MAINE, USA — The earth is warming. At this point, very few people, even in the depths of the internet, deny this fact. But what I still hear over and over is this: “How do we know it’s us?” "How do we know this is not just a natural cycle?" I get it. After all, at one point Manhattan was under a mile of ice. Climate change has happened before. But scientists have been sure since about the 1960s that THIS change in the climate is caused by humans. How do we know?