Thanks for that, I'll look into it and get back to you. I can certainly imagine that the actually extractable quantity of carbon is less than Hansen is saying - that's one thing to check. Then it's a question of working out what "game over for the climate" means. We all know picking one specific ppm target is relatively meaningless, but if this one project can push us up towards 450ppm...? Anyway, I'll get back to you, and thanks for the link.