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John Holdren is no stranger to the spotlight. Over his long career in science, Holdren — a physicist by training — has worked on controversial issues such as climate change and nuclear non-proliferation.

But for nearly eight years, he has enjoyed an even higher profile, as US President Barack Obama’s science adviser and director of the White House Office of Science and Technology Policy (OSTP).

With Obama due to leave the White House in January 2017, Holdren — now the longest-serving US science adviser — recently sat down with Nature for a wide-ranging chat. The interview has been edited for length and clarity.

Opinion polls continue to show a divide between what the American public thinks about science and what scientists think. Has Obama done enough to change the way that science is perceived?

The president has done an incredible job in making science cool for young people. This is already evident in all kinds of numbers: you see more kids enrolling in science courses, more kids participating in science fairs, more kids going to ‘makerspaces’. We have substantially increased the number of engineers graduating from college in this country. I say ‘we’, but obviously, that is a large cooperative operation that includes colleges and universities.

I’m not sure which polls you are referring to, but my impression is that the public is more interested in and enthusiastic about science, technology and innovation than it was at the beginning of this administration.

Leaders at the National Institutes of Health (NIH) and other government agencies have discussed the widespread perception that we are training too many PhDs. Do you worry about that?

If every PhD we train believes that her or his only acceptable career trajectory is a tenured professorship in a college or university, then it’s true: we are training more PhDs than there are slots of that kind. But the PhD is, in fact, a very versatile degree. Far more than just demonstrating that you know more than practically anybody else about one narrow topic, it demonstrates that you have the fortitude, the focus, the commitment and the intellectual capacity to tackle a very tough problem.

PhDs are finding constructive and rewarding employment all across the economy, and, overall, our view is that there are still more opportunities for highly trained people in science, technology and innovation than there are people being trained.

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If you were to go back in time, would you become a scientist again? Would you do anything differently?

I would certainly become a scientist again. My wife is a biologist — she has a PhD in biology from Stanford — and I have sometimes envied the biologist’s life because they get to do their work in so many spectacular locations. She did her work on insect–plant interactions at high altitude in the Rocky Mountains. We have dived together on coral reefs all around the world, while she was actually doing work. I’ve sort of envied that life from time to time.

Do you worry about future science funding?

The president has consistently recommended more money for science and technology than Congress has been willing to pass.

The success ratio of proposals to the NIH is something like 17% — that is, we are funding one-sixth of the proposals that the NIH gets. And those proposals are already self-selected. Investigators don’t bother writing a proposal to the NIH unless they think they have got a really good idea, a capable team and a plausible strategy. If you ask Francis Collins, the NIH director, what fraction of the proposals they get that are worthy of funding, he’ll tell you 50%.

That means we are funding about a third of the potentially productive, influential, path-breaking research that is proposed to the NIH. But the NIH has a budget of over US$30 billion per year. It’s not very easy in these budget times to increase a $30-billion budget by a large factor, like 50% — never mind 100% or more, as director Collins would say is warranted in terms of the quality of the research. The same is true at the National Science Foundation — far more worthy proposals than they are able to fund. This is a consistent problem. I would like to see more public support for raising public spending on research and development.

The comprehensive climate bill that failed to pass in 2010 is sometimes mentioned as the administration’s biggest failure. What did you tell the president then, and do you have any regrets?

One of the rules of the game in this environment is I don’t talk about what I told the president or what the president said to me. But I will tell you that both the president and I very much wanted to see comprehensive climate legislation pass. We didn’t get it. And so, of course, we were disappointed.

We did everything we could using executive authority to advance a sensible climate-change agenda. We put in place the most ambitious fuel-economy and carbon dioxide-reduction standards for light-duty vehicles ever thought about in this country, and followed them with heavy-duty-vehicle standards. We put in place a large number of new standards to advance energy efficiency in appliances, in buildings, in industry. We boosted — to the extent that budgets allowed — Earth observations and climate science.

Even today, we would love it if we could get a bill out of Congress that would enable us to do more than we are able to do with executive authority.

The administration’s regulations to cut power plants’ CO 2 emissions are already in limbo because of legal challenges. And Republican presidential candidate Donald Trump has said that if he is elected, he will try to pull the United States out of the Paris climate agreement. Are you optimistic that these policies are going to survive?

