I think that the concept of 'runaway' is valid for all self-sustaining temperature transitions. I do not think that it should be restricted to Venus-type events. However, this is clearly NOT applicable to all positive feedback mechanisms. A feedback might make things warmer/colder then they otherwise would be, but unless that process is self sustaining then it's not a runaway. Interestingly, by this definition, ice-ages and interglacials are runaways as they are STARTED by milanko-whatnot cycles but sustained by carbon release. And it's actually the carbon that keeps them going.
http://en.wikipedia.org/wiki/Ice_age#Variations_in_Earth.27s_orbit_.28Milankovitch_cycles.29 A 2009/2/6 dsw_s <[email protected]> > > >There is pretty good evidence based on past climate history that long term > temperature > > changes occur monotonically on a scale of thousands of years but not for > shorter times > > Really? I had thought the opposite, from badly-out-of-date > information. I think it was some series of measurements of oxygen > isotopes that was talked about in an undergrad course, looking as > though larger versions of year-to-year changes like El Nino happened > at transition points and then never went back. > > On Feb 6, 8:43 am, "Eugene I. Gordon" <[email protected]> wrote: > > I agree with Andrew. A positive feedback is not a runaway mechanism > unless > > it does not saturate. For sure 540 million years of temperature history > show > > there are long term temperature maxima and minima. That is not runaway. > The > > positive feedback is clear but it saturates. If we are engineers let us > be > > accurate and not fall back on careless prior nomenclature. There is > pretty > > good evidence based on past climate history that long term temperature > > changes occur monotonically on a scale of thousands of years but not for > > shorter times so there is slow positive feedback that saturates (not > runaway > > not even a slow jog.). > > > > As also a scientist I never fall back on hypothesis until it passes > certain > > requirements that elevate it to theory (logical arguments based on > > established fact is not enough) . Comfort is fine but it is too casual. I > > think a more professional approach is to use the word "suggests" or "is a > > reasonable but not yet proven hypothesis." or :"is attractive but more > work > > is needed." > > > > _____ > > > > From: [email protected] > > [mailto:[email protected]] On Behalf Of Andrew Lockley > > Sent: Friday, February 06, 2009 7:28 AM > > To: John Nissen > > Cc: geoengineering > > Subject: [geo] Re: runaway arguments ripped to bits > > > > You might be convinced by this hypothesis, but science works by proof. > All > > we have been able to demonstrate is a risk, not a probability. > > > > It's all a matter of gain. A positive feedback is NOT a runaway. It is > > only a runaway if the gain is sufficient. You need to prove the gain to > > prove the argument. > > > > Bearing in mind the water seems to re-freeze each winter, the feedback > does > > not seem to be the principle forcing mechanism in operation here. The > > feedback may well dramatically accelerate the effect of CO2 emissions, > but > > it does not seem to be the central effect. Fortunately, as the Arctic > is > > dark for 6mo the system has plenty of time to recover from any seasonal > > runaway. Can you cite papers to show the ice-albedo feedback is > sufficient > > to start a runaway effect? Which paper are you taking the 30W/m2 from? > > > > The methane effect similarly is unproven. This doesn't mean it's not > true, > > just that you haven't demonstrated it to be true. I can find no papers > > which show a rapid degeneration of clathrates. Buffett and Archer > > specifically failed to show such an effect, but I understand that they > > considered only deep clathrates which are slow to outgass. Permafrost > > slumping may be a crucial mechanism in faster degeneration of clathrates, > > but has anyone modelled it and the outgassing rates that result? > > > > I can also find no papers which give the original research for the effect > of > > increased atmospheric methane. I personally don't really need to be > > convinced that a massive outgassing of methane might be a slight problem, > > but others do. Can you cite papers which indicate the expected > temperature > > increase from a predicted outgassing event? > > > > Don't take this all personally, John. I believe you're right. We just > need > > to prove it. This is science, not dogma. > > > > A > > > > 2009/2/6 John Nissen <[email protected]> > > > > Hi Andrew, > > > > It depends what kind of proof you want. I myself am convinced of things > if > > there is a logical argument based on established facts. > > > > I am convinced by anthropogenic global warming because if you put an > extra > > 100 ppm CO2 in the atmosphere, you EXPECT to have greenhouse warming. I > > don't need "proof" to be convinced. To be persuaded otherwise, I would > need > > a convincing explanation of why the CO2 wasn't causing global warming, or > > how this was somehow neutralised. I would need to be PROVED WRONG. > > > > Similarly with methane runaway feedback. There's a vast amount of > methane > > trapped in frozen structures. Nobody disputes this fact. If you put > enough > > of this methane in the atmosphere, you expect global warming. You then > > expect positive feedback as a result of this, as the frozen structures > > unfreeze to release more methane until it's all gone. Unless there is an > > argument against this logic, I will remain convinced by it. > > > > Similarly with the Arctic sea ice and domino effects. The "forcing" from > > the sea ice albedo effect is of the order of 30 Watts per square metre, > so > > you expect this to drive regional warming. Nobody is suggesting how this > > warming would reverse naturally. So, as the region continues to warm, > you > > expect the domino effects of methane release and