Which logical informal fallacy is committed in the following argument, "No one has proved that global warming is actually occurring, so there is no reason believe that it is actually occurring"?

The correct option is Appeal to ignorance.

An Appeal to ignorance (Latin: argumentum ad ignorantiam) is an informal logical fallacy that occurs when someone argues that a proposition is true simply because it has not yet been proven false, or that a proposition is false because it has not yet been proven true.

In this argument, the premises and conclusion are structured as follows:
1. Premise: "No one has proved that global warming is actually occurring..."
2. Conclusion: "...so there is no reason to believe that it is actually occurring."

This argument commits the fallacy because it equates a lack of evidence or proof (ignorance of the truth) with positive evidence for the opposite conclusion (that global warming is not occurring or there is no reason to believe it is). A lack of proof does not automatically establish that a claim is false or unfounded; it merely means the claim has not yet been definitively proven. Therefore, the reasoning relies on an appeal to ignorance.