'No one has ever been able to prove that glaciers in the Arctic region are melting because of global warming. Therefore, glaciers in the Arctic region must be melting on their own.' Which fallacy is committed in the above statement?

The conclusion rests only on the absence of proof, which proves nothing.

No one showing that warming melts the glaciers does not establish any rival cause.

Failure to prove a claim false is not evidence that it is true, and the reverse holds too.

Treating the unproven as thereby settled is the mark of this error.

This is the appeal to ignorance (argumentum ad ignorantiam).