PHOENIX (3TV/CBS 5) - From building a better toilet to preventing premature births, Bill and Melinda Gates use their influence to tackle life-changing issues.
Every year they write up a letter to talk about what they've learned about these problems.
One of the issues they address in this year's letter is climate change.
Gates said the majority of harmful emissions doesn't come from cars and electricity.
"Between those, it's about a third of the emissions. There's a lot that comes when we make materials like cement and steel. There's a lot that comes from cows as we're making milk and beef. So really looking at all those sources and saying, 'OK, how can we innovate so we can get the same things without a huge price increase but also with zero emissions?'"
"It's more daunting than people may realize," he continued, "because the term clean energy has them focused on the electricity piece and even that won't be easy when the sun's not shining and the wind's not blowing."
The letter also addresses the increase in violence in the U.S.
To get a better idea of what leads to this, he and his wife, Melinda, visited prison inmates.
In Chicago, they talked to men who are in a program called "Becoming a Man."
"They would talk about controlling anger and how you channel anger in a constructive way and I thought that was pretty brilliant to say, 'Yeah, anger's gonna come up but you can use it or it can use you,'" Bill said.
The Gates also touch on education, how data is sexist and the need for better toilets worldwide.