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The Habitable Planet: A Systems Approach to Environmental Science 

Atmosphere Interview with Pieter Tans

Interviewer: What is the history of The Global Monitoring Division (GMD)?

PIETER: I’ll start further back a little bit. Mankind’s use of energy depends on burning fossil fuels, coal, mineral oil, and natural gas, which all come out of the earth. And the major product of that combustion is carbon dioxide. As a result, carbon dioxide has been increasing in the atmosphere since the late part of the nineteenth century. The first accurate measurements of carbon dioxide in the atmosphere were done in 1956 by David Keeling, who recently died. He was at the Scripps Institute of Oceanography in San Diego. He was the first to start continuous monitoring of carbon dioxide from a mountaintop in Hawaii, the Mauna Loa Volcano. This started in ‘58. This lab, the global monitoring division, that I’m a part of started in the late ‘60’s. It had a different name then. So, our first measurements date actually from 1968. And, what we see in these data is that carbon dioxide has increased every single year that we’ve measured. And, we know also why that is. It’s mostly due to the burning of fossil fuels. And, it continues to increase every year. Last year was one of the highest rates of increase we’ve ever observed.

Interviewer: What is your mission in monitoring these global greenhouse gases?

PIETER: We made these measurements because they will force the climate on Earth to change. They cause it to be warmer on Earth. There are all kinds of effects that go with that, of course. It’s possible that warming produces stronger hurricanes. It’s still in a debate, but it’s likely that that’s one of the results. The Arctic ice might melt. I mean, the Arctic Ocean is mostly covered by ice that might melt. Frosted, high latitudes might thaw out and then release more carbon as a response, making the forcing of climate change even stronger. So, we try to keep track of this. And not only do we measure this in one spot, like at Mauna Loa in Hawaii, but we monitor this all over the Earth, because we want to do these measurements of carbon dioxide and other greenhouse gases. Carbon dioxide – it’s the main one – but there are other ones too, such as methane, nitrous oxide and purely man made gases, such as sulfur hexafluoride. There’s a whole row of them. And we monitor all of them in many, many different places all over the Earth.

We do that because we see spatial patterns as a result of this monitoring effort and from the spatial patterns we can determine where these gases come from and where they are taken up or destroyed. If we are downwind from a major source region, say downwind of the East Coast of the United States, we see higher concentrations. It’s like we’re looking at plumes. And likewise, if you have a region where there is uptake of carbon dioxide, the Southern Oceans, for example, it’s a plume, if you will, of negative CO2. Because CO2 is disappearing into the water, we see a region downwind of where the CO2 concentration is a little bit lower. So, by looking at these patterns, and seeing how they change over time, we can figure out what’s happening to this gas after we’ve emitted it.

Interviewer: Can you explain how these greenhouse gases are actually making the Earth warmer?

PIETER: It’s called the greenhouse effect. You can look at it like a blanket. The Earth receives energy from the sun. And, in fact, we can all feel that. When we sit in the sun, we feel that we’re being heated. But the Earth also emits that energy back into space, In a different part of the spectrum; it’s radiation, it’s not visible to the naked eye. It’s infrared radiation. We can’t see it. You can still feel it actually. You may, if you are familiar with heat lamps, for example, they can really produce heat, or when you’re standing close to a hot object, like a furnace, you can feel the heat. You can’t see it. You can feel it, without touching it. That is infrared radiation that you’re absorbing. Well, the Earth is emitting that radiation to space. And, when we put a lot of these absorbing green house gases into the atmosphere, that infrared radiation will be prohibited from reaching space. It will be trapped in the atmosphere, and emitted back to the surface. And, that causes heating of the surface of the planet.

Interviewer: What is the research question that you’re trying to answer right now?

PIETER: Because of the current widespread concern about climate change caused by us, by humans, we really want to do our measurements in such a way that we can get an understanding of where does the CO2, or the other greenhouse gases, for that matter, where does it go? What is taking it up? And also, what are the natural processes that are releasing CO2 or other greenhouse gases? If you can get an understanding of what the natural system, what the Earth itself is doing with this excess of gases that we’ve caused, then we can actually make better prognoses of what future climate change might be like. How much further this, we call it forcing of climate change, will go.

