The debate was billed as a showdown of sorts between two titans: Chevron's CEO Dave O'Reilly versus Sierra Club's executive director Carl Pope.

At the Commonwealth Club in San Francisco lat night, the two men debated publicly about their views on what it would take to fight climate change and encourage consumers to use more renewable energy – electricity and transportation fuels – and rely less on fossil fuels and coal in their daily lives.

O'Reilly summed up the different philosophies and goals between him and Pope with this statement in his opening remark:

"I believe Chevron and Sierra Club share many of the same goals. We both want to protect the environment and expand renewable energy. We do disagree on how best to achieve these goals."

Both men said they believe that climate change is real, not fiction, and shaping people's views and energy consumption are good ways to minimize more environmental damage.

Pope called for setting aggressive goals of reducing the manmade greenhouse gas emission by 90 percent from today's level by 2050. He said lawmakers, businesses and average folks must rely on renewable electricity instead of coal-derived power by 2030.

"That means we can't be burning, by 2030, any more coal unless it's carbon sequestered. By 2040, we have to stop using petroleum to move goods. You can't get the numbers to move it any other way," Pope said.

By 2030, Americans also should drive more electric cars, although he added that he didn't think the roads would only be filled with electric vehicles by then then when O'Reilly pointed out that Americans often hold on to their cars for 15 years or longer. But Pope believes that the production of gasoline-powered cars should stop by 2030.

O'Reilly said he thought Pope's emission reduction goal is unrealistic. Even if Americans replace their electricity generation and transportation fuels with zero-emission energy, the country could reduce national emissions by 74 percent, not 90 percent, he said.

"We would be lucky if we can get 20 or 25 percent by 2050," O'Reilly said. "Customers vote with their wallets. People need incentives. Our view is that it's going to take a lot longer. It's human nature. It's economics."

O'Reilly went on to emphasize that the cost to consumers for carrying out emission-cutting programs – whether it's to mandate the use of carbon fuel or the more expensive renewable electricity – would play a big role in influencing Americans' behavior.

Pope, on the other hand, challenged San Ramon, Calif.-based Chevron to do more to move away from oil field development and compensate communities affected by the company's operations.

"You've done a phenomenal job of developing technologies to find oil," Pope told O'Reilly.

"In our energy system, we routinely accept the fact that we drive cars with chassis developed in the 1970s and light bulbs that Thomas Edison would recognize. We need to turn the technologies over faster and that would be good for the economy," Pope added.

The government should promote the use of natural gas powered cars, he said.

O'Reilly didn't agree. He said natural gas should replace coal for electricity generation than to replace gasoline. Automakers should develop more electric-gasoline hybrids instead.

Although O'Reilly seemed to support electric car development, he said the company is "not in the electricity business. We are in the fuel business" when asked why Chevron hasn't invested more in wind energy.

Currently, 2 percent of the energy produced by Chevron comes from renewable sources, and most of it is geothermal power, O'Reilly said. The company also is in the business of installingsolar energy systems, often in schools and government buildings.

He said the company doesn't have a goal for producing more renewable energy by 2050. When pressed, he estimated that the percentage might climb to 10 percent to 15 percent by then.

Both men believe that energy efficiency measures are great ways to cut emissions.

Pope asked O'Reilly whether Chevron would set up a trust fund to invest in communities whose environment and lives have been damaged by nearby oil exploration.

O'Reilly's reply: "If you set up a fund, everybody is going to pay for it."