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JEleazarian
Trad climber
Fresno CA
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Jul 17, 2010 - 09:11pm PT
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Thank you, Dr. Deeg, for adding another informed, informative, measured and non-pejorative voice. There have been too few.
I am an econometrician who has been trying to estimate marginal costs and benefits of various ameliorative strategies -- a rather daunting task. Needless to say, the fact that uncertainty exists does not eliminate the need for amelioration. I greatly appreciate your factual presentation, as well as those of Chiloe, who turned me on to some good statistical sources a couple of years ago when I expressed skepticism, and, of course, Ed.
I also practiced law actively from 1979 until a few years ago. As an advocate, I've learned that insulting my audience seldom convinces them of the correctness of my position. Your non-insulting tone should go a long way toward helping us to hear you over the din of name-calling that permeates the discussion here.
Welcome to the debate. I hope we continue to hear from you.
John
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the Fet
climber
Tu-Tok-A-Nu-La
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Jul 17, 2010 - 11:56pm PT
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It's interesting to come on the taco and read good summaries about a lot of topics.
Some people will never be convinced about the correct view of certain facts no matter what type of discussion you try to have. You do the best you can do and hope that those with open minds appreciate your efforts.
Trading insults with those who throw them first is just entertainment, it's not meant to convince them of anything. Their minds are made up, facts and reason are worthless.
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DrDeeg
Mountain climber
Mammoth Lakes, CA
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Jul 18, 2010 - 03:13am PT
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Response to Timid TopRope:
In my post, by aerosols I meant solid and liquid particles. Mainly these are soot, dust, salt, and sulfates. Soot comes from combustion, dust from the surface, salt from the ocean, and sulfates from both combustion and from natural sources like volcanic eruptions. Your post refers to aerosol propellants, e.g. in spray cans, the idea that the can sprays stuff out (like deodorant) in small droplets. In the past (but no longer) CFCs (chlorofluorocarbons) were used as the compressed gas. Their major use was in refrigeration, including air conditioning, but they were also used in fire extinguishers.
When first used in refrigerators and air conditioners in the 1930s (they were synthesized much earlier, before the turn of the century), CFCs were considered the ideal refrigerant. They have a low boiling point (good for the evaporation/condensation cycle in your refrigerator), they aren’t reactive, and they aren’t toxic. If your refrigerator leaked it, you wouldn’t die, whereas the earlier refrigerants – ammonia, chloromethane, and sulfur dioxide – were toxic.
But here the story gets interesting. If CFCs are not reactive, what happens to them when released in the atmosphere? They are entirely manmade, with no natural source. In the 1970s Sherwood (Sherry) Rowland (prof at UC Irvine) and his grad student Mario Molina (now a prof at UC San Diego) did some lab experiments to answer this question. They discovered that CFCs would be broken up by ultraviolet light. And where do we have high UV light? In the stratosphere, where the ozone layer protects us by blocking much of the UV radiation from reaching Earth’s surface. Essentially (I’m compressing a lot of interesting chemistry here) the breakup of the CFCs releases free chlorine, which bonds with free oxygen (O, also produced by UV radiation breaking up O2) and prevents the formation of ozone (O3, produced by combining normal O2 with atomic O). So the low reactivity of the CFCs is great for their use as refrigerants, but a curse for their role in the atmosphere. Because they are not reactive, they hang around in the lower atmosphere (the troposphere) for a long time before they eventually diffuse into the stratosphere where they are exposed to high UV dosages. This is the only way to get free chlorine into the stratosphere; volcanic eruptions produce chlorine, but it is so reactive that it combines with other molecules in the troposphere.
For their work on this problem, Rowland and Molina, along with Paul Crutzen from Germany, received the 1995 Nobel Prize in chemistry.
The Montreal Protocol (1988) phases out the production of CFCs. Recycled CFCs are still used in large commercial refrigeration systems, but they are scheduled to be cycled out of use this year (I think). For refrigerators and air conditioners, CFCs have been replaced by more ozone-friendly substances – HCFCs (hydrochlorofluorocarbons) have only about 1/50 the destructive power of CFCs, and HFCs (hydrofluorocarbons) have essentially zero effect on ozone but they are greenhouse gases.
