It rather depends on the scientific theory you subscribe to, doesn't it? Some people deny that global warming even exists.
If nothing that the world has done in the last ten years can even "dent" the trend of global warming, there are a lot of people who would say that one is overestimating what we can do -- or have done -- to contribute to global warming.
Of course, if one is dogmatic about the idea that the last 150 years of industrialization is responsible for global warming, and that thus it would take many decades to reverse it, then there is also the argument that there isn't much of a point to trying to reverse it NOW rather than in a couple of decades.
And, in such case, is it really so absurd to ask for empirical evidence that the effects of a 150-year-old phenomenon can be affected by incremental decreases in emissions called for in a global warming treaty?
The argument clearly cuts both ways, doesn't it?
What's fair is fair.