Note that those light green "ancillary electrification" lines are identified as requiring electrification, but given lower priority as no suitable method has been defined (yet).
In the case of Exeter to Plymouth/Penzance, it may well be that the sea wall section would make any scheme prohibitively expensive but the one that really seems to stand out is Worcester to Hereford. Is there anything on this route which would make electrification difficult?
My understanding of "ancillary electrification" was not that "no suitable method has been defined" but that the business/financial case for electrification wasn't great but that nevertheless electrification was considered to be the best (or only) way of decarbonising such routes. If I'm correct on that, a route that is straightforward and relatively cheap to electrify could still be categorised as "ancillary electrification" simply because it doesn't see sufficient traffic to deliver a large enough financial return. I suspect some routes with infrequent services are earmarked for 'ancillary' electrification only because they carry freight traffic which cannot run on battery or hydrogen, and others (with infrequent services and no freight) simply because they would require a micro-fleet of battery or hydrogen units with no suitable depot facility nearby.
Ledbury tunnel might pose a significant challenge. Colwall tunnel and Worcester Viaduct might also give some headaches.
Not familiar with those places, but they sound like candidates for limited battery power to traverse short sections of the line that cant be affordably electrified.
ALL new electric trains should
IMHO▸ have either a battery or a small diesel engine for when the wires come down, and limited use of same should be considered for short sections that cant be electrified affordably.
I don't agree with the installation of a diesel engine for this purpose (as has been done on the class 801 units) unless this is massively lighter than the battery alternative because it adds alot more complexity/expense/moving-parts making maintainance more complicated (and requiring fuelling facilities on depots) - one of the benefits of electrification is of course supposed to be simplified train maintainance (reducing rolling stock costs).
I would however agree with the installation of batteries on new electric stock to provide 'hotel' power (HVAC, toilets etc.) for several hours in the event of a electrification system failure. I am less certain of the usefulness of batteries to actually move the train (except on the routes where the
TDNS▸ does NOT recommend electrification) since, in the event of a power failure, there is likely to be an older train without traction batteries in the section ahead preventing movement anyway. Admittedly we would eventually get to a point where there are no such old trains, but even then a dewirement episode is likely to mean the train that has OHLE tangled in its pantograph is not going anywhere meaning any trains behind it are similarly stuck. I would therefore not want to increase the weight or cost of a train by installing more battery capacity than is necessary to provide 'hotel' power for several hours - however if the same quantity of batteries can (with minimal extra cost or complication) be used to move a short distance to the nearest station (at the cost of reducing the 'hotel' power from hours to minutes in the event that the batteries are used for traction) feel free to build that in.
The burning of any individual tree can not release more carbon dioxide than was absorbed by the tree when growing
That may be true, but remember that plants respire. The amount of CO2 absorbed while the tree was growing could well be less that the total amount of CO2 released over the lifetime of the tree (
including the emissions from the tree being burt). Also, as you correctly pointed out later in your post, the idea that harvesting trees is carbon neutral ignores fuel used by chainsaws, vehicles, timber mills etc. Being really pedantic, I could also point out that my heavy breathing from swinging the axe around to split logs for the fires that help heat the house that I call home will have increased my CO2 emissions slightly!
If a new forest is established in an area not previously forested, then extra carbon is absorbed from the air by the new tree growth. After a few decades to a few centuries, the new forest will stop absorbing any new carbon. Trees will be harvested by man, or allowed to die and decompose naturally, and this will release carbon similar to that absorbed by the growing of the new trees.
Intuitively, this seems correct; a young tree (increasing its volume and therefore carbon stored relatively quickly) should to my mind absorb CO2 at a faster rate than a mature tree. However, to my surprise a few months ago I heard someone say (on a TV programme about climate change) that a study on the particular forest they were looking at found that the young forest was absorbing less CO2 (and possibly even emitting more than it absorbed) than an area of mature woodland. I mentioned this to my mother (who is growing a forest garden) who backed this up by saying that saplings of large trees are poor absorbers (and/or emmit more CO2 than they absorb) and only become benifical in reducing greenhouse gas concentrations in the air once they are 10 years old or more. If true, it has implications for the idea that growing such trees for firewood and felling them at a relatively young age.
If trees are harvested not for fuel but for furniture manufacture or building, then the carbon is locked up, not forever but until the furniture or building is destroyed by fire, or decomposes naturally.
Wooden furniture lasts on average from 5 years to a hundred years, but when disposed of returns the carbon to the air.
Wood used for construction lasts on average from a hundred years up to several hundred years, and carbon in the construction timber returns to the air when the building burns down or is knocked down.
When wooden furniture or the timber parts of a building are no longer needed for the original purpose, they should be burnt as fuel when possible. This produces no more carbon than than burning on a bonfire or dumping in landfill. A home may be heated thereby, perhaps displacing oil, gas, or coal.
That seems to make alot of sense. If the wood is waste and is going to be burnt or decompose anyway you might as well use it to heat a house or generate electricity. The amount of waste wood available is probably not going be sufficient to make much of a difference, but I cannot think of any reason to object to the burning of genuinely waste wood as a fuel, except perhaps the emissions from transporting it somewhere to be burnt (rather than just leaving it where it is to decompose).
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