CURWOOD: The White House prefers he remain silent, but a prominent scientist continues to speak out about the eminent danger from climate change. A conversation with James Hansen is just ahead. Stay tuned to Living on Earth.

[MUSIC: The Lounge Lizards "The Birds Near Her House" from 'Queen of All Ears' (Strange & Beautiful – 1998)]

CURWOOD: It's Living on Earth. I'm Steve Curwood. Back in 1988 as the United States was scorching under the impact of the worst drought in 50 years, the head of NASA's Institute for Space Studies, James Hansen, took the microphone at a U.S. Senate hearing on a sweltering summer day.

"It's time to stop waffling so much and say the evidence is pretty strong that the greenhouse effect is here," Dr. Hansen told senators as the network television cameras buzzed. And before long, people started talking about the phenomenon we now call global warming.

James Hansen has continued to be outspoken through the years and, most recently, he's been in the news alleging that the Bush administration has been trying to silence his latest warnings about climate change. James Hansen joins me from New York City where he still heads NASA's Goddard Institute for Space Studies and has been studying climate change since, what, 1967?

HANSEN: Uh yes, since I got my degree in '67.

CURWOOD: What should we be concerned about now? Are we reaching a point of no return?

HANSEN: I think that we are.

I think that if we continue on the path of business as usual for another decade it will be impractical to keep the global warming less than one degree Celsius. And the reason that's an important level is that's the most warming that we've had in the last 700,000 years, and probably the last million years. We just don't have the data for the full million years. But we know that the changes in that period, although they're significant, they're probably something we could adapt to.

But if you start talking two or three degrees Celsius, then you're really talking about a different planet from the one we know. There would be no sea ice in the Arctic in the summer and fall. That means the species that live there now – polar bears, the seals that live on sea ice, and reindeer on the tundra – they would not be able to survive. So it's like the million-year flood; it's never happened in the past century. So, were talking large regional changes.

And for people, well, we can adapt. I mean, we can move from New York to Atlanta and the climate is different but we can certainly survive there, and we notice the difference. But for the wildlife and the trees and things that have adapted to a particular climate, they don't move as easily. It's not a good idea to have a climate change of that magnitude that quickly.

CURWOOD: What is the point, if there is such a point, where we won't be able to reverse the impact of global warming? And how do you measure that?

HANSEN: Yeah, that's a very important question, and one that we've only begun to debate the last year or so. And my argument is that that point is at a warming of about one degree Celsius warmer than it is now. That to some people is surprisingly small, and we're surprisingly close to it.

CURWOOD: I believe one time you gave a talk at the Society of Environmental Journalists where you said, 'you know, the ice core samples out of Greenland show that we may have shifted from the previous Ice Age temperature regime to something much warmer in as short as a hundred years or maybe even 30 years.' I mean, are we looking at abrupt climate change in various places?

HANSEN: Well, the rate of change right now is extremely high and it's difficult to say how it compares with some times in the past when we don't have the time resolution. But I would be very surprised if there were more rapid rates of change in the past because if you look at how fast the greenhouse gases are increasing, there's simply nothing in the record that approaches this.

That's the big issue because if we continue on this path, which is business as usual, with the rate of emissions, of greenhouse gasses, continuing to increase at a couple of percent per year; then this century we would have warming of two and a half or three degrees Celsius. Once we get that kind of temperature we'll be having a sea level change at a rate of probably a few meters per century. So we would have a continually changing shoreline which would be extremely difficult to live with. You can't easily adapt to that sort of a situation.

So, we really need to avoid staying on a business as usual scenario. We'd have to slow down the rate of growth of CO2 emissions and flatten that out within the next decade or two, and before the middle of the century we would have to have a significantly decreasing rate of CO2 emissions. In addition, we would have to get some absolute decrease in the other large climate forcings, and that means, in particular, methane and tropospheric ozone and black soot.

But there are other good reasons to try to decrease those non-CO2 forcings. So, I think that significant decreases, again I'm not advocating specific policies, that's not my job but I can say how the forcings would have to change in order to keep us from passing the point of no return. What I'm saying that we're going to have to start now.

CURWOOD: Now recently you told the New York Times that the Bush administration has been trying to silence you about your findings on climate change and the implications for public policy. What's going on?

HANSEN: Well, the public affairs office at NASA headquarters has put unusual restrictions on me with regard to speaking to the media, requiring that any request for interview be that I not respond to it, but rather just to send it to headquarters. And they would have the right of first refusal, which means someone there will actually do the interview rather than me. I have some objection to that because that policy has not been enforced on other people.

So that's what the discussion has been about. The restrictions on communications have become unusually severe in the last year or two. And it certainly applies to other agencies as well as NASA. You don't hear a lot about it. I can understand that scientists are reluctant to complain about it. And you know, most scientists are not affected because it's only the messages which are sensitive that are restricted.

CURWOOD: James Hansen, how concerned are you about getting fired now for speaking out?

HANSEN: (Laughs) I am concerned about it. The reason I was late for this interview was that I was checking with a lawyer what I could say and what I couldn't. But I'm more concerned about how we will be judged in the future if we don't say what we know. One fellow told me that history will not judge us very well if we pass the tipping point, the point of no return, and the public simply wasn't aware of the dangers that we were facing. I don't want my grandchildren to say 'Opa understood what was going to happen but didn't succeed in warning people about it.'

CURWOOD: James Hansen is director of NASA's Goddard Institute of Space Studies and leads the climate research there at Columbia University where the Goddard group is based. Thank you, sir.

HANSEN: Thanks.

CURWOOD: In response to Dr. Hansen's allegations, Dean Acosta, deputy assistant administrator for public affairs at the space agency, has told the press that there has been no effort to silence Dr. Hansen and that NASA promotes openness and speaks with the facts.