The problem is not their method or whether they publish it. I believe their methods are quite sound.
The real problem is two-fold: First, weather is an extremely complex process. I doubt that we understand enough of it to reliably predict what's going to happen if one or more factors change.
Second, as was said before, the data they have to work with is very young. And what they use to 'create' older data might or might not be very accurate.
I don't quite believe that we are able to say without a doubt whether this change we are seeing now is unnatural.
That said, prudence suggests that we limit our consumption and production of waste of any kind to a tolerable minimum. Even if climate change were not caused by us, that doesn't mean that we're not running out of resources.