You make a choice. There is no training, no courses on how to be unbiased and no bible to swear on.
The entire discipline of science is based on well developed critical thinking skills applied in a systematic way in a constant testing of theories.
There is no proven science, it's all open to testing or it isn't science. Theories that stand up to repeated testing over years, decades and even centuries become widely accepted.
The science behind the greenhouse effect goes back to at least Joseph Fourier about 200 hundred years ago and has been built on consistently since then by the work of scientists like John Tyndall, Svante Arrehenius, Guy Callendar, Gilbert Plass, Charles Keeling, James Hansen, Lonnie Thompson and many others.
It's ridiculous to state that they all had a common agenda to create a conspiracy to mislead people who in some cases would be centuries in the future. The science behind climate change is about as solid as science gets, the politics behind climate change denial is about as sleazy as politics get when you consider the source and the likely outcome.