He told me that on Tuesday when we met in Washington, where Ban is continuing to lend his eloquent voice and diplomatic finesse to the most pressing environmental problem of our time.
Ban has traveled from the Arctic Circle to the deserts of sub-Saharan Africa to get a first-hand look at the ravages of global climate change. He hosted President Barack Obama and more than 100 heads of state in New York this September for a climate change conference. And his tireless efforts to pull together global consensus on how to address this widening scourge has added immeasurably to the momentum building worldwide for change.
Raising Copenhagen to the level of a heads-of-state summit is yet another sign of movement. It's not yet clear whether Obama will go. Much depends on what he feels his presence might add.
What's important, also, is that the Senate demonstrate forward motion on the clean energy and climate legislation pending there now. Few expect to Senate to pass this complex bill in the next several weeks. Principles and progress, though, count.
If key Senate leaders can send a message to Copenhagen that this country is serious about doing something about climate change -- and about helping developing countries deal with the fallout - that would go a long way toward reflecting the urgency and hope Ban is sensing around Copenhagen.
In my own way, I'm trying to help. I presented Ban with a copy of my new book, Clean Energy Common Sense: An American Call to Action on Global Climate Change.
This is part of our effort to reach out and explain how we can put Americans back to work, reduce our reliance on foreign oil and create a healthier future for ourselves and our children, I told him.
"It's a very short book," Ban said, smiling at the small paperback. "It's handy."
Ban slipped it into his suit pocket, as though he might keep it "handy" for his next airplane flight.
"I'd like to thank you and the NRDC for your strong commitment and advocacy, especially now, just a few days from Copenhagen," said Ban. "Receiving this is a good message."
I smiled back, because that's exactly why I wrote the book -- and why I wrote it now.
Addressing climate change is something we need to do for ourselves, as Americans, because it will make our economy stronger and our country more secure. There's an added benefit, though, in showing American leadership at a time when it's needed most.
Leadership is something we know something about.
We led in World War II. We led during the Cold War. We have led a democratic and free-market revolution that has changed the world. And we can lead once more in an effort to consolidate the gathering global consensus around the need to address climate change.