Bjorn Lomborg was one of the first high-profile "climate change skeptics". In 2001, he argued in his book The Skeptical Environmentalist that fighting global warming would be a waste of money.
Now, in a new book Smart Solutions to Climate Change, Lomborg is calling climate change "undoubtedly one of the chief concerns facing the world today", and calling for a carbon tax to collect $50 billion a year.
The Week has a brief on him and five other climate "skeptics" who have come around.