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k-man
Gym climber
SCruz
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Topic Author's Reply - Jul 18, 2010 - 10:11pm PT
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"Relinquish the notion that you are above the all knowing mind of the universe."
Deep indeed.
But Chief, I don't think that Ed is trying to be above the all knowing "mind" of the universe (if there really is such a "thing"). Instead, I see Ed (and our newest poster with a scientific background and knowledge of the subject at hand) trying to educate us on the science of what is happening to the Earth's climate. As such, these are two important voices, they actually know what they are talking about and are not handing out opinions based on beliefs.
If you don't like science, or believe that it can measure and predict some things, that's OK.
As I see it, these computer things are miracles and it amazes me that through science, we can make atoms and molecules work in a way the benefits us. The transistors in these things work at the molecular level and yet they are very predictable. Amazing, no? So yeah, I have no choice but to believe that the scientific method has a lot going for it.
In other news, I've noticed that most of the Climate Change skeptics have drifted off. My belief is that they cannot rebut the science.
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k-man
Gym climber
SCruz
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Topic Author's Reply - Jul 19, 2010 - 12:23am PT
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Chief,
"The hallmark of good science is the testing of a plausible hypothesis that is then either supported or rejected by the evidence."
I agree with this, and if the previously unpublished work can withstand peer scrutiny, then so be it.
But, there seems to be a lot of science, peer reviewed, that points to CO2 being an enemy of ours just now. Cap-n-trade? I don't know if that will go far enough either.
Energy, energy, energy...
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DrDeeg
Mountain climber
Mammoth Lakes, CA
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Jul 19, 2010 - 01:12am PT
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Hi Chief,
I have looked at Willie Soon’s web pages and searched the Web of Science for his work. The problem with the web page http://www.newmediajournal.us/staff/soon/2009/03052009.htm that you provide is that it presents no data to back up his assertions, but I did read some of his papers he cites. The paper in Physical Geography 2007 (Implications of the secondary role of carbon dioxide and methane forcing in climate change) states that the major swings of climate during the Ice Ages (glacial to interglacial) were not forced by carbon dioxide or methane. I think most of the scientific community would agree; the major glacial and interglacial cycles seem to be driven by the regular variability in Earth’s orbit –- called the Milankovitch Cycles after the Yugoslavian scientist who discovered them. Over a period of about 100,000 years, Earth’s orbit varies between more circular to more elliptical. Over a period of about 40,000 years, the tilt of Earth’s axis varies from 21.5 to 24.4 degrees (currently it is 23.45). Over a period of about 22,000 years, Earth’s orbit precesses; right now we are closest to the Sun in January, but in 11,000 years we will be closest in July.
These effects combine to either amplify or cancel each other. The periods that correspond to more ice are when there is less difference between winter and summer in the northern hemisphere. A warmer winter means more precipitation; a cooler summer means less melt. Even though the forcings are asynchronous between the hemispheres, the northern hemisphere drives global glaciation. The northern hemisphere has much more land at high latitudes, so when the glaciers start to cover more area, the albedo (reflectivity) gets larger and cools the whole Earth and the glaciers grow in both hemispheres. In the southern hemisphere, Antarctica is already covered with ice, Africa and Australia don’t extend very far south, and South America is pretty skinny at its higher latitudes.
During these cycles, driven by changes in orbit, we see in the ice cores less CO2 during the cold periods and more during the warm periods. There are some interesting associated questions – where did the carbon go? – but climate scientists generally agree with Dr Soon that these atmospheric changes result from climate change rather than cause them.
However, the same explanation does not apply to recent climate variability over the past millennium, and especially the last half century, because orbital variability is insignificant at this time scale. The driver that is consistent with what we know about atmospheric radiation is the increase in CO2 and, to a lesser extent, methane. As explained in earlier posts, solar radiation mostly passes through the atmosphere, warms Earth’s surface, which in turn emits infrared radiation in the 4-50 micrometer wavelenghts, where CO2, methane, CFCs, and water vapor are absorptive. When the concentrations of these gases in the atmosphere increase, the atmosphere absorbs more of this outgoing infrared radiation and gets warmer. The recent global temperature record is consistent with these concentrations, especially when we also factor in a cooling effect caused by more sulfate aerosol production before we had scrubbers on coal-fired power plants to reduce them. These aerosols effectively increase Earth’s albedo, so the observed warming is a bit less than one would calculate based only on the CO2 concentrations.
