There's a new IPCC report coming out and that, inevitably, leads to confusion about what scientists mean when they say things like "we are 95% certain that climate change is being caused by human behavior." The AP's Seth Borenstein used this as a jumping off platform to talk about certainty, and other (less popularly/politically controversial) ideas that also have 95% certainty attached to them. Are scientists 100% sure that climate change is caused by people? No. But they're at least as certain of that fact as they are of the fact that smoking is hazardous to your health.