I'm a climate scientist who has spent 20 years studying models and data. I know the research inside and out. I've testified before Congress. I've been called "one of the leading experts in the field." But the truth is, I'm increasingly aware of how much we don't know. Our models have significant uncertainties. New data keeps surprising us. The more I learn, the less confident I am about specific predictions. The problem is: when I express this uncertainty publicly, it gets weaponized. Deniers quote me out of context. Policy makers use my caveats as excuses for inaction. My colleagues say I'm "providing ammunition to the enemy." They want me to project confidence, even when I feel doubt. "The big picture is clear," they say. "Don't confuse people with nuance they can't handle." But I became a scientist because I believe in truth. If I overstate certainty, am I any better than the deniers who overstate doubt? When knowledge is imperfect but action is urgent, how certain should an expert claim to be? — The Expert Who Doesn't Know in New York

Welcome to this Knowledge & Certainty debate. Our central question: "I'm a climate scientist who has spent 20 years studying models and data. I know the research inside and out. I've testified before Congress. I've been called "one of the leading experts in the field." But the truth is, I'm increasingly aware of how much we don't know. Our models have significant uncertainties. New data keeps surprising us. The more I learn, the less confident I am about specific predictions. The problem is: when I express this uncertainty publicly, it gets weaponized. Deniers quote me out of context. Policy makers use my caveats as excuses for inaction. My colleagues say I'm "providing ammunition to the enemy." They want me to project confidence, even when I feel doubt. "The big picture is clear," they say. "Don't confuse people with nuance they can't handle." But I became a scientist because I believe in truth. If I overstate certainty, am I any better than the deniers who overstate doubt? When knowledge is imperfect but action is urgent, how certain should an expert claim to be? — The Expert Who Doesn't Know in New York" Isaac Newton, you've said "I do not feign hypotheses—truth is ever to be found in simplicity, and we must follow evidence wherever it leads" — but I want specifics. Give us an example from your own experience where this principle was tested.