Although Dr Soon proposes alternative explanations, his papers do not refute the basic physical explanations in the previous paragraph. I also looked at the Climate Research 2003 paper by Soon and Baliunas. The review of climate reconstructions is in general agreement with the 1000-year analysis of global climate by Tom Crowley (Science 2000, Causes of climate change over the past 1000 years). Crowley, in agreement with Dr Soon, is able to correlate the Little Ice Age and the Medieval Warm Period with changes in solar output and increased/decreased volcanic dust, but he is not able to explain the 20th century without the increased concentrations of carbon dioxide. His paper explores the other plausible mechanisms.
Finally, I looked at the Soon et al. paper in New Astronomy 2000. The issue we face if we look at solar variability as a driver of recent climate change is that the sunspot cycles etc. do not seem to have caused much variability in total solar irradiance, but only changes in the very short wavelengths. See Judith Lean’s paper in Physics Today 2005 (Living with a variable sun) for a very readable review of the ways that solar radiation varies. She explains why that variability explains only about 0.1 degree C of warming in the 20th century, and needs to include the secular warming from CO2 to explain the temperature record. The Soon et al. New Astronomy 2000 paper postulates a mechanism whereby these small changes in solar output could cause significant variability in climate, but the explanation seems rather speculative and not nearly as consistent with atmospheric radiation processes as the CO2 explanation. We should allow for the possibility that their explanation has some validity, but I would want to discuss with people who understand atmospheric dynamics (neither my expertise, nor that of Soon and Baliunas). The issue is how a bit more absorption at very high altitudes in the atmosphere, above the stratosphere, could propagate to significant changes at Earth’s surface. The CO2 explanation is more viable because the atmospheric changes occur in the troposphere, next to Earth’s surface.
Finally, the argument that we should reduce carbon emissions is not entirely based on their effect on climate. We are also seeing increases in ocean acidity and associated inability of some critters in some regions to develop their shells. The idea of some, mainly the Idso brothers in Arizona, that CO2 is an unexpected benefit of the Industrial Revolution is one that I would treat with skepticism. For example, the putative benefit to agriculture (more CO2 means less evapotranspiration because the plants’ stomata don’t have to open as much) seems to be rather small, because Scott Denning’s work shows that the extra CO2 increases atmospheric buoyancy, so the plants can’t get to the extra CO2. I use some of Sherwood Idso’s other work (mainly to estimate incoming infrared radiation based on measurements of temperature and humidity) but here I think he is more speculative than the evidence warrants.
I realize this post is rather long. I am trying to shed more light on the discussion, rather than more heat.
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DrDeeg
Mountain climber
Mammoth Lakes, CA
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Jul 19, 2010 - 03:36am PT
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Chief,
Why do we buy insurance? We make a modest investment, on which we expect to lose money (the insurance companies make money, so we must be losing it), to avoid a catastrophic loss. And we recognize that the probability of the catastrophic loss is uncertain. I tend to view the argument to mitigate future climate change by reducing current carbon emissions through the same lens.
The problem is that we have to rely on models about the future, because the current and future levels of atmospheric CO2 are well above anything experienced in the past during the time when the continents were in the position they are now. The really deep past doesn’t help much because ocean circulation would have been completely different, and solar output was possibly different. The more recent past had lower CO2 (nothing above about 270 ppm in the ice cores). It’s not like a test of a new drug in a pharmaceutical experiment, where we have a control group that takes a placebo instead. We have just one Earth, so we have to base plausible future scenarios on model calculations, fortunately with models that do a reasonable (but not perfect) job of reproducing the past and present.
But here is the problem with uncertainty. We have more confidence in the modeled response to a modest change rather than a drastic change. We can observe how Earth behaves with an atmospheric CO2 concentration of 370 ppm, and therefore we have more confidence in our calculation of what things look like at 450 ppm than they do at, for example, 900 ppm. The reasonable question that society asks of climate science is, What is a worst-case scenario? It turns out that is a very hard question to answer. A paper by Gerard Roe and Marcia Baker (Science 2007, Why is climate sensitivity so unpredictable?) gives a highly mathematical explanation about why this is the case. The basic argument is that even if the model is perfect, we have to know the statistical distributions of the input variables in order to get the statistical distribution of the output.
