To take some amount of action (with some cost, including the cost of turning away from other issues), we have to ask how important, and conclude that it's very important. Fortunately, most people when presented with the facts don't find that it competes very well against other priorities. From a Wall Street Journal piece today on skeptic Bjorn Lomborg:
In 2004, he [Lomborg] invited eight of the world's top economists--including four Nobel Laureates--to Copenhagen, where they were asked to evaluate the world's problems, think of the costs and efficiencies attached to solving each, and then produce a prioritized list of those most deserving of money... While the economists were from varying political stripes, they largely agreed. The numbers were just so compelling: $1 spent preventing HIV/AIDS would result in about $40 of social benefits, so the economists put it at the top of the list (followed by malnutrition, free trade and malaria). In contrast, $1 spent to abate global warming would result in only about two cents to 25 cents worth of good; so that project dropped to the bottom.

"Most people, average people, when faced with these clear choices, would pick the $40-of-good project over others--that's rational," says Mr. Lomborg. "The problem is that most people are simply presented with a menu of projects, with no prices and no quantities. What the Copenhagen Consensus was trying to do was put the slices and prices on a menu. And then require people to make choices."

...the Copenhagen Consensus Center, held a new version of the exercise in Georgetown. In attendance were eight U.N. ambassadors, including John Bolton. (China and India signed on, though no Europeans.) They were presented with global projects, the merits of each of which were passionately argued by experts in those fields. Then they were asked: If you had an extra $50 billion, how would you prioritize your spending?

Mr. Lomborg grins and says that before the event he briefed the ambassadors: "Several of them looked down the list and said 'Wait, I want to put a No. 1 by each of these projects, they are all so important.' And I had to say, 'Yeah, uh, that's exactly the point of this exercise--to make you not do that.'" So rank they did. And perhaps no surprise, their final list looked very similar to that of the wise economists. At the top were better health care, cleaner water, more schools and improved nutrition. At the bottom was . . . global warming.