A recent article in The Guardian trumpeted the findings of a new study published in Science that found massive tree planting would be--by far--the cheapest and most effective approach to mitigating climate change. Ironically, the new thinking shows the pitfalls of political approaches to combating so-called "negative externalities." The good news about tree planting disrupts the familiar narrative about carbon taxes that even professional economists have been feeding the public for years. The whole episode is an example of what Ronald Coase warned about, in his classic 1960 article showing the danger in the traditional approach of using taxes to fix alleged market failures.