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This week, to accompany our cover story on worst-case climate scenarios, we’re publishing a series of extended interviews with climatologists on the subject — most of them from the “godfather generation” of scientists who first raised the alarm about global warming several decades ago.

The oceanographer Wallace Smith Broecker is the man who coined the term “global warming,” way back in 1975, in a paper called “Climate Change: Are We on the Brink of a Pronounced Global Warming?” Broecker had already distinguished himself in his work on what’s called the “ocean conveyor belt” — the system of jet streams and other circulatory patterns that stir the planet’s waters, regulating heat along the way. Today, he is 84, still working at Columbia’s Lamont-Doherty Earth Observatory, and has given up hope that emissions reduction alone could avert dramatic climate change.

Just reading the U.N.’s IPCC reports and related research on climate change, it seems as though the track we’re on is considerably worse than most people appreciate.

Exactly.

Even the estimates in the IPCC reports — those seem to be relatively conservative. They don’t include the feedback mechanisms that are concerning a lot of people.

Yeah, 180 nations have to agree to it, so it becomes conservative. But there’s no bullshit in there.

So what are the big things we should be worrying more about?

I really think that ice melting and sea level are the big things.

If we leave the CO2 in the air, it’s probably going to melt the Greenland ice sheet and probably Antarctica on a timescale of probably a thousand years. Of course once you get that ice in the ocean you’re never going to get it back on the continent, so it’s a net loss forever, or for a really long time.

How fast do you think the melt will be?

We don’t know. It probably won’t be catastrophic, it’ll probably be gradual, with maybe bursts of activity. But the big thing is that sea level is going to go up several meters, and maybe as much as ten meters. And that really eliminates a lot of stuff.

In 1950s, when I was in graduate school, we got 15 percent of our energy from renewables and nuclear, and 85 percent from fossil fuels. Today it’s the same. Both of them have been increasing at 3 percent a year.

Renewables and nuclear are not changing in their percentage share. And in order to stop the CO2 from rising we have to go to a factor-of-ten reduction in fossil-fuel burning — at least a factor of ten. And that means changing all the world’s infrastructure.

Which will be very difficult, even if we decide to do it.

The energy companies — their whole value is what’s in the ground, and if it’s not going to be burned their stock isn’t worth very much. So they’re going to do everything they can to burn what they got — $5 trillion dollars or so worth of stuff. And India, China, and Mexico are going to start using more energy, so if rich nations cut down, it’s still going to be overwhelmed by the others. Unless something really dramatic happens, it seems like we’re on a course where we’ve been going up in fossil fuels 3 percent every year. It’s still accelerating.

So you haven’t been too encouraged by the recent news in green energy — the price falling …

Well, it’s going to change, but it’s a long thing, and Trump has removed funding for renewable energy. The Chinese of course are going like gangbusters, and that’s very difficult to predict. But still it’s hugely expensive to do all that. I’m very optimistic in most things, but not about this. This is a huge problem, and we don’t have a clue how to solve it. It’s got to involve a tax, and the word tax is death to a politician. You can clothe it some way, but still somebody’s got to pay to remove it.

Tell me about how we might remove that carbon.

In order to balance what we’re putting in today — not taking out any of what we put in yesterday — we have to take out one ton of CO2 a day. A lot is known about how to do this, although there is no test module ever built.

These devices would be about the complexity of an automobile, and the cost of material would probably be — let’s say they cost $30,000 each. You know how many of those we’d need? 100 million. To take carbon down three parts per million, you’d have to have another 100 million. Optimally spaced, so putting them so they don’t compete with one another, they’d cover all of Arizona. There are plenty of places to do it — you’d want to do it in dry climate, which is good because there’s plenty of dry land without many people living on it.

But 100 million at $30,000 would be several trillion dollars, just to build them. To operate them would be a 10 percent increase. If we’re going to take out all that we put in, that’s an enormous amount of money.

You believe that extraction is totally necessary? That we can’t deal with this problem without it?

There is one way to deal with part of it, though not all of it.

Doubling CO2 is like cranking up the sun by 2 percent. And so if we reflected away 2 percent of incoming solar radiation, we could compensate for the warming. And that would be probably 50 times cheaper than taking it out.

But this would also have other effects, right?

Yes. It involves putting SO2 in the stratosphere. The SO2 becomes sulfuric acid, with droplets that are very fine, and they back scatter 10 percent of the solar rays that hit them. So that means if you want to get rid of 2 percent of the sun’s rays, then 20 percent of all sun rays have to hit those droplets. And of course that would make our sunsets very red, would bleach the sky, would make more acid rain. But that would be spread around the planet.

