trevw

I would also be interested in the opinion of other experts in the field. It all seems plausible but who knows? I picked it up from a discussion thread on realclimate where it seemed to get lost amongst other points.. Isn't that in itself quite significant though? Various magazines/TV programs have taken this as a theme and as far as I remember all have claimed the majority of our additional warming is due to the gulf stream etc. If instead of freezing winters and damp gloomy summers, year round ice forming glaciers in scotland etc. we are just looking at a 1 deg ish fall in CET (and a reduction in cyglogenisis caused by warm currents?) the effects are presumeably going to be very different. Presumeably the prevailing weather direction would still be from the west? But there would be less in the way of 'activity' generated by the atlantic? Had to look 'FUD' up handy word. I had always thought that the 'shutdown scenario' and it's supposed effects if it occurred were beyond doubt.. now it looks like the more extreme scenarios could well be FUD..? (is that correct usage?) trevw

Found this rather interesting article (apologies if it's already been discussed) - apparently the reason we are unusually warm for our longitude has very little to do with the gulf stream and thermohaline circulation and everything to do with a 'standing wave' caused by the rockies.. btw - I'm not a GW skeptic, however if what is described in the article is true (and it seems genuine) then I feel it's things like this that undermine the AGW 'cause' it seems to me it's often presented as fact in the UK that a shutdown would plunge us into arctic conditions and this is held up as a reason to act against climate change, a sort of 'trump card', whereas it sounds like it is more likely to affect storm generation etc rather than general temps and if this became accepted general knowledge - it could appear to be a body blow against the AGW lobby (as well as dissapointing the odd poster on here ) whereas in my humble opinion there are still plenty of reasons to take AGW seriously. http://www.americanscientist.org/template/...print=yes#52131

This is definitely an interesting discussion :huh: , in part I think because while people have their viewpoints none of us are coming across as having completely made their minds up - I certainly don't feel I'm convinced of AGW beyond turning back, but it's the way I currently 'lean' given the evidence I have seen. The various interesting comments and links on here have prompted me to do some more reading around, particularly in the area of CO2 not being the main greenhouse gas (as you mention above BFTP). The general understanding (correct me if I'm wrong) is that the warming effect of CO2 is much less than that of water vapour, which is why sometimes it is confusing that climate scientists spend _so_ much time banging on about CO2... I found a very interesting article here: http://www.realclimate.org/index.php?p=142 This agrees and breaks down the difference in effect to between 66% and 85% of warming due to water vapour/clouds and to between 9 and 26% for CO2. However, basically what it is saying is that CO2 is so important because it is a 'forcing' while water vapour is purely a 'feedback'... my initial thoughts were 'why' and 'how' as on the face of it that made little sense. The difference apparently is that the lifetime or 'residence' of water vapour in the atmosphere is only about 10 days (as opposed to 100s of years for CO2) making it 'reactive'. For a given temperature the level of water vapour thus stabilizes very quickly. So if CO2 were to cause an increase in temp of a fraction of a degree this would increase water vapour levels which would increase temps (and further increase water vapour) until a new equilibrium was reached (to an approximation the water vapour adjusts to maintain constant relative humidity). However if CO2 is reduced for some reason and a slight temp drop occurs then this will cause water vapour to reduce quickly reducing temps and further reducing water vapour until a lower temp/water vapour equilibrium is reached. so this is the reason that CO2 'is' a big enough driving force to change the climate - it's like a gangster with some water vapour 'heavies' to do the grunt work for it whatever CO2 does water vapour follows.. as mentioned, enjoying all the discussion on here - a distraction from a dull week at work Trevw

