Subject: Warmer ground--> warmer troposphere? Date: Mon, 20 Jul 1998 12:54:57 -0700 From: ogryzlo@despamchem.despamubc.ca (Elmer) Organization: AMPEL, UBC Newsgroups: sci.environment ogryzlo@chem.mubc.ca (Elmer): > Is there a simple answer to the fact that the troposphere near 7 km >does not seem to be rising "in concert" with the increasing CO2 and ground >temperature? Hi, Yes, I think the simple answer is that the satellite that made the measurment did not correct the data for the effect that the atmospheric drag had on the satellite altitude. Read this from the current issue of the New Scientist: "One of the last props supporting critics of theories of global warming is crumbling. Satellite data which suggested the Earth's lower atmosphere is cooling were a red herring. No one was aware that the satellites slipping from their orbits and giving misleading readings, scientists say. The data in question come from several satellites called microwave units, by the National Oceanic and Atmospheric Administration (NOAA). They seemed to show that the Earth's lower troposphere, at an average height of about 3·5 kilometres, had cooled at a rate of 0·05 °C per decade since. But the models did not predict cooling in the lower troposphere, so apparent cooling has been a sore point for climate researchers. Greenhouse sceptics have hailed it as a fatal flaw in theories of global warming. But Frank Wentz of Remote Sensing Systems in Santa Rosa, California, became suspicious of the satellite data, because they also showed the lower troposphere was cooling much more than the troposphere. "That result was puzzling," he says. "It didn't agree with anything." Wentz and his colleague Matthias Schabel found that no one had accounted for the gradual slippage of the satellites from their orbits over time. Atmospheric friction would have dragged the satellites down --especially during 1979 to 1983 and 1989 to 1992 when the Sun was particularly active, making the lower atmosphere more dense. On average, the satellites would have fallen in altitude by 1·2 kilometres every year. These orbit changes would have altered the angles at which the satellites viewed the atmosphere. Taking these changes into account, Wentz and Schabel found that the mysterious cooling trend was actually a warming trend of 0·07 °C per decade (Nature, vol 394, p 661). AND: Summary of Perspective article, SCIENCE 281, 930-932, 14 August 1998. ------------------------------------------------------------ GLOBAL WARMING: Global Climate Data and Models: A Reconciliation James E. Hansen, Makiko Sato, Reto Ruedy, Andrew Lacis, Jay Glascoe The debate over the existence of global warming and climate change has been muddled because of satellite data showing a cooling trend in Earth's troposphere. This apparent cooling is in disagreement with measurements at surface stations and with climate models. In their Perspective, Hansen et al. discuss a correction to the satellite data published by Wentz and Schabel in Nature that may have profound implications for discussions of climate change. Wentz and Schabel discovered that the original satellite data, published in 1995, was not adjusted for the natural decay of spacecraft altitude caused by atmospheric drag. When this adjustment is made, the satellite data agree with both surface data and model calculations. The authors of the Perspective conclude that the question now is not whether global warming exists--it clearly does--but what should be done about it. --------------------------------------------------------------- Furthermore, the authors present data indicating that the temperature trend in the MSU LT data are very close to that predicted by GCM experiments, ie. a warming near the surface and a cooling above 500 mb pressure height.... ogryzlo@chem.mubc.ca (Elmer)(again): > I have come to believe the following description of how the >"greehouse effect" works: "Atmospheric CO2 strongly absorbs radiation originating from the Earth's surface in the 15 micron band. At pressures just below one atmosphere, such CO2 molecules suffer about 4x10^8 collisions per second. The radiative lifetime for the emissions of an IR photon by CO2 at this wavelength is about a millisecond. This means that any CO2 molecule that absorbed the radiation at 15 microns, suffers many collisions before it has a chance to re-emit the radiation (in all directions). These many collisions bring it into thermal equilibrium with its surroundings at each altitude. As the radiation works its way up in the troposphere, since the temperature of the atmospheric gases drops, the temperature of the CO2 at greater elevations is lower. At an altitude of about 7 km, the 15 micron radiation is emitted into space because there is so little CO2 above it that the atmosphere is essentially transparent at that wavelength. However, at that altitude the intensity of the emitted radiation (at 15 microns) is decreased because of the lower temperature there (recall the Steffan-Boltzmann law says that "I" is proportional to T^4). Thus the radiative loss of energy to space at this wavelength drops. Since less radiation is radiated to space, the equilibrium temperature of the planet rises until a new steady state is achieved in which the total energy being emitted by the Earth again equals the energy being absorbed from the Sun. This means that the temperature in the troposphere must rise (especially at that 7 km level). Since it does not appeear to be rising , I am having trouble correlating the currently increasing CO2 levels with global warming. Any constructuve comments would be appreciated."