Richard A. Houghton - Carbon Dioxide and a Runaway Greenhouse

I'd like to welcome you. My name is Joseph Kellendorfer. I'm a senior scientist here at the Woods Hole Research Center. Thanks for coming out on this beautiful summer evening to the Woods Hole Research Center. We're glad to have you here. Tonight's talk is the start of a three part lecture series that we're offering to the public on environmental tipping points. On September 26, we will hear from Dr. Richard Williams, who's in the audience. Hi, Richie. Who will talk about the impacts of changes in glaciers, sea ice and permafrost. And on October 24, we will hear from my colleague, Dr. Michael Koh, who will discuss deforestation in the Amazon basin and how it can lead to radical climate shifts. We also hope that you will join us for these presentations. It's my honor to introduce Kee Houghton tonight as the speaker. A couple of words on Ski. He's an ecologist whose longtime research has been on the role that terrestrial ecosystems play in climate change and on the global carbon cycle. His area of expertise is in the documentation of of changes in land use and determination of historic and current sources and sinks of carbon resulting from those human activities. Dr. Richard Houghton has held positions at the Ecosystem center of the Marine Biological Laboratory and the Brookhaven National Laboratory. Last year he was named a fellow of the American Geophysical Union, an honor reserved for those who have made exceptional scientific contributions. Dr. Houghton currently serves as our acting director of the Woods Hole Research Center. Now, many of you have known Dr. Richard Houghton for years. And like many of you, I have wondered, where does this name Ski come from? Dates back I talked to him. To an old cartoon character named Skeezix from a cartoon that maybe some of you remember called Gasoline Alley. Now how fitting for Ski to be named after a gasoline alley. And is now dealing with the carbon cycle driving hybrid cars. So without further ado, please welcome Ski Houten. Thank you.

And thank you, Joseph. You never know what you're going to learn when you come to these events. You like that? All right, well, let me add to Joseph's welcome, my own welcome to you all and thank you for coming. I'm to talk about tipping points in the carbon climate system and I'll get into exactly what all of that means. Eventually I'm going to start out with a little introduction about what tipping points might be. And it seemed to me the best way to familiarize, get us all on the same page. Was found a camel just loaded with straw. Just lots and lots of straw. So you might think of the tipping point as that last straw that goes on the camel, it has several points, or yes, several aspects to a tipping point. One, it's just a small increment, has a very large impact. In this case, one little piece of straw breaks the back. The large impact is irreversible. And it's difficult to predict ahead of time what that last straw will be. And I'm going to connect that somehow to carbon and climate. It's a fact that as carbon dioxide increases in the atmosphere, the Earth warms. That's the greenhouse effect. But it's also true that as temperatures go up, carbon dioxide is released from soil and plants and the ocean. And so if you knew nothing else but these two statements, you realize you're in a very unpleasant place because the warming raises CO2 levels, which causes more warming, which causes more CO2 emissions and so on. And so eventually you have what is called a runaway greenhouse. And a runaway greenhouse just means that the temperature goes up and up and up and up go the greenhouse gases at the same time. And a runaway greenhouse sort of by definition is too hot for life. All burning up. It's burned up. And there's some indications that Venus went that route. But anyway, I think it's very unlikely that we will have a runaway greenhouse effect. But I do think that we will exceed the 2 degree centigrade warming that is sort of out there as a safe limit. And I'll come back to that later. A couple of other examples of tipping points besides runaway greenhouses is right now the International Convention on Climate Change is geared toward our being able to manage the carbon cycle. In a sense, we can reduce emissions, we can plant trees. There are things we can think of to do with carbon that will help control, if you will, the rate of climate change or to prevent it. And it's possible that if the warming gets too much that we will lose that capacity, that nature will take over and our management effects will be just trivial. That's a tipping point. And one other tipping point that I'll come to again at the very end, just to mention it, is there's a tipping point in society. At some point we decide tip from being deniers to being outraged at the fact that we're not doing anything about it. And in this case, the straw is always temperature. And the camel could be the Earth or it could be human civilization. Here's the outline. I'm going to talk about four different