Microsoft Founder and philanthropist Bill Gates. (GeekWire Photo / Kevin Lisota)

Renewable energy is getting cheaper and more efficient. Environmentalists, like Bill Gates, celebrate that as progress toward reducing our reliance on polluting power sources. But it is also a source of concern for the Microsoft co-founder, who has emerged as a climate change crusader in recent years.

In an interview with “Axios on HBO” this week, Gates explained why he’s worried that too narrow a focus on renewable energy obscures the larger climate change puzzle.

“A lot of people think renewable energy,” he said. “Wind and solar has gotten a lot cheaper. Isn’t that it? When electricity is only a quarter of the problem. In fact, we’ve got to solve the entire 100 percent.”

As Gates and Axios note, electricity only accounts for 25 percent of the world’s greenhouse gas emissions. Shifting to wind and solar power doesn’t reduce the other 75 percent of emissions created by transportation, manufacturing, buildings, agriculture, and other sources.

“We’re very far away from getting all these sources down to zero, which is what we have to do to solve this problem,” Gates told Axios.

That’s the focus of many of the initiatives Gates has started or backed over the past few years. The Bill and Melinda Gates Foundation has zeroed in on climate change philanthropy and Gates supports Breakthrough Energy Ventures, a $1 billion private fund to help entrepreneurs launch clean energy companies.

Gates also publicly and financially backed a ballot initiative in his home state of Washington to impose a fee on carbon emissions. That effort was ultimately unsuccessful.

Despite setbacks, Gates told Axios “I am optimistic,” that the international community can solve climate change. But in the same breath he added, “Part of the problem is there’s not a broad awareness of how challenging it’s going to be to bring down greenhouse gas emissions.”

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