"It's us" could use much more work. Suppose you could make the case
1. It's warming.
2. It's not us.
3. We're sure.
4. It's bad.
5. We can fix it.
What would be different? That point speaks exclusively to the morality of the issue (It's us: environmentalists are noble! - It's not us: environmentalists are evil!), not to what's happening or what should be done.