Myles Allen explored the likely scenarios in the climateprediction.net experiment, whereby about a quarter-million people around the world ran various parameters of a PC-based climate model of a doubled-CO2 environment (540 ppm, 2x the preindustrial maximum). The results were rather startling, with a real cliff in the histogram at about 2C of warming (i.e., you get at least 2 degrees no matter what assumptions you make about cloud feedbacks etc) and a long tail extending out to about 10-12C. Wow! This is not a prediction that we will see 10C of warming in this century, but it says there is a finite probability, a greater probability than less than 2C of warming.
So what do we do? My response is, let’s not go there. We can’t tell you precisely what catastrophe is going to get your descendants, but we can say that you reduce the risk of catastrophe if you can mitigate the magnitude of change. In that sense, spending money to reduce carbon emissions is an insurance investment. It also reduces ocean acidity (no getting around that one, more atmospheric CO2 means a more acidic ocean) and it makes American economic and foreign policy less dependent on the price of oil (you don't want a carbon tax, but we are really already paying one, to Saudi Arabia, Iran, Russia, etc).
A little-acknowledged feature of science is that the initial consequence of better knowledge is often an increase in uncertainty! Goethe said something like this 200+ years ago, “We know accurately only when we know little, with knowledge doubt grows.” Let me tie this to predictions of future sea level. In the mid 1980s, I helped organize a session at the annual meeting of the American Geophysical Union about sea level. The ideas presented in the talks led to our conservative projections of sea level in a warmer climate. We reasoned that a warmer ocean would evaporate more water, thereby moving water from the ocean onto the ice sheets; the latent heat of fusion (the amount of energy needed to melt ice) is high; and even if melt rates increased in, say, central Greenland, it would take a while for that extra water to get to the ocean. Even the recent IPCC assessment had a pretty modest upper bound for sea level rise in this century, with 58 cm being the biggest estimate.
But look what has happened. Our satellite observations reveal a much larger decrease in the ice mass in Greenland and Antarctica than we had expected, and we see thinning ice sheets, accelerating glacier flow, and astonishing decay of sections of the ice shelves. We don’t understand heat exchange between the ocean and the ice shelves well, but clearly something is happening and it’s bad news. The newest ocean altimeter data seem to show that sea level rise is changing from ~1 mm/yr to ~3 mm/yr. Our mistake back then was to view the problem in terms of energetics; we had not considered the effect on glacier dynamics. So our increased knowledge about glaciers has widened the uncertainty about future sea level. A 1+ m rise in this century is quite plausible, which would hit places like Bangladesh and Florida pretty severely; recall that the 1994 Brahmaputra floods affected about 60% of the country. Even in places with steep coasts (California) realize that all the process that go on now would occur 1 m higher.
So what about climate change in general? CO2 causes warming (no disagreement about that, by anyone), and the warmer ocean evaporates more, so atmospheric water vapor increases and thereby intensifies the warming (no disagreement about the process, but a difference of opinion about the magnitude with the climate skeptics saying not much and others saying quite a bit). And then what happens to clouds? If we get more low clouds, we raise Earth’s albedo and we don’t trap much extra infrared radiation (because the clouds are close to the ground and therefore not much different in temperature), and the clouds help mitigate the effect of the extra CO2. Let’s call that the “Lucky Solution” that some believe will happen. On the other hand, if we get more high clouds, they trap more infrared radiation and thereby intensify the warming. The satellite measurements from the CERES instrument (Cloud-Earth Radiant Energy System) show that in general clouds warm the Earth more than they cool it, so the “Unlucky Solution” seems more probable.
Signing off . . .
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DrDeeg
Mountain climber
Mammoth Lakes, CA
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Jul 19, 2010 - 03:00pm PT
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No no. Lindzen agrees that CO2 causes warming. I shared an office suite with him. His dispute lies in the feedback mechanisms and their magnitude.
