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quote:Originally posted by Acoustic Samuraiso suppose that our global warming isnt attributed to the ozone effect but the fact that in the past century, human beings have created much more heat energy through forms such as industrialization and the growth of fuel burning products.
quote: Also take into account the increasing population which is constantly growing with each year. The chemical reactions that take place within our body create heat too, so could the increased population plus recent industrialization (recent in relation to the age of the earth) have anything to do with the increased global temperatures we are experiencing?
quote:I'm probably very misinformed and sounding like an idiot, but it was a thought that crossed my mind while sitting in physics class.
quote:Originally posted by crandleshttp://www.climateprediction.net/board/viewtopic.php?t=2723covers the same ground. Not sure if the calculations are accurate but the conclusion was that CO2 is massively more important than that of all mankinds energy creation.
quote:Energy recieved from sun: radius of earth = 10,000 km energy in incident radiation = 2.4 kw/m2 proportion of incident radiation absorbed = 0.2 Total rate of energy absorption = 1.5 x 10^14 kw Energy consumed by people: No of people = 6bn Energy consumption per head = 30 kwh/day (this is my wildest guess) proportion released as heat = 100% Total rate of heat production = 7.5 x 10^9 kw Ratio of man made heat to solar heat = 5 x 10^-5
quote:Originally posted by crandlesSee also:What does the lag of CO2 behind temperature in ice cores tell us about global warming?http://www.realclimate.org/index.php?p=13
quote:Originally posted by crandlesHowever, the totality of the evidence is much greater than the historical correlation. The science of how CO2 acts as a greenhouse gas is well understood.
quote:Without feedbacks, we are sure there would be a positive feedback of approx 1C for a doubling of CO2. The feedbacks are less certain but the main ones we know of increased water vapour and ice albedo are positive. There are several independant lines of research that suggest the climate sensitivity is about 3CIf you want to suggest there are negative feedbacks such that climate sensitivity might even be negative then you are going to have to come up with some important feedbacks that are currently unknown and provide reasons why all those different estimates are wrong. If there was no positive climate sensitivity, you would also have to explain the unpresidented rates of warming at coincidentally just the time we would expect rises if there was a positice climate sensitivity.
quote:The climate is dynamic, but with multiple stable (transiently) states. In order to be able to achieve such short term stability, there must be negative feedback loops. In order to switch states, there must also be positive feedback loops. I do not think one can discuss whether there are positive or negative feedback loops, but must inevitably accept that there are both, most of which we have not the slightest understanding of.
quote:This seems like a very selective interpretation of the data. Ofcourse, being selective does not make it provably wrong, only that it makes it suspect.There is a clear acceptance that the first 800 years of global warming (in the historic records of past warm periods) was not caused by CO2. It then suggests we can ignore this 800 years when we look at the subsequent 4,200 years. While it is true that we cannot prove that the subsequent 4,200 years have the same cause of warming as the preceding 800 years; but would not Occam's razor suggest that we should first look for one mechanism, rather than postulate two separate mechanisms. Ofcourse, Occam's razor is not always right, but why assume it to be wrong before having shown it to be wrong?George
quote:Originally posted by another_someoneFurthermore, since it is clear that historic CO2 levels have consistently risen after the initial rise in temperature, we may reasonably deduce that there are non-anthropogenic mechanisms within the biosphere that actually cause a rise in CO2 as a consequence of rising temperature. To what extent can we even be sure that present rises in CO2 levels are actually caused by human activity, and to what extent are they themselves part of the mechanisms that have in the past been a response to increasing global temperatures (the fact that humans produce CO2 does not of itself prove that humans control the balance between CO2 and O2).George
quote:Originally posted by crandlesWhat makes you so sure of this? Why cannot the appearance of multiple stable states be a result of the forcings applied eg Milankovitch cycles. To first order, the most important consideration is that the hotter the earth the more heat it ratiates. This creates the stability in the same manner as the leaky bucket analogy. A steady state can be reached. Reduce the size of the hole and the water level starts to rise but it doesn't necessarily overflow the bucket a new equilibrium level is likely to be reached because the flow out of the hole depends on the height of water.Since there appear to be net positive feedbacks at more than one point in time (eg current, LGM, and other times from which estimates of climate sensititivity have been made), it is possible that at another point in time the net feedbacks could be different but that doesn't mean they are likely to become negative and I suggest that the experts know enough to say they are very unlikely to become negative soon.
quote:Originally posted by crandlesThis is actually funny. [)] Who is being selective? Is it the climatologists at realclimate for ignoring the other cause?or could, just perhaps, it be the case that they are considering both causes of warming (one known to have a positive contribution and the other which is unknown whether it continues or not) and it is you being selective in wanting to consider only one cause of warming and deliberately ignoring the CO2 when that is the cause we know to have a greenhouse effect which will have a positive effect on temperature.I don't think occam razor suggests ignoring a known cause in favour of an unknown one.
