Carbon Emissions | March 29, 2011 |
Aircraft Contrails Stoke Warming, Cloud Formation
It indicated that contrails -- white lines of vapor left by jet engines -- also have big knock-on effects by adding to the formation of high-altitude, heat-trapping cirrus clouds as the lines break up. The findings may help governments fix penalties on planes' greenhouse gas emissions in a U.N.-led assault on climate change. Or new engines might be designed to limit vapor and instead spit out water drops or ice that fall from the sky. "Aircraft condensation trails and the clouds that form from them may be causing more warming today than all the aircraft-emitted carbon dioxide (CO2) that has accumulated in the atmosphere since the start of aviation," the journal Nature Climate Change said in a statement of the findings. The study, by experts at the DLR German Aerospace Center, estimated that the net warming effect for the Earth of contrails and related cirrus clouds at any one time was 31 milliwatts per square meter, more than the warming effect of accumulated CO2 from aviation of 28 milliwatts. A milliwatt is a thousandth of a watt. Aviation emissions now account for about three percent of annual CO2 emissions from fossil fuels, more than a century since Orville and Wilbur Wright made the first powered airplane flight. 9/11, ICELAND But a key difference is that CO2 lingers for decades while warming from contrails quickly ends if flights are grounded, such as after the September 11, 2001 attacks in the United States, or in Europe after last year's Icelandic volcano eruption. "You can get rid of contrails very quickly. You can't get rid of CO2 quickly," lead author Ulrike Burkhardt at DLR told Reuters. The main climate effect of white lines and related cirrus clouds is to trap heat radiating back from the Earth's surface. They also have a smaller, counter-effect by slightly dimming sunlight and so slowing warming. Contrails are especially dense over parts of Europe and eastern United States. "This is a breakthrough in modeling and understanding of contrails," Olivier Boucher, of the Met Office Hadley Center in England who wrote a related article in Nature, told Reuters. He said the findings might bring changes in air traffic control, for instance diverting planes from regions or altitudes where air moisture was high and favored cirrus formation. But a problem was that any benefits of fewer contrails might be canceled out by higher fuel use on longer routes. He also said that it could spur a novel engine concept that would seek to condense some of the water vapor "before it leaves the engine. The condensed water could be vented in the form of large ice crystals or droplets that would fall quickly through the atmosphere." The U.N. panel of climate scientists has estimated that fuel burned at altitude is roughly twice as damaging for the climate as when used at ground level. Boucher said that the study might slightly raise that estimate, adding to potential costs.
Reprinted with permission from Reuters
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But I'm not so ctairen that adjusting the tropospheric temperatures to remove the stratospheric cooling effect is appropriate at all. It seems to me that the models, if they are worth anything at all, would have INCLUDED stratospheric cooling in their calculations of tropospheric temperature changes. Surely the modelers KNEW that AGW would lead to a cooling stratosphere, right? (They're ctairenly claiming that the real-world evidence of a cooling stratosphere supports the AGW theory.) Surely they KNEW that the cooling stratosphere would exert a cooling effect on the otherwise-warming troposphere, right? So why would they not have included this effect in their calculations of tropospheric temperature changes? If they did not (either because they didn't know about it, or because they chose to ignore it), then it seems to me that the models are drastically over-predicting SURFACE warming. If the stratosphere can cool the troposphere, then some portion of that cooling will in turn be transferred to the surface, right? So, it seems to me that, if the models DON'T include the effect of stratospheric cooling on tropospheric temperatures, they are missing a huge ameliorating influence on surface temperatures, an the models are even more useless than I thought. That, of course, would help to explain the UTTER FAILURE of the models to predict the complete LACK of warming seen in the last decade or so. But I don't think this is what happened. I think the modelers KNEW about the stratospheric cooling effect, and INCLUDED it in their estimation of the ratio of tropospheric warming to surface warming. I believe this because the models all predict a HIGHER ratio (~1.54) of tropospheric warming to surface warming in the tropics, where the troposphere is thicker and stratospheric cooling will therefore be minimized. But on the other hand, Fu et al seem to be blaming the higher ratio in the tropics on a "moist adiabatic lapse rate". Though I have some understanding of this phenomenon, I'm not sure whether it is related to the thickness of the troposphere or not. In any event, if the models do not include the effect of stratospheric cooling on tropospheric temps, then I believe they are vastly over-predicting surface warming by a large fraction of the degree to which they are over-predicting tropospheric warming (which is over 100%). And on that basis alone, it seems that we should be able to throw out the climate models as USELESS.On the other hand, if the models DO include the effect of stratospheric cooling on tropospheric temperatures, it is ENTIRELY INAPPROPRIATE to adjust the measured tropospheric temperatures for stratospheric cooling.So, what say you, Dr. Motl? Am I on the right track here? Do you have any information about whether the climate models (the ones that predict a ratio of 1.2 for tropospheric warming to surface warming) include the stratospheric cooling effect on tropospheric temperatures? Is there some fault in my reasoning here?I'm very much interested in your advice and guidance on this exploration. If it turns into something publishable (which I seriously doubt), rest assured that I will give you ample credit for your contributions.Please send me your comments and/or suggestions at btrevoryoung@yahoo.com. I thank you for taking the time to read this lengthy post.Regards,TrevorVirginia, USA
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