In my post, I pointed out that the CO2 in the ice cores follows the warming (which is caused by orbital variability at the glacial/interglacial time scales). I agree with the point you are making with the Vostok graph. But . . . the same mechanism cannot explain the recent warming because the time scale of orbital variability doesn't fit.
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DrDeeg
Mountain climber
Mammoth Lakes, CA
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Jul 19, 2010 - 08:59pm PT
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Stephen Schneider 1945-2010
Steve Schneider, Stanford professor, an expert on climate science and dedicated to communicating science to the public, died of a heart attack on a flight from Stockholm to the U.S. today. I have known him since about 1980, and I have always appreciated the quality of his science (one of the earliest climate modelers, who studied the contrasting effects of CO2 and aerosols) and his tenacity and sincerity in trying to explain climate science to anyone.
In a preface to one of his books, Steve relates a story from Reid Bryson, who was worried about climate change long before it became a public issue. Reid was a weather forecaster in the Pacific during World War II, and he made an incorrect weather forecast that resulted in the death of a plane crew. No matter that the forecasting tools in those days were primitive, Reid was haunted by this event for the rest of his life, and he imparted to Steve Schneider (who transmitted this to the rest of us) that if we ever had the chance to use a forecast to save human lives, we must do so.
Steve was a survivor of an aggressive cancer, mantle cell lymphoma, the subject of his book The Patient from Hell. He was a MacArthur (“genius”) Fellow, a member of the National Academy of Sciences, and a Nobel Laureate as part of the IPCC.
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Mighty Hiker
climber
Vancouver, B.C.
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Jul 19, 2010 - 09:04pm PT
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Thank you Dr. Deeg, for your excellent posts!
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corniss chopper
Mountain climber
san jose, ca
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Jul 19, 2010 - 09:14pm PT
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Like many others I reject the unspoken premise that climate change would be bad if it happens.
How about an alternate premise: climate change would be a good thing if it happened. Innovation will be driven faster and in a hundred yrs what problem
could not be solved?
------
Stephen Schneider RIP.
A Q&A where he explains his ideas on climate quite well.
http://www.stanfordalumni.org/news/magazine/2010/julaug/features/schneider.html
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DrDeeg
Mountain climber
Mammoth Lakes, CA
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Jul 19, 2010 - 09:34pm PT
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Rokjox – Simple answer is yes, but there are three kinds of variability – orbital eccentricity (100,000 years), inclination of Earth’s axis (40,000 years), and precession of the orbit (22,000 years). There is a statistical technique (called spectral analysis) that can be used to see whether there really are strong periodicities in data. When we analyze temperature records from ice cores and sea sediments, we see the periodicities in the data, strongly. The conclusion that jumps out at you is that the cause must be orbital, because there are no other periodicities in nature that are so strong (except at the annual scale, daily scale, and quantum scale).
Also note that these periodicities can either amplify or cancel each other’s effects. The physical reasoning for their relationship to the Ice Ages and their interglacial stages is that glaciers will grow when there is less difference between winter and summer in the northern hemisphere. In warmer winters, we get more precipitation, and in cooler summers we get less melt. Then there is a feedback: the northern hemisphere has a lot of land area at high latitude, and once you get a lot of snow cover you make Earth brighter and therefore cooler in both hemispheres. So the glacial periods in both hemispheres correspond to the radiation forcing in the northern.
To bring this home, think what the Sierra Nevada would be like if it were always March/April or September/October, and especially if worldwide temperatures were 5C cooler. The glaciers would grow; we have snowfall in those months, but only a little melt.
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DrDeeg
Mountain climber
Mammoth Lakes, CA
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Jul 19, 2010 - 10:12pm PT
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Corniss – Your position is defensible. There are likely some parts of the world that would be more pleasant in a warmer climate. Two policy-related questions come up: (1) Would people move? (2) There would be winners and losers, for example in agriculture. Would the winners help the losers?
There are some attributes that would almost certainly be bad though: (1) Ocean acidification from the extra CO2 – hard to see how that would be a good thing. (2) Rising sea level - where are the Bangladeshis going to go? (3) The uncertainty about the future is part of the cost. We pay money now to reduce uncertainty – we buy insurance. Generally we avoid actions when we are uncertain about the consequences. On lead well above your protection, would you jump for a hold that might or might not be a good one?