A lot of scientists seem really worried about those effects.

I mean, if we have a problem, you have to think of the magnitude.

We’ve got to watch that we don’t say that the giant problem shouldn’t be solved because it creates a few smaller ones.

Do you think that SO2 approach is feasible?

There’d have to be an agreement by all nations to do it, because if only some nations do this, it would move rainfall around, and everything that happened to agriculture would get blamed on it. It would be very hard to prove any of these claims were wrong. Also, it wouldn’t stop ocean acidification, so coral reefs would still get wiped out. And, of course, if we ever stopped the program then the temperature would go back up again. If there were a war, or some catastrophe, we’d be stuck with all that extra CO2 in the air and no SO2 to combat it. But I think that in your lifetime whether to do that or not will become a big issue.

Because it will become clear that emissions reductions alone aren’t going to do the trick?

It’s going to get warmer and warmer. It’s probably going to be 20 years before it’s a hot issue.

It seems to me people don’t really appreciate how dire the situation is.

It’s hard to make it real. We’re seeing it already — birds are arriving at a different time. They seem to know what’s going on, whereas we don’t. With our big brains we can’t figure it out; they’ve figured it out.

If you think about the way that the Syrian refugee crisis has really disrupted global politics, whatever happens coming out of Bangladesh will be many times worse.

There’s something astronomers use called the Drake equation, and that asks, “What is the probability that there is a planet out there that we could communicate with that has intelligent life?” And the biggest uncertainty in that has nothing to do with astronomy. It has to do with the lifetime of a civilization. How long does it take it to destroy itself? So if you have intelligent thing for a thousand years, the chances we’ll have to communicate with another planet, on the timescale of billions of years, it becomes almost certainly not possible.

I saw recently that Stephen Hawking was saying we need to find a way to colonize other planets within 100 years.

Well … I mean, it’s going to be pretty hard to devastate the Earth to the point we can’t live on it. But if we’re ever going to get this thing solved, we’re going to need an international group that has a lot of authority. It’ll have to be like the Fed, but to manage carbon. That would mean we’d all have to give up a lot of our sovereignty, but I think that’s the only way it would happen. It couldn’t be the U.N., because the U.N. doesn’t have the power. They’d have to be able to penalize, they’d probably have to have an army, because cheating would be very, very lucrative.

It doesn’t seem as though that’s very likely.

I’d say it’s one chance in a thousand. I mean, we may get to that. Maybe China will get so powerful that it can start to dictate. That’s what we need. Our democracy is shot, I think. It just doesn’t work.

Climate is one of the clearest case studies of its dysfunction, I’d say.

Yeah. You know, I used to work for Steve Bannon.

Really?

Yeah.

In what context?

You’ve heard of Biosphere 2? Well, that was created by a true cult leader, John Allen, and a guy named Ed Bass — the son of a wealthy Texas oil man. Their idea was to put eight people in there, and they’d stay two years.

But in a small volume of air, you’ve got bacteria eating up the oxygen like mad, plants producing oxygen, and CO2 goes into the plants and comes out from the bacteria. CO2 went down and down and down. And when it got down to 19 percent from 21 percent, Allen had a friend of his get in touch with me to figure out why oxygen was going down but CO2 wasn’t going up.

Before the first two years were out, Bass’s financial guys finally did in the cult — the cult is spending all their money, they thought the cult were idiots. The sheriff swept in, like a military thing, because they didn’t want them to destroy anything, which worked — they got them all out without any damage being done. And then the property was without management, so they hired Steve Bannon, who was at the time running some company — you know, he’s done a lot of different stuff. He came and stayed there. The idea was to convert the biosphere to study the effects of CO2 on plants, and since I was the only scientist who was still involved who had any reputation at all, he appointed me science adviser.

How was that?

We got along well. When I saw his name first appear around Trump, I thought, it couldn’t be the same guy! And then I saw his picture! His brother Chris is still at Biosphere. I wrote an article once where I mentioned pulling CO2 out of the atmosphere. I sent that via Chris Bannon to Steve —Chris promised me that Steve would get it. And I said, “Steve, you know, you may not do anything about this, but you ought to think about preparing for what might happen if you don’t.”

What happened?

I never heard back from him, obviously. His agenda is to destroy the planet, I think.

Generally speaking, what do you think this administration means for clim﻿ate?

Doesn’t mean anything good. But, you know, what if we had signed the Paris accords? The U.S. still wasn’t going to keep its commitments, so as far as what we would do it wasn’t going to make much difference. You know, when we reached an agreement in Kyoto, that didn’t really change things significantly. Until carbon taxes really become common, we’re not going to do anything.

