When you are ill do you trust radio show hosts to diagnose you over the airwaves? Do you go to a faith healer to cure you with the power of God? Maybe, but the majority of people go to a doctor who has been trained, practices medicine, and is part of a professional association, etc.
Similarly you should listen to climate scientists regarding global warming, not pundits and politicians. Climate scientists are in strong agreeance about the main points of Global Warming: it is happening and it is a result of human activity.
Global Warming is a process where increased greenhouse gas concentrations in the atmosphere raise the global energy balance by preventing heat from escaping. Human activities which contribute to this include agriculture, burning of fossil fuels, and land-use changes (such as forest clearing).