When the history of humanity’s struggle to combat climate change is written, few characters will play as prominent a role as Charles David Keeling. A geochemist, Keeling developed an accurate method of measuring CO2 in the atmosphere, and in 1958 began recording background levels of the gas at the Mauna Loa Observatory in Hawaii.
That was the start of the famous Keeling Curve, which has tracked the steady rise of atmospheric carbon dioxide. Those levels have soared from 315 parts per million when Keeling began, to a grim milestone reached last week, as atmospheric concentrations exceeded 400 parts per million.
Yale Environment 360: Given your father’s work and your continuing work, what do you see as the significance of this milestone of exceeding 400 parts per million of CO2?
Ralph Keeling: Well, people like round numbers, and they remember round numbers. So this is really a moment for human awareness, just like passing a 50th birthday. This is a point to think about where we are in the course of the rise of carbon dioxide. It feels a little bit like we’re moving into another era, in that somehow between 350 and 400 parts per million feels like a certain kind of range of CO2, and now we’re moving into a different range. It feels like we’re moving into the future. Of course, we’re doing that all the time, but this is a moment to realize that that’s happening and some of the profound implications it might have.
e360: We have been passing other climate milestones, such as Arctic sea ice disappearing and glaciers melting worldwide. What do you think it’s going to take to move the public and politicians to finally begin facing up to this problem?
Keeling: Well, it’s tough, and part of it is just being aware of the significance of it. I mean, our small role here in measuring CO2 concentrations is to not just track it, but also make people aware of it. The magnitude of what’s needed can be expressed in many terms. It can be expressed in terms of what you have to do just to stabilize emissions. One way to put it in perspective is to ask the question, “What would it take to stop CO2 from continuing to grow, but just to stop at 400, not going higher?”
And the answer is that we would have to reduce immediately our burning of fossil fuels by something like 55 to 60 percent. So it’s a pretty drastic change. That is clearly not going to happen. If it did happen, it would be an economic catastrophe. So, it’s not in the realm of something we should
“We practically have to go fossil-fuel free in the next half-century or century.”hope for, but it tells you where we have to get to at some point. We have to actually move away from fossil fuel burning in such a way that we practically go fossil-fuel-free within the next half a century or century, if we’re going to avoid going above considerably higher levels like 500 parts per million. But even stopping it at 450 or 500 is going to take similar kinds of cuts, although we would have more time to do it if we started now.
e360: Is it known when the earth last had a concentration above 400 parts per million of CO2?
Keeling: The reconstructions before the ice core period, which take us only back 800,000 years, are a lot less secure. In the case of ice cores, we actually have samples of old air. And subject to some small caveats, you can simply analyze those and figure it out. In earlier geologic eras, the reconstruction of carbon dioxide depends on more indirect measurements. The work of people like Mark Pagani at Yale, who is in the business of reconstructing paleo CO2, shows that the last time that CO2 was around this level was probably in the mid-Pliocene, 2 to 4 million years ago.
e360: Let me ask you some questions about your father. Could you briefly describe his achievement and explain how it was that no one before him had accurately measured CO2 in the atmosphere?
They were not very precise… And that was paired with the fact that most of these measurements were done in places that were not very pristine. If you’re near a city or in a city or if you’re in a forest or near a forest, you see fluctuations in carbon dioxide that are potentially quite large. So it was kind of a fog as to what the large-scale atmosphere was really doing. Now, my father started making measurements of carbon dioxide as an offshoot of a project to study carbon in rivers. But the air measurements very quickly became more interesting, and he developed a more precise measurement method.
In the 1950s when he was doing this, liquid nitrogen, this very cold liquid, had become commercially available. And it turns out carbon dioxide is condensable in liquid nitrogen. So he basically was able to use a very
“He realized there was a stable [CO2] background, and the question was how was it changing?”simple dry method where you separate out the CO2 with this cold trapping, and then separately measure the amount of air and the amount of CO2. And it was precise to considerably better than one part per million. And he already could see a lot of structure in the variability that had never been seen before. Among the things he saw was that if he got away from a city or away from a forest, he almost always got the same value of carbon dioxide, something around 315 parts per million.
And this is a discovery that I think only in hindsight we can see as actually a key turning point in the field. He never published that as a discovery, but he used it to inspire people who could basically put together larger programs to actually track CO2 levels in the atmosphere. And the idea was that the only way you could have this stability in the concentrations if you were far away from forests and cities was if there was actually a large bit of the atmosphere that was nearly homogenous. And the setting up of the instrument at Mauna Loa, and the beginnings of measurements out there was really inspired by this idea of trying to track what was happening to this background over time. So he had a vision that it could work because he already realized there was a stable background, and then the question was, “How was it changing?”
e360: Your father passed away in 2005, and he was obviously seeing this very rapid increase in CO2 levels. What was he saying in his later years about what was happening because of this increase in CO2? And how do you think he would react to this 400 part-per-million milestone?
e360: Do you see your role as one that should be more public?
Keeling: I think it’s important that the science we do be something that the public can access and understand. What I’m putting out there on the Web is focused on materials that are close to what we do. So there isn’t an in-depth discussion about implications for climate per se because that’s really someone else’s job to put that out there. But the fact that CO2 is rising, the fact that we’re crossing a milestone, the fact that it’s accelerating, and some appreciation for the magnitude of what is going on is something that really falls within the realm of what we do. And it’s an incumbent on us to make that clear to people.
e360: If emissions continue at this trajectory as we move deeper into the 21st century, how quickly do you think we could pass milestones like 450 parts per million, 500, or a doubling of CO2 from the pre-industrial era, which would be about 550 parts per million?
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e360: That’s what is known as total equivalent CO2?
Keeling: Yes, exactly.
e360: And that’s about 478 right now?
Keeling: Yeah, I think that’s right.
e360: So you think by mid-century or before we could hit that real doubling, if you add in other greenhouse gases?
Keeling: Oh, I think it’s almost for sure we will.
e360: What steps would you recommend be taken fairly soon to begin to rein in emissions?
Keeling: Again I’m not the person to think in detail how this can work or what the constraints are. But clearly we have to wean ourselves off fossil fuels. That requires developing renewable sources of energy, and we need a marketplace that allows that to happen. As long as fossil fuels are too cheap, that’s going to be hard to see. So we need some system in which the cost of the damage caused by CO2 emissions is paid at the gas pump or at the point of extraction and not by generations living later.
e360: Given this sobering milestone, is there anything out there that gives you hope?
Keeling: I’m surprised at the level of attention this is getting. It’s nice to see that people are paying attention in this way. And I think that bringing about change in the first place requires people to be aware of what’s going on, and people are seemingly quite aware. So that’s hopeful.
e360: The next step is action, but obviously that’s the hard part.
Keeling: Yes. But if you don’t see that it’s happening, it’s hard to act on it.