They're not reliable sources on the science of global warming, but they may be reliable sources on other aspects of global warming, namely their own opinion on the science (which might appear in other articles since the individuals are notable, as long as it is clearly identified as the opinion of a non-expert), or political and social aspects of global warming, and so on.  Regardless, the fact that these people are scientists (or were at some point...) needs to be clear to the reader.