When you compare possible natural causes (orbital, solar and volcanic activity) over the course of the last 100+ years, to possible manmade causes (aerosols, deforestation and greenhouses gases), the winner is clear. Greenhouse gases directly correlate to an increase in Earth temperature.
Credit: NASA/GSFC GISS Video Rating: / 5
They build transparent boxes, fill some with CO2 and methane, then monitor temperature differences. Video Rating: / 5