Yeah, I’m optimistic. A lot of these policies — all of them — are being enthusiastically pursued by career civil servants and not just political appointees, because they are very clearly the right thing to do. And I think it’s important to recognize that there is now a huge amount of global momentum behind this. The United States would become a pariah if we backed out of the Paris agreement.

And while I don’t want to get into politics, I suspect that if Mr Trump were elected, he would discover that what he said during the campaign about Paris is not quite right. He said in the campaign that the Paris agreement means that foreign bureaucrats would be able to determine America’s energy choices. That simply isn’t true. It’s far from true. If he is elected, he’ll figure that out, and I think he — as any new president is likely to do — will stick with the Paris agreement.

Science is global today. How do you think that complicates matters? Can the regulators keep up?

I’m going to China this week for a strategic and economic dialogue and for a US–China dialogue on innovation policy. I’ll be talking with my Chinese counterpart, Wan Gang, the minister of science and technology, about some of these very problems and what we are doing about them.

We have a lot of cooperation with China on biomedical issues. We talk to them all of the time about gain-of-function research and about gene-editing issues. And in fact, when the current round of interest in gene editing emerged with the rise of the CRISPR technology, the [US] National Academies of Science, Engineering, and Medicine gathered leading scientists from all over the world in a format very much like Asilomar [a landmark conference in 1975 that set rules for research on recombinant DNA], but strongly inter­national. The top Chinese people came to talk through what the implications of these technologies are, and how we should think as a global science community about regulating them.

With Asilomar, every scientist working on recombinant DNA came together. But now there are researchers in China who are editing the human germ line using CRISPR, because it’s legal there — and there are plenty of others elsewhere. It’s arguably legal here.

And we’ve got high-school kids who can use CRISPR technology, so I’m not saying this is all tied up neatly with a bow. This is a very challenging question. When the technology is so widely available and so relatively easy to use, this is a very different matter than, for example, controlling nuclear-weapons technology. That has been a big challenge as well, as we know, but this is hard work.

Some scientists and policy experts worry that the United States is losing its edge in space, despite the rise of a commercial space industry here. How do you feel about the future of the US space programme?

We knew when we came in that we had to rebalance NASA, and we had a committee chaired by Norm Augustine that looked at the space programme and declared that Constellation [NASA’s human space-flight effort] was “unexecutable”. And that report informed what we did to scale Constellation way back. We still have an Orion multi-purpose space capsule. We still have the Space Launch System, a heavy-lift rocket, under development. But we scaled them back to the point that there was enough money to revitalize Earth observation, to revitalize planetary science, to revitalize robotic exploration, to think about new missions.

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Shortly after he took office, Obama said that this was going to be the most transparent administration ever. But journalists have found some agencies to be fairly opaque.

In the first months of the administration, the president issued executive orders on transparency, on scientific integrity, on openness in government. I was put in charge of a number of the implementation [efforts]. That has been a focus of OSTP throughout this administration. We’ve gotten virtually all of the departments and agencies to produce for public review and comment, and then to finalize, policies on openness and on scientific integrity. I think we’ve made great progress in terms of open data, in terms of the publication in open venues of federally funded research. But I would not argue that that job is finished.

There is always a tendency in government, some of it quite legitimate, not to expose internal deliberations prematurely. You know, it’s quite challenging to have a discussion between the president’s senior advisers with reporters from Nature, Science and The New York Times sitting around in the room, because if you do that, nobody will float a trial balloon for fear that the trial balloon will get into the news as a done deal.

What is your greatest regret?

The biggest regret I have, first of all, is that we have not been able to do better on the budgets. And again, I don’t think that is our fault. I don’t know whether I really have a strategy to pass on to my successor to say, ‘Here’s how you can do better’.

You’ve spent almost eight years inside what is arguably the most powerful institution on Earth. Do you come away more or less optimistic about humanity’s ability to deal with its problems?

I come away more optimistic, and that’s in large measure due to the extraordinary leadership that President Obama has provided. I have felt for many decades that science, technology and innovation are crucial if human society is to get its arms around the biggest challenges we face. And I’ve had the pleasure of working for a president for nearly eight years now who shares that view.