Person A: "Nobody can deny that climate change is occurring. The question is whether human activity is causing it." Person B: "But there actually are a few people that deny that climate change is occurring." Person A: "Oh, all right. OK. Let me soften that. Few can deny that climate change is occurring. The question is ..."

Paulo, a few means a little. Which means the sentence says that only some people will deny something. Nobody or no one are both correct, but change the meaning of the sentence, because in this case not one single person is denying, whereas as commented above already, " few" is less extreme.

"Few can deny" is a little bit less extreme. It recognises that there are people who deny it, which is the only difference between the 3. I would use "few" in a more formal setting, or anywhere that it is more important to be accurate/reasonable than it is to make a point.