Meet the guilt-ridden oil billionaire trying to save the planet

As the Finnish wind thrashes outside, Mika Anttonen disrobes and enters his sauna. He dumps water on the embers, which spit back a cloud of steam. The temperature rises to a level just above painful. Here, on some days, the billionaire ponders his latest mission: saving a planet that, like the sauna, is rapidly growing too hot.

“Conditions are getting worse,” says Anttonen, 53. “We have to act as quickly as possible.”