It turned out, Carl Pope, executive director of the Sierra Club and Dave O'Reilly, CEO of /*Chevron*/ actually see eye to eye on a lot of things.
"We both want to protect the environment, we want to advance energy efficiency and conservation," O'Reilly said.
But where the two disagree is over how long it will take to transition to clean energy.
It is no surprise that pope wants big changes now. He hopes by 2050, every human being would have a budget of no more than two tons of carbon dioxide emissions a year -- which means the U.S. would have to reduce its carbon dioxide emissions by 90 percent from where it is today.
"That means we can't be burning by roughly 2030 anymore coal," Pope said. "And by roughly 2040 we have to stop using petroleum to move our goods."
But Chevron's CEO says it's simply not realistic. O'Reilly agrees the world needs to diversify energy sources, but says it is going to take a long time to get there, considering the world consumes the equivalent of 245 million barrels of oil every day.
"When you look at the data, there really is no avoiding that the sheer scale of our energy needs is far beyond the capacity needs of anyone source or one technology," O'Reilly said.
Some in the crowd were unconvinced by anything O'Reilly had to say. A handful of environmental activists came to protest the way chevron has handled contamination in the Ecuadorian Amazon.
But for the most part, it was a civil discussion, not a smack down. Both sides agree there is too much at stake.
"Seas are rising and acidifying, forests are burning," Pope said. "These are real threats, these are measurable threats. They're dangerous."