During her argument, Katrina vanden Heuvel quotes a British government official who called global warming skeptics "climate loonies." Explain how this is arguably an ad hominem attack.

Argumentum ad hominem is a fallacious argumentative strategy where the issue at hand is neglected and the individual is maligned instead. In her argument, quoting the British officer and calling global warming skeptics loonies already deviates from the argument and is more of a personal attack on the individuals.

A better approach would have been the use of published facts on global warming and it's effects to support her stand. That would have been more objective rather the verbal attack of skeptics.