What three things keep Barack Obama up at night?
The former U.S. president says that neither nuclear weapons nor terrorists make the list.
Instead, three newer issues have emerged that worry him: political polarization, climate change and social media.
If those issues are not tackled soon, "we could end up having even greater problems than we do today," he told a sold-out audience in Singapore on Monday at an hour-long event, "In Conversation with President Barack Obama."
One worrying new trend is political polarization, both in advanced economies and in developing countries.
"If you ask me, probably the biggest trend that I've seen over the last decade is a return to some of the political trends and societal tensions that, you know, help lead to World War I and World War II," said the 58-year-old former politician.
Noting people his age and younger have lived during times of "relative tranquility," he recalled major events that resulted in "enormous optimism" around the globe: the fall of the Berlin Wall, the unification of Europe, the prison release of South African anti-apartheid icon Nelson Mandela, Chinese economic reform, globalization and a billion people lifted from poverty.
Even after the September 11 terrorist attacks on the U.S., there was still a sense that the event was an anomaly in a world that was becoming more integrated, better educated and more tolerant, he said.
But things started to change after the financial crisis of 2008.
"Even as the standards of living were rising and it looked like a relatively tranquil time, under the surface there was enormous disruption," Obama said. "As a consequence of globalization, outsourcing, automation, blue-collar workers were losing jobs and status and felt as if their kids were not going to do as well as they were. There were winners and losers."
"And the losers started feeling besieged," he said.
Cultural disruptions in the Middle East, Asia and U.S. were also a factor, he said. "People who had traditional cultures felt as if those traditional arrangements were under assault."
"And, as a consequence, what you start seeing is this populist backlash — sometimes from the left, more often from the right — and a fallback to tribalism, racism, misogyny, ethnic or sectarian conflicts and strong men who would come in and oftentimes exploit some of those divisions."
Another worrying trend is climate change.
"Those of you who still aren't convinced on the science," he said to the audience, "we can talk later."
He noted the "rapidity" of rising sea levels, melting polar caps, increases in the force and frequency of droughts, forest fires, hurricanes, tsunamis, flooding and the resulting population displacement.
"You're starting to see mass migrations resulting from things like that," he added. "There's fairly strong evidence that part of what precipitated the crisis in Syria had to do with this massive, longstanding drought that you're going to see repeated in other parts of the world."
He warned that extreme weather shifts could affect the lives of millions around the world.
"If you think about places like South Asia and the entire subcontinent, if monsoon season shifts rapidly or droughts or temperatures continue to rise in those areas, you're looking at hundreds of millions of people who potentially are unable to feed themselves."
"So I worry about that."
The third trend that keeps Obama up at night is the rise of social media, which he called "an accelerant to some of these other trends."
"What we thought of as an enormous good — and I was an early adapter… but what we've seen is an increasing use of that technology to promulgate falsehoods and narratives of hate in the United States, in Europe, in Myanmar, around the world."
"And when you start contesting what's true and what's false, when debates aren't just about opinions. It's not just about how you or I may disagree on the best way to educate children or the best way to organize the economy, but now we're disagreeing on: Is this a table? Or is this a chair? Or is this an elephant?" he said, touching the table in front of him.
"There's no agreed upon set of facts that we can agree to, and then test our ideas and opinions against some objective facts, but rather everybody has their own facts. You start seeing political breakdown as a consequence of that."
During the discussion, Obama also talked about what he misses about being president: the positive impact he could make, the intellectual challenge and his team. However, there are some things he doesn't miss about it, such as the security bubble, the "pomp and circumstance" of cameras, and people standing up when he walked into a room.
He also talked about how he kept his cool during the most stressful times of his presidency.
"We set up a process that I trusted, where I had confidence we looked at every problem from every angle, using logic and reason and facts and data," Obama said. "And so I could go to sleep at night feeling as if what I decided may not work. But nobody could have made a better decision than I made in that circumstance."
"I could always feel like we did the best we could — for the right reasons."