Dear Group, To me a runaway greenhouse means the negative feedbacks have been overwhelmed by accelerating positive forcing. In such a case only an ice age could reverse the runaway effect, a few other checks could contribute (CLAW hypothesis). If an ice age cannot cool the planet and stop the positive feedbacks, temperature will increase until we reach a new steady state. I don't know what that would be. Some have said that we could end up as the next Venus.
Sincerley, Oliver Wingenter On Feb 2, 4:59 am, Govindasamy bala <bala....@gmail.com> wrote: > Runaway feedback means running its course completely. It is feedback > specific. > > A good example is the presumed water vapor feedback on Venus. > Apparently, earth and venus started with similar amount of h2o. > Because Venus started with much higher surface temperature, the evolution of > temperature and water vapor never intercepted the phase line of vapor and > liquid. The climate warmed until all the water got evaporated. Basically, > there was no sink for vapor which precipitation. On earth, this is not going > to happen because we got the precipitation sink on earth...how lucky we are. > > But I guess we do have runaway ice-albedo feedback on earth. we could get > ice-free planet or snowball earth........ > > Cheers. > Bala > > On Mon, Feb 2, 2009 at 5:03 PM, Eugene I. Gordon <euggor...@comcast.net>wrote: > > > > > I guess it is not going to end. > > > A runaway train meets only #2 and even that has to be qualified because the > > train eventually runs out of (fossil?) fuel or track. Certainly climate has > > run away a half dozen times in 540 million years but always hits a limit > > which seems to be 24C except when an asteroid hits. It eventually turns > > around after remaining at the limit temperature for many millions of years. > > We have been in a runaway mode for the last 18,000 years but with some > > superimposed small wiggles in temperature. Without geoengineering the > > temperature will certainly get to the 24 C limit. > > > I think runaway is appropriate for the current situation even if there may > > be better suited terms. > > > -----Original Message----- > > From: geoengineering@googlegroups.com > > [mailto:geoengineer...@googlegroups.com] On Behalf Of John Nissen > > Sent: Monday, February 02, 2009 6:08 AM > > To: Tom Wigley; Andrew Lockley > > Cc: geoengineering; Prof John Shepherd; Tim Lenton; David Lawrence > > Subject: [geo] Re: runaway climate change > > > Dear Tom, > > > The concept of "runaway" has certain connotations: > > > 1. Significant in resultant effect > > 2. Uncontrollable > > 3. Exponential initial behaviour - characteristised by acceleration of > > process 4. No obvious limit 5. Irreversible 6. Rapid. > > > These can all be applied to climate change: > > > 1. "Significant" could be over 5 degrees global warming, sufficient for a > > mass extinction event. Or it could be applied to several metres of sea > > level rise. > > 2. "Uncontrollable" could be where anthropogenic greenhouse gas emissions > > reduction would not have a significant effect on the rate of climate > > change. > > 3. Exponential behaviour could be caused by a "tipping" of some part of > > the > > climate system, such as Arctic sea ice or methane release, where there is > > strong positive feedback. > > 4. There would be no obvious final equilibrium temperature - mainly > > because > > of the difficulty of modelling positive feedback and its behaviour over > > time. > > 5. It would be extremely difficult or impossible to reverse processes such > > as methane release or Greenland ice sheet disintegration, although it is > > conceivable to halt these processes or even reverse their effects > > (presumably through geoengineering). > > 6. "Rapid" could be anything from one season to 3000 years, on a > > geological > > timescale. > > > Therefore I think that "runaway" captures the semantics that we require for > > the climate change that would result from, for example, a massive methane > > release, triggered by Arctic sea ice disappearance. Can you think of a > > better word to capture the six characteristics above, especially as > > applicable to climate change? > > > Cheers, > > > John > > > ----- Original Message ----- > > From: "Tom Wigley" <wig...@ucar.edu> > > To: "Andrew Lockley" <andrew.lock...@gmail.com> > > Cc: <j...@cloudworld.co.uk>; "geoengineering" > > <geoengineering@googlegroups.com>; "Prof John Shepherd" > > <j...@noc.soton.ac.uk>; "Tim Lenton" <t.len...@uea.ac.uk>; "David Lawrence" > > <dlaw...@ucar.edu> > > Sent: Monday, February 02, 2009 3:43 AM > > Subject: Re: [geo] Re: runaway climate change > > > > Andrew, > > > > Poor analogy. running does not equal running away. > > > > More importantly, just because a term has been misused in the > > > past does not mean we should perpetuate its misuse (or use). > > > If the word is to be used at all (and, as a practicing scientist, > > > I never have or will), one should start off by saying that the > > > word runaway is open to misinterpretation, that it does not > > > mean running off to infinity, and that it's real meaning is ... > > > etc. etc. Then talk about irreversible changes (with the caveat > > > that even these are probably not irreversible), positive > > > feedbacks (which also have limits), etc. > > > > Tom. > > > > +++++++++++++++++++++++==== > > > > Andrew Lockley wrote: > > >> For better or worse, the term is now in general use in scientific, > > >> industrial, environmental and general media. (See > > >>http://en.wikipedia.org/wiki/Runaway_climate_changefor refs.) > > > >> I don't agree with Tom about 'to infinity and beyond'. I run as a > > >> hobby, and I've never run to infinity (or beyond). I think most > > >> people realise that runaway doesn't mean run-for-ever. > > > >> However, a general definition would be very useful. > > > >> A > > > >> 2009/2/2 <wig...