Over the posts so far, I have been exploring how aircraft effect the environment in terms of the emissions they release when they fly. I aim to put this into context and compare it with other modes of transport - after all as I mentioned in my very first post (and is talked about in the video in the second post), although planes appear to be absolutely detrimental to the environment from the media attention they receive, they only account for around 2% of annual global CO2 emissions.
Fugletvedt et al. (2008) wrote about how although contributing significantly to global emissions, the contribution of different modes of transport has not been quantified. They predict that whereas today (or in 2008!) transport in general accounted for 20-25% of total annual CO2 emissions, by 2050 this is estimated to rise to 30-50%.
The paper describes four main mechanisms through which all transport related emissions can effect the climate. These are:
1. The direct emission of greenhouse gases, notably CO2.
2. The emission of indirect greenhouse gases, for example gases like nitrogen oxides, and carbon monoxide that affect the oxidising capacity of the atmosphere.
3. The direct emission of aerosols or aerosol precursors such as black and organic carbon and sulphur compounds.
4. The indirect emission of aerosols that trigger alterations in the distribution and properties of clouds.
Note that many of these effects has already been discussed in relation to aviation in previous posts.
Attributing these effects to certain modes of transport is difficult because multiple chemical and physical mechanisms can occur when these emissions are released. The paper highlights further difficulty in calculating the climatic costs of transport due to the differing time scales involved. The effects of transport emissions on ozone, sulphates and black carbon may last months and days, where as more well mixed greenhouse gases (methane, CO2, and NOx) have an adjustment period of decades and centuries. Based on these timescales, it is estimated that current emissions from transport will be responsible for 16% of the integrated net forcing over the next 100 years for all man made emissions. The paper places road transport as being responsible for the most warming and shipping for producing the greatest cooling effect.
Complementing the above mentioned paper is Berntsen and Fuglestvedt (2008). They have expanded on how depending on time scale, different modes of transport, have differing effects on the climate (not surprising seeing as the same author worked on the aforementioned paper). They reiterate that different effects and emissions from transport can result in either a warming or cooling effect. Looking at the year 2000, road transport is seen to have the largest effect on global mean temperature. Road travel comes before aviation, which despite having strong but short-lived effects, they can resonate up to a decade after emission. In contrast shipping results in a cooling effect (through the release of sulphur dioxide and NOx) which can last up to 4 years after emission but on a longer timescale, shipping too leads to a warming effect.
More work on the matter was done a couple years later by Borken-Kleefeld et al. (2010) - also featuring Fuglestvedt as a co-author (I would have been more surprised not to have seen his name!). Anyway, they again emphasise looking at the timescales of modes of transport in relation to the type of radiative forcing caused. They mention that air travel results in a lower temperature change per passenger-kilometre than the car... in the long run. And that per passenger-hour travelled, aviation's impact is higher than for cars, which doesn't really come as a surprise!
By looking into the effects of different modes of transport, it has become apparent that there is no one way at looking and comparing them. There are many variables to consider: the time scales involved with the emissions, frequency of use, size of the emissions released, passenger-kilometre, passenger-hour.. maybe if you stop for food a the service station? I agree with Berntsen and Fuglestvedt (2008) in the difficulty of accounting for different modes of transport on creating policy for the improvement and reductions of this sector... when for example would you set a time scale when at first the effects of shipping emissions are cooling but then revert to warming? And that air travel is worse on a short scale but road travel is worse overall in the long run.
Fugletvedt et al. (2008) wrote about how although contributing significantly to global emissions, the contribution of different modes of transport has not been quantified. They predict that whereas today (or in 2008!) transport in general accounted for 20-25% of total annual CO2 emissions, by 2050 this is estimated to rise to 30-50%.
The paper describes four main mechanisms through which all transport related emissions can effect the climate. These are:
1. The direct emission of greenhouse gases, notably CO2.
2. The emission of indirect greenhouse gases, for example gases like nitrogen oxides, and carbon monoxide that affect the oxidising capacity of the atmosphere.
3. The direct emission of aerosols or aerosol precursors such as black and organic carbon and sulphur compounds.
4. The indirect emission of aerosols that trigger alterations in the distribution and properties of clouds.
Note that many of these effects has already been discussed in relation to aviation in previous posts.
Attributing these effects to certain modes of transport is difficult because multiple chemical and physical mechanisms can occur when these emissions are released. The paper highlights further difficulty in calculating the climatic costs of transport due to the differing time scales involved. The effects of transport emissions on ozone, sulphates and black carbon may last months and days, where as more well mixed greenhouse gases (methane, CO2, and NOx) have an adjustment period of decades and centuries. Based on these timescales, it is estimated that current emissions from transport will be responsible for 16% of the integrated net forcing over the next 100 years for all man made emissions. The paper places road transport as being responsible for the most warming and shipping for producing the greatest cooling effect.
Complementing the above mentioned paper is Berntsen and Fuglestvedt (2008). They have expanded on how depending on time scale, different modes of transport, have differing effects on the climate (not surprising seeing as the same author worked on the aforementioned paper). They reiterate that different effects and emissions from transport can result in either a warming or cooling effect. Looking at the year 2000, road transport is seen to have the largest effect on global mean temperature. Road travel comes before aviation, which despite having strong but short-lived effects, they can resonate up to a decade after emission. In contrast shipping results in a cooling effect (through the release of sulphur dioxide and NOx) which can last up to 4 years after emission but on a longer timescale, shipping too leads to a warming effect.
More work on the matter was done a couple years later by Borken-Kleefeld et al. (2010) - also featuring Fuglestvedt as a co-author (I would have been more surprised not to have seen his name!). Anyway, they again emphasise looking at the timescales of modes of transport in relation to the type of radiative forcing caused. They mention that air travel results in a lower temperature change per passenger-kilometre than the car... in the long run. And that per passenger-hour travelled, aviation's impact is higher than for cars, which doesn't really come as a surprise!
By looking into the effects of different modes of transport, it has become apparent that there is no one way at looking and comparing them. There are many variables to consider: the time scales involved with the emissions, frequency of use, size of the emissions released, passenger-kilometre, passenger-hour.. maybe if you stop for food a the service station? I agree with Berntsen and Fuglestvedt (2008) in the difficulty of accounting for different modes of transport on creating policy for the improvement and reductions of this sector... when for example would you set a time scale when at first the effects of shipping emissions are cooling but then revert to warming? And that air travel is worse on a short scale but road travel is worse overall in the long run.
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| Future temperature change (in K) from different modes of transport based on constant emissions for the year 2000. Taken from Berntsen and Fuglestvedt (2008) |
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