Depends on how you define legitimate. Also, given today's research "climate", I imagine publishing a dissenting opinion is tantamount to career suicide. Good luck getting funded to prove anything. Particularly considering how politicized climate science has become.
Which is unfortunate, because skepticism should be a part of healthy scientific practice - and I think it'd be a stretch to say that climate science isn't subject to the same problems, like p-value abuse and selective publishing, that plague other non-experimental, purely model and statistics based fields. No one is going to publish negative results when they can tweak any of hundreds of model variables to force agreement with data.
I think a valid proxy for bias is the relative lack of publications discussing possible benefits of climate change.