James Hansen.

Photo: nasa.gov

James Hansen, NASA’s top climate expert, believes scientists have an obligation to speak out when their findings have important implications for the public — and he certainly put that belief into practice last year when he told The New York Times that the Bush administration was trying to muzzle his calls for reducing greenhouse-gas emissions.

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Hansen has been speaking publicly about the threats posed by climate change for more than two decades, though it’s only in the last couple of years that the public has begun to listen. These days, Hansen is the closest thing climate science has to a celebrity. Lately, he’s been using his star status to draw attention to the evils of coal-fired power plants and to chastise the Intergovernmental Panel on Climate Change for not making strong enough statements on sea-level rise.

During a recent stop in Seattle, Hansen spoke with Grist about the growing urgency of global warming, why a molecule of CO2 from coal is worse than a molecule of CO2 from oil, and what we need to do to get the climate crisis under control.

You’ve been speaking out about climate change since the ’80s. How have your own observations and predictions changed over the years?

Unfortunately, they’ve changed in the sense of it becoming more urgent.

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The question is, what is the level of global warming that would constitute dangerous climate change? We wrote an article in about the year 2000 in which we argued that 1 degree Celsius additional warming might be OK, but 2 or 3 degrees is not. But what’s now become clear is that maybe 1 degree Celsius is dangerous, because already we’re seeing on West Antarctica a net loss of ice and the ocean is warming and it is beginning to melt the ice shelves.

The other change that has occurred, as many people predicted, is that China and India, the developing world, have increased their emissions at a significant rate in the last decade. So it really is becoming more urgent.

You said a few years ago that we had 10 years before we hit that tipping point where we couldn’t go back. Is that a hard and fast number?

I think I said that in 2005, so I was really thinking 2005 to 2015. Now we’ve come two years into that period, and I haven’t seen the numbers in the last year, so I can’t really say what the two-year change is just yet.

There’s plenty of potential to achieve an alternative scenario, but we would have to become serious about vehicle and building improvements in efficiency. If we did that, then the need for new coal-fired plants would greatly decrease. We had been going from coal to oil to [natural] gas, each one being less carbon-intensive. But now all of a sudden we’re leaping back toward coal. That is the big concern, because that’s where the huge potential CO2 amount is.

What needs to happen, in your opinion, in the next few years if we’re going to prevent reaching that point of no return?

A moratorium on coal-fired power plants and phasing those out over the next few decades. I think that’s perhaps the most important thing.

Then we also need to conserve the liquid and gas fuel so that we can develop the next phase of the industrial revolution because we’re going to have to find energy sources that don’t produce CO2. In order to give us time to do that, we need to use oil and gas, which are precious fuels, as if they were precious.

Another one is addressing this ice-sheet issue. For example, if the National Academy of Sciences would issue a report on this, that would help draw attention to the fact that we are so close to a major tipping point.

We’re probably going to pass the dangerous level of atmospheric CO2, and we’re going to have to figure out some ways to draw down atmospheric CO2. That tells us we should have greater emphasis on good agricultural and forestry practices and perhaps even burning biofuels in power plants that capture CO2.

What is your opinion on the IPCC reports that have come out this year?

I was very disappointed that their comments about sea level didn’t make clear that there’s been a huge change in our understanding of that situation, and it’s a much more dangerous problem than we had realized. Their report actually caused confusion by giving smaller numbers than they gave in the previous report. They should have underlined that more clearly so they didn’t confuse people.

I thought the public reaction and the press reaction was good, in that they did point out that now the consensus was getting ever stronger. [The reports got] the consent of many countries that you know would be very reluctant to sign on if they didn’t have to. So I think [the reports were] very good.

You have a new paper that will be coming out on the implications of peak oil in the climate debate. Can you tell us a little about the conclusions of that report?

The main point of that paper, which I think is fairly important, is that gas and oil already have enough CO2 in them to take us to approximately the dangerous level, and perhaps beyond the dangerous level. It’s pretty clear we’re going to use those fuels, and it’s not practical to capture the CO2 in oil since it’s used in mobile sources. Some of the CO2 from gas used in power plants, you could capture the CO2, but there are no plans to do that yet.

That means that the only way to keep CO2 from exceeding 450 parts per million would be to say we’ll have no more emissions from coal, and that would mean that we should not be building any more coal-fired plants until we have the sequestration technology. A molecule of CO2 from coal, in a certain sense, is different from one from oil or gas, because in the case of oil and gas, it doesn’t matter too much when you burn it, because a good fraction of it’s going to stay there 500 years anyway. If we wait to use the coal until after we have the sequestration technology, then we could prevent that contribution. I don’t think that has sunk in yet to policy makers, because there are many countries going right ahead and making plans to build more coal-fired power plants.

You’ve taken a lot of flak for speaking out over the years, since scientists aren’t usually very vocal about their observations or beliefs. What do you think should be the role of scientists in addressing climate change?

I think that scientists need to help connect the dots, because otherwise the dots are connected by special interests. The public doesn’t easily connect all the dots themselves, especially when public affairs offices at scientific agencies are controlled by political appointees.

I’ve actually written a paper and submitted it called “Scientific Reticence and Sea Level Rise” [PDF], because it just seemed to me that there was a gap between what scientists really thought and what was in the public knowledge in regards to ice sheet stability and sea level rise. That first became very apparent to me when I was being questioned by the lawyer for the automobile manufacturers in the Alliance of Automobile Manufacturers vs. California Air Resources Board case. The lawyer said, “Can you name one scientist who agrees with you that sea level is likely to go up one meter?” and I couldn’t do that. I couldn’t name a glaciologist, even though there are some that I have spoken to who believe that. They’re reticent to say it and I sort of understand why. If you make a bold assertion like that, there can be negative repercussions. It seems to me that the funding agencies treat more conservative scientists as being more authoritative. On a problem that you have a long time scale to figure out what’s right and what’s wrong, then maybe it doesn’t matter. But in fact we do have this inertia in the system and these tipping points, and it [is] very dangerous to hold back.

Do you think the politicization of science is going to continue? Are you hopeful about political changes making a difference as far as climate policy?

Unfortunately, it’s likely to continue because the scale of the economics of what’s involved is so huge.

Obviously, there’s a lot of change in the air. It seems like there will be some action in the next couple of years, but it’s a question of what that action will be and whether it will be commensurate with the problem. The fact that now some of the industries that were denying that there was a problem are coming around and coming to the table is more a reflection of the fact that they want to help determine what is done. And if they succeed in making what is done negligibly small or much less than what is needed, then that will be very unfortunate. But it remains to be seen. It’s going to be interesting in the next few years.