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Post by socold on May 18, 2009 0:49:06 GMT
Positive feedbacks in relation to climate do not imply runaway. I believe someone (a skeptic) on another thread already pointed out that the positive ice albedo feedback has diminishing returns. When you see "positive feedback" in relation to climate, think "amplification" not "inifinite runaway". It doesn't matter how SMALL the positive feedback is - if there are no negative feedbacks the rise in temperature is now totally unstoppable. In the context of climate a feedback is: Temp Change = Forcing * Feedback When Feedback is > 0 it's referred to as a positive feedback. A positive feedback causes temperature change to be greater in magnitude than the forcing alone can produce. So instead of a 4wm-2 forcing causing 1C total temperature rise, you could have it causing 2C temperature rise. It doesn't mean it runs away to infinity.
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Post by sigurdur on May 18, 2009 2:16:43 GMT
Socold: One of the things you have to understand is that the "detailed calculations" in those climate models are now being shown to be wrong as the predictive value of those models is about as useless as tits on a boar.
It amazes me, an old farmer and student of life that I am, that people will cling to false data no matter how much the reality hits them in the nose. Kinda like saying an old wheat is soooo much better than a newer variety.....why......I would swear on me life it is....even tho data over and over shows that not to be the case.
I am in love with neither AGW, nor others who vehemently oppose that theory. I am in love with reality.
Even tho it may stink at times.
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Post by icefisher on May 18, 2009 15:12:09 GMT
It doesn't matter how SMALL the positive feedback is - if there are no negative feedbacks the rise in temperature is now totally unstoppable. In the context of climate a feedback is: Temp Change = Forcing * Feedback When Feedback is > 0 it's referred to as a positive feedback. A positive feedback causes temperature change to be greater in magnitude than the forcing alone can produce. So instead of a 4wm-2 forcing causing 1C total temperature rise, you could have it causing 2C temperature rise. It doesn't mean it runs away to infinity. So then do you believe what you just said? Or are you a proponent of Al Gore's Tipping Point?
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Post by nautonnier on May 18, 2009 18:12:34 GMT
In the context of climate a feedback is: Temp Change = Forcing * Feedback When Feedback is > 0 it's referred to as a positive feedback. A positive feedback causes temperature change to be greater in magnitude than the forcing alone can produce. So instead of a 4wm-2 forcing causing 1C total temperature rise, you could have it causing 2C temperature rise. It doesn't mean it runs away to infinity. So then do you believe what you just said? Or are you a proponent of Al Gore's Tipping Point? You got there first This "its only going to be a small amplification on a forcing and when that forcing goes away its going to stop" - is not what is being sold by Hansen and Gore.
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Post by socold on May 18, 2009 21:32:43 GMT
Socold: One of the things you have to understand is that the "detailed calculations" in those climate models are now being shown to be wrong as the predictive value of those models is about as useless as tits on a boar. I disagree. There's a lot of wishful thinking from skeptics wanting to believe the models have been shown to be wrong and so they frequently jump to false conclusions. That's all I have to understand.
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Post by socold on May 18, 2009 21:35:19 GMT
In the context of climate a feedback is: Temp Change = Forcing * Feedback When Feedback is > 0 it's referred to as a positive feedback. A positive feedback causes temperature change to be greater in magnitude than the forcing alone can produce. So instead of a 4wm-2 forcing causing 1C total temperature rise, you could have it causing 2C temperature rise. It doesn't mean it runs away to infinity. So then do you believe what you just said? Or are you a proponent of Al Gore's Tipping Point? A tipping point doesn't mean runaway to infinity either. Glacial -> interglacial state involves a tipping point. Temperature didn't run away to infinity.
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Post by socold on May 18, 2009 21:37:18 GMT
So then do you believe what you just said? Or are you a proponent of Al Gore's Tipping Point? You got there first This "its only going to be a small amplification on a forcing and when that forcing goes away its going to stop" - is not what is being sold by Hansen and Gore. Yes it is. It pays to actually understand what you attack. Neither Gore nor Hansen are proposing temperatures running away to infinity. How do I know this? I guess I must have actually read something about this subject. How people who have supposedly followed this for years don't grasp the meaning of "tipping point" or "positive feedback" when I grasped it almost immediately is bizzare. How these same people almost always seem to be skeptics is downright suspicious.
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Post by icefisher on May 18, 2009 22:48:17 GMT
So then do you believe what you just said? Or are you a proponent of Al Gore's Tipping Point? A tipping point doesn't mean runaway to infinity either. Glacial -> interglacial state involves a tipping point. Temperature didn't run away to infinity. Unfortunately Socold you are leaving something out here. Positive feedback by definition will run as long as the feedback is positive. When the feedback goes negative then it will reverse. If you don't understand when the feedback will go negative you quite simply do not understand the feedback. So one more time, how will positive feedback cause temperatures and how will it reverse (as you are now maintaining it will). . . .keeping in mind of course that increasing temperatures also increase CO2 in the atmosphere. PLease provide the primary elements of your system and a brief description on how any limits or negative feedback plays into the system to limit or reverse temperature increases.
