Good god, look at all the naysayers here, did we all start the cynical pre-xmas drinking already? :P
Carbon Neutral is a very loose terms these days Tail Wheel, often something is Carbon Neutral by paying for offsets elsewhere, ie you're creating pollution doing something but pay to get a butt load of trees planted somewhere else to offset it. But they don't actually mention carbon neutral in here, just that the Aircraft itself will be zero emissions.
I for one am very excited to see RR putting their hand up in this area and pushing things forward, or rather ACCELerating it...little pun there if you read the article :P