pieces, a little reminder of what climate change is all about, which will probably be repeat for many of you. Then I'll Talk about the global carbon cycle, an introduction to that, talk about feedbacks. And lastly what we can do. I'm going to start right out by saying that global warming or climate change is not a scientific controversy. We know the natural greenhouse gases that are responsible for a natural greenhouse effect and the increases in those are responsible for, for the enhanced, which is what we're worried about. The concentrations of those gases are increasing largely as a result of human activity. Is this going in and out? Okay, okay. It sounds to me like it. Ok, try to keep it up. And we know the temperature's rising. So if you know these three things and you're a denier, you have trouble because you have to show either why the physics isn't right and secondly, you have to show what is causing the temperature to go up. And we know. When I say we know something about greenhouse gases, we know their properties that make them greenhouse gases. Most of the gases in the atmosphere, 99.9% are not greenhouse gases. But what determines a greenhouse gas is its radiative properties. Light can go through it easily, but heat from the earth radiated not as much, so it traps heat inside the atmosphere. The longer a gas lives in the atmosphere, if you will, the greater its effect. And some of these gases are broken down more rapidly than others. And then finally, the quantity emitted is clearly important in determining the relative importance of different greenhouse gases. And I don't want you to read this at all, but I want to make the point that on the far left there's a bar that goes up high. Those are the greenhouse gases. And I'm not sure you can read it, but carbon dioxide is as important as all of the other greenhouse gases combined. The other items along here are aerosols, solar radiation and so on. I'm not going to go into those, but the point here is that carbon dioxide is the most important of greenhouse gases under human control. The greenhouse gases of carbon dioxide, methane and nitrous oxide have all increased. This shows a graph from about 1000 AD to 2000 AD. And so you can see the last 200 years or so is when the big increase has happened in all three of those greenhouse gases. Then we passed a sort of milestone a couple of months ago. In May 2013, the concentration of carbon dioxide as measured at Mauna loa, Hawaii reached 400 parts per million. That's the first time that it's been measured that high. Measurements began there continuously in 1957. At that point, concentrations were 315 parts per million. And the best estimates for what the concentration was pre industrially, that is 1750 or before was about 278 parts per million. So we've recently seen a 44% increase over the last two or 300 years. But it's going up more steeply at present and the temperature's going up. This shows temperature from 1880 to 2005 or 6. And you can see there it hasn't gone up continuously. Other things have been going on, but in recent decades it has risen. Here's another view of the temperature, this time going back again to 1000 AD up to the present. If you look very carefully before 1850 or so, you can almost convince yourself that that trend inside the shaded area is downward. And in fact, geologically speaking, the earth should be cooling very, very slowly, but it should be cooling because it's been at an interglacial period and it's going back toward glacial. But since about 1800 or so, since 1850, the temperature has again gone up with some decades there between 1940 and 1970 when it did not go up consistently. So if you use models to predict what climate will look like or what the temperature will look like, oops, that was not the right button to push. Recovered from that there. We have some projections as to up to the year 2100. You can see there's a big range there. And that range is determined almost entirely by how much carbon dioxide and other greenhouse gases we release in the next hundred years. All of those curves assume that the carbon cycle that exists now is going to continue in the same way it always has been. And that that's just a part of all of these projections. I'm going to be talking about whether that's true or not, or whether the carbon cycle is already showing some signs that it's going to change in the direction which would make all of these estimates a lot little bit on the low side. And the other point to make about these projections is that if we look at these projections were made in the 1990s and if we look at what's happened since, we're on the high end of all those projections in terms of the emissions of carbon dioxide, the concentrations in the atmosphere, the temperature, the sea level rise and the Arctic sea loss, they're all occurring at rates that are on the high end of what the predictions were 10 years ago or so. And the adverse impacts are already evident. Just to summarize Those, in the 1990s there were an average of 200 natural weather related disasters