Jerry Melillo, “Changing the Land: Environmental Stresses and the Terrestrial Biosphere's Capacity to Store Carbon” - Kendall Lecture
MARIA ZUBER: Welcome to the annual Kendall lecture. In association with this lecture, one of things we do is award the MIT Global Habitability Award. And here to talk a little bit about the award is Mr. Fred Middleton, who's sponsoring the award. And Fred graduated from MIT in 1971 with a degree in chemistry and then has a Harvard MBA, which he received in 1973.
He was a consultant with McKinsey in San Francisco after graduation. And then he and his college roommate founded the Genentech, Incorporated, which is a biotech company based in South San Francisco. And he served as Vice President of Corporate Development and the CFO there. And he is now founder and managing director of Sanderling Ventures, which is a biomedical venture capital firm based in San Mateo, California since 1987, where they work with startup companies established to develop advances in biomedical technologies.
He lives in Hillsboro, California with his wife and three children. And we're happy to welcome Fred here to say a little bit about the award. Thank you.
FRED MIDDLETON: Thanks, Maria. And I will be brief. The Global Habitability Award was started with the intention of recognizing students, faculty members, or anyone in the MIT community contributing to the knowledge of our global habitat and the sustainability of it over time. And part of the reason being that my belief is that the kind of quality science and work done at MIT, and in this department in particular, has an opportunity to enlighten the rest of the world, and in particular, public policy about these issues. And I think we're at the point where there hasn't really been yet an enlightened public policy formed around these issues. And I think it's the role of science and the MIT community to assist the rest of us in providing the knowledge and information about environmental trends affecting the habitat, and the sort of public policy that would be enlightened to deal with it in the future. So that's my thinking behind making this award.
MARIA ZUBER: OK, this year's recipient of the award is Mick Follows. And unfortunately, Mick isn't here today, because he's interviewing for a faculty position. So this award could not have come at a better time for him. But let me just tell you a little bit about what he did to merit this award.
Mick is a principal research scientist in EAPS. And the work that he did is study of mechanisms that control the flux of carbon dioxide between the atmosphere and ocean. And this work has been published in a series of papers in the last couple of years. And in this work, Mick combines a deep knowledge of the biogeochemistry of the ocean with an understanding of fluid mechanics. And what he has been able to do is develop models that describe the factors that control the air-sea flux of CO2 and other soluble gases. And he's been able to distill the essence of a very complicated process and express it in simple models that actually come up with hard numbers that can and are being tested against observations.
So we congratulate Mick. There's an award that goes with this. And when he gets back, we will give it to him. But he is delighted and asked me to express his appreciation to Fred for this award. Now, Ron Prinn will introduce the Kendall speaker.
RON PRINN: Certainly let me add my congratulations to Mick Follows for winning this award. By the way, it's worth $25,000. I don't know why people are not mentioning that. Depending on who you are, that's a lot of money. For Mick, it's a lot of money. So I'm sure-- I know he's very, very pleased.
It's my distinct pleasure to introduce the Henry Kendall lecture. But before doing so, I want to say a little bit about Henry Kendall himself. Henry, of course, was a Nobel Laureate in physics, in particle physics, and a very remarkable scientist. But this lecture does not memorialize his Nobel Prize winning work, but rather the work that he did particularly within the Union of Concerned Scientists about the global environment and great concern for what human activity might do to the environment, both now and going into the future.
And one of the things that I hope you picked up as you came in was this little brochure that is a copy of the 1992 declaration that was sponsored by the Union of Concerned Scientists. It's called "World Scientists Warning to Humanity." The text was very much the work of Henry and certainly championed by him. And it was signed by a very large number of people, including 104 Nobel laureates. And you can read that at your leisure. But in reading it, it gives you a sense of the deep concern that Henry had for the environment.
I always remember that when the Center for Global Change Science was set up, and I was just moving into some offices on the 13th floor. And I had on old clothes and I was covered with dust lugging stuff from the 18th to the 13th floor, that he rushed in. And I wondered-- I thought he was lost. I knew who he was. And he said, this is a wonderful event, that you guys are finally going to worrying about global change and so on. So we had a really nice, long conversation.
And I was most impressed with the fact that when you talk to him, he is a very ordinary guy. He just walked in the room. And as I said, I thought he was lost. And then he really had come for some particular reason. So a wonderful person. And this is a wonderful memorial to him.