quote:Originally posted by another_someoneA system that has pure positive feedback, and no negative feedback component, will always be in a runaway condition – this is not what the Earth has ever done historically.
quote:We have a hypothesis that suggests that temperatures should rise after an increase in CO2 levels, and that temperatures will continue to remain high as long as CO2 levels remain high. We know that this hypothesis conflicts with observation.
quote:Originally posted by another_someoneSorry but that is rubbish. Feedback can be positive but less than a factor of 1 and then you won't get a runaway condition.Take something really simple likexi=x(i-1)+forcing+feedback factor * ( x(i-1) - x(i-2) )try it out with a feedback factor of greater than 1 and you do get a runaway condition. Try it with a feedback factor of between 0 and 1 and you do not get a runaway effect. The eventual change is greater than the forcing so the feedback is positive but there is no runaway effect.The above alone defeats your "will always be"
quote:With temperature it is much harder to get a runaway effect because of the first order effect that a hotter planet emits more radiation.
quote:Sorry, but how is the above a pure positive feedback mechanism – you have a term -x(i-2) – by my reckoning that amounts to a negative term, and thus a negative feedback component.
quote:Ofcourse, as long as the effect is linear, then the effect will only reduce the rate of runaway, but not be sufficient to stop it. If you can demonstrate that proportion of temperature radiated increases with increasing temperature, then you would maybe be able to show it was sufficient to stop runaway; but at present, the indications are actually contrary, that as temperature increases, so the amount of ice on our planet reduces, and so the albedo of our planet reduces, and so the negative feedback becomes less effective (i.e. we have a positive feedback cycle that dominates over the negative feedback cycles). Ofcourse, there may be other planets, with different surface chemistries, that might have a different relationship between albedo and surface temperature.
quote:Originally posted by another_someonequote:With temperature it is much harder to get a runaway effect because of the first order effect that a hotter planet emits more radiation.But that too is a negative feedback, since it is a factor that increases the cooling as an increase in temperature occurs.
quote:Originally posted by crandlesDo you want to try again on that one?800 years is less than 20% of the 5000 year period. Given that there are lots of these periods and some show those 800 year periods and that the hypothesis is that CO2 (not alone but among other things affects temperature) then that is good observational evidence that CO2 does have the effect expected and that other causes do not dominate over the effect of CO2.
quote:Originally posted by crandlesSorry not sure how to do subscripts on this forum yet. The i, i-1 and i-2 terms are all supposed to indicate time periods.
quote:So start at a temperature of 10C. Apply a forcing that causes a 1C rise (This could be doubling of CO2 or something else. The temp initially goes to 11C then the feedback starts kicking in. If the feedback factor is 0.5 the temp would go to 11.5 then 11.75 then 11.875 and so on up to 11.999999. That is clearly a positive feedback that does not not lead to a runaway effect.
quote:Originally posted by crandlesquote:Originally posted by another_someonequote:With temperature it is much harder to get a runaway effect because of the first order effect that a hotter planet emits more radiation.But that too is a negative feedback, since it is a factor that increases the cooling as an increase in temperature occurs.No that is part of the system not a feedback.
quote:When a change of variable occurs in a system, the system responds. In the case of positive feedback the response of the system is to change that variable even more in the same direction.
quote:Originally posted by crandlesArtificially spliting my feedback funtion into two simply is not appropriate.
quote:In cybernetics and control theory, feedback is a process whereby some proportion or in general, function, of the output signal of a system is passed (fed back) to the input. Often this is done intentionally, in order to control the dynamic behavior of the system. Feedback is observed or used in various areas dealing with complex systems, such as engineering, architecture, economics, and biology. Continuous feedback in a system is a feedback loop.
quote:Originally posted by crandlesBut suppose I describe another system which initially is in equilibrium at 10 we apply a forcing which moves the system to 11 then a feedback kicks in equal to 3 times the forcing (lagged by 1 timestep so the system moves to 14 and it then stays in equilibrium at 14.Surely there is no negative feedback in that system and it does not go into a runaway effect.
quote:Originally posted by crandlesSuppose:A barrel contains 120 litres of water. The inflow appears fixed at 12 litres a minute. The outflow depends on the height of the water and so is equal to 10% of the volume in the barrel per minute.This is currently in equilibrium. We now reduce the size of the hole so the the outflow is only .075 times the volume in the barrel (units still litres per minute). Given the current knowledge of the system we would expect a new equilibium to be reached with the barrel containing 160 litres and inflow and outflow equal to 12 litres per minute.In fact we notice the quantity in the barrel goes above 160 lites so we investigate and discover that the inflow is not fixed at 12 litres a minute but there is a system feedback such that if the outflow in one minute is greater than 9% of the volume in the barrel then the inflow is fixed at 12 litres per minute but if the outflow is less than 9% of the volume then the inflow is set at 15 litres per minute.
quote:Originally posted by MjhavokA heat wave in the UK has been happening and I think temperatures have reached 37 degrees celsius.