evidence: Despite the many climate "skeptics" in key positions of power today, 97 percent of working climate scientists agree that the warming of Earth’s climate over the last 100 years is mainly due to human activity that has increased the amount of greenhouse gases in the atmosphere. Why are they so sure? [...] Here is how scientists know that the climate change we are experiencing is mainly due to human activity and not a result of natural phenomenon. [...] Findings from NASA’s Goddard Institute for Space Studies show clearly how much natural and manmade factors contribute to global warming.