Porterbrook claim that they "have calculated that every ‘half-life’ rail vehicle that we dispose of results in 77 tonnes of carbon dioxide being wasted"
In perspective, a Boeing 777 will emit about that much carbon between London and Tokyo, one way. It's not an earth-shattering volume of carbon, in the big picture.
Assuming we scrapped a 2 car DMU (based on Northern Class 158 data
here, roughly 2 kg per train km emitted), electrified the line and replaced it with a new EMU:
- Emissions 3 kg per train mile/1.5 kg per vehicle mile
- 77 tonnes of carbon will be emitted per vehicle in about 50,000 miles
- At 500 miles per day, that's only 100 days of CO2 emissions (purely by the diesel engines, not accounting for full life cycle)
Put another way, if you scrap a DMU that's only half-expired but replace it with an EMU on low carbon electricity, it will take only a few months to save the CO2 generated by the operation of that train.
To get more of a lifecycle view, Porterbrook
here report the RSSB estimate for the CO2 equivalent of producing "an electric train" in 2011 was 146 tonnes - not sure how many vehicles that assumes, but let's assume that's worst case, 146 tonnes per vehicle:
Carbon cost of replacing two car DMU with two car EMU = 292 tonnes CO2e
Carbon emissions avoided by operating EMU over DMU = 77 tonnes per 100 days
Carbon payback time = 379 days
So electrification is critical - I realise this is back of the envelope and this ignores the cement and steel required, and the current carbon emissions of National Grid electricity. However this gives an order of magnitude to the value in avoided carbon given by electrification. The payback in environmental terms is incredibly short.
