No, we talk about the evidence we do have and use that to convince people. I’ve talked to a lot of climate deniers (unfortunately). These people may be saying

No, we talk about the evidence we do have and use that to convince people. I’ve talked to a lot of climate deniers (unfortunately). These people may be saying and doing ignorant things but largely they are not stupid. They know when you make unfalsifiable claims, and that becomes part of their justification to ignore you.