Public policy debates are about more than values. They usually include facts about what is, and predictions based on those facts about what’s coming. Informed speculation, some might call it or, for the cynical, crystal-ball gazing.

But eventually the future arrives, proving one side right and the other mistaken. In personal relationships -- at least those doomed to failure -- the vindicated might crow: “I told you so.” But this rarely happens in policy debates.

A case in point is climate change. Since the early 19th century, scientists have been pointing to data indicating humans were changing the climate. By the 1990s, the scientific consensus was that human-caused emissions were warming the globe with devastating consequences.