When international negotiators reached a first-of-its kind climate change agreement in Paris this month, the United Nations' normally low-key leader, Ban Ki-moon, celebrated onstage, arms raised in victory and more exuberant than many had ever seen him before.
Nearly nine years had passed since, in his first days as secretary-general, Ban surprised world leaders by making global warming a top item on his agenda. Now, on the eve of his final year in office, the cheers in Paris marked the culmination of his nonstop campaign, pressed with world leaders at summit after summit and in locales including melting glaciers and islands at risk of disappearing.
It was an emotional moment, and looking back at the road to Paris in an interview with The Associated Press, Ban paid tribute to many people, including the leaders of the United States, China, India and France. He also spoke proudly of his own role.
No other leader in the world "has been raising, without fail, all the time, climate change," Ban said. "I have spent real passion ... and most of my time and energy on this issue."
It was quite a shift for the former South Korean foreign minister, whose main focus before becoming the eighth U.N. secretary-general in 2007 was his country's standoff with North Korea.
Ban traced his interest in climate change to his yearlong campaign to lead the United Nations, which took him to many countries and broadened his vision of global issues.
Two weeks before he was sworn in as secretary-general, Ban told Tim Wirth, then president of the United Nations Foundation, that one of his two highest priorities would be climate change, along with empowering women.
"You could have blown me away," Wirth said of Ban's choice of tackling global warming. "He had a deep commitment then, and he has stayed with it, and stayed with it, and stayed with it."
At the time, climate change was not a popular topic.
The 1997 Kyoto treaty, which required only rich countries to limit emissions blamed for global warming, was set to expire in 2012. Negotiations on a new agreement had almost collapsed, Ban said.
"I thought that I needed to revive this one," he said.
His first high-level meeting as U.N. chief was with then-President George W. Bush.
The original agenda for their January 2007 meeting didn't include climate change, Ban said, and Bush "seemed to be a little bit surprised" when he raised it.
Undeterred, Ban decided to hold the first-ever climate change summit at the United Nations in July 2007.
He invited Bush and told him that the success of the summit would depend on his participation. Bush came, though he didn't address the summit.
That connection paid off at a U.N. conference in Bali in December 2007.
The United States, the lone major industrial nation to reject Kyoto, was opposing India's proposal to strengthen requirements for richer nations to help poorer countries with technology to limit emissions. In one of the most memorable moments in climate change diplomacy, tiny Papua New Guinea implored America to lead or get out of the way.
An isolated United States capitulated, and the first roadmap for addressing climate change was adopted.
"Miraculously, I was able to save this one, but I didn't know why," Ban said.
In early 2009, he finally found out.
Ban and his wife were invited to dinner at the White House in last of the last days of the Bush presidency. Bush told the U.N. chief that when the Bali meeting reached a difficult moment, he got a call from the head of the U.S. delegation asking for instructions.
Ban said Bush told him: "Suddenly, you came to my mind. Then I told the delegation head, 'Do what the secretary-general of the U.N. wants to do,'."
The secretary-general said he still feels "very much grateful" to Bush.
"That was the beginning of our success," Ban said.
But then came the disappointment of the 2009 Copenhagen climate change negotiations.
In Copenhagen, a newly elected President Barack Obama showed "great commitment," even working on proposed global text from his laptop, Ban said. But there were too many differences and negotiations ended with no agreement.
"From the failure of Copenhagen, we learned a great lesson," Ban said.
One was to have every country provide its own national action plan to combat climate change. Another was to get countries to agree to have a universal climate change agreement by 2015.
Meanwhile, Ban was traveling the world to spotlight the impacts of climate change. His visits to Antarctica and the Arctic showcased melting ice, and his visits to the Aral Sea in central Asia and Lake Chad in west Africa warned of their disappearance. He visited the low-lying Pacific island nation of Kiribati, where he found a life jacket in his room in case of inundation.
He also asked to attend annual meetings of the World Bank and the International Monetary Fund — a first for a U.N. secretary-general — to talk to finance ministers on the need to mobilize $100 billion in climate financing annually by 2020.
As the summit in Paris approached, Ban participated in monthly strategy videoconferences with the leaders of France and Peru and later, Germany. One key decision was to reverse the usual negotiations process and have country leaders attend the start of the summit to give impetus and clear direction to negotiators.
The Paris opening was the largest-ever gathering of country leaders, with 150 assembled, the secretary-general said.
But there were about half a dozen "spoilers," countries ready to block consensus on an agreement. Nicaragua refused to submit its national plan, arguing that rich nations should be compelled to make deeper emission cuts.
Ban recalled the moment the Nicaraguan delegation said "we will not block" a deal. The French foreign minister immediately gaveled approval of the agreement, which was later adopted unanimously.
The Paris agreement, adopted by nearly 200 nations, calls on both poor and rich countries to cut greenhouse gas pollution. It aims to keep global temperatures from rising another degree Celsius (1.8 degrees Fahrenheit) between now and 2100.
Ban's perseverance and leadership were essential, said former Norwegian Prime Minister Gro Harlem Brundtland, who headed a U.N.-appointed commission that published a groundbreaking report in 1987 outlining the dangers of climate change.
"This is not a one-man show, but the one man is important," Brundtland said.
Without him, "we cannot take for granted that we would be here."
Ban's priority for the rest of his term has not changed. With the climate deal imposing no sanctions for non-compliant countries, the secretary-general said he will focus on establishing a framework to ensure U.N. member states follow through on the climate change promises he worked so hard to get.