Bill Gates warns of the dangers of cow farts - and the world should take his words seriously

• Bill Gates has a $1 billion fund, collected from a who's who of fellow billionaires, ready to invest in startups and research to solve climate change.
• On Tuesday, in his annual letter with wife Melinda, he points out that really fixing climate change involves way more than renewable electric energy, though he's encouraged by progress there.
• Manufacturing and agriculture are overlooked problem areas.
• He's looking for climate friendly ways to make concrete and steel, as well as ideas on dealing with methane produced by cows "when they belch and pass gas."

"I wish more people fully understood what it will take to stop climate change," Bill Gates laments in his annual letter published on Tuesday.

Each year the Microsoft founder and his wife Melinda publish a letter that outlines the areas that cheer, worry and surprise them.

The topics in the letter are taken from the couple's experiences trotting the globe to combat poverty, disease and other problems.

Bill Gates is tackling climate change through programs funded by the Bill and Melinda Gates Foundation as well as through Breakthrough Energy Ventures. BEV is a $1 billion investment fund he's spearheaded, backed a who's who of billionaires including Jeff Bezos, Marc Benioff, Richard Branson, Reid Hoffman, Jack Ma, George Soros, Tom Steyer, Meg Whitman and Mark Zuckerberg.

BEV is looking to invest in startups and research that tackle five areas, which he calls "grand challenges." These are agriculture, buildings, electricity, manufacturing and transportation.

In the letter Gates points out that promising progress has already been made with renewable energy for electricity.

But he says there are two areas that account for 21% and 24% of worldwide greenhouse emissions, respectively, that are sorely ignored: manufacturing of building materials and agriculture.

Making building materials like steel and cement requires a lot of fossil fuels and processes that belch out carbon, he says.

The world is currently on track to double its buildings by 2060 which Gates points out is like building "an entire New York City every month for 40 years."

"We need to find a way to make it all without worsening climate change," he says.

Agriculture is another gas-producing culprit. Despite the healthy, pastoral image of cows grazing on green rolling hills, Gates notes that cattle "give off methane when they belch and pass gas. (A personal surprise for me: I never thought I'd be writing seriously about bovine flatulence.)"

He's not advocating that cattle farming be banned, nor is he saying that we end construction or transportation. He just wants the world to focus more on solutions to all the areas hurting the climate.

"Solar panels are great, but we should be hearing about trucks, cement, and cow farts too," he says.