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 I¹ll 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 we¹ll 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" <[email protected]> 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:[email protected]> >> >> To: [email protected] >> >> Cc: geoengineering <mailto:[email protected]> >> >> 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 >> >> [2] http://en.wikipedia.org/wiki/Enterprise_risk_management >> >> [3] http://answers.yahoo.com/question/index?qid=20090329215018AAxqYFk >> >> [4] 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 <[email protected]> >>> >>>> 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 <[email protected]> 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 [email protected]. >>>> To unsubscribe from this group, send email to >>>> [email protected] >>>> <mailto:geoengineering%[email protected]> . >>>> 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. >>> To post to this group, send email to [email protected]. >>> To unsubscribe from this group, send email to >>> [email protected]. >>> 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. >> To post to this group, send email to [email protected]. >> To unsubscribe from this group, send email to >> [email protected]. >> For more options, visit this group at >> 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 [email protected]. >> To unsubscribe from this group, send email to >> [email protected]. >> 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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