Secondarily, we also want to try to measure from the atmosphere…we want to quantify directly human caused emissions. I think that’s going to be important in the near future and beyond as our society will start trying to limit emissions. This is already happening to a limited extent with the countries that have signed onto the Kyoto protocol. But, I don’t think there is any way around the fact that the whole world will have to actually start cooperating. We have to decrease the rate at which we emit this gas. Again, carbon dioxide mostly. And there needs to be a system in place where we can actually verify, from what we measure in the atmosphere, what is happening. How successful are the various policy measures that will be taken in the new, in the near future.

Interviewer: You described the process of heat coming into the atmosphere and being absorbed by this blanket of gases that in turn heat the Earth’s surface. Why do you then need to make measurements in a variety of different places? Why not just do the measurement in one place and you’ll have your data?

PIETER: Yes, we don’t measure it in just one place. We could. And we do actually measure at Mauna Loa together with the Scripps Institution of Oceanography. We have two independent measurements programs right next to each other. You know, so we have great confidence in their data. What we can track there is the rate at which the global atmosphere increases in various greenhouse gases. These measurements are done very carefully and we are very confident that we get good answers there. And, we really know what’s happening.

But, that doesn’t give us any diagnostics. We would like to go further than that. We would like to know what are quantitatively the different sources that contribute, and also secondly, what is the Earth’s system response itself. For example, we can change our agricultural practices and do low till or no till agriculture. One of the reasons for doing it would be to sequester carbon. So plants fix carbon dioxide into organic matter. And, instead of plowing the soil, we leave it in the soil, basically, taking CO2 out of the atmosphere and storing it into carbon compounds, organic compounds in the soil, which would help ameliorate the primary forcing problem. And, there’s money to be made there. Now, we’d like to be able to measure from the atmosphere how effective a policy measure like that would be. And, there has to be some way of, or actually there have to be several ways of checking how effective that is.

Interviewer: Can you give an example of some research undertaken by the Carbon Cycle Greenhouse Gases Group (of NOAA GMD) that has told us something we didn’t already know about the atmosphere?

PIETER: I can give you an example of something that we discovered. It was in the late ‘80’s. Then we had a global network less dense than we have now of measurements. And we could see that concentrations of carbon dioxide in the Northern Hemisphere were larger than in the Southern Hemisphere. This was no surprise, because most of the fossil fuel emissions, the emissions caused by burning of coal, oil, and natural gas, were taking place in the Northern Hemisphere, thereby pumping up the concentrations in the Northern Hemisphere. And, it takes a while before what you emit in the Northern Hemisphere makes its way to the Southern Hemisphere. Therefore, we only saw a concentration gradient between the two hemispheres with the Northern Hemisphere a little bit higher. Well, we also had transport models of the atmosphere. And they told us for a given amount of emissions, we would expect a concentration gradient to have a certain magnitude. In fact, in those days, we expected the gradient to be about 5 ppm (parts per million), out of a background concentration of around 350, 360 ppm at the time. But, we saw only 3 ppm. And, we made the hypothesis that there was a sink that we had not been aware of working in a Northern Hemisphere taking up some of that extra carbon dioxide. And this, so far, this has held up, this finding. We could also determine from other types of measurements that the sink had to be on the land rather than in the ocean in a Northern Hemisphere. And, this is actually still somewhat controversial. Because ecologists, they tend to not find it, at least not in a magnitude that the atmospheric measurements seem to indicate.

Interviewer: Can you explain sinks and sources?

PIETER: A sink of a greenhouse gas is either a place or a mechanism where it gets destroyed or taken up. And, a source is basically a place or a process by which it’s emitted. We talk about the budget of the greenhouse gases that is to the atmosphere that is, the sum of the sources and the sinks. So, if there’s more sources than sinks, the concentration will go up.

Interviewer: Why should the person on the street be concerned about the carbon cycle and greenhouse gases?

