Because for truly reliable information on a subject matter as extensively researched as earth's climate, what you should be looking for are statements of large and independent scientific organizations of good reputation. In the case of climate change, that would be national or international bodies of geologists, climatologists, biologists, geophysical unions, stuff like that. Once you check out what they have to say, you will find out that there really isn't much of a debate:
An increasing body of observations gives a collective picture of a warming world and other changes in the climate system [...] There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.
- Climate Change 2001: Working Group I: The Scientific Basis, IPCC, January 2001.
That is just one of the many statements of prominent organizations. Even those statements should be checked against others of equal standing: That is the level on which we determine whether there is a consensus or an actual controversy. In the case of climate change, there is an overwhelming consensus. Not a single scientific body of national or international standing has maintained a dissenting opinion. There is no controversy; just some big money trying to dispute the facts. Kinda like creationism, only without the weird rituals.