Photo: christine zenino (chrissy575) Flickr, CC BY
Yes, you know that human activity is causing the global climate to change. But do you know exactly how we know this? Like, if some smart-alecky climate skeptic said 'prove it--how do you know humans are causing it?' and for some reason actually agreed to openly listen to your reasoned response? Then you'd want to point to any one of these indicators that reveal the "human fingerprints" on global warming that Joe Romm and John Cook have sorted out for us.