You want an idea of the scale of the challenge global warming presents? A friend who works for Operation Noah put it like this: invisible gases produced by everything man does are allegedly affecting people on the other side world in ways that have not yet become clear. The problem is that by the time they do become clear it will be too late.
And, of course, what makes it even more difficult it that lots of people say this is all nonsense.
This blog, indeed the entire Ethical Man Reborn in the USA project, has been about exploring how one country, the United States, is trying to rise to this challenge.
We've covered some amazing stories on this journey - forget the pig swill (which was featured on Have I Got News for You!), the billion dollar car, the wind turbines, the Hollywood stars - because what our journey was really all about was the issues.
We asked how might we begin to change the behaviour of a whole society.
The idea is to set a carbon price - to charge polluters to emit carbon dioxide. Now carbon pricing may excite economists, but are voters going to support it?
There is no question that a lot of Americans are sceptical. One congressman described the carbon pricing mechanism proposed by Mr Obama to me as "anti-American".
Attitudes like that may explain why we saw the Obama administration wooing an army of eco-activists to lobby for legislation.
At one point I became convinced that I was watching a historic change, nothing less than a revolution in attitudes to climate change.
But I'd only been back in Britain for a couple of weeks when that optimism dissolved.
I would like you to go back and read some of our blog entries, if you haven't already, and tell me what you think. Because this is a crucial time for the US and the world. There are a selection of photos from journey here too.
What the US does on the climate will be crucial in determining whether a global treaty to limit emissions can be concluded as planned at Copenhagen in December.
In the meantime you can sign up to my Twitter feed here and I'll keep you posted about all my ethical activities and any interesting environmental developments I spot.
For those of you on Spotify, we have made a playlist of all the great music that's been featured in the Ethical Man: Reborn in the USA series. Everything from Gwen Stefani to Wynton Marsalis and Simian Mobile Disco.
And by the way, there will be one last Ethical adventure from America. It includes a genuine television first - footage of an Amish man yodelling with a horse! We'll post up a trail as soon as we can.