PIETER: Why should the person on the street be concerned about climate change? When you’re talking about increasing greenhouse gases, you’re talking climate change. There’s not much doubt that they will cause a difference, we call it a radiation budget. They will retain more of that infrared radiation that’s emitted to space and thereby cause the surface to heat more. You could say the blanket will get thicker around the atmosphere. So people should be concerned about climate change because it could lead to serious social issues.

Take, for example, a country like Bangladesh. A large part of it is going to go under water. Its sea level rises. These people are going to move. They’re going to move probably to India, which may not want to welcome them. Or the Midwest in this country could dry out, for example. And the average summer temperature increases, partially because the snowfall from the mountains melts too soon, and partially because it is warmer. So you don’t get the water at the right time and it could create problems for agriculture. I’m not saying it will, but it’s, it’s plausible. Or we could suffer more intense hurricanes in the South Atlantic and the Gulf Coast. And we know that it could be very damaging. Katrina recently displaced a lot of people. Half of New Orleans has been displaced. That’s a big social issue and I think people should be concerned about that.

In a general sense, I think it’s actually very fundamental. I mean, our economy has always operated as if resources were infinite ultimately. There’s always cheap resources somewhere. And that paradigm, or that way of thinking, might be in trouble here. You could say our footprint on the Earth has become so strong that as a result of our economic activities, particular energy use, we’re changing the Earth’s climate. This could well be a fundamental limitation that we’re running up against. And, you know, it’s not only climate change. We’re overfishing the oceans. We’re creating invasive species all over the Earth, like the zebra mussel, for example, that has been invading the Great Lakes, and is like a plague for local ecosystems. We’re doing that all over the place. I think we’re basically endangering our own existence.

Interviewer: So what must we do in order for life as we know it to be sustainable?

PIETER: Actually, life as we know it is going to change. I mean, the Earth will do its thing, whether we like it or not. And we will have to change. It may not be pleasant. I’m also not saying that climate change is the only big risk that we run, or at least, it’s not the only challenge we have to overcome as a society, you know, to change our ways into a more sustainable type of economic system. I mean, sustainable in that we don’t use resources in such a way that they become unavailable for the next generation. You have to look at resources also in a very broad way. It’s more than just physical resources and biological resources. It’s also knowledge, that’s also a resource, to cope with problems that come our way. So, I’d say sustainable would be the society in which you could say total wealth doesn’t decrease from one generation to the next. And, total wealth is the sum of natural resources as well as our social resources, a knowledge base. Now, I don’t know how to weigh these things actually but we have to get into a society like that if we are to survive. I mean, if we are to survive as a society that remotely resembles the one we have.

Interviewer: What is the Carbon Cycle Greenhouse Gases Group (of NOAA GMD) researching in 2006 and 2007 that’s going to tell us something about the atmosphere that we didn’t already know?

PIETER: Now I can’t predict, of course, what we’re going to be measuring next year. We do have expectations of what we will see. Further increase of carbon dioxide, we expect that. Further increase of nitrous oxide, we’ll expect that. The increase of methane has been fairly flat the last couple of years, so not much increase–which was a surprise. And, the increase might resume next year or not, we don’t know. If it does, we will probably discover something about the budget of methane, the sources versus the sinks. It could be, for example, that because of the warming that’s already going on in the Arctic, and the melting of permafrost that is going on, that methane emissions from the Arctic regions start to increase. And perhaps next year, we’ll see the first sign of that. I don’t know. It’s possible. So we’re trying to keep track of these, of these processes by looking in the atmosphere. There are a few things that we can predict reasonably well, and others we can’t really predict very well.

Interviewer: You already have a global air sampling network in place, so why are you trying to add more sensors in tall towers? If you have all this data that is showing pretty consistently that CO2 is going up roughly two parts per million every year, why do you have to continue to get different types of data?