Greenland ice sheet > > accelerated discharge. > > > > This is all highly uncomfortable to contemplate, and I'd like to be > proved > > wrong. However we do have a possible way out of this situation with > > geoengineering. So all is not lost. > > > > Please can we now persuade politicians and potential funding bodies of > the > > inescapable logic of this situation, so that they fund the necessary > > geoengineering developments? Or prove me wrong. > > > > Cheers, > > > > John > > > > ----- Original Message ----- > > From: Andrew Lockley <mailto:[email protected]> > > To: John Nissen <mailto:[email protected]> > > Sent: Friday, February 06, 2009 1:13 AM > > Subject: Re: [geo] runaway arguments ripped to bits > > > > I'm not saying you're wrong. I'm just saying I haven't been able to > PROVE > > you're right. > > > > A > > > > 2009/2/5 John Nissen <[email protected]> > > > > Dear Andrew, > > > > That is very unfair - a stab in the back. > > > > 1. I have given you several references to methane in the past, e.g. from > > David Lawrence. And there are plenty of references already in wikipedia, > > e.g. here:http://en.wikipedia.org/wiki/Arctic_methane_release > > (I am sorry I can't help on the shoreline slumping.) > > > > 2. I am trying to answer your basic question: Is there REALLY a big and > > immediate risk from the clathrate gun/permafrost? You seemed to be > arguing > > only about the methane, without taking into account the Arctic sea ice > > albedo effect. > > > > 3. The argument that the Arctic sea ice albedo effect is causing > regional > > runaway feedback is new to this list. The argument that we should > reverse > > the Arctic sea ice retreat is also new - previously I had argued we > simply > > had to halt the retreat. > > > > 4. These are common sense arguments. If anybody can find some evidence > to > > dispute them, may they come forth. > > > > 5. I have given my own conclusion repeatedly, because it bares > repeating: > > > > If we do not act quickly with our SRM geoengineering, then thermal > runaway > > from methane (and also disasterous sea level rise) could become > inevitable. > > > > 6. Your criticism is a stab in the back, because you seemed to be one of > > the few people who accepted this conclusion, because of all the evidence > I > > gave you. > > > > Et tu, Brute. > > > > John. > > > > ----- Original Message ----- > > From: Andrew Lockley <mailto:[email protected]> > > To: John Nissen <mailto:[email protected]> > > Cc: Geoengineering FIPC <mailto:[email protected]> ; Prof > > John Shepherd <mailto:[email protected]> ; John Gorman > > <mailto:[email protected]> > > Sent: Thursday, February 05, 2009 1:12 PM > > Subject: Re: [geo] runaway arguments ripped to bits > > > > John, > > You've repeated these arguments on this list on numerous occasions. > > However, you've failed to back them up with peer-reviewed science. > > > > I've already emailed the list asking for scientific support for these > very > > ideas in the last 24hrs. Specifically we need help with the alterations > to > > methane GWP, the decay rate of clathrates due to shoreline slumping in > the > > Arctic and calculations of the overall warming load arising from a > methane > > pulse. > > > > I hope you can assist with the search for solid backing for your case and > > not re-iterate oft-rehearsed arguments. > > > > The relevant wiki is actually athttp:// > en.wikipedia.org/wiki/Runaway_climate_change#Current_risk > > > > A > > > > 2009/2/5 John Nissen <[email protected]> > > > > The term "runaway" has an accepted meaning in the context of "thermal > > runaway", and is characterised by positive feedback and resulting > > acceleration in temperature change. So the temperature rises more than > > linearly, and may even rise exponentially or "explosively": > http://en.wikipedia.org/wiki/Thermal_runaway > > Eventually the feedback peters out, and the temperature change becomes > > linear again. > > > > This process is happening with the Arctic sea ice. At present the albedo > > feedback effect is causing an acceleration in temperature change in the > > polar region - but this positive feedback will eventually peter out, when > > all the ice and snow in the region has melted, including the Greenland > ice > > sheet! So we are facing thermal runaway on a regional scale, affecting > > local climate and ecosystem. This will have a domino effect on methane > > release. > > > > As the Arctic region warms, methane will invitably be released in larger > and > > larger quantities. The speed of methane release depends critically on > the > > temperature above the frozen structure holding the methane. For > permafrost > > on land, if the average surface temperature is maintained above freezing, > > the permafrost will inevitably melt. This is what is happening over vast > > areas of Canada and Siberia, as the isotherms (lines of equal temperature > on > > a map) move northwards. > > > > The methane itself provides feedback equally to both regional and global > > warming, through its greenhouse effect. The regional warming will > increase > > the rate of methane release. Thus there could be thermal runaway on a > > global scale and "we are toast", as Hansen puts it. > > > > We have to find a way to quickly halt the Arctic regional warming. I > > maintain that the key to this is to halt and partially reverse the > retreat > > of the Arctic sea ice, by cooling the region. And I maintain that the > key > > to cooling is use of solar radiation management (SRM) techniques - a > > combination of stratospheric aerosols and marine cloud brightening. > > > > If we do not act quickly with our SRM geoengineering, then thermal > runaway > > from methane (and also disasterous sea level rise) could > > > > ... > > > > read more ยป > > > --~--~---------~--~----~------------~-------~--~----~ 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=en -~----------~----~----~----~------~----~------~--~---