---Elmer Hi, me again. That sounds reasonable to me. Except that the temperature in the lower troposphere is increasing when properly corrected. But two comments: First, since the "lower" part of the atmosphere would be expected to be "warmed" by the increased CO2 levels, but the "upper" part would be expected to be cooled, it is not clear just where the "cross-over" point would be expected. What is the altitude where there would be no temperature change expected? And, (related to that), to measure the effect of the CO2 ADDED to the atmosphere by human activity, it would be necessary to compare two different heat adsorption vs height profiles. One based on the 250 ppm (or whatever) CO2 level that existed before the industrial revolution, and the other based on the current level. AND:Subject: Re: Warmer ground--> warmer troposphere? Date: 14 Aug 1998 15:41:40 GMT From: irv115@aol.com (Irv115) Organization: AOL http://www.aol.com Newsgroups: sci.environment References: 1 >First, since the "lower" part of the atmosphere would be expected to >be "warmed" by the increased CO2 levels, but the "upper" part would >be expected to be cooled, it is not clear just where the "cross-over" >point would be expected. What is the altitude where there would be >no temperature change expected? > That one I can answer: The effective radiation temperature of the earth is unchanged, so the mean effective radiation height is the crossover point. If you want to get picky, the mean radiation height has increased just a bit because the CO2 layer is a bit thicker so the crossover point is probably not far above the mean radiation height. If you want to go to the next order, because the effective radiation height has increased a bit the earth looks just a bit larger, so the mean radiation temperature dropped a bit. Probably by an ammount that is too small to measure. Sounds like a great problem for the student. If you are not the student. >And, (related to that), to measure the effect of the CO2 ADDED to the >atmosphere by human activity, it would be necessary to compare two >different heat adsorption vs height profiles. One based on the 250 ppm >(or whatever) CO2 level that existed before the industrial revolution, >and the other based on the current level. Irv @ Webster: Nice to rational discussion on this group. Thank you both. Hi, Can you translate that into km? The firgure cited for the satellite measurments was 7 km; is that above or below this crossover height? Also are these heights (for the satellite measurement and the mean radiation height) "constant" or do they vary with location, season, or during the day/night cycle? Irv @ Webster: I have been thinking abou that. There are two different temperature profiles with altitude: The dry rate, the steeper one, and the wet rate. The difference is that when warm air rises it cools at the dry rate untill its relative humidity reaches 100%. At this altitude the excess moisture starts to condense and release latent heat. Above this altitude wet air cools at the wet rate as it rises. To solve the whole thing you need to use one of those General Circulation Models. Another way the stratosphere could be cooled. Because the greenhouse insulation is slightly more efficient it may be able to maintain the lapse rate to a slightly higher altitude. I note that according to the standard upper atmosphere model in the poster on my wall, in July the tropical tropopause is higher than the arctic tropopause, but the arctic tropopause is about 10 degrees K warmer In fact the US standard atmospher, as of 1965, had most of the arctic stratosphere warmer than the tropical one in the summer. I scarfed up that one when my boss got a newer oned. The earth's surface is about 32 degrees C above the equilibrium radiation temperature. Most of that is due to absorbtion of IR by H2O, about 3 degrees is due to CO2. The IR band is very broad and the absorbtion coefficients vary considerably due to tha complicated absorbtion band structure of H2O and CO2. Some of the IR that is radiated to space is radiated at ground level, some is radiated at stratospheric levels, and some from in between. The book Principles of Atmospheric Physics and Chemistry attempts to explain this in chapters 3 & 4. anyways, there is no one level, it is spread out. The wet & dry lapse rates are important too, depending on the relative humidity. I think, don't know, but think, that the added absorbtion due to added CO2 causes the tropopause to rise just a bit and that is what makes the stratosphere cooler. Irv @ Webster AND: >Can you explain to me why the upper part of the troposphere would be >expected to be cooled by an increased CO2 content? peter.j.vanzant@boeing.com (Peter): My understanding is that IR coming up from the earth is absorbed at a lower altitude by the CO2 and other greenhouse gasses. It is then re-radiated, but equally likely down as up. Therefore, less IR makes it to the stratosphere to excite molecules there and cool them. It also appears to me that this would be a transient condition, that the earth would warm until the IR going out to space would equal all the energy--UV, IR, and visible--coming in from the sun. REPLY: Hi, I think of this simply as: if more IR is absorbed lower in the atmosphere, there is less reaching the upper atmosphere TO be absorbed there. So it will be cooler there. All of the IR energy that was absorbed "low" and transferred to other molecules by collisions has become kinetic energy and will not be reaching the upper atmosphere. Less energy, cooler temperature. Irv @ Webster: >Some of the IR that is radiated to space is radiated at ground level, some is >radiated at stratospheric levels, and some from in between. The book >Principles of Atmospheric Physics and Chemistry attempts to explain this in >chapters 3 & 4. anyways, there is no one level, it is spread out. This is an important idea to remember when trying to actually MEASURE any atmospheric temperature change due to increased CO2 level, and especially from space "looking down". Another case where the basic principles are simple and obvious, but it is difficult to actually measure the effect. I will add this from my web page section on CO2; on trying to experimentally measure the warming effect of a light bulb in a swimming pool: FROM http://www.geocities.com/capitolhill/4834/co7.txt In fact, consider this situation: the thermometer used to measure "the temperature" of the pool is located below the light bulb along one side of the pool. And the water in the pool is stratified due to low circulation: it is warmer on top and is colder on the bottom. Then when the light is turned ON, the thermometer reading will drop, as cold water from the bottom rises past the thermometer, and when the light is turned OFF, the thermometer will stop falling, and may even warm up as the cold water sinks back to the bottom. Repeat the experiment: light ON, thermometer falls, light OFF thermometer stabilizes or rises. Someone who knew nothing about physics might decide that the light- bulb was CAUSING the water to cool. Or at least that this experiment disproved the "theory" that adding heat to a swimming pool will cause "pool warming". ,,,,,,, _______________ooo___(_O O_)___ooo_______________ (_) jim blair (jeblair@facstaff.wisc.edu) Madison Wisconsin USA. This message was brought to you using biodegradable binary bits, and 100% recycled bandwidth.