The reason for the uncertainty is that although the climate models reproduce global reality reasonably well, they are not perfect. In particular, Earth will not warm uniformly, and the models give us less confidence in future regional variability, particularly about precipitation. I noted in an earlier post that uncertainty is part of the scientific process, and if we wait till the models are perfect, we will be paralyzed.
As the future unfolds, we will make choices between mitigation and adaptation. If we don’t do anything about mitigation, then adaptation will be our only option. We should explore the mitigation options, particularly in energy efficiency and alternative production. Improving energy efficiency is actually not that expensive for buildings; it is quite feasible to design a building that will cut energy use in half, and you recover the investment fairly quickly, 5 years or so. There are homes being built in Germany that use about 5% of that of conventional homes of the same size. As electricity gets just a little more expensive, the alternatives become attractive. Finally, carbon capture and sequestration face some problems in implementing, but the idea is not fantasy for stationary sources like power plants.
In summary, the problem of climate change is the rate, not the "new" climate. We should face the problem squarely. Denying that it exists or that humans are a major contributor just distracts us from really addressing what we could do, how much it would cost, how much would adaptation cost, and what is not feasible.
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corniss chopper
Mountain climber
san jose, ca
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Jul 20, 2010 - 12:10am PT
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DrDeeg -CCS. The stored CO2 acidifying the ground water, leaching minerals into solution which can migrate to the aquifers people use is indeed a problem.
Its one major reason of the world wide retreat of private groups from the CCS solution at present. I imagine the large expense for security designs needed on some CCS sites where a tornado or terrorist incident, for example, could release the CO2. Which then would flow down hill killing everything in its path has something also to do with dropping CCS for now.
CC
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DrDeeg
Mountain climber
Mammoth Lakes, CA
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Jul 20, 2010 - 02:53am PT
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OK Chief - Thanks for sending. I have read the paper. It seems the paper itself (as published in Geophysical Research Letters) simply reinforces what I said a bit above about Richard Lindzen. His dispute with the climate models is NOT with the basic warming mechanism about CO2, but with the feedback mechanisms and magnitudes. The Lindzen-Choi paper asserts that the ERBE data show a different feedback mechanism than the climate models emphasize.
A subsequent paper by Murphy, published in the same journal, explains why he thinks Lindzen is incorrect: "In particular, because of heat transport between regions, obtaining the equilibrium temperature change by multiplying the forcing by a climate sensitivity is valid only for a global domain. The analysis of Lindzen and Choi (2009) erroneously applies global concepts to a limited region." But this kind of dialogue is what science is about. Murphy thinks Lindzen & Choi are wrong, but he is not throwing stones or accusing them of being charlatans.
CO2 absorbs outgoing longwave radiation, and the more CO2 the more absorption. Richard Lindzen would agree with that statement. If there were no CO2 in the atmosphere, Earth would be quite colder (and there would not be any plants either, and hence no oxygen). The issue then is how the atmosphere behaves in response to the CO2-induced warming. Specifically, how do water vapor and clouds change? I need to postpone the full discussion to a later post, but this is the area where Lindzen disagrees with most of his colleagues. The solution to the disagreement was a more advanced satellite instrument than ERBE (which has been around since the early 1980s). It is CERES, with more precise measurements of the components of Earth's radiation budget.
The quotes in your post, specifically the last paragraph which is quite strongly worded, are not in the Lindzen-Choi paper.
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DrDeeg
Mountain climber
Mammoth Lakes, CA
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Jul 21, 2010 - 11:16am PT
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Steve Schneider's obituary in the New York Times includes a quote we should pay attention to (and I think we are -- this thread seems to be focusing more on evidence and rational argument than on invective):
"Let’s discover our differing value systems, and then look for a foundation of shared values where we might find a way to live together."
In the Denver Airport after a meeting in Boulder, I am trying to put together a post that explains crisply where all climate scientists agree (from Hansen through Lindzen), where the sources of disagreement are and how data might resolve them. The "crisply" part is the hard part.
In a nutshell (my plane is starting to board) we all agree that a CO2 level of 500+ ppm, without any feedback mechanisms, would raise global temperatures about 1C over the 1880-1950 average.