Now, it's my distinct pleasure to introduce the sixth annual Henry Kendall lecturer. It is Dr. Jerry Melillo, who got his bachelor's and master's degrees at Wesleyan University in 1965 and 1968. He then went on to Yale and got a master's degree in forestry, and then followed by a PhD. That was in '72 and '77. In, I guess '67, beginning in 1967, is that right? You joined the ecosystems center? Or was it--
JERRY MELILLO: '76
RON PRINN: '76, that's it. 1976, Jerry joined the Ecosystems Center at the Marine Biology Lab at Woods Hole. And by 1988, he was the director of the Ecosystems Center. And he is now co-director of that center. And has been ever since that time.
And so he's really been in one place most of the time. However, he did take some trips to Washington, where he did some very influential things. First, he was director of NSF's Ecosystems study program from 1986 to 1988. And then in 1996 to 1997, he was Associate Director for environment in the Office of the President and played a lot of role in the Clinton administration in helping formulate policy in global change issues.
He's very well known for his scientific leadership. To just give a few examples, he was chair of the United States Scientific Committee on Problems of the Environment. That's known as SCOPE to those of us in the environmental area, and a very important committee. He then became vice chair of the International Global Geosphere Biosphere program headquartered in Sweden. He then later became president of SCOPE itself, International SCOPE. And he is now President-elect and may be about to become president of the Ecological Society of America.
Jerry has won many honors, including, most recently, he was elected to the American Philosophical Society. I've known Jerry myself for perhaps 17 or 18 years, beginning with the IGBP experience. And we shared many interesting discussions. And it was in 1991, 1992 that we approached Jerry to see if he would join the Global Change joint program at MIT, because we desperately needed some ecosystem expertise. And the great thing is that he joined us. And we enjoyed many, many joint projects.
So with that as an introduction. We are indeed privileged to have such an expert in ecosystems to speak to us today. His topic is changes in the land, environmental stresses, and the terrestrial biosphere's capacity to store carbon. Thank you, Jerry.
JERRY MELILLO: Ron, I want to join you in congratulating Mick on that award. And now that I know there's money attached to it, I'm expecting to see some very fancy vests. Those of you who know him.
Ron, I want to thank you for the invitation to speak in the Kendall lecture series. I knew Henry Kendall as a sailor first, a brilliant scientist, and a citizen committed to using science for the benefit of society. I'm delighted to continue my association with him in my mind as I talk with you today.
Let me see if I can make the technology work. At the end of J.R. McNeill's Something New Under The Sun, An Environmental History of the 20th Century World, there is a table titled The Measure of the 20th Century. Many of the two dozen entries in the table are related to either fossil fuel burning or land use, the two primary drivers of changes in the global carbon cycle. Recognition of the human's capacity to alter the planet's carbon cycle has to be one of the major accomplishments of earth system science during the last century.
Our challenge for this century is to understand the global carbon cycle well enough to manage it to promote human well-being while protecting the biosphere and its life support functions. Now, in this slide is the book cover from McNeill. And he has reproduced Diego Rivera's painting Man, Controller of the Universe. If you ever get a chance, look at it very closely. There are lots of people that you would recognize through history represented in that painting. And it reminds us of the difficulties humans encounter when they try to manage complex systems. The message is, proceed with caution.
Today, I want to give you a terrestrial ecologist's perspective on the global carbon cycle, with a particular focus on the factors controlling carbon storage in the mosaic of ecosystems that make up the biosphere. What are these factors? How are they functioning currently? And how do we expect them to function in the future? Answers to these questions should help us to think about how best to manage the global carbon cycle in the coming decades.
I've divided my talk into four parts. I'll begin with a quick review of the global carbon cycle. But as I look out at this audience, I'm not sure that that was necessary. And I'll stress the role of land ecosystems. Second, I will discuss the factors controlling carbon storage in terrestrial ecosystems in their relative importance in recent decades. Next, I will pay special attention to regional scale carbon cycling. I will give you my understanding of how the controllers of carbon storage vary in importance from region to region. In the last part of my talk, I will give you my thoughts about the potential for carbon storage and terrestrial ecosystems over the 21st century. Here, I will consider both natural and managed systems.
Now, I think we all know that over the past 200 years, humans have introduced about 400 petagrams of carbon into the atmosphere through deforestation and the burning of fossil fuels. The oceans and terrestrial biosphere have absorbed part of this carbon with the remainder accumulating in the atmosphere. Numerous pathways, as shown in this slide, connect the land-atmosphere-ocean system. The dynamic behavior of this system is determined by the relative sizes of the different reservoirs and fluxes together with the biogeochemical processes and human driving forces controlling the exchanges.