per year. And a decade later that number instead of 200 was about 350. So the extreme events are happening with bigger consequences for insurance industries, for individuals and so on. One other thing I would just point to was in 2003, there was a record breaking heat wave in Europe. Actually, I was there, but that's an accident. That's another story. And at that point, it's that. It's the point right there. Around 2003, you can look backwards in time, you don't see anything that high. But I'm sure there were events. I don't know Whether this is one in 100 years, one in 50 years seems like it wasn't that. But it turns out that with these projections from different climate models, by the time you get to 2050, you'll have heat waves of that size scale once every two years, not once every hundred or five hundred. And all of these things, all of these weather extremes, all of these heat waves, whatever, have happened with a warming average of less than 1 degree centigrade. So if it's not a scientific controversy, why is there so much argument? What else do we need to know? I would list that we don't really know how much warming is safe. I'll come back to the 2 degree limit that's out there as the cutoff between safe and dangerous. But I'm not sure what the basis for that is. We don't know how fast it will happen and what the local and regional effects are in detail. And we're not sure about the feedbacks and tipping points. I'll come back to feedbacks later. One example of a feedback, though, is the permafrost, which Richie Williams will talk a little bit about in a month. This is a slide of the tundra somewhere in the Arctic. And all of this soil has organic matter in it. Oftentimes it's peat, very deep, rich, rich in carbon, and much of it is frozen. So as the Earth warms, as these regions warm in particular, that permafrost will thaw, make the carbon available for oxidation or respiration, and thereby release that carbon to the atmosphere as carbon dioxide, or part of it as methane. The big questions are, well, how much carbon is that, when will it come out, under what forms? And just to show some of the calculations that have been made, these are the emissions that have happened over the last 150 years from fossil fuel emissions, 365 billion metric tons over that 150 years from land use change, or think of that as deforestation for croplands or cultivation, logging, those sorts of things. A release of about 150 billion metric tons over the last 150 years. And in comparison, those estimates that have been made of how much carbon may be lost from permafrost, it's in those same ranges. It's 120 to almost 200 billion metric tons released now. I mean, if it were to be released between now and 20, 100 would be on the order of what we released over the last hundred years. And that number, 120 to 195, is larger when you account for the fact that some of the carbon released will be as methane rather than carbon dioxide. Methane is a stronger greenhouse gas. That's a feedback because the warming leads to thawing of permafrost, which leads to releases of carbon, which leads to more warming and so on. That's why it's called a feedback or a self reinforcing vicious cycle. It has different names. All right, so just a little summary to the climate part of this talk. Climate is changing. It's not a scientific controversy. And the disruption's already here in terms of food production, weather severity, melting of ice sheets, sea level rise. And those are global phenomena. You can talk about them as global averages, but they're right here on Cape Cod as well. All right, let me introduce you to the global carbon cycle. It's simple. There are only four boxes, if you will, four reservoirs, the atmosphere, the oceans and land and fossil fuels, because that's the big perturbation. I'm going to show a series of slides that have this as a basis. I want to make the point that number or graphs, colors above the 0 line or above the line right in the middle, charts up here, ribbons up here, let's say, are sources of carbon to the atmosphere. Graphs that showed up down here are called sinks of carbon. I want to get you used to the terms source and sink. A source is a smokestack. It's releasing carbon to the atmosphere. A sink is something that takes carbon out of the atmosphere. All right, so, and the units in all of this will be billions of metric tons every year. Now, these ribbons refer to the annual emissions from managing land, that is from cutting down forests to put them into agriculture or from, as I said, forestry, things of that sort. Most of those emissions were from outside the tropics. They were from North America, Australia, Europe until pretty well until 1950 or so, when the big emissions started coming from the tropics, tropical deforestation. And in fact, some of these lands are now extra tropical lands are probably, if I drew this correctly, would be actually coming down here a little bit. They're sinks Again, all of this due to management, direct human effects. Now, in contrast, we have the emissions annually