I don't think many serious people deny that human-caused climate change exists (although the theory that a relatively small increase will bring about Armageddon due to feedback loops is far less of a scientific consensus). It's just a question of how much should be done about it, and whether the massive resources it would take to significantly reduce our carbon footprint, would be better spent feeding the world's 3 billion poorest people and improving economic conditions to help them escape from poverty.