The arguments (at least between Lindzen and Hansen) are about the feedback mechanisms and their magnitudes. The majority of climate scientists say feedbacks would amplify the warming intially caused by CO2 by factors from 2-6. A few say that the feedback is less than 2. But I agree with The Chief that fact that one group is in the majority is not the scientific way to resolve the disagreement. One answer is indeed better than the other, and I think we all would rather not wait till the end of the century to find out which.
I think there is also general agreement that Earth is warmer now compared to the mid 1800s (but some disagreement about earlier times because for them we have to use proxy temperature indicators). Those who agree that Earth is warming but disagree about the CO2 cause are generally invoking a solar driver. The CO2 crowd questions the mechanism for the solar explanation. Clearly if the Sun were brighter then Earth would warm, but they say that observed changes are small and in wavelengths where the absorption would happen in the very upper part of the atmosphere.
More later, they may close the doors on me.
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DrDeeg
Mountain climber
Mammoth Lakes, CA
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Jul 21, 2010 - 10:38pm PT
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Chief - The models do include natural forcings, some generated (e.g. the Intertropic Convergence Zone), some forced (e.g., El Niño).
Ed - In the models, one has a choice of how to use the computing power, and the options as computing gets cheaper:
(i) Refine the resolution, but because of numerical stability issues in partial differential equations, refining the spatial and vertical resolutions also requires a smaller time step, so for example cutting the spatial resolution in half raises the number of floating ops by a factor of about 10.
(ii) Do more models runs, explore more parameters and forcings (for example different aerosol amounts, different solar values), run over longer time periods, etc.
(iii) Make the model more realistic, but more complex. The earliest models used prescribed ocean temperatures, for example. Improvements include coupled ocean-atmosphere, hydrologic cycle, carbon cycle, sea ice feedback etc.
A short elementary tutorial on climate modeling is by Gavin Schmidt:
http://www.giss.nasa.gov/research/briefs/schmidt_04/
For a full treatment, but only for those really really interested, the Hansen et al. 2007 paper in Climate Dynamics gives an in-depth explanation of how the GISS (Goddard Institute for Space Studies) model works. The abstract is here - http://pubs.giss.nasa.gov/abstracts/2007/Hansen_etal_3.html - and there are links there to the full paper. It's a 25 MB download and nearly 50 pages, but it is a frankly written paper with considerable discussion of where the model and observations differ. I like it because it is written to educate, not to impress. Hansen has been a forceful spokesman about the benefits of mitigating climate change, but in this paper (and I think in general) he has not compromised his scholarship. This doesn't mean he is always right (same with Lindzen) but if your hypotheses are never wrong, you have probably been too timid.
(This also applies to climbing. Among Eric Beck's many notable sayings is, "If you prepare to bivouac, you probably will." A climber who has never had a cold, unprepared, unplanned bivouac is probably too cautious.)
Hansen's model (and the other major climate models) in fact do pretty well. For example, it indeed does reproduce the early 20th century warming, in contrast to the assertion of Soon & Baliunas. Here is a comparison with global temperatures. The red (model) and the observations (blue) correspond (the various "Alt..." scenarios are different aerosols and different solar values).
The following graph shows the individual forcings. Among the positive forcings (causing warming) the greenhouse gases dominate. Among the negative forcings, the major ones tropospheric aerosols (steady trend but leveling off recently as combustion from power plants, autos etc has become cleaner), and stratospheric aerosols (volcanic eruptions - the big downward spike in the 1880s is Krakatau, the most recent one is Pinatubo). The right-hand graph shows the sum of the forcings, in Watts per sq m.
One way to compare a model with data is with long-term observations. Another way is to take advantage of a significant natural event, like a big volcanic eruption. I remember when El Chichón went off in 1982, Richard Somerville from Scripps said, "This will be a good test of the climate models, to see if the cooling in the models compares with the cooling I expect we will see." The graph below shows global data and model calculations for the Krakatau 1883 and Pinatubo 1991 eruptions. The model fit with Krakatau is not as good, but the observation network was sparser then, particularly in the oceans. The fit to Pinatubo 1991 is excellent, especially when compared with the land+ocean temperatures instead of just surface temperatures.
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