from fossil fuels. And obviously this only goes to 2006, but that number has kept on going up. Those are the big emissions. That's the major driver of changes in climate. Now all of those emissions have to go somewhere, so. So we can draw the mirror image of the total emissions and those are the sinks. The question is, what are the sinks? Well, I've told you, there are four major components. And here we have fossil fuels and land. So the other major component is the atmosphere. The reason it's jumpy on the right and not so much on the left is because the left is based on bubbles from ice cores. They're not taken as rapidly or they're not as finely dispersed in time as actual measurements. The ocean has taken up another about a quarter of the total emissions. And what's this? I mean, there are the four components that I talked about and there's something missing. There's a sink somewhere else that isn't counted in the Oceans, in atmospheric CO2 or in management or in fossil fuels. And it looks as though it's unmanaged lands. It's the lands that humans are not managing. And those lands are accumulating carbon for reasons we're not entirely sure. It's likely that they're responding to a higher level of carbon dioxide and growing bigger, faster. Could be nitrogen available from human activities. So I want to make the point that there are two processes affecting the carbon balance, or let's say the carbon storage on land, direct human management effects. That effect has been to release carbon, but also a sort of an indirect or natural effect, which is taking carbon out of the atmosphere. And it's done it pretty consistently, although it has been increasing in recent times. And I'll come back to that. There's just showing that same slide again, showing the management. The effect of management is to release carbon. That doesn't mean that there aren't sinks of carbon as a result of human activity. It's just that they are dominated by the sources. So where forests have been planted, they are a sink, but it's and its management counted in this ribbon. Whereas those lands never managed our accumulating carbon. And I'm going to talk a little bit about management first. Very little. That's a good slide to show you the one effect of management. You can look at this slide and understand that not long ago there was a lot more carbon sitting on this piece of earth and it's been taken away. We use historical Maps up above, it's green is forest area in New Hampshire in 1870 and a lot more in 1998. Below is Massachusetts. And you can see there's much more forest present in Massachusetts now than 150 years ago or so. We use that kind of information, plus we use information from satellites. This is from Landsat. The red is intact Amazon rainforest. The light blues are roads and farms for a specific development project. So we use those sort of information too, to get at rates of land use change and attach a carbon value to it and calculate the emissions. Now, I can't say so much about the natural effects. We can see it's a growing sink over time, like the oceans and like the atmosphere. What I want to make the point is that this band, remember I said it sort of came up by difference. We understand the emissions from fossil fuels, from management. We understand the uptake in the oceans and the atmosphere. And this is something that just has to be there to make the carbon cycle balanced. You can't go. And we don't have methods for measuring this directly globally. So we're really not sure why it's there and we're really not sure how long it's going to continue. And that's the main point. There are two. It says three, but it really means two, I think. Why is carbon accumulating in lands not managed by humans? And will it continue? Let me jump a little bit to feedback. How would you expect the carbon cycle to respond to a warming? We can ask something called the airborne fraction. The airborne fraction is just the fraction of emissions this year that remain in the atmosphere, the fraction that remains in the atmosphere. Think of fossil fuel emissions and the emissions from management. That's the total emissions. And some fraction of that ends up in the atmosphere each year. In theory, it could vary between 0 and 1 0. If none of the emissions stayed in the atmosphere, they were all taken up by the oceans or land, then we would have nothing to worry about in terms of climate change, because the sea concentration wouldn't be changing. On the other hand, if that fraction's 1, that means all of the carbon emitted in a year remains in the atmosphere, then we would have quite a bit more rapid rate of climate change than we have had. Because for the last decades, five or six decades, that airborne fraction has been about 0.5, meaning half of what we release each year stays in the atmosphere, but the other half goes back into land and ocean. Let me. I haven't told you why. Why we're lucky, why nature's been our side but the point is, if the fact that that airborne fraction has been 0.5, say, for five decades, that means that not