@ucar.edu>: > > >>> Dear All, > > > >>> I've said this before, but here goes again. > > > >>> If one sticks to dictionary definitions of words (which I > > >>> think is wise) then there is no such thing as "runaway" > > >>> climate change. Strictly, using the words of Buzz Lightyear, > > >>> "runaway" must mean "to infinity and beyond". > > > >>> Further, the word "runaway" is loaded and should be eschewed > > >>> in the climate context. > > > >>> The confusion here is that what some people are calling > > >>> "runaway" climate change is really better referred to as > > >>> "irreversible" climate change. For instance, the sudden release > > >>> of a large amount of CH4 would possibly cause large warming > > >>> that would put the globe in a new state that was much warmer > > >>> than present. But the climate (or global-mean temperature) would > > >>> *not* runaway -- it would eventually stabilize. Even this change > > >>> would not strictly be irreversible, as the excess CH4 would > > >>> slowly be oxidized (more slowly than today because of the well > > >>> known positive feedback of CH4 on its own lifetime due to OH loss), > > >>> but a lot of the excess CH4 would slowly disappear and be replaced > > >>> by CO2 that has less forcing. This CO2 would, of course, stay > > >>> around for a long time. > > > >>> If anyone is interested, this case can easily be run with MAGICC, > > >>> but some minor tweaks are needed to get the CH4 to CO2 flux right. > > >>> Conceptually trivial. > > > >>> So, please, please try not to cry wolf with these loaded and sadly > > >>> oft-misused words. > > > >>> Tom. > > > >>> ++++++++++++++++++++++++++++ > > > >>>> Andrew, > > > >>>> 1. I think the concept of runaway climate change is kosher. See this > > >>>> quote > > >>>> from > > >>>>http://www.meridian.org.uk/_PDFs/FeedbackDynamics.pdf > > > >>>> "The possibility of a tipping point in the earth system as a whole > > >>>> which > > >>>> prevents the recovery of stable equilibrium and leads to a process of > > >>>> runaway climate change, is now the critical research agenday, > > requiring > > >>>> the > > >>>> concerntration of global resources in a "Manhattan Project" style > > >>>> engagement. All other work on impact assessment, mitigation and > > >>>> adaptration > > >>>> depends on the outcome of thie overarching issue" > > > >>>> I would prefer to have "runaway global warming", because that's what > > we > > >>>> are > > >>>> really talking about, but "climate change" is almost interchangeable > > >>>> with > > >>>> "global warming" these days. > > > >>>> 2. The domino effect is mentioned here: > > >>>> http://researchpages.net/ESMG/people/tim-lenton/tipping-points/ > > > >>>> The release of methane is likely to be triggered by the loss of Arctic > > >>>> sea > > >>>> ice, according to David Lawrence: > > >>>>http://www.ucar.edu/news/releases/2008/permafrost.jsp > > > >>>> 3. I believe it is generally accepted that the Arctic sea ice albedo > > >>>> effect > > >>>> contributes to the accelerated warming trend in the Arctic region. It > > >>>> is > > >>>> also accepted that this effect presents a strong positive feedback on > > >>>> the > > >>>> local warming, but currently presents only a weak positive feedback on > > >>>> global warming. Thus if the local warming can be halted, and methane > > >>>> release domino effect thereby avoided, then we can avoid passing a > > >>>> point > > >>>> of > > >>>> no return, or going "over the waterfall" as you put it. > > > >>>> I'd be interested to know if Prof John Shepherd agrees with this > > >>>> assessment. > > > >>>> 4. Additional point - only albedo (shortwave radiation) > > geoengineering > > >>>> has > > >>>> any chance to halt the local warming in the Arctic. > > > >>>> Again I'd be interested to know whether Prof Shepherd agrees with > > this. > > > >>>> Cheers, > > > >>>> John > > > >>>> ----- Original Message ----- > > >>>> From: "Andrew Lockley" <andrew.lock...@gmail.com> > > >>>> To: "geoengineering" <geoengineering@googlegroups.com> > > >>>> Sent: Sunday, February 01, 2009 12:33 PM > > >>>> Subject: [geo] runaway climate change > > > >>>> I'm working onhttp://en.wikipedia.org/wiki/Runaway_climate_change > > > >>>> and there are a few crucial questions I could do with help on: > > > >>>> 1) Is the term 'Runaway climate change' seen as kosher, or is it > > >>>> purely a pop-science concept? > > >>>> 2) How widespread is support for the idea of an ice-albedo followed by > > >>>> a clathrate/permafrost domino effect? Is it speculative or accepted? > > >>>> 3) Is there > > ... > > read more » --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to geoengineering@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=en -~----------~----~----~----~------~----~------~--~---
