends up as CO2, in >itself a major issue. However, the CO2's likely effect is nothing >compared to the devastating temperature spike which may result from >a sudden methane excursion. > > >I don't oppose John's argument, but the evidence on the severity of >the problem is far from conclusive. We need much more research >into: > >1) The methane reservoir in clathrates and permafrost > >2) The size of potential methane sources currently frozen as organic detritus > >3) The likely changes to the GWP of methane in future atmospheres, >as the levels of hydroxyl radicals etc. shift over time and as a >direct result of methane excursion. Recent research on this asks >more questions than it answers. > > > >My personal feeling is that the range of likely outcomes is from a > significant amplification of AGW, right up to a 'Great Dying' sized > mass-extinction event when we come within a sneeze of sterilising >the entire planet. I'd be tempted to bet on the latter, but I >wouldn't be around to collect the winnings, so I'll keep my wallet >in my pocket. > > > >My suggestions is that geoengineers look at ways to clean up the > methane from the atmosphere, and then lock down the resulting >carbon. My guess is we've got about 50 years to do this, but >virtually no time at all if the methane can't be dealt with once >it's in the atmosphere. Therefore, I'd support John out of >precautionary principle-based reasoning. > > > >A > > >2009/11/15 jim woolridge <<>jimwoolri...@hotmail.com> > > >Nice one, John; the train of argument is clear (of limpid clarity, in >fact!) The problem is that the people and institutions addressed are >in the business of politics, the art of the possible, rather than in >the business of logical evaluation. They hear what you are saying and >must see the validity of it. But politically what is true and what is >doable do not always coincide, as we all know from as many examples as >one cares to ennumerate. > >We have to keep hammering away at the arguments, to the point at which >they are generally understood and accepted, and also keep on >politicking in the sure and certain hope that eventually the >acceptance of the arguments and the cowardice/caution/horse sense/ >opportunistic careerism of the politicos will achieve the right kind >of intersection. In the next year or so (& wouldn't it be a great >help to have the environmental NGOs on board.) > > > >On Nov 12, 10:51 pm, John Nissen <<>j...@cloudworld.co.uk> wrote: >> It is incredible. It is so obvious. >> >> 1. Global warming is driven largely by atmospheric CO2 according to the >> concentration above its pre-industrial level; and >> >> 2. After emissions are stopped it could take millenia for the >> concentration to fall back to that level, because the effective lifetime > > of some of that excess CO2 is many thousands of years. >> >> Therefore: >> 3. Drastic emissions reduction, even to zero overnight, cannot and will >> not stop the Arctic continuing to warm for decades. >> >> Therefore: >> 4. The Arctic sea ice will continue to retreat, accelerating the warming >> due to the albedo effect. >> >> Therefore: >> 5. The permafrost will continue to thaw releasing increasing quantities >> of methane, a potent greenhouse gas, potentially adding many degrees to >> global warming; and >> >> 6. The Greenland ice sheet will become increasingly unstable, >> potentially contributing to an eventual sea level rise of 7 metres. >> >> Therefore: >> 7. To avoid these two catastrophes, we need to cool the Arctic quickly >> enough to save the Arctic sea ice; and >> >> 8. Probably the only feasible way to do this is through solar radiation >> management (SRM) geoengineering. >> >> 9. SRM is not a last resort, it is needed now to cool the Arctic. >> >> It is incredible that people do not seem to follow this train of logic - >> it is so obvious. >> >> Yet when I challenged a panel of geoengineering experts to refute this >> argument, the response was that geoengineering (even just to cool the >> Arctic) was too dangerous - not that the argument was false! [1] >> >> So we continue to hear politicians and their advisers claiming that >> emissions reduction alone can be sufficient to keep the planet safe. [2] >> >> And we continue to hear geoengineering experts saying that >> geoengineering should only be used as a last resort. [3] >> >> How can this mindset be changed quickly, to avoid leaving geoengineering >> too late? >> >> John >> >> P.S. Apologies to those who have heard this all before and accept the >> logic as self-evident. >> >> [1] This challenge was put to the panel at the launch of the Royal >> Society geoengineering report, on September 1st, with response from the >> team leader and panel chairman, Professor John Shepherd. >> >> [2] For example at the geoengineering hearing at the House of Commons, >> November 2008. >> >> [3] For example at the congressional hearing on geoengineering, November >> 2009. > >-- > >You received this message because you are subscribed to the Google >Groups "geoengineering" group. >To post to this group, send email to <>geoengineer...@googlegroups.com. >To unsubscribe from this group, send email to ><>geoengineering+unsubscr...@googlegroups.com ><<mailto:geoengineering%2bunsubscr...@googlegroups.com>mailto:geoengineering%2bunsubscr...@googlegroups.com> > >. >For more options, visit this group at ><http://*groups.google.com/group/geoengineering?hl=>http://*groups.google.com/group/geoengineering?hl=. > > > > >-- >You received this message because you are subscribed to the Google > Groups "geoengineering" group. >To post to this group, send email to <>geoengineer...@googlegroups.com. >To unsubscribe from this group, send email to ><>geoengineering+unsubscr...@googlegroups.com. >For more options, visit this group at ><http://*groups.google.com/group/geoengineering?hl=>http://*groups.google.com/group/geoengineering?hl=. > > > > > >-- >You received this message because you are subscribed to the Google > Groups "geoengineering" group. >To post to this group, send email to <>geoengineer...@googlegroups.com. >To unsubscribe from this group, send email to ><>geoengineering+unsubscr...@googlegroups.com. >For more options, visit this group at ><http://*groups.google.com/group/geoengineering?hl=>http://*groups.google.com/group/geoengineering?hl=. > > > > > > > >No virus found in this incoming message. >Checked by AVG - www.*avg.com >Version: 8.5.425 / Virus Database: 270.14.67/2505 - Release Date: >11/15/09 19:50:00 > >-- >You received this message because you are subscribed to the Google >Groups "geoengineering" group. >To post to this group, send email to <>geoengineer...@googlegroups.com. >To unsubscribe from this group, send email to ><>geoengineering+unsubscr...@googlegroups.com. >For more options, visit this group at ><http://*groups.google.com/group/geoengineering?hl=>http://*groups.google.com/group/geoengineering?hl=. > >-- > >You received this message because you are subscribed to the Google >Groups "geoengineering" group. >To post to this group, send email to geoengineer...@googlegroups.com. >To unsubscribe from this group, send email to >geoengineering+unsubscr...@googlegroups.com. >For more options, visit this group at >http://*groups.google.com/group/geoengineering?hl=. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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