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Air travel less harmful to the environment than rail travel?
Air travel is probably less harmful to the environment than rail
travel. Aircraft leave vapour trails which aid in the reflection of the sun's radiation back into space. As these trails are at high altitude their shadows cover immense areas. On the other hand vast quantities of fossil fuels are burnt to produce the electricity (at only 10% efficiency) to power the railways. If someone would do the calculations, all things considered (the upkeep of track and bridges for instance) they would probably find that Aircraft are less of a cause of global warming than an equivalent railway system. |
#2
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Air travel less harmful to the environment than rail travel?
"Nelson" wrote in message oups.com... Air travel is probably less harmful to the environment than rail travel. Aircraft leave vapour trails which aid in the reflection of the sun's radiation back into space. As these trails are at high altitude their shadows cover immense areas. On the other hand vast quantities of fossil fuels are burnt to produce the electricity (at only 10% efficiency) to power the railways. If someone would do the calculations, all things considered (the upkeep of track and bridges for instance) they would probably find that Aircraft are less of a cause of global warming than an equivalent railway system. You have a great future ahead of you as a science adviser, but only if you can get your resume in to the Bush Administration while they're still in a position to be hiring... Bob M. |
#3
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Air travel less harmful to the environment than rail travel?
Nelson wrote:
Air travel is probably less harmful to the environment than rail travel. Aircraft leave vapour trails which aid in the reflection of the sun's radiation back into space. As these trails are at high altitude their shadows cover immense areas. On the other hand vast quantities of fossil fuels are burnt to produce the electricity (at only 10% efficiency) to power the railways. If someone would do the calculations, all things considered (the upkeep of track and bridges for instance) they would probably find that Aircraft are less of a cause of global warming than an equivalent railway system. To start with, your effiency for power generation is woefully low. The average thermal power plant is about 35 percent efficient, and how to you rank the efficiency of hydroelectric or nuclear? The newest thermal power plants are now pushing 60 percent thermal efficiency, which is 6 times what you suggested. Aircraft engines are in the range of 40 to 50 percent efficient when they run at full power, but gas turbines are horribly inefficient at lower power settings. That means when you consider efficiency of an aircraft, you have to look at how long the trip is, since if the aircraft doesn't have a long cruise, the inefficiencies of landing can overpower everything else. Of course the shorter trips, when aircraft are the least efficient, are the ones that are rail competitive. Contrails do reflect sunlight, but they also absorb heat from the surface, and won't let it escape. There is debate about the net effect of the two, and there is some indication that the increased cloud cover as a result of aircraft operations is resulting in global warming: http://www.nasa.gov/centers/glenn/about/fs10grc.html Aircraft also produce both CO2 and NOx, which are major contributors to atmospheric pollution. Overall, aircraft aren't so great. |
#4
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Air travel less harmful to the environment than rail travel?
On 13 Aug, 22:33, James Robinson wrote:
Nelson wrote: Air travel is probably less harmful to the environment than rail travel. Aircraft leave vapour trails which aid in the reflection of the sun's radiation back into space. As these trails are at high altitude their shadows cover immense areas. On the other hand vast quantities of fossil fuels are burnt to produce the electricity (at only 10% efficiency) to power the railways. If someone would do the calculations, all things considered (the upkeep of track and bridges for instance) they would probably find that Aircraft are less of a cause of global warming than an equivalent railway system. To start with, your effiency for power generation is woefully low. The average thermal power plant is about 35 percent efficient, and how to you rank the efficiency of hydroelectric or nuclear? The newest thermal power plants are now pushing 60 percent thermal efficiency, which is 6 times what you suggested. Aircraft engines are in the range of 40 to 50 percent efficient when they run at full power, but gas turbines are horribly inefficient at lower power settings. That means when you consider efficiency of an aircraft, you have to look at how long the trip is, since if the aircraft doesn't have a long cruise, the inefficiencies of landing can overpower everything else. Of course the shorter trips, when aircraft are the least efficient, are the ones that are rail competitive. Contrails do reflect sunlight, but they also absorb heat from the surface, and won't let it escape. There is debate about the net effect of the two, and there is some indication that the increased cloud cover as a result of aircraft operations is resulting in global warming: http://www.nasa.gov/centers/glenn/about/fs10grc.html Aircraft also produce both CO2 and NOx, which are major contributors to atmospheric pollution. Overall, aircraft aren't so great. The average thermal power plant is about 35 percent efficient, and how to you rank the efficiency of hydroelectric or nuclear? Yes, 35 percent efficient then loose x % of this in power transmission, another x % lost on motor efficiency, more lost on running trains only 10% full etc. The figure of 10% is that actually used in doing useful work. Nuclear produces heat which is what we are trying to avoid. Hydroelectricity not often available. At least aircraft are more fuel efficient than cars or busses. |
#5
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Air travel less harmful to the environment than rail travel?
In article .com,
Nelson wrote: Aircraft leave vapour trails which aid in the reflection of the sun's radiation back into space. A study of the no-fly period following 9/11 showed a full extra degree (Celsius) of cooling over the US during those four days, apparently due to the lack of contrail vapor, which contributes to the cirrus cloud layer that reflects nighttime longwave radiation back to earth. -- Randy Hudson |
#6
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Air travel less harmful to the environment than rail travel?