Now, this cartoon, which actually comes from a SCOPE volume, produced in a garden spot, Ubatuba, Brazil, and Ron was forced to spend one full week there as part of this activity, notes the sizes of the major pools and fluxes. The human driven fluxes and pools are outlined in red. And the natural fluxes are in black. Let me focus on a couple of-- I've got it right here-- and it's green. So I think we're going to be in good shape.
Let me focus on a couple of the fluxes. This is the natural flux between the land and the atmosphere. And just let me define two terms. That term NPP, which stands for Net Primary Production. And it is the net amount of carbon transformed into biomass per unit time by plants. And the unit of time, normally, is a year. And so this flux represents 57 petagrams of carbon captured by plants on net during the course of the year. And most of that carbon is emitted back to the atmosphere through either respiration or fires.
Ocean fluxes are also large, relative to the human dominated fluxes. And I want to point out two of the human dominated fluxes that we're going to be talking about. One is land use change. And right now, the estimates of land use change are approximately a petagram of carbon per year, 1.2 in this diagram. And this other term, the land sink, which is the uptake of carbon across the landscape, and we'll talk about where in a minute, by vegetation of all kinds. These fluxes that are represented here are averages for the 1980s and the 1990s.
This is a fairly full table. And I'll try to focus your mind on just a couple of parts of it. Carbon storage and fluxes vary by major vegetation associations, which we call biomes. Tropical forests contain the largest plant carbon pool. And they are the most productive. That is, again, annually, they produce the most plant biomass. Interestingly, tropical forests also contain the largest soil carbon pool. And this is something that people hadn't recognized for many years and only recently have we been stressing this particular point in the global carbon cycle.
Now, the tropical forest plant pool is being diminished by deforestation. And this is a prominent feature of the part of the contemporary carbon budget driven by human actions. And I'll come back to this again and again. Forest clearing in the tropics is estimated, as we saw on the previous slide, to be releasing about 1 petagram of carbon per year to the atmosphere.
Parenthetically, I should tell you that this flux is not well-understood and could easily be off by at least 50% in either direction. The uncertainty derives from two major sources. First, estimates of the area cleared each year, and second, the mass of the vegetation that is being cleared.
A couple of other things I'd like you to notice about this particular table. One of them is that the temperate-- whoops, sorry, wrong button. The temperate forests, represented in this row, contain large stocks of both plant and soil carbon, and, in fact, in the global context, are the second largest carbon pool in the terrestrial biosphere. And third are the boreal forests. The take home message here is that forests are important in the global carbon cycle. Yes.
AUDIENCE: Sorry, but for the laypersons among us, can you just very briefly explain flux? What is flux? Is flux just an exchange?
JERRY MELILLO: Flux is an exchange. The exchange in one direction or another. I'm sorry. The other thing to look at is this row right here. This row tells us something about, in this last column, the store of carbon frozen in high latitude soils. It is very large. And in a warming world, potentially quite vulnerable to decay. The decay would result in either carbon dioxide emissions to the atmosphere or methane emissions to the atmosphere, depending upon whether it takes place under aerobic or anaerobic conditions.
So this is sort of background information I'd like you to keep in mind as we talk through. Again, the key points, forests are important. Tropical forests are the major storehouse of carbon in the terrestrial biosphere. And frozen soils contain a vast pool of carbon that is potentially vulnerable in a warming world to decomposition and flux back to the atmosphere.
Now, a less busy cartoon. Early 21st century look at the major fluxes among the carbon pools. We have fossil fuel burning releasing now over 6.5 petagrams of carbon to the atmosphere. Forest clearing estimated to release another 1, so that 7.5 grams of carbon put into the atmosphere. 3.5 of the 7.5 remain. And the oceans and the land take up the remainder. That's also important to keep in mind.
Now, this is a cartoon, as I mentioned, because there's tremendous interannual variability in these fluxes. And this is represented by this graphic that was copied from Sarmiento in Gruber and then updated a bit. It illustrates the interannual variability in the uptake very well.
In the dark blue at the bottom, we have accumulation rate of carbon in the atmosphere. And the units are petagrams of carbon per year. And it looks like a cityscape. And in green, we have the accumulation of carbon in oceans and land, not differentiated, just oceans plus land. And the point is that the amount of carbon accumulated in the ocean and in the land varies substantially year to year. And we'll talk about this a little more later on.
The main interannual feature of the record is clearly correlated with climatic variations, such as the El Nino Southern Oscillation or major climate anomalies, such as the Pinatubo eruption. However, the variability does not seem to be equally distributed. And terrestrial ecosystems seem to be the culprits in the variability picture, rather than the oceans.
