Considering that there has been a lot of talk on this site recently about environmentalism, return on investment and big versus small impacts I thought I’d provide some background information on sources of pollution, namely greenhouse gases. It’s important to note that many sources of global warming gas sources are also large producers of other pollutants ranging from sulfur dioxide to ozone to dioxins.
One thing that is important to consider is that CO2 is not the only global warming gas of importance. It certainly has the largest impact, but this is due to the enormous volume produced, not its potency. Other gases, such as methane and nitrous oxide also have a very appreciable impact on global warming. The emissions of these gases is low by volume but considerably higher by effect, due to the higher potency in terms of global warming effect. Estimates range from 15% to 20% of total effective global warming gas emissions. Though significantly smaller than CO2, this is certainly large enough to be concerned about and reducing these emissions can make a big difference. The chart shown to the right is of the US, but it’s a pretty good representation of much of the world and helps give a general impression of the scale of the problem. Worldwide, Co2 accounts for slightly less proportionately than it does in the US. (source)
The next chart is from Wikipedia and can be found here. It factors in carbon dioxide as well as other major greenhouse gases. The data for this chart indicates that non-CO2 emissions may be responsible for as low a proportion as 72% of the effective greenhouse gas emissions worldwide. Sources will vary slightly in the estimates of greenhouse gas emissions depending on methodology and data collected, but they are generally in agreement within reasonable margins.
Although not the entire picture when it comes to global warming, CO2 is clearly the most dominant source of the effect. It is also associated with fossil fuel use, which presents numerous other problems ranging from supply to other emissions which cause enviornmental damage and effect health. As such, reducing CO2 emissions and fossil fuel use in general tends to have benefits beyond climate change. The following excellent chart shows the relative amounts of CO2 production from manmade sources. I found it on Energy From Thorium, but this is the original source. (My one issue with the chart is that coal fires seem to be excluded. They may be factored in with other uses of coal) **correction: The chart bellow includes non-CO2 greenhouse gases from various man made sources as well as CO2**
Considering this data, there are a few things which immediately become apparent:
Electrical generation is clearly the elephant in the room, clearly exceding all other sources of CO2 and greenhouse gas in general. Coal-fired electricity is also disproportionately heavy in CO2 production. Coal makes up only about 60% of worldwide electrical generation but it dwarfs natural gas combustion, which produces more water than CO2 when burned due to the high hydrogen content of methane. Of course, coal is a filthy fuel in general and causes numerous other problems.
Transportation is significant in terms of CO2 production, but considerably less than electricity. It also may surprise some the relative amount passenger cars contribute, which is significant but less so than other sources. Clearly the largest sources of CO2 are fixed site sources, power generation, industrial, heating and other. This is an important aspect to keep in mind because it goes back to the importance of electricity in the equation. Moving to cleaner industrial processes will necessitate an energy source which does not produce CO2 and electricity is the logical choice, but only if it is generated cleanly. If clean electricity can be provided in bulk, it then becomes possible to move to more electric-centric processes and reduce CO2 in industrial, commercial and heating applications. For example, replacing fossil fuel burning metal furnaces with plasma arc smelting and moving toward electric heating methods. This should not be a difficult transition to make, considering that electric systems have other advantages in terms of maintenance and capability. The key is providing an economical source of clean electricity.
With only this data avaliable it becomes pretty obvious what the most successful mitigation stratigy will be. It can be broken down into five major priorities.
1. Eliminate singular large sources which are the most economical to tackle and have the highest single carbon footprint.
2. Phase out fossil fuel electric systems with the highest priority being the elimination of coal fired power plants.
3. Begin to phase out fossil fuel based industrial processes in favor of clean electric energy.
4. Move toward an electric-centric transportation model including electrified rail, public transportation, plug-in hybrids and eventually fully electric or hydrogen vehicles.
5. Only after all these have been tackled should priority shift to other sources of smaller footprint and with less apparent solutions and alternatives.
Cost Risk and Benefit:
This might not seem like rocket science but it’s something that many do not seem to get. Sources which have a high cost of mitigation, a high probability of being unsuccessful and a relatively low benefit should be the lowest priority. A good example of this would be aviation. The carbon footprint of aviation is certainly not insignificant, although it is considerably lower than numerous other sources. The benefit of eliminating aviation CO2 would be small but helpful.
However the options for doing so are rather limited:
Reduce the amount of air traffic - Unless you plan on doing so very dramatically (50% or more) this will not do much. Reducing aviation by such a dramatic amount would have enormous costs. Tens of thousands of jobs from airlines and support jobs would be lost, travel would be dramatically reduced, possibly destroying the economies of tourism-base areas. Populations located in areas not entirely served by other transportation would be hit hard. Companies defendant on fast shipments would be devastated. An increase in travel by other means could negate much of the gains.
Increase standards for effeciency - Unlikely to do much. This might shave a few percent off of an already relatively small sector, especially because most reasonable measures to improve effeciency are already being used. Since fuel is a major expense in aviation, most jet aircraft already use the highest effeciency high-bypass turbofan engines and are designed to be as light as reasonably possible. There’s very little room here for improvement. There may be some gains, but at best they would be very modest.
Use other fuels - You can’t run a full sized aircraft on batteries. They’re simply too heavy and nowhere near the energy density needed. Only small slow limited-range aircraft have been demonstrated to work with electricity. Hydrocarbon fuels, it turns out, are about the only way to provide the kind of energy needed efficiently and are very well suited to the need. Boron-based fuels had been experimented with in the past and could reduce CO2, but they tend to gunk up jet engines and they create a trail of thick toxic black smoke which has other enviornmental impacts.
About the only thing you could run an aircraft on other than hydrocarbons is hydrogen fuel. This presents a huge problem, however, as the volume needed is enormous. This would increase the weight and drag of the aircraft so much as to limit only to shorter routes for most aircraft. Long haul flights would need to devote most of the aircraft to fuel with little room left for passengers. Safety is not established and hydrogen is not an energy source but only an energy carrier, so in order for this to be clean, you still are left with the need for a massive source of energy to produce the hydrogen to begin with. It also is difficult to store, inefficient to produce and generally not very easy to transfer and use. It is likely that the lower energy density and increased drag would also reduce the speed of air travel. The aircraft shown is a concept for what a short-haul hydrogen aircraft might look like.
Conclusion: The cost is enormous. The idea of replacing any portion of the world’s aircraft with the thing to the right borders on the absurd. The problems which are presented are huge and the system is useless without avaliable clean energy. Aviation also cannot be reduced significantly without huge costs and possibly more problems created than solved.
The benefit of eliminating aviation Co2 is small. The benefit of reducing it by a nominal amount is tiny.
Therefore, it is not worth worrying about. At least not until all the other sources with a very favorable cost-benifit analysis have been tackled. Only then should resources be diverted to aviation. This same principal can be applied elsewhere.
And yes, environmentalists do whine about aircraft. They do so less than about cars but a hell of a lot more than about coal fires.
This entry was posted on Tuesday, February 5th, 2008 at 11:32 am and is filed under Bad Science, Education, Enviornment, Good Science, Politics. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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