The extent of the human contribution to modern global warming is a hotly debated topic in political circles, particularly in the US. During a recent congressional hearing, Rick Perry, the US energy secretary, remarked that “to stand up and say that 100% of global warming is because of human activity, I think on its face, is just indefensible”.
CLAIM: Today’s global warming is no different from previous warming periods in Earth’s past. Natural changes in the Sun and Earth cannot explain today’s global warming. Human activities are causing Earth to heat up in ways that are different from warm periods in the past. Since 1900, the average surface air temperature has risen 1.8.