Nelson wrote:
James Robinson wrote: The average thermal power plant is about 35 percent efficient, and how do you rank the efficiency of hydroelectric or nuclear? Yes, 35 percent efficient then loose x % of this in power transmission, another x % lost on motor efficiency, more lost on running trains only 10% full etc. The figure of 10% is that actually used in doing useful work. Nuclear produces heat which is what we are trying to avoid. Hydroelectricity not often available. At least aircraft are more fuel efficient than cars or busses. No, 10 percent is far too low, even with those efficiencies taken into account. Further, load factors are more like 70 percent on high speed train services that are competitive with airlines. The other factor that you haven't taken into account is that it is far harder to push an airliner through the air at 800+ Km/h than a train at 300. (Air resistance rises as the square of speed.) When you boil all that down, airliners use about twice the BTUs as a train per passenger-mile. Nuclear power is considered to be about 70% efficient, which is higher than the other thermal plants, plus there are no air pollutants, just nuclear waste. |
#7
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Air travel less harmful to the environment than rail travel?
Randy Hudson wrote:
In article .com, Nelson wrote: Aircraft leave vapour trails which aid in the reflection of the sun's radiation back into space. A study of the no-fly period following 9/11 showed a full extra degree (Celsius) of cooling over the US during those four days, apparently due to the lack of contrail vapor, which contributes to the cirrus cloud layer that reflects nighttime longwave radiation back to earth. Can you cite a source for this report showing the entire US dropped exactly one degree Celsius and that was directly attributable to the reduction in aircraft? |
#8
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Air travel less harmful to the environment than rail travel?
On 14 Aug, 03:55, James Robinson wrote:
Nelson wrote: James Robinson wrote: The average thermal power plant is about 35 percent efficient, and how do you rank the efficiency of hydroelectric or nuclear? Yes, 35 percent efficient then loose x % of this in power transmission, another x % lost on motor efficiency, more lost on running trains only 10% full etc. The figure of 10% is that actually used in doing useful work. Nuclear produces heat which is what we are trying to avoid. Hydroelectricity not often available. At least aircraft are more fuel efficient than cars or busses. No, 10 percent is far too low, even with those efficiencies taken into account. Further, load factors are more like 70 percent on high speed train services that are competitive with airlines. The other factor that you haven't taken into account is that it is far harder to push an airliner through the air at 800+ Km/h than a train at 300. (Air resistance rises as the square of speed.) When you boil all that down, airliners use about twice the BTUs as a train per passenger-mile. Nuclear power is considered to be about 70% efficient, which is higher than the other thermal plants, plus there are no air pollutants, just nuclear waste. Aircraft generally fly at 32000ft which is 6 miles high and where the air pressure is almost down to one tenth of that on the surface so I am not convinced. There is still the question of the infrastructure of the railway system and the amount of fuel required to keep that going? Our nuclear powers stations are situated by the coast to make use of sea water cooling systems! Sea is the one thing we should try not to warm up. I notice the protestors at Heathrow have arrived in their 4x4s, not a very convincing lot! |
#9
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Air travel less harmful to the environment than rail travel?
Nelson wrote:
On 14 Aug, 03:55, James Robinson wrote: Nelson wrote: James Robinson wrote: The average thermal power plant is about 35 percent efficient, and how do you rank the efficiency of hydroelectric or nuclear? Yes, 35 percent efficient then loose x % of this in power transmission, another x % lost on motor efficiency, more lost on running trains only 10% full etc. The figure of 10% is that actually used in doing useful work. Nuclear produces heat which is what we are trying to avoid. Hydroelectricity not often available. At least aircraft are more fuel efficient than cars or busses. No, 10 percent is far too low, even with those efficiencies taken into account. Further, load factors are more like 70 percent on high speed train services that are competitive with airlines. The other factor that you haven't taken into account is that it is far harder to push an airliner through the air at 800+ Km/h than a train at 300. (Air resistance rises as the square of speed.) When you boil all that down, airliners use about twice the BTUs as a train per passenger-mile. Nuclear power is considered to be about 70% efficient, which is higher than the other thermal plants, plus there are no air pollutants, just nuclear waste. Aircraft generally fly at 32000ft which is 6 miles high and where the air pressure is almost down to one tenth of that on the surface so I am not convinced. There is still the question of the infrastructure of the railway system and the amount of fuel required to keep that going? Our nuclear powers stations are situated by the coast to make use of sea water cooling systems! Sea is the one thing we should try not to warm up. I notice the protestors at Heathrow have arrived in their 4x4s, not a very convincing lot! The air pressure at cruising altitude is 1/4 of that at sea level, not 1/10th: http://www.sensorsone.co.uk/altitude...onversion.html Effect of speed difference (900 v. 300 km/h = 81/9 = 9 times the air resistance) So, the overall effect is 9/4 = twice the air resistance. Plus, you have to add energy to keep the aircraft in the air, and pass through denser air getting to and from altitude, which you will do more of as a proportion of the overall flight on shorter, rail-competitive routes. Instead of chasing theory, here is a link to some numbers that show the energy intensity of various modes: http://www.bts.gov/publications/nati...tistics/html/t able_04_20.html http://tinyurl.com/wy26b It is a US comparison, where average flight distances are relatively long, and passenger trains are relatively heavy per passenger, with sleeping cars, low density seating, and heavy locomotives. You can see how much better rail is than air, even with these characteristics. |
#10
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Air travel less harmful to the environment than rail travel?
mrtravel wrote:
Randy Hudson wrote: Nelson wrote: Aircraft leave vapour trails which aid in the reflection of the sun's radiation back into space. A study of the no-fly period following 9/11 showed a full extra degree (Celsius) of cooling over the US during those four days, apparently due to the lack of contrail vapor, which contributes to the cirrus cloud layer that reflects nighttime longwave radiation back to earth. Can you cite a source for this report showing the entire US dropped exactly one degree Celsius and that was directly attributable to the reduction in aircraft? Here's one article on the effect: http://www.sciencenews.org/articles/20020511/fob1.asp There are lots of other examples. |
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