Aside from crazy conspiracy theorists, real skeptics of this would be people who acknowledge there is some climate change happening but it's not because of us. A lot of people simply believe it's a natural process. I don't know too much about it but I definitely don't believe the government or whoever is faking it.
Let me get this straight. Humanity has been burning lots of fossil fuels for over two centuries now. It took nature millions of years to remove the CO2 from the atmosphere and sequester it in the form of fossil fuels. Now humanity is converting this form back to CO2 by burning it. Yet, if climate change is related to an increase in CO2 levels, it can't be tied to human action? OK whatever. I don't follow the logic. Even if the bulk of the CO2 is released by volcanoes, nature has been slowly sequestering this excess over millions of years. The contribution of humanity now taking this sequestered CO2 and releasing it back into the atmosphere cannot be helping the situation. This is compounded by the fact that the sun is putting out much more energy than it did eons ago. Therefore, we need less CO2 in the atmosphere to keep this planet habitable, not more.