Pulling a worn, yellowed copy of the 1992 U.N. climate change convention from her handbag, Farhana Yamin points to the paragraph that states its goal: To stabilize greenhouse gas concentrations at a level that would prevent dangerous warming.

It doesn't provide any guidance on how to do that.

But Yamin does. And, in a historic first, dozens of governments now embrace her prescription. The global climate pact set for adoption in Paris next year should phase out greenhouse gas emissions by 2050, says the London-based environmental lawyer.

"In your lifetime, emissions have to go to zero. That's a message people understand," said the Pakistani-born Yamin, who has been instrumental in getting that ambitious, some say crucial, goal into drafts being discussed at U.N. talks in Lima this week.

Since she launched the idea in 2013, it's exploded. Papers have been written, seminars held. U.N. Secretary-General Ban Ki-moon, environmental groups and celebrities including Leonardo di Caprio have backed variations.

Critics call the idea unrealistic because it restricts us to two hard options. Either we abandon fossil fuels, our main current source both of energy and greenhouse gas pollution, or we find ways to capture emissions from coal, oil and gas and bury them underground.

The first would require a tectonic shift to renewable energy. The second would mean rapid deployment of expensive technologies yet to be tested at scale.

This would need to happen within decades, even as the developing world's energy needs grow rapidly.

"I do not think this is realistic when 2 billion people do not have access to energy," said Saudi Arabia's chief negotiator in Lima, Khalid Abuleif. "Concepts like zero emissions ... aren't really helping the process."

Yamin, 49, is a veteran of the U.N. climate talks — these are their 20th iteration. She has been "island hopping" throughout, advising a range of small island states that fear being swallowed by the rise in sea levels scientists attribute to global warming.

In Lima, she's an adviser for the Marshall Islands. She has also worked for the European Union.

While scientists have long said the greenhouse gas emissions blamed for global warming need to be phased out, the overarching goal of U.N. climate negotiations is to stabilize them at a level that keeps global warming below 2 degrees C (3.6 F), compared with pre-industrial times.

It was Yamin who urged that an emissions phase-out by mid-century be incorporated in the Paris deal, whose focus is on more near-term emissions cuts beginning in 2020.

"Yamin had the original idea," said Niklas Hoehne, a German climate researcher inspired by her work.

In May, she presented it at a symposium in Norway.

"That was when this idea started to get more attention," said Aslak Brun, chief of Norway's delegation in Lima.

Several world leaders, including Norway's prime minister, expressed support for some form of phase-out goal during a September climate summit in New York.

Di Caprio also backed it, though he, like many green activists took it a step further and called for a phase-out of fossil fuels.

Yamin's 20-year-old daughter Aliya, the oldest of four children, helped her track the statements and put them in a spreadsheet, she said.

In Lima, Norway is now pushing for a "net zero emissions" goal by 2050, meaning no more carbon emissions than the world's forests can absorb. Other options being discussed at the slow-going talks use different timelines and words like "carbon neutrality."

"Some people don't like 'zero' — it's kind of harsh and scary," Yamin said.

Chris Field, a scientist on the Intergovernmental Panel on Climate Change, says the net zero emissions goal is consistent with staying below the 2-degree target.

Dozens of the most vulnerable countries, including small island states and some European countries, support a long-term emissions phase-out, but the biggest countries have not taken a clear stance.

U.S. climate envoy Todd Stern told reporters in Lima he could imagine a long-term goal in the Paris agreement "but I'm not sure what kind, whether it would be 'net zero emissions' or something else."

China — the world's top carbon polluter — hasn't announced its position and didn't immediately answer a request for comment by The Associated Press.

Jennifer Morgan of the World Resources Institute said many businesses welcome the idea of a long-term emissions goal "because they want clarity and predictability" to guide their investments.

Oil companies aren't thrilled about the zero emissions idea, though, because it could encourage thinking that investments in fossil fuels are a bad idea.

ExxonMobil on Tuesday predicted that oil will remain the world's largest fuel source in 2040.

In a speech earlier this year, Shell CEO Ben van Beurden said expectations of a zero-carbon future need to be tempered with the "understanding that there are significant technological and economic obstacles."

Yamin said she was optimistic that the phase-out goal would survive in the Paris agreement, once people "get over the shock of the idea."

But if it does, don't expect her to take credit.

"It's a great idea. But if it survives it will because thousands of people worked on it," she said. "I'm just a nerd and a mother."