A fossil-fuel company could theoretically extend its business life by figuring out carbon capture or geo-engineering.

Why they’re not doing this is a big question. First they had to admit it’s a problem. Now they are admitting it’s a problem, but they’re playing the tobacco game. The longer they can sell their product, the more of their underground wealth can be used. They know they’re going to lose at some point, so they’re probably not going to build something that will last longer than 50 years.

You worked with Exxon for a while, right?

That was a curious thing. A guy who got his degree here with me ended up going way up high at Exxon. He had a corner office when they were on Sixth Avenue. And he asked me to write some stuff about CO2 as a consultant, and I did. I wrote a lot, because I wanted to make some money! What he did with that I have no idea.

Did you talk to him about whether it all weighed on his conscience?

Well, this is still pretty early — back in the early ’70s. But eventually he quit.

It’s interesting to think about in light of the victories won in the past — regulating the CFCs that caused the hole in the ozone, more recently the chemicals in air conditioners. But oil companies are so much more powerful.

They have the money to pay for all the best lawyers. I was surprised when Jim Hansen won his case in Oregon, do you know about that?

Yeah — it’s an amazing case. When I talked to him, he seemed hopeful that they could win at the Supreme Court.

I have a disagreement with Jim. His solution is to have a tax and then give all the money back to the public. He says if we do that, the incentives introduced by the tax into the market will make sure that everything will take care of itself. Bullshit. You have to use the money to solve the problem directly — retrieving the CO2. What he’s saying would help but it wouldn’t solve the problem.

Well, he showed me a paper which he’s trying to publish in which he emphasizes the importance of taking CO2 out of the atmosphere.

Really? That’s a reversal. I like Jim, but I rarely talk to him because he’s so confident that he’s right. And it’s hard to talk to people like that when you’re talking about complicated problems. Plus, I know enough about the science he writes about that’s skewed, and that’s bad. It’s very hard to do what he’s doing, to be a scientist and an advocate without crossing over the line and making the problem look worse.

Sometimes it can be really hard to judge that, though, no? I mean, how confident can you be in particular models?

One of the more interesting things being done is just running a single model over and over again to see the divergent results. In these models there are dozens and dozens of assignable parameters, because you don’t really know the physics well enough to write equations. In one case in particular, they did something like 3,000 runs made with all possible combinations of parameters, putting them in a reasonable range — in other words, you don’t know for sure, but it could be this, it could be this. And what they found is that they got a spectrum of results that ranged from one degree to eleven degrees.

And it has skewed. The mean was about 3.5 degrees Celsius of warming. But it showed there was something like 15 percent probability that it’d be more than four degrees, just on these model runs. So these models have to make a lot of assumptions.

What’s a dramatic worst-case scenario, as you see it?

The worst scenario is the scenario we’ve been talking about for an hour —we’re warming the planet and we’re shifting the rain belt and we’re going to have to do something that we probably never dreamed we’d do, which is put SO2 into the atmosphere. I just think this immense warming will have huge repercussions in every way.

One thing we didn’t talk about was the methane bubbles in the ocean, and methane in the permafrost. How do you rate the risk of that?

It’s like ice. If we were to leave the CO2 in the air for a long time, we’re going to warm up the ocean over all these clathrates. Eventually they’re going to start to melt. There’s an interesting thing we call the PETM, you probably never even heard of that.

No, of course I have!

Well, one thing that appears to be the case is that, for something like the PETM, you need an initial burst of 2,000 gigatons or something, in a timescale of less than 5,000 years, and then you need a long tail that goes out tens of thousands of years. I’m not sure that is true, but if it is true then the analog pulse could be what we’re doing with fossil fuels and CO2, and if that sits there a long time, and starts to release methane …

Wouldn’t methane be more dramatic than carbon? It has such a dramatic short-term effect.

Methane is a better greenhouse gas but it doesn’t last very long. So it will add an increment, but it would never dominate. One scenario is, you could say, if we warm the Earth five or six or seven degrees, then we’ll start to release methane from clathrates, and that would reinforce what was happening and also extend its duration. And I think that’s one of the most important things that the PETM can help us with.

But the PETM didn’t make any extinctions — that’s interesting, it’s encouraging. But in the western United States something like 70 percent of the species disappeared during the PETM and then came back. Only two or three didn’t come back.

Weren’t there extinctions in the ocean?

Yeah. The deep ocean really got acidified. It was a severe event.

Which, of course, is something we’re going to do, too.

The interview has been condensed and edited.