The morning Mr. Obama unveiled the final version of the Clean Power Plan last year, he summoned his senior climate adviser, Brian Deese, to the Oval Office. Mr. Deese expected that the president would hand him some last-minute changes to his speech. Instead, he brought up an article in the journal Science on melting permafrost.
The research not only documented faster increases in temperatures, but also drew direct links between fossil fuel emissions and extreme weather.
Mr. Obama scrutinized reports like the 2014 National Climate Assessment, which tied climate change to events like flooding in Miami and longer, hotter heat waves in the Southwest.
“More and more, there are events that are happening that are astoundingly unusual, that knock your socks off, like the flooding in Louisiana,” said Michael Oppenheimer, a professor of geosciences and international affairs at Princeton University. “Those are the kinds of events where it’s becoming possible to draw attribution.”
Benjamin J. Rhodes, one of the president’s closest aides, recalled Mr. Obama talking about “Collapse: How Societies Choose to Fail or Succeed,” Jared Diamond’s 2005 best seller, which explored the environmental changes that wiped out ancient societies like Easter Island and discussed how modern equivalents like climate change and overpopulation could yield the same destruction.
The president’s Pacific roots also came into play. In Honolulu last week, he told a meeting of Pacific Island leaders that few people understood the stakes of climate change better than residents of their part of the planet. Crops are withering in the Marshall Islands, he noted. Kiribati is buying property in another country for the day that its own land vanishes beneath the waves. And villagers in Fiji have been forced from their homes by high seas.
Shifting monsoon patterns in South Asia could affect a billion people who depend on low-lying agriculture, Mr. Obama said in his interview.
“If you have even a portion of those billion people displaced,” he said, “you now have the sorts of refugee crises and potential conflicts that we haven’t seen in our lifetimes.”
“That,” he added, “promises to make life a lot more difficult for our children and grandchildren.”
Joining Forces With China
Mr. Obama and Hillary Clinton never seem to tire of telling the story of Copenhagen: In December 2009, with the climate conference on the verge of failure, the two learned of a meeting of the leaders of Brazil, China, India and South Africa, from which they had been pointedly excluded. Elbowing their way past a Chinese security guard, they crashed the meeting, and over the course of 90 minutes of tense negotiations with the abashed leaders, they extracted an agreement to set goals for lowering emissions.
The Europeans, who had been cut out of the talks, derided the deal as toothless, but Mr. Obama learned from the experience. A global climate accord could not simply be a compact among developed economies, he said. It had to include the major developing economies, even if they resented being held to standards that had never applied to the club of wealthy nations. And any agreement had to be led by the two largest emitters, the United States and China.
Mr. Obama set about persuading President Xi Jinping of China to join the United States in setting ambitious reduction targets for carbon emissions. Tensions were already high over China’s hacking of American companies, and the United States was balking at China’s slow-motion colonization of the South China Sea. A casual, get-acquainted summit meeting between Mr. Obama and Mr. Xi at the Sunnylands estate in California in June 2013 had failed to break the ice.
Mr. Obama with President Xi Jinping of China in California in June 2013. Despite their differences, the two leaders have worked together on landmark agreements to address climate change. Credit Christopher Gregory/The New York Times