PIETER: Especially for the U.S. for example, or North America slightly more broadly, it is likely that there is a significant sink, a significant absorption of carbon dioxide, on this continent. Right now we really can’t tell where or why. So we need to do more specific measurements closer to where these sources and sinks are to try to untangle that. We would like to be able to quantify how much, if any, carbon dioxide is taken up by, say, soil management in the agricultural belt of this country; re-growth of the forest in the Southeast – how much carbon uptake that corresponds to.
And, again, we don’t only use CO2, but we use a whole spectrum of other gases as well, because they tell us about the different processes that are working. For example, we can see correlations between urban emissions of carbon dioxide and some trace gases. We can see a relation with HFC134A, which is a gas that is in automobile air conditioners. So when we see a high CO2 signal, when they’re relatively close to an urban area, we can then trace that to automobile emissions. And likewise, there are other tracers that signify other processes. We really try to determine why we see what we see, with all the variations.

Interviewer: If you’re able to quantify how much CO2 and other gases are stored due to agricultural and processing forest management, what will that tell you?

PIETER: It is pretty certain that the biggest contributor to the rise in carbon dioxide is the emissions caused by burning coal and gas and oil. That’s the biggest factor. It’s bigger than natural processes that counteract these emissions a little bit. So it’s uptake by force or agricultural soils. But, of course, our society will try to use such processes to ameliorate the increase of CO2 to make it less than it would otherwise be.

And, likewise, we’re now starting to experiment with sequestration and geological formations. Say you could capture CO2 out of a stack of a power plant and pump it into ground as a liquid and then compress it. And, hopefully, it will stay there. Then we need to quantify how effective is that. Because you can pump it in, but maybe it’s pumping out some other place because these reservoirs are not entirely leak free. But it may, or it may not pop out; it may leak out just gradually in some other places.

We need to have ways to monitor that the Earth is really doing what we hope it is doing. And we need to monitor that our own plans are working out the way we design them. And similarly, we need to monitor what’s going in the Arctic as the Arctic warms, because that is a potentially dangerous feedback. The Arctic, the warming of the Arctic, and the disappearance of permafrost could lead to additional emissions of carbon dioxide as well as methane that are huge. And, we could actually be causing that inadvertently because the Arctic is warming. The fact that there is so much carbon buried in the soil there, in the first place, is because it is frozen. Not much biological activity going on when the water is frozen. And we would liberate all that and make it possible for microbes to start chewing on that and eat it up.

Interviewer: Do you predict the rate of increase of CO2 and greenhouse gases will increase?

PIETER: Well, yes, I expect the rate of increase of CO2 to increase. There are two reasons, the main reason being that I expect the global rate of emissions of carbon dioxide to increase from the burning of fossil fuels. As China and India, for example, join the developed countries, at least the countries that use a lot of energy per capita, as they increase in wealth and use of resources, they’ll be burning more fossil fuels. Per capita energy used in India is still very small compared to that in the U.S. Some time ago it was only ten percent of the U.S. per capita energy use. Now, it’s maybe one eighth of the U.S., I’m not quite sure. It’s still very low. But I do I expect emissions to go up significantly in the coming decades. And, therefore, I expect the rate of increase of CO2 to also go up.

A second cause could be natural feedbacks in the Earth’s system such as warming of the Arctic which could accelerate the atmospheric increase of CO2, which would bring on further global warming sooner.

Interviewer: Describe the tall tower network?

PIETER: For many decades we’ve had the global flask-sampling network, whereby people send us air from specific locations that are typically downwind from the large stretch of ocean water. We get air that is very clean and well mixed, so that a weekly sample actually means something. It really indicates this is a concentration over a very large area. Or we get these samples from deserts or mountaintops, typically, away from vegetation, terrestrial vegetation. We’ve been measuring that for decades. More recently, since the mid ‘90’s, we decided that since the terrestrial ecosystems are a very important and dynamic part of the global carbon cycle, we need to do measurements that are closer to these terrestrial ecosystems. So, we started to move inland with our measurements and we did that by measuring from very tall TV and radio transmitters as well as measuring from private airplanes, Cessna type airplanes. So, we have instrumentation that is largely automated and goes on the airplanes, and we take individual flask samples and we analyze them here in the laboratory. In addition to that we have a bunch of instruments that are continuously measuring at some of our lab’s observatories, which are globally spread from Point Barrow in Northern Alaska to the South Pole. We have five of those. But that’s really to measure the background as it exists over oceanic areas. For example, at Point Barrow, we measure what’s coming from the Arctic Ocean mostly. But, in addition to that, we’ve also started to instrument these tall towers with continuously measuring instruments, not only taking weekly flask samples.

