DW: Since childhood you've been a very international person. You have two passports, Brazilian and German, and you've lived and worked in so many different countries. Where do you feel most at home?

Achim Steiner: One of the wonderful things that you learn to appreciate when you have lived in different places is that you can call many corners of the world your home. One reason why I wanted to work in the international field is that I enjoy immensely this moment when you arrive in a country, you are completely ignorant, and you learn to live there. You discover it.

There are a growing number of people who are nationalistic and who shun any kind of internationalism. What do you say to these people? How do you bridge that gap?

First of all, by not telling them that they do not understand what is going on, because populism usually has an origin in something that is real. If you feel badly treated, if you feel alienated, if you feel that you are not in control of your own destiny, you start reacting. There is a feeling that they have somewhere in the context of globalization lost control. Into that come extremists and populists. My personal response to that is always to engage, to try and provide perspective, because only when we share a common perspective do we start thinking of common solutions. Most people are neither by nature nor by conviction racist, but they are very easily manipulated into becoming a negative force in society. 

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We face lots of different global problems. How do you even begin to change things for the better?

First of all, by committing myself to something that I believe is fundamental to all of us. And that is a recognition of and also a belief in and a commitment to multilateralism. Or, to put it more simply, [the belief] in the idea of the United Nations. So my decision to go back into the United Nations in 2016, especially at a moment when I could see how the politics of the day was becoming more nationalistic and more isolationist, was a very deliberate decision. Secondly, I believe in the power of development to prevent societies from falling apart. So to have the opportunity to lead the largest organization of the UN and the one dedicated to sustainable development made a great deal of sense to me. We have 200 years of the most extraordinary developmental successes behind us. The failures of development are a reminder of where we need to do things differently. But I deeply believe in the narrative of development as being something that unifies and unites us.

Can you give an example of how the UNDP is trying to do that? With all these mounting problems isn't there a danger of falling back?

There is actually no room for complacency right now. The economic system in which we in some ways are trapped is destroying our planet. This is where it is important to remind ourselves that we have choices to make. We can help nations across the world address and tackle some of these issues. The UNDP is the largest provider of climate change advisory services in the UN family. We literally help more than 170 countries accelerate climate action in their national development interests. We tackle the issue of migration from the perspective of root causes because in many countries where we work we are actually at the front line of combating the root causes that will make people give up and leave the place they call home. Young people live in the digital age. They know the opportunities that exist in the world. If their nation cannot provide them with hope they will pack up. And we can't quite manage these movements at the moment.

The UN has been criticized a lot for not being efficient enough. At the same time there is a lack of finances from big donors. Do you think the UN is still effective? 

There are three ways of answering that question. Firstly, are the UN and our individual agencies, funds and programs the paragon of efficiency and effectiveness? No, we are not. We are public institutions and many of us have indeed been caught sometimes in this phenomenon of public institutions which have regular budgets and still continue doing what they're doing. The second point is that member states are not actually honoring paying the commitments that they have made. It's created a cash crisis. And thirdly we are actually doing a lot to make our institutions more efficient and effective, and I think sometimes the world would be surprised if it realized with how little we actually live up to the mission of the UN to keep the peace, provide humanitarian support and help countries address their development needs.

How little is it?

Well let me give you one figure for comparison. The citizens of New York pay $2.5 billion dollars (€2.75 billion) a year from their own taxes to protect themselves. That's roughly the equivalent of what the secretary-general has available to run the United Nations Secretariat to essentially address the major crises in the world. It is, in a sense, a totally inadequate sum of money. 

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You are an optimist despite everything — or maybe a professional optimist. What frustrates you?

Part of the reason why I'm an optimist is that almost every day I meet extraordinary people doing extraordinary things. I think the self-indulgence of being pessimistic is really that — it's a self-indulgence. Look at that young lady from Sweden, Greta [Thunberg]. I have great admiration for people like her and there are actually tens of thousands of Gretas around the world. But my biggest frustration right now is the lack of time we have. We live in an age where the impact that we humans collectively have on our planet is truly transforming the fundamentals of life on Earth. This is no longer just a product of ignorance. It is complacency and above all it is an irresponsible attitude towards the future of our children.

Reconciling ecology and economy has been one of your big themes and of course you were also very instrumental in helping bring the Paris agreement about. Do you think that the goal of limiting global warming to 1.5 C can still be reached?

There is every reason to believe that we can do this, but our leaders lack courage and they lack the honesty to engage with their communities to change the way we essentially define responsibility to act. And the responsibility to act derives from the capacity to do something, but also the fact that you know that without taking a different course you are mortgaging future generations. And the extraordinary thing is, at the beginning of the 21st century — in an age where we're richer, more educated and more capable of acting — we still have political leaders who are telling us, well, maybe it's not the time to act. It's an age of irresponsibility that we are living through and that needs to be challenged.

Achim Steiner is a Brazilian-German environmentalist and is the current administrator of the United Nations Development Program (UNDP). From 2006-2016 he served as the executive director of the United Nations Environment Program (UNEP), and he has also served as the director general of the International Union for Conservation of Nature (IUCN).

This interview was conducted by Anke Rasper. It has been edited and condensed for clarity.