Until proven otherwise, deforestation and fossil fuel consumption are solely human activities.
Both activities release huge amounts of CO2 in the atmosphere, and those activities were years ago predicted to cause global warming.
The polar ice cap is melting, etc....All kinds of reproducible proofs show it is happening.
That's science.

Those who negate this take a completely different point of view: not used to hard science and because they don't want to listen to it (too boring), they don't appreciate the constant reminders (often not argumented enough, true) and feel attacked and it indeed looks like an opposing religion to them.