Interviewer: What do you see looking into the future, given the current state of the environment?

PIETER: I see serious, serious issues ahead that we have to deal with globally in a very constructive manner, not by ignoring them. We have to really reform our energy system. We have to get energy to run our society in such a way that it does not involve emitting carbon dioxide. That’s a tough job because ninety percent of our energy production now involves emitting carbon dioxide. This will have to be brought down to zero – certainly, in this century. And even then, we will likely see very significant climate change because if we manage to bring emissions down to close to zero at the end of this century, we will have emitted before that point still an awful lot of additional CO2. It’s very likely, I’d say that we would at least double pre-industrial concentrations. And there’s a whole range of estimates for climate change. But it will be several degrees Centigrade likely. So, this is a serious issue.

Now, if we ignore it, like the world still has pretty much, I mean, what I’m saying is that Kyoto is just the beginning. We have to really continue on that path, but much more aggressively. And, so, now you could say, oh my God, it’s going to cost us money. Our economy is going to collapse. And, actually, that’s not necessarily true. You could look at it as a challenge, which also means a business opportunity. I can also give you examples of countries where they cut their emissions, per capita emissions, of carbon dioxide in half, such as Sweden. From the early Seventies to the mid 1990’s, they cut their per capita emissions in half. Did their economy collapse? No. So, it is possible. But it does require serious attention and effort.

Interviewer: What got you interested in science originally?

PIETER: I got into science because I was intrigued by the theory of relativity and quantum mechanics in high school. So, I studied physics. And, then I got into theoretical physics as a student. But, I was a little bit disappointed at that point. It became too abstract for my taste. I wanted to do something that had a more direct connection with everyday life. And I ran into a little book in a bookstore, not in a library, and it was called, Inadvertent Climate Modification. This was in 1972. My first reaction was, oh, this is nonsense. I mean, how can we humans influence the climate of this planet, you know, we’re just too small for that. But I leafed through it and I saw about infrared absorption by certain gases, and I thought, okay, there may be something to that. So I bought the book. And I was convinced right then that this was going to be an important problem. That was in ‘72 and I’ve been on this track ever since. I love to do science and be hard nosed about what we see and what we learn. And, what we can really take seriously or believe and what is still speculative. But at the same time, I want to do that in a field that I feel has great relevance for human kind. You can do that in many ways. There are many fields where you can do that. But, in my case, it happens to be climate change. I also have a preference for physics and chemistry, and physics and chemistry of the Earth.

Interviewer: Is North America a net sink or a net source for CO2?

PIETER: It’s a net source, quite a large one. But again, it’s dominated by the direct production of carbon dioxide. If you take that away – because we know that the U.S. alone emits about 1.6 billion tons of carbon per year – so, if you take that away, it looks like it’s actually a sink…but not as large as the source from fossil fuel burning. And if you take that away, there is some uptake taking place in forests, perhaps more likely in the Southeast or East, because it used be agricultural land not that long ago which is now growing into forests. Carbon is being stored in wood growth. And perhaps the Midwest is a sink because of accumulation of organic matter in soils, perhaps partially due to fertilization with nitrogen fertilizers. We don’t know, but it might well turn out to be the case. So there are some compensating, partially compensating things that work in this country. But, the net, the net is still positive. It’s a source.

Interviewer: Is there anything that we haven’t asked that you would like to answer? Anything you’d like to say, or tell high school science teachers about why they should be learning and teaching about the atmosphere?

PIETER: I think I may have already answered that. This is a serious global problem we have to deal with. This is my most important message. And it’s difficult because it’s so fundamental. Our way of generating any useful energy in society is just not sustainable, at least if we want to avoid major climate change – which I think we ought to.

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The Habitable Planet: A Systems Approach to Environmental Science