It's very difficult to explain observed warming with purely natural causes. They contribute, but human influences are stronger and have been for around half a century. 

A North Korea-like 100% of scientists believe in gravity.  Sometimes agreement happens because the evidence is just that strong. 

(Government funding does not presuppose a certain outcome, and I don't know a single scientist that spent 10 years in grad school and post docs to blindly echo someone else's finding, they become scientists in the quest to find new knowledge. Again, high levels of agreement between studies are what you'd expect of a very robust theory)