Fateful milestone of the Keeling Curve

Ralph Keeling was two and a half years old when his parents took him on a family trip to Mt. Rainier, formed by volcanic explosions more than a million years ago.

In an interview with the Los Angeles Times, his father, environmental scientist Charles David Keeling, recalled his son’s excitement over the ice on the mountain. “How do you make glaciers?” the little boy wanted to know. It was at that moment, the elder Keeling joked, that his son got his start in natural science.

Charles David Keeling in the lab

Charles David Keeling in the lab.

Ralph Keeling did eventually follow in his late father’s footsteps, even taking over the landmark study that made his father famous. In the 1960s, Charles David Keeling pioneered the systematic measurement of carbon dioxide in the atmosphere. His readings, charting a consistent year-by-year rise in atmospheric carbon dioxide (CO2), traced what has come to be called the Keeling Curve. That curve gave birth to global climate change research, and it continues to be the basis for predictions of a warming planet.

For a time, both Charles David Keeling and his son Ralph worked together as scientists at Scripps Institution of Oceanography in La Jolla, Calif. When the elder Keeling died unexpectedly in 2005, Ralph Keeling took over as director of the Scripps CO2 Program. He is also a professor and principal investigator for the Scripps Atmospheric Oxygen Research Group.

Last May, the Keeling Curve hit a grim milestone, reaching 400 parts per million (ppm) atmospheric CO2. In an interview with writer Peter Jaret this July, Ralph Keeling reflected on the meaning of the number, his father’s legacy, and the growing threat caused by CO2 and global climate change.

A family photo from 1967 shows Charles David Keeling atop Mt. Whitney with sons Drew (left) and Ralph.

A family photo from 1967 shows Charles David Keeling atop Mt. Whitney with sons Drew (left) and Ralph. (Photo courtesy of Keeling family)

Let’s start with the troubling news that CO2 levels hit a major milestone of 400 parts per million in the atmosphere. What’s the significance of that number?

The number 400 is really a psychological milestone, like a birthday with a zero at the end of it. We’re all getting older every day, but we don’t think about it most of the time. But when we hit one of these milestones like 60 or 70, we say, oh yeah, things have changed. When my father first started measuring atmospheric CO2, the level was about 310 ppm. Since then we’ve seen a steady rise. There is seasonal variation, and the northern hemisphere is higher than the southern hemisphere. (But) we got surprisingly close to having a monthly value in May over 400. We hadn’t expected it to be that high. We had to scramble to get our data updated.

When was the last time the earth saw CO2 levels this high?

We don’t know exactly. High quality measurements only go back to the 1950s. By analyzing air trapped in Antarctic ice, we have measurements that go back to about 800,000 years ago. Over that time, CO2 levels were almost always considerably lower than 400. There are some converging lines of evidence that suggest that CO2 levels got up to around 400 ppm back in the Pliocene, around four million years ago. Of course, the world was a very different place back then, and considerably warmer. So in some respects, we’re moving toward the climate of the Pliocene.

But let me point out while the absolute number is important, the pace of change is more of a worry. We are changing CO2 levels so rapidly that what’s happening is almost certainly unprecedented. The pace of change affects the consequences and the details of what we will experience.

How soon are we likely to reach other milestones?

The levels have been going up about 2 ppm every year. That would put us at 450 in about 25 years if we stay on the course we’re on. We’ve seen a significant increase in fossil fuel consumption in the last few years. So it may take only another 20 years after that to reach 500, and another 20 years after that to reach 550. There are certainly people alive today who will live to see 550 ppm unless we take significant action.

What are the consequences that you worry most about?

Heat waves will be a problem in many places, of course. But temperature per se isn’t the greatest worry. The biggest concern is the impact of rising temperatures on habitability, particularly on rising sea levels, flooding, and also in some places the lack of water, leading to drought and fires. We’re moving into a mode where large fractions of the big ice sheets will be melting away. If you look at the Paleolithic record, you see that the earth was only a shade warmer than it is today, but sea levels were a lot higher. So we’re probably facing centuries of continuing sea level rise. That means the coastline is not going to be a fixed feature of the landscape but rather one that is constantly changing.

Part of the challenge of climate change is that there’s not likely to be a single big global catastrophe that serves as a wake-up call. It’s more likely that it’s going to be a series of regional problems that seem only indirectly linked to climate change, such as droughts that cause starvation, mass migrations, or conflicts over water. But we have to get ready for the consequences. We have to realize that the planet will be different, and a lot of things we’ve taken for granted are not going to be the same in the future.

Thanks to your father’s pioneering work, we have solid measurements of atmospheric CO2 going back more than a century. What was it like growing up with a famous scientist as a father?

A lot of my friends at the time had parents who were scientists, so my situation didn’t seem special or different. I vaguely knew what my father was doing, but I didn’t know much about it, and I guess it was really in high school and college that I first started to absorb the significance of what he was doing. I should say that among his colleagues at Scripps at the time, what he was doing didn’t seem all that extraordinary, either. It was just one other thing that was happening. But I do think my father knew he was onto something important. He set a pretty high bar for himself, and even he sometimes had trouble living up to it. It took a lot of attention to detail and getting good people to work for him, people dedicated to getting good numbers. That’s what the game was all about, to make sure that the measurements were not compromised in any way. I sense from the way he worked that he viewed his main audience as the people of the future, not the people of the present. He knew he was going to be on the stage for people’s attention decades in the future. He knew the science he did would have to stand the test of time, because of the way it would be scrutinized.