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Post by socold on May 19, 2009 1:04:05 GMT
Unfortunately Socold you are leaving something out here. Positive feedback by definition will run as long as the feedback is positive. When the feedback goes negative then it will reverse. I've already explained what feedback and positive feedback are in the context of climate. If we are discussing something in climate we have to look at the definition in the climate field. Not a definition from electronics or engineering. In climate a feedback is measured in wm-2/C and if the value is positive then the feedback is positive. A positive feedback doesn't mean it runs away infinitely. If a 4wm-2 forcing causes a direct 1C temperature rise and net feedbacks are positive at 1wm-2/C then the total temperature rise from 4wm-2 forcing is about 1.58C. More than if there were no feedbacks, but not an infinite amount more.
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Post by icefisher on May 19, 2009 5:54:46 GMT
Unfortunately Socold you are leaving something out here. Positive feedback by definition will run as long as the feedback is positive. When the feedback goes negative then it will reverse. I've already explained what feedback and positive feedback are in the context of climate. If we are discussing something in climate we have to look at the definition in the climate field. Not a definition from electronics or engineering. In climate a feedback is measured in wm-2/C and if the value is positive then the feedback is positive. A positive feedback doesn't mean it runs away infinitely. If a 4wm-2 forcing causes a direct 1C temperature rise and net feedbacks are positive at 1wm-2/C then the total temperature rise from 4wm-2 forcing is about 1.58C. More than if there were no feedbacks, but not an infinite amount more. You don't follow directions well. I asked for a description of a specific feedback, how it operates, what drives it, and how it finds a limit and/or reverses into a negative feedback.
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Post by steve on May 19, 2009 16:53:31 GMT
I've already explained what feedback and positive feedback are in the context of climate. If we are discussing something in climate we have to look at the definition in the climate field. Not a definition from electronics or engineering. In climate a feedback is measured in wm-2/C and if the value is positive then the feedback is positive. A positive feedback doesn't mean it runs away infinitely. If a 4wm-2 forcing causes a direct 1C temperature rise and net feedbacks are positive at 1wm-2/C then the total temperature rise from 4wm-2 forcing is about 1.58C. More than if there were no feedbacks, but not an infinite amount more. You don't follow directions well. I asked for a description of a specific feedback, how it operates, what drives it, and how it finds a limit and/or reverses into a negative feedback. Observations indicate that relative humidity stays approximately constant. This means that as the atmosphere warms (through any effect including CO2, solar, El Niño etc.) the amount of water vapour in the atmosphere increases. Since water vapour is a greenhouse gas, extra water vapour would add to the warming and is therefore counted as a positive feedback. It doesn't necessarily reverse into a negative feedback at any point. As socold says, the definition of feedback in climate science is different. Sensitivity of the climate is described as the amount of warming for each watt of forcing. Anything that causes the sensitivity to go up (such as increase in water vapour) is a positive feedback. If tropical clouds were to increase so as to reflect away more solar radiation then that would reduce the sensitivity and be a negative feedback. I suppose changes in ice might start as a positive feedback as it reflects away less and less sunlight as it melts, but at some point it stops acting as a feedback if all the ice melts.
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Post by icefisher on May 20, 2009 3:05:33 GMT
Observations indicate that relative humidity stays approximately constant. This means that as the atmosphere warms (through any effect including CO2, solar, El Niño etc.) the amount of water vapour in the atmosphere increases. Since water vapour is a greenhouse gas, extra water vapour would add to the warming and is therefore counted as a positive feedback. It doesn't necessarily reverse into a negative feedback at any point. As socold says, the definition of feedback in climate science is different. Sensitivity of the climate is described as the amount of warming for each watt of forcing. Anything that causes the sensitivity to go up (such as increase in water vapour) is a positive feedback. If tropical clouds were to increase so as to reflect away more solar radiation then that would reduce the sensitivity and be a negative feedback. I suppose changes in ice might start as a positive feedback as it reflects away less and less sunlight as it melts, but at some point it stops acting as a feedback if all the ice melts. Thats all well and good but you did not explain the mechanism for the feedback from stopping (except the ice). For instance water vapor makes it warmer because of its greenhouse effect, right? Additionally, this warming is releasing CO2 from the oceans as well. At what point does it stop getting warmer and why? And I am not asking for some weenie philosophical statement but some actual figures and some support for the figures (why not lower or higher). And for good measure maybe you can explain how with all this elevated moisture floating around above the planet we get desertification all over the place.
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Post by nautonnier on May 20, 2009 11:17:10 GMT
You got there first This "its only going to be a small amplification on a forcing and when that forcing goes away its going to stop" - is not what is being sold by Hansen and Gore. Yes it is. It pays to actually understand what you attack. Neither Gore nor Hansen are proposing temperatures running away to infinity. How do I know this? I guess I must have actually read something about this subject. How people who have supposedly followed this for years don't grasp the meaning of "tipping point" or "positive feedback" when I grasped it almost immediately is bizzare. How these same people almost always seem to be skeptics is downright suspicious. "Hansen is arguing that simply reducing our emissions and stabilizing CO2 at about 450 parts per million, as many scientists argue is necessary, is not nearly good enough. We must reduce the concentration from today’s 387 ppm to below 35o ppm.
