The physics that lead to the conclusions that high (cirrus) clouds exert an overall warming influence is pretty clear. Overall, in the solar, they are not very reflectivea lot of light passes through them (and, of course, this effect only operates when the Sun is up). Throughout the day, the cirrus clouds radiate in the IR, and they do this pretty well. So, looking from space, the radiation coming out is from the cold cirrus instead of from lower, warmer layers (so tending to warm the globe). And this is also clear looking up at them from below, for downward radiation comes from the cirrus instead of from, for example outer space, the latter being far colder than the cirrus. Thus, the cirrus effectively block outgoing IR and reradiate energy back down toward the Earth that would, without them head out into space. So, let¹s not enhance cirrus (and, by the way, there was a special report on aircraft effects on climate done by the IPCC (go to http://www.ipcc.ch/publications_and_data/publications_and_data_reports.htm#2 and it is the sixth of the special reports).
By contrast, low clouds tend to be brighter, so reflect more solar to space, and because they are lower and so warmer, they do not so much cut down the IR out to space. They do, however, because they are warm intercept and reradiate back to the surface a lot of energy in the IR, keeping the surface from cooling off so much on cloudy nights. Sulfate particles, on the other hand, tend to be reflective of solar radiation (they are not very efficient at back scattering, most of their effect being to scatter the direct beam forward), but they are not important in the IR, to they tend to cool in the clear sky. And if they interact with cloud water, they can enhance cloud reflectivity, so reflect more energy. Mike MacCracken On 1/10/10 6:10 AM, "Andrew Lockley" <[email protected]> wrote: > The met office considered cirrus clouds, and my understanding of the research > is that their results show an increase in warming in response to cloud seeding > by jets. It is unlikely to be viable to get jets to fly so low as to seed > other types of cloud, as the effect on fuel consumption would be huge. > Therefore, 'stacking' the contrails may actually be more beneficial. It may > be that the methods have to be tweaked according to the weather conditions. > For example, in December, when the Northern hemisphere is losing heat into > space, carefully stacking the clouds may be beneficial, and in high summer, > when it's heating up, spreading them out may help reflect heat. I don't have > access to the 'tweaked' models which would help answer that question in > detail. > > I'm not sure that in any event it's practical to get aircraft to follow each > others' trails in either a stacked or unstacked format, due to the drift of > these clouds as weather systems move. Air traffic control would be a > nightmare if the routes were bending all over the place in real-time. > > Maybe someone with full journal access can post the original research (subject > to copyright). > > I know that various additives have been proposed to jet fuel to enhance > contrail effects. However, I'm not sure that the modellers fully understand > their implications, as little experimentation has been done. Even this > experiment was considered groundbreaking, and that only included unmodified > jet fuel. > > Coincidentally, I've taken my own advice and tried to engage some > anti-geoengineers in constructive dialogue. It has been a waste of time. > This lot, who are connected to the blog post I recently sent to the list, are > convinced that the US military have been secretly spraying > aluminium-containing materials and possibly other substances for years to > manipulate the Californian climate. I've tried to explain the basics of > evidence collection, controlled studies, and peer review to them, but sadly > the mere suggestion that this theory is a complete load of tosh without any > direct evidence is enough to provoke ad-hominem attacks (which quite amuse > me). I though it was particularly funny that during these exchanges the met > office data came to light, suggesting a completely different modus operandi > for the experiments, and the openness with which they are conducted. Rather > cruelly, I suggested that the only possible conspiracy was that the plane was > piloted by Elvis, whose actions were controlled by a brain chip implanted by > the CIA. They're still asleep, so I've yet to see how they respond to my > shameless trolling. > > A > > 2010/1/10 Oliver Wingenter <[email protected]> >> Dear Andrew, >> >> A holding pattern that does not result in overlapping contrails would result >> in more reflected sunlight but depends on temp (altitude) and the fuel >> consumption at that time (water vapor produced). The balance between any >> reflected short wave light reflected and IR would need to be evaluated. >> >> Sincerely, >> >> Oliver Wingenter >> >> Andrew Lockley wrote: >>> Is it possible to alter the flightpaths of commercial aircraft to ensure >>> that their contrails make the right kind of cloud to alter the radiative >>> balance favourably? >>> >>> A >>> >>> 2010/1/9 Veli Albert Kallio <[email protected] >>> <mailto:[email protected]>> >>> >>> >>> The British Army created a circular holding pattern to create an >>> immense artificial coil in the sky made of the military >>> aeroplane's contrail. This was then easy to distinguish and track >>> by satellites to see undisputed, how aeroplane emissions can be >>> made to turn clear skies to artificial cirrus covered clouds. >>> Link to the slide show: >>> http://news.bbc.co.uk/1/hi/sci/tech/8309629.stm >>> >>> ------------------------------------------------------------------------ >>> Got a cool Hotmail story? 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