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. [...] "There are a number of ways that can happen, but each of them has a different fingerprint. If the sun were brighter, we would see warming all the way up through the atmosphere from the surface to the stratosphere to the mesosphere. We don’t see this. We see instead warming at the surface, cooling in the stratosphere, cooling in the mesosphere. And that’s a signature of greenhouse gas forcing, it’s not a signature of solar forcing. So we know it’s not solar."