Now, back to this cartoon again. And it's the last time you'll see it. I want to focus on this land sink term, the terrestrial uptake term. And there are basically two questions of interests that I'm going to talk about. The first is, where's the carbon sequestration occurring? With the capacity to store large amounts of carbon in wood, forests are considered important candidates for storage. But which forests?
Are we talking about the boreal forest of Eurasia, the temperate forests of the mid-latitudes, or the tropical forests in Latin America, Southeast Asia, and Africa? Perhaps the answer is all of them. We'll come back to this.
The second question to keep in mind is what factors are affecting the net uptake of carbon in any region? And I list here a set of candidates, climate change, changes in land use, CO2 fertilization, this is the stimulation of photosynthesis by elevated concentrations of carbon dioxide, nitrogen fertilization, and here I mean inadvertent fertilization, nitrogen deposited on terrestrial ecosystems in rainfall. And in this place each year, about 9 kilograms of nitrogen per hectare rains on the city. And so, basically, we're sort of eutrophying across the landscape with nitrogen. The final candidate is ozone pollution. And ozone pollution operates to diminish the capacity of plants to take up carbon through photosynthesis.
So we have some things that are going to benefit or enhance carbon uptake, include, certainly, CO2 fertilization and nitrogen inputs. And two things that definitely are going to cause releases under some circumstances, changes in land use and ozone pollution. And then climate change, which can do a variety of things. And we'll talk about those also.
Now, approaches to estimating the fluxes between the land and the atmosphere. There are four major approaches, which I've listed here. Atmospheric inversion modeling, and Ron and his group have expertise in that area. Process-based surface modeling, which attempts to build from detailed process understanding of ecosystems to flux estimates. Extrapolations of in situ observations, such as time series measurements of tree growth across large areas, and then trying to extrapolate either carbon accumulation or release as a result of those studies. And finally, carbon cycle tracer studies that include isotopes of carbon, oxygen, and nitrogen in very creative ways.
Now, first of all, to the inversion studies. This is a summary slide of a comparison of 16 inversion models and model variance. The data show the annual mean latitudinal ocean land distribution of non-fossil fuel carbon sources and sinks for the five year period between 1992 and 1996. It's a bit of a busy graph, but very informative. The boxes represent a priori fluxes and uncertainties, those big, green and blue boxes. The crosses are the inferred mean fluxes. So these crosses here are the inferred mean fluxes for those latitudinal bands. And the vertical bars and open circles show the between-model and within-model uncertainties.
The thing to note here, I've pointed to in red, right here. And that is that the northern hemisphere estimates exhibit substantial CO2 uptake on land. So if we're looking for contemporary carbon sinks, we want to look at the land ecosystems of the northern hemisphere. By the way, the sign conversion here is the atmospheric sign conversion where negative numbers represent a sink relative to the atmosphere. I'll change that convention a little later on. And I will remind you that I'm doing it.
While the inversion model approach can provide insights into the distribution of source sink behavior on large latitude bands, they do not provide understanding of the mechanisms responsible for the fluxes. For the past decade, a small, but growing number of research teams, including my own, have been using process-based surface modeling to address the issue of mechanisms. We've been told where to look. And now we're going to try to look carefully. And that's going to be much of the message of this part of the talk.
Now, we've developed a very simple model in our group. And several of my group are here Dave Kicklighter and Ben Felzer. And they do yeoman's work and provide tremendous input to this activity. These process-based models are spatially referenced. Ours is as well. And they use information on climate, elevation, soils, vegetation, and water availability to make monthly estimates of vegetation and soil carbon and nitrogen fluxes in pools.
We run the model at a variety of spatial resolutions. But the one I will talk about today is half degree by half degree, approximately 50 kilometers on a side, at the equator. Although in the modeling activity, we carry along sub-grid square or pixel information. So that we provide some insight.
This is a reduced form model. But one of the important things I want you to notice is that it contains both descriptions of what is happening to carbon and nitrogen in terrestrial ecosystems. This is important, I think, in modeling global climate change, because the carbon and nitrogen cycles are intimately coupled in many ways. And very often, the carbon cycle rate is limited by the availability of nitrogen in terrestrial ecosystems of the high latitudes, including the ecosystems that we have outside here, especially the forest systems.
Let me show you why one might want to think about carbon and nitrogen together in a model that is trying to think about carbon storage. Simple question, will the warming of soils increase or decrease the net amount of carbon stored in a land ecosystem? And I've put up here on this little diagram some of the things that we think