only are the sinks not declining as the Earth warms, actually increasing, the sinks get bigger in proportion to the emissions. And that's just, to me, that's just remarkable. It's saying the more carbon you put in the atmosphere, the more the land and oceans are taking up for reasons that we don't fully understand. So that's the point. That's why nature's been working for us, taking half of what we release out, putting it in oceans and land. And it would be nice to understand that. But there's also some indications that it is changing, that those things are saturating and they're not continuing to take up half of what emissions are. And, and if that were to happen, if the sinks on land and ocean are beginning to decline, that has several implications. More of the carbon that's emitted stays in the atmosphere. That means the rate of climatic disruption is faster than it has been. It means it's more difficult to manage the carbon cycle because we don't have this natural, helpful carbon sink out there. Instead it's being smaller, so we have to take on a heavier role. And finally, it means the carbon cycle isn't behaving as those projections that I showed earlier all assumed. So it's all in the wrong direction. The airborne fraction is starting to go up, meaning a greater fraction of what's released is, is remaining in the atmosphere. You would like to see it go down when it's not. And I have to say this is on the cutting edge. There's quite a bit of controversy about whether that airborne fraction is changing or not, or how else it might be interpreted and so on. But it's something to watch every single year just to get an idea whether the carbon cycle is beginning to change. And. All right, I have one more section besides some conclusions, and that is what can we do? I mentioned 2 degrees a couple of times, and that's sort of out there as a tipping point. Some think on this side of 2 degrees warming, it's safe, but if we go over 2 degrees, it's no longer safe, it's dangerous. But that's, it's not really based on any scientific definitive statement or study that says 2 degrees is the place. I think it's more about, more of a compromise between what scientists say is needed and what the politicians say is possible. And 2 degrees may be too much of a warming. As I made the point earlier, we have 0.75 degree warming so far and we're already seeing one. Lots of consequences. I'm ahead of myself. So this is the warming we've seen so far. Global average of 0.75 degrees centigrade. We're committed to a warming of almost twice that if we stopped all emissions. Now, that's the lag in the ocean's thermal lag. Just the oceans will continue to not cool, but slow the warming until they're up to this average temperature level. So until that happens, we're not as hot as we will be. But when it happens, we'll be almost twice as high as we've seen today. Add those two together and we're up to almost 1.5. That's getting close to 2. And one further point to make is that the Global average of 0.75 degrees is 2 times higher at the high latitudes or 2 to 3 times higher at the high latitudes. It's a global average of 0.75. But you can go to places and where it's particularly high is at high latitudes. And that's where the permafrost is that I talked about earlier. So another reason to be concerned. I want to spend a little time with this because it's a. But it's complicated, but it's also a very compelling graph. I think I'm wireless, I can move along. Here are possible targets for climate. So here's two. Here's two degrees warming. So think of a line that's going along here. Here are the dates 2020, 2040, when you might begin doing something about reducing emissions. So for example, if in 2010 you wanted to not exceed 2 in 2010, if you drew this line, you'd have to reduce emissions every year by about 2% to the 2. But if you wait until 2020, then you have to reduce emissions by 3% every year to not exceed 2 degrees. And if you wait to 2040, you're somewhere up like 10% or more per year. And if you wait till 2050, it ain't going to happen. And there's no way you can limit to 2 degrees if you've waited to reduce emissions by 2050. The other way to just say that bring the point home is there's no way we can stop at one degree. We're committed to at least one and a half degrees and probably quite a bit more. I just think that has a great. It just shows the commitment. You can think of that as a tipping point, if you will, what's possible, what's no longer possible, sorry. Whether 2 degrees is safe or not, whether it's a tipping point or not, we're almost certainly going to exceed it. Which doesn't mean it's too late. It just means the longer we go on without doing anything, 2 degrees will perhaps disappear in the past and we'll be worrying about three and so on. So to stop a warming, we really need to stabilize. We need to stabilize the concentrations of greenhouse gases. And there are really only two ways to do that. One is to reduce the emissions. We've talked about those. And the other is to increase the uptake by land and