I certainly accept AGW and the need to do something about it, but this is rather...

I certainly accept AGW and the need to do something about it, but this is rather weak. A big, scary round number that we must avoid - and then a not-as-big, scary round number we really should avoid - but the very first sentence suggests that we should try for "less (possibly much less)".

So it's a big, scary, arbitrary number.