U.N. Secretary-General Ban Ki-Moon says the challenges facing the world today require dialogue and collective action. He lists the main issues, as he sees them.

"You have international , abject poverty, sanitation, pandemic diseases, and most importantly these days, climate change issues," he said.

Ban, who addressed San Francisco's World Affairs Council Thursday, said global warming will a U.N. priority during his tenure. He says the United States, the leading emitter of greenhouse gases such as carbon dioxide, which contribute to global warming, can play pivotal role in solving the problem.

"The United States is the largest emitter," he said. "But what is fortunate is that the United States is the biggest technological ."

Ban is the former South Korean foreign minister, and he has been at the helm of the United Nations for just seven months. He says the world body under-appreciated in the United States, and he cites a poll in which two-thirds of Americans said they believe the United Nations is doing a poor job.

On a positive note, the U.N. chief says, nearly three-quarters of Americans believed the United Nations should play a bigger role in solving the world's problems. He says he is to reforming the organization, increasing its efficiency and effectiveness and making its operations more transparent.

Ban notes that the United Nations was created in San Francisco in 1945, says the city also gave him his first glimpse of America. As an 18-year-old student, he spent eight-days in suburban San Francisco, and he paid a visit Thursday the woman who hosted him, 90-year-old Libba Patterson.

She described him as a focused and serious teenager. Today, Ban is a soft-spoken and careful diplomat, who defends his -key manner, saying he is a man who gets things done.

"I may not offer soaring rhetoric, but I do promise results," he said.

Friday, the secretary-general will meet a man with a more forceful style but a similar focus on environmental issues, California Governor Arnold Schwarzenegger. The two will discuss global warming and the aggressive measures has taken to address it. Then they will visit a company that has developed technology to curb greenhouse gas emissions.