US President Barack Obama said the move was "historic", as he set a new goal of reducing US levels between 26%-28% by 2025, compared with 2005 levels.
China did not set a specific target, but said emissions would peak by 2030.
Wednesday's pledge is the first time it has agreed to set a ceiling, albeit an undefined one, on overall emissions.
An undefined ceiling eh? Hmm... let's see... is that similar to no ceiling?
I think it is.