@danielashby @AdamWJT @Greens4HS2 @TheGreenParty @GarethDennis @XRebellionUK @Hs2RebelRebel @HS2ltd I'll bite. Let's try to keep it factual. There's a reasonable basis to some aspects of this question, that it might be possible to agree on. Then there are other, more variable, elements which depend on external factors such as transport and energy policy. /1

@AdamWJT @Greens4HS2 @TheGreenParty @GarethDennis @XRebellionUK @Hs2RebelRebel @HS2ltd First up, we know reasonably well how much energy it takes to propel a high-speed train along the HS2 route. We can translate that into effective CO2 generated by making some assumptions about how green the electricity grid is. /2

@AdamWJT @Greens4HS2 @TheGreenParty @GarethDennis @XRebellionUK @Hs2RebelRebel @HS2ltd Secondly, we have a reasonable grasp of how much CO2 is going to be generated by building HS2 - there are standard methods of working this out, based on the amount of steel, concrete, earthmoving, machine-fuelling etc required. /3

@AdamWJT @Greens4HS2 @TheGreenParty @GarethDennis @XRebellionUK @Hs2RebelRebel @HS2ltd Thirdly, we can estimate how much CO2 is generated by cutting down trees, and how much is captured by planting new trees. We can also estimate how much CO2 is needed to keep the railway running and generated by maintaining the track /4

@AdamWJT @Greens4HS2 @TheGreenParty @GarethDennis @XRebellionUK @Hs2RebelRebel @HS2ltd We know how much CO2 is saved by moving goods by freight train on the lines freed up by moving the express trains on to HS2, rather than by truck. /5