BFTP, which bit haven't you seen proof of? That CO2 in the atmosphere causes warming? I believe it can be demonstrated in the lab that CO2 allows UV etc. to pass but absorbs/scatters infra red - as such it is impossible for CO2 not to cause a warming of the atmosphere - in fact I believe we rely on it along with the same effect from methane and water vapour.. I think the current understanding of the instance that people refer to of CO2 'following' temps at the end of a glacial period is the following: Temps rose due to orbital changes causing retreat of ice over 800 years which in turn reduced albedo causing further warming. A threshold was reached at which point the increasing temperatures _caused_ an increase in CO2 The CO2 amplified the warming further (as it must) which resulted in more CO2 release etc. (probably from melting permafrost etc.) for the next 4200 years. This does means that historically CO2 does not tend to initiate warmings (how could it?) but does amplify them once under way. This is to be expected as there is no _natural_ source of enough CO2 to cause warming without a climate change to drive it (possibly excluding supervolcanoes which would undoubtedly effect the climate in other ways). Unfortunately we in our 'technological brilliance' have changed this fact - we can skip the requirement for a natural generator of CO2 as we are ripping millions of years worth of carbon out of the ground and flinging it in the air in its gaseous form. So I guess the answer really to 'causation or consequence?' is 'both'. Yet another positive feedback mechanism which we can only hope there is a natural negative counter for. I am quite skeptical of long term 'runaway global warming' where natural positive feedbacks turn us into a venus like planet, I feel that if the CO2 output were to be stopped then the earth would return to an equilibrium of sorts, but this relies on us stopping which I think is very unlikely in the mid term (next 50 years). There is no natural sink I am aware of that can absorb what we are emitting now let alone what will be being emitted once china ramps up so the CO2 will have to continue to rise and has to contribute to continued warming - with luck at some point a self regulating negative feedback (high altitude clouds etc?) will kick in and mitigate the CO2s effect, but that really is clutching at straws in my humble opinion.. Trevw

Surely though one of the main factors 'appearing' to redress the balance (or to mitigate CO2 rise) is the purely 'mechanical' absorbtion of CO2 by the worlds oceans, and as the CO2 is increased and as time passes it's ability to do this will reduce and all other mechanisms to reduce the CO2 balance will be even further overwhelmed than they are now..? (blimey that sounds all doom and gloom!) Definitely agree that the cooling factors and their alteration one way or another are key to future trends though, it seems to me that it's entirely possible that a negative feedback to do with albedo might eventually completely cancel the heating effects of CO2 (not that this would change the fact that the CO2 was much higher) unfortuately it seems equally probably to me that it will go the other way.. Trevw

fair point TWS, I think the piece I was reading was more along the lines that the CO2 we have emitted is 'more than enough to account' for the entire atmospheric CO2 rise and the majority of the PH increase caused by CO2 absorbed by the ocean - this doesn't mean that some other generator of CO2 might not have contributed some of the extra CO2 that is actually in the atmosphere on a 'per molecule basis', but from a 'CO2 accountancy' point of view you could assume that all natural sources have been absorbed by the ocean - sort of like shuffling debt around on credit cards

I believe that it's actually fairly well accepted that not only is the entire atmospheric increase due to our CO2 production but that is only the tip of the (melting ) iceberg - we have emitted enough to pretty much double the atmospheric CO2 levels but the ocean has been sucking it up like a sponge.. something that can only go on for so long. The fact that the rate of CO2 increase has accelerated over the last few years is worrying as it could indicate that the oceans have 'had enough' or that the land is turning into a net generator of CO2 - either or both of which could herald an acceleration of the warming.. The extra CO2 we have emitted is warming the atmosphere (an indisputable physical fact) - the only actual 'question' is how much of the universally accepted warming is due to this and other anthropogenic climate forcing and how much due to natural forcings, some of which we may not be aware of and may subside or reverse with time. It seems that this is the question that causes so much trouble as the climate system is so large and complex it is hard to pin down all the different forcings and feedbacks to the point that we are sure we know the split between natural and anthropogenic warming. my two penneth anyhoo Trevw

Not sure that the breathing out of CO2 by humans will have any net effect as it's from respiration and the carbon comes from foodstuff which is ultimately fixed from the atmosphere whether you are talking meat or plants? The deforestation and changes to planetary albedo caused by a large population probably have more effect. as for CO2 increases being due to the rise in temps rather than the other way round, this link explains the current situation pretty well I think: http://www.realclimate.org/index.php?p=160#more-160

brings up an interesting point.. short term changes aside, long term I imagine the climate is going to go through a 'natural variation' that is not great for us or any of the life we share the planet with. At that point I think I would say lets mess with the climate any way we can and try and make it more suitable for human life.. for instance if a new ice age kicked in or runaway global warming then why not use mass intervention to change the planets albedo, pump whatever gunk into the atmosphere that is required to turn it around - if the natural result has the potential to collapse our current civilization then what is there to loose..? just seems to be that sometimes natural cycles are considered to be 'universally good' whereas inevitably at some point they are going to be bad news.. personally if that happens I say 'adapt it to us if at all possible'. :lol: Trevw