“We have already passed into the dangerous zone,” Hansen said. If we don’t reduce CO2 in the atmosphere, “we would be sending the planet toward an ice free state. We would have a chaotic journey to get there, but we would be creating a very different planet, and chaos for our children.” Hansen’s argument (see a paper on the subject here) is based on paleoclimate data which show that the last time atmospheric CO2 concentrations were this high, the Earth was ice free, and sea level was far higher than it is today."www.cejournal.net/?p=1590“The climate is nearing tipping points,” the NASA climate scientist James E. Hansen wrote in The Observer newspaper of London. “If we do not change course, we’ll hand our children a situation that is out of their control.”" The resulting calamities, Dr. Hansen and other like-minded scientists have warned, could be widespread and overwhelming: the loss of untold species as ocean reefs and forests are disrupted; the transformation of the Amazon into parched savanna; a dangerous rise in sea levels resulting from the melting of the mile-high ice sheets in West Antarctica and Greenland; and the thawing of the Arctic tundra, which would release torrents of the greenhouse gas methane into the atmosphere." www.nytimes.com/2009/03/29/weekinreview/29revkin.html"The difference is that now we have used up all slack in the schedule for actions needed to defuse the global warming time bomb. The next president and Congress must define a course next year in which the United States exerts leadership commensurate with our responsibility for the present dangerous situation." "Otherwise it will become impractical to constrain atmospheric carbon dioxide, the greenhouse gas produced in burning fossil fuels, to a level that prevents the climate system from passing tipping points that lead to disastrous climate changes that spiral dynamically out of humanity's control.".....<snip>.... "What is at stake? Warming so far, about two degrees Fahrenheit over land areas, seems almost innocuous, being less than day-to-day weather fluctuations. But more warming is already "in the pipeline," delayed only by the great inertia of the world ocean. And climate is nearing dangerous tipping points. Elements of a "perfect storm," a global cataclysm, are assembled."...<snip>...... "Conviction of ExxonMobil and Peabody Coal CEOs will be no consolation, if we pass on a runaway climate to our children. Humanity would be impoverished by ravages of continually shifting shorelines and intensification of regional climate extremes. Loss of countless species would leave a more desolate planet".www.huffingtonpost.com/dr-james-hansen/twenty-years-later-tippin_b_108766.htmlSocold _you_ are the one talking about infinity - Hansen only talks about an unstoppable catastrophic runaway to a 'desolate planet'. Which is close to what I actually said that he was stating in my post. Perhaps YOU should read what your leaders are saying?
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Post by steve on May 20, 2009 13:58:07 GMT
Observations indicate that relative humidity stays approximately constant. This means that as the atmosphere warms (through any effect including CO2, solar, El Niño etc.) the amount of water vapour in the atmosphere increases. Since water vapour is a greenhouse gas, extra water vapour would add to the warming and is therefore counted as a positive feedback. It doesn't necessarily reverse into a negative feedback at any point. As socold says, the definition of feedback in climate science is different. Sensitivity of the climate is described as the amount of warming for each watt of forcing. Anything that causes the sensitivity to go up (such as increase in water vapour) is a positive feedback. If tropical clouds were to increase so as to reflect away more solar radiation then that would reduce the sensitivity and be a negative feedback. I suppose changes in ice might start as a positive feedback as it reflects away less and less sunlight as it melts, but at some point it stops acting as a feedback if all the ice melts. Thats all well and good but you did not explain the mechanism for the feedback from stopping (except the ice). For instance water vapor makes it warmer because of its greenhouse effect, right? Additionally, this warming is releasing CO2 from the oceans as well. At what point does it stop getting warmer and why? And I am not asking for some weenie philosophical statement but some actual figures and some support for the figures (why not lower or higher). And for good measure maybe you can explain how with all this elevated moisture floating around above the planet we get desertification all over the place. It stops getting warmer, because radiation is proportional to the fourth power of the temperature. Rough calculation with a rough model: If, say, the extra greenhouse gases including water vapour, reduce outgoing longwave by average 10 watts/metre squared from 235 to 225 W/m^2, then the earth will warm up due to the excess 10W/m^2. As it warms, it emits more radiation. If the earth warms 3C then the amount it radiates increases by about 5% (assuming temperatures in the range 250-300 Kelvin) which would be enough to counteract the reduced outgoing radiation and stop further warming.
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Post by poitsplace on May 20, 2009 16:07:17 GMT
I think people in the AGW camp are missing a fundamental issue with ice albedo. Even at current temperatures ice pretty much just fills in the darkest areas during the winter...then it quickly vanishes once the sun returns. The areas where ice remains year round just don't get much sun to start with.
On top of this the tundra that would be opened up is actually kind of light colored already. So even if the ice was gone it wouldn't be replaced by a dark, lush green. It would be that pale, half-dead looking scrub with a lot of soil showing through.
The earth is already incredibly far into diminshing returns with ice albedo. It has little opportunity to feedback because the only time ice is around is when there's very little energy available for the affect.
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