Ban Ki-moon led the United Nations from 2007 to 2016, an era that saw the rise of multilateral climate action culminating in the Paris Climate Agreement.

Since leaving the U.N., he has used his leadership positions at civil society groups to continue his campaign against climate change. He founded the Ban Ki-moon Centre for Global Citizens in 2018 and is a deputy chair at The Elders, a multilateral convention of senior political and civic leaders brought together by Nelson Mandela. One of his driving messages is that the U.S. and other rich nations need to do more individually and collectively through the World Bank and other international institutions.

His message is resonating. On July 22, U.S. Treasury Secretary Janet Yellen convened multilateral development banks to discuss how to align their portfolios with the goals of the Paris agreement and mobilize more private capital to combat climate change.

Ban spoke with POLITICO. This interview has been edited for length and clarity.

In your new book, you called climate activism one of your proudest moments. Why is that?

Climate change has been approaching much, much faster than what we might have thought. Before I became the secretary-general, there were some science and climate skeptics from European countries like the United Kingdom. That really was a cold shower on our efforts. I really worked very hard to erase that kind of misperception. These days, nobody believes in climate skeptics because there have been so many unexpected natural disasters.

Yet the skeptics remain.

Particularly your President Trump, he was following the skeptics. His withdrawal from this hard-fought, hard-negotiated international agreement, the Paris Agreement, was very much irresponsible. I left the United Nations before his administration began, but I have been very critical that his decision was politically very short-sighted, economically irresponsible, scientifically very wrong. I warned that he will be standing on the cold side of history.

I am very encouraged that President Biden has taken as his first presidential action to rejoin the Paris climate change agreement. People are now waking up. I was also encouraged by the G-7 countries, their meetings in the United Kingdom recently.

You began this conversation in 2006, 2007. Did you think we'd be further along by now?

We are much better now than 2007. It was very difficult to [have a] dialogue with President Bush.

I first met him in the White House, it was Jan. 16, 2007, if my memory serves me correct. I was warned by my staff, please don’t raise this issue. He’s not believing in climate change.

I raised the subject and his immediate reaction was the U.S. is ready to do as much as China. He was pointing fingers at China.

I invited him to a summit meeting. Of course, he agreed. Then he would not deliver his statement in the general assembly. That was embarrassing, very embarrassing. The president was in New York, participating in the United Nations General Assembly meeting but would not say anything.

Bush later changed his position. He invited you to lunch just before he left the White House.

Later on, after my retirement, I met him briefly on occasion and I really thanked him for his leadership on climate. It is a very interesting story. In the end, I got President Bush in this climate agreement.

Fast forward to today. Is it time to ban financing and subsidies of fossil fuels, especially where the World Bank and IMF are concerned?

I think it is necessary. There are many countries who have been financing [fossil fuels] through public financial organizations. Unfortunately, my own country, Korea, was one of them. I raised this issue very strongly with the office of the president of Korea and other ministers. Now Korea has decided not to provide any public financial support, except those which are now going on.

I made a strong case that Korea must phase out all its 16 coal-fired power stations by 2045. That’s a policy now. I also recommended strongly that the old internal combustion engine cars must not be produced by 2035. It is now government policy.

How do you assess the current situation globally?

Unfortunately or fortunately, the Covid-19 crisis has made people realize much more seriously the importance of the interrelationship between climate and all these pandemics. Nature has its own way.

Let's talk about the World Bank, the largest source of climate finance to developing countries. Are rich member nations stepping up? What should bank President David Malpass be doing?

Mr. Malpass was critical of the World Bank before he was appointed as president and also because of his alignment with his boss, former President Trump. So there was some concern of how much the World Bank would be doing.

Is the World Bank mobilizing enough money?

Of course the World Bank is not printing money. I think they need to reach out to rich countries to contribute much more money. Without money, the World Bank has no power.

What should Malpass do next?

There's a lot of talk that we have to reduce greenhouse gas emissions, but you're not investing for the future wisely, investing in wise ways, in adaptive activities like infrastructure for small farmers, for water, green energy. For small island developing countries, even planting mangroves. It’s very small, but that will help.

$100 billion was committed by the United States and Japan and European Union, and that has not been kept.

You think the U.S. is not doing enough to help?

That’s right. They must make up for the loss over the last four years. President Obama in 2014 promised $3 billion and paid $1 billion, and $2 billion is still pending. This is an outstanding $2 billion. The U.S. must, should lead this campaign, otherwise the European Union and other countries will not do it. I’m counting on your support.

I’ll pass on that message.

This is part of your responsibility, working together. I'm a lone soldier now.

Let's talk about the private sector. In the U.S. during the Trump administration, a lot of private companies made a lot of promises. Are they delivering?

In fact, the private sectors are doing better and more than government. Government has their restrictions and laws and opposition parties. But corporations, when the owners, presidents or chairmen have conviction, they can do more.

Business says it needs government leadership. In the U.S. for example, there’s resistance to massive spending and carbon pricing.

We have to do twofold, threefold, tenfold investing in green energy, and make sure that the OECD countries raise their ambition by announcing a nationally determined contribution of 45 percent by 2030.

Europeans are trying to lead this campaign, but my own country, Korea has not been able to do that. I’ve been in the process of trying to convince business sectors in Korea: Look, whatever you may do, if the European Union imposes a carbon tax by 2035, then whatever you manufacture, you will not be able to sell there. So it’s no use. You have to change.

You’ve talked about your concern for your children.

I have three children, two girls and one boy, but more important is I have four grandchildren, three granddaughters and one grandson. I am worried for them.

It is us and our forefathers who have been abusing the privileges given by nature. I am also blaming political leaders. This is a sort of a presidential campaign period in Korea. I've been watching the conversation today and no one is talking about it.

Really? No one’s talking about climate change in the campaign?

They’re talking, you know, housing prices. This is really disappointing.

Has the world become more divided since you were secretary-general?

On climate change they are more united. Because they have been hit, they are experiencing it by themselves. They know that climate change is now happening. At that time I was a lone voice speaking out. Convincing leaders was very difficult. One European leader I won’t name, he gave me a book about climate skeptics. He said he wrote it. Then when I was convening a summit meeting on climate, one environment minister of that country came to me and said, look, Mr. secretary-general, please do not invite my president. He will spoil your summit.

I think most of the climate skeptics, they’re gone. Now people understand climate change is happening much, much faster. Pope Francis is a strong supporter. He issued his own decree.

Yes, the encyclical. What did he tell you when you met him?

He told me, "God always forgives. Human beings sometimes forgive. But nature never forgives."