Charles David Keeling with Scripps Pier in the background, 2002

Charles David Keeling with Scripps Pier in the background, 2002

At times your father struggled to get funding to continue his measurements. Is that still a challenge?

Absolutely. The problem is that the science of global climate change requires a decade or longer perspective. The normal funding cycle is a few years. If you can’t turn around some kind of test or hypothesis in a few years, you don’t have a viable proposal. The only way to get funded through the normal science channels is to pretend that you’re really focusing on something else. The measurements keep going anyway, but you can’t argue that that’s the main reason you’re doing them. I do think there needs to be an understanding that everyone has a stake in keeping these long-term measurements going.

Let’s talk for a moment about biofuels. What role do you think they can play in reducing fossil fuel consumption?

The benefit of biofuels is that you’re basically taking carbon that was recently absorbed by photosynthesis and burning it. Presumably wherever that carbon was grown, there’s a place for more carbon to grow. So biofuels can be viewed as a sustainable form of energy that in the long term has no impact on atmospheric CO2. But the devil’s in the details. Some biofuels require fossil energy to be developed, which makes them less beneficial. And there are issues of land and water use that need to be addressed. There are efforts to grow biofuels using salt water, which would be a great way around some of those issues.

You’ve talked about the consequences of warmer temperatures. Will they affect biofuels?

There’s a potential for biofuels to become slightly more viable than they appear to be today, but it’s very hard to say with certainty. Because of the increase in CO2, land plants are actually becoming more photosynthetically active, and there may also be more plants. Carbon dioxide has a direct fertilization effect on plants. We definitely see evidence of some sort of greening going on. So-called natural forests are no longer behaving naturally anymore. They are growing in a world with far different CO2 levels and a far different climate. Some of what we’re seeing is the movement of forests northward, and probably an increase in photosynthesis.

According to recent measurements, the amount of fossil fuel we’re burning exceeds what’s appearing in the atmosphere as CO2, so we know carbon is being taken up either by the oceans or by land plants. The more we pump into the air, the more the oceans can take up. The ocean is a big reservoir, and it could potentially hold a lot of CO2. But carbon dioxide has consequences on sea life, because it raises the acidity of seawater. And the oceans can’t absorb it all. They will only absorb down to at best something like 80 percent. So we’re certainly going to see atmospheric levels continue to rise if we go on burning fossil fuels.

Charles David Keeling (second from left) with children (left to right) Drew, Emily, and Ralph. The Keelings loved music and enjoyed playing instruments together. Heidelberg, Germany, 1970

Charles David Keeling (second from left) with children (left to right) Drew, Emily, and Ralph. The Keelings loved music and enjoyed playing instruments together. Heidelberg, Germany, 1970.

Awareness of the threat of climate change has increased since your father began measurements. How well do you think most people understand the science behind it?

I think there’s still a lot of confusion. I don’t think people fully understand that fossil fuels represent a form of carbon that’s deep in the earth that we are pulling out and burning and releasing into the air. People don’t fully grasp the difference between urban air pollution and greenhouse gases. With urban air pollution, if you reduce pollutants in a city, the air quality will get better very quickly. That’s because the loading of particles is a reflection of what has been emitted over the last few days. Even a windy day can blow the particles away. Carbon dioxide is different. When you increase CO2 in the atmosphere, it stays there. Even if we stopped emitting CO2 today, it would take centuries for the carbon already in the atmosphere to be soaked up.

Magnitude is something else that many people don’t understand. It’s a little hard to grasp what’s big and what’s small in this business. One notion out there is that we can counteract the problem by planting more trees. But we would need to plant many trees for every car on the road. When you scale that up by the number of cars in the world, you realize very quickly that you aren’t going to counteract CO2 simply by planting trees. People also have the impression that the atmosphere is vast, that we can dump things into it and it won’t matter. But as reservoirs of carbon go, the atmosphere isn’t particularly big. The ocean is a much bigger reservoir. Land plants have about as much carbon as the atmosphere. So you can’t scrub the atmosphere down to low levels without radically changing the structure of the land surface. The total amount of carbon that’s potentially in fossil fuels is many times the original CO2 that was in the atmosphere, and many times the total amount of carbon in trees and soil.

According to your ongoing measurements, CO2 levels continue to rise. Are you able to remain optimistic about the future?

It’s hard to see a shining light out there except maybe the untapped potential for innovation and transformation. I hope a lot of young people recognize the threat and take up the challenge. That’s what we need at this point.

We can’t pretend at this late stage that we are going to avoid significant harmful consequences. We’re way too deep into it now. Four hundred parts per million is already unsafe in my estimation. And we’re racing right past that level.

One thing I want to emphasize is that while it’s late to take action, it never gets too late. It never gets to the point where the worst is behind us. I wish we had taken action several decades ago, so we could have stabilized the levels of CO2 at something like 400 ppm. But the consequences of future emissions of CO2 are just as significant in causing further warming and further transformation as past emissions. So you never reach a point where you say, okay, well, let’s just give up and live with the consequences because it’s too late to do anything. There’s been an urgent need for action for decades and there will continue to be. Now we just need to get on with it.


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