oceans. And that's hard to do. We can manage land. There are things, and I'll talk about it, you can imagine things that would enhance the uptake in oceans as well. Can we reduce emissions? These two lines show emissions in red from fossil fuel burning every year. They're approaching 10, going up very steeply. Now, the blue line is what we've calculated are the emissions from land management. So it looks from this graph as though there's very little you can do with land. I'm going to make the point that's not quite true. Not true at all. In fact, we could stabilize the concentration in the atmosphere quickly by reducing emissions by less than 50%. You have to reduce them by that airborne fraction I was talking about. And we could do that by managing forests. If we stop deforestation, that would be reducing emissions by 1 billion metric tons a year. If we allowed forests that are secondary young forests to grow up all around the world, we might remove from the atmosphere on the order of 1 to 3 billion metric tons a year while they were growing up. And if we could expand the area of forest into degraded lands and take up more carbon that way, add all of these together and you could reduce emissions or increase uptake, their equivalent for carbon by 3 to 5 billion metric tons of carbon per year. And that's a big chunk of total emissions. These again are the emissions from fossil fuels, almost 8 over this period. Now they're higher than 8. In fact, they're approaching 10. Land use change something like 1 billion metric tons per year during this decade, per year. So if we could reduce those emissions by this much, by four, we take that number, cut it down to four, we could stabilize the concentration at least temporarily in the atmosphere. I'll show you the. Here. The emissions from fossil fuels we assume are the same. But in this case, we've stopped deforestation, we've planted forests, we're letting things grow up. So instead of a source of a billion metric tons, we're taking three to five out of the atmosphere. That takes the total emissions down to four. And that this much by four, we take those that number, cut it down to four, we could stabilize the concentration at least temporarily in the atmosphere. I'll show you the here. The emissions from fossil fuels we assume are the same. But in this case, we've stopped deforestation, we've planted forests, we're letting things grow up. And so instead of a source of a billion metric tons, we're taking three to five out of the atmosphere. That takes the total emissions down to four. And that means the atmosphere might not increase at all that year because we still have uptake by oceans and unmanaged land. That won't last for long, partly because forests will grow up and then they'll stop accumulating. But it's also true that as that this number will not stay zero as these sinks get fuller and fuller of carbon. The point is you'll have to reduce emissions further, but at least for a while, you could stabilize concentration. So just let me summarize that part by saying that what the global carbon budget tells us is, number one, that deforestation degradation, land management in general accounts for 10 to 15% of emissions. The four terms don't balance. We have this thing that we didn't know existed really and has greater interest. What's driving it? Nature's been good to us so far and consistent and that you can't count on that to continue. And finally, large reductions are possible, at least in the short term. And in conclusion, I have a few more slides to go on. The highest priority should be in reducing fossil fuel use. I mean, that's the big, the big culprit, the big driver. But in the near term, I make the point that forest and land management could reduce emissions substantially. However, if the warming itself increases the source or reduces the sinks on land and oceans, that would make carbon management that much more difficult. And so we might be approaching a tipping point there. All right, just summarize up with tipping points. We don't really know enough about this particular tipping point to predict what temperature is safe and what temperature tips it. We may not even know that until it's tipped, and we may not know it until quite a while after it's tipped. That's not true for all tipping points, but this is a particularly troublesome one. And then that just we should be very careful. I think, as I said in the beginning, I think a runaway greenhouse is unlikely, But I do think we're going to exceed 2 degrees with its consequences which will include extreme weathers of floods, droughts, fires, crop failures which will drive the price of food up, sea level rise, forests die back in the Amazon for one, but in other places as well, changes in weather could change the West African monsoon, for example, and really change the climate there. So my last question, which I hinted at earlier, was what will the tipping point be for us? When will we tip from denying to outrage that we're not doing enough? And with that, it's your questions. Thanks very much.