How do you make sure billions of people around the world have access to food?

You start a revolution.

At least that’s what two leading U.S. scientists argue in a new report. Feeding people will require cleaner energy, smarter farming and women’s rights, but also a “fundamental cultural change,” according to Paul Ehrlich, president of the Center for Conservation Biology at Stanford University, and University of California, Berkeley, professor and researcher John Harte.

“What is obvious to us is ... that if humanity is to avoid a calamitous loss of food security, a fast, society-pervading sea-change as dramatic as the first agricultural revolution will be required,” they wrote in their report published last week in the International Journal of Environmental Studies.

The amount of humans on Earth is growing—projections point to an extra 2.5 billion people by 2020. But tangled within the problem of more hungry mouths is environmental degradation, social injustice and humans pushing toward the very boundaries of the planet when it comes to resources such as food, water and energy, according to Ehrlich and Harte.

For many people across the world growing, buying or finding food is a daily struggle. More than 800 million people are estimated to be malnourished, according to the United Nations.

Billions don’t have stable, secure access to food.

“Some people say the whole problem is too many people and other people say it’s misdistribution of the crops we grow,” Ehrlich said in an interview. “They’re both right but this can’t be fixed by dealing with only one end of the problem.”

Scientists for too long have been looking at how to feed the world in “fragments,” Ehrlich said.

“Some look at solving food problems with crops grown in higher temperatures; some look at reducing waste,” he said. “It’s crystal clear that none of the things that need to be done are being done on a scale that would be helpful.”

It’s not just about pumping out more crops or reducing the amount of people. “Planning for a sustainable and effective food production system will surely require heeding constraints from nature,” Ehrlich and Harte wrote.

They argue that economic equality, population growth and environmental health are all linked. Governments must address the whole system to avoid future famine.

This means limiting greenhouse gases that warm the planet, avoiding biodiversity losses and reducing populations, they say. It means cutting back on all of the pesticides and antibiotics used to grow food. It means moving climate change to the top of political agendas and ending incentives to pull fossil fuels out of the ground.

As the planet’s population grows, environmental issues will grow too, Ehrlich said.

"We need to get a grip on population," Harte added. But addressing climate change will be a “critical issue.”

“Nothing is worse for future food security than a future climate with more extreme events like droughts, floods,” Harte said.

Harte pointed to the ongoing California drought as an example. A University of California, Davis, report in June estimated that, in 2015, the drought would cost the California farm industry $2.7 billion and 18,000 jobs.

Solutions, like challenges, are intertwined Ehrlich and Harte say.

But they exist. Ehrlich said a good start in addressing population growth would be full women’s rights, including access to contraceptives and abortions. For agriculture, it’s a “big shift” toward organic farming, getting rid of large industrial farms that rely on pesticides.

Harte said curbing continued climate change has two natural solutions: the wind and the sun. He said expanding wind and solar farms combined with greater efficiency in electricity use is entirely possible.

“Germany is much less sunny than most of the United States, and they’re approaching almost half of all electricity production from renewables," Harte said. "There’s no reason we can’t too.”

Underlying all this, the two say, is a fundamental shift in people’s values, including a turn away from everything being driven by financial interests. Instead, they write, society's focus should shift to “resilience, a striving for virtue, equitable distribution, and extreme vigilance to insure that governance is working in parallel, not in opposition, to achieve these goals.”

In other words, a revolution.

Ehrlich and Harte are optimistic about the solutions. But when it comes to the full-scale revolution, not so much.

“U.S. Congress is ruled by a majority that doesn’t want to listen to facts.... Most don’t believe in science,” Harte said. “They don’t understand the magnitude of the threat civilization is facing.

“If they listened to engineers and scientists and did the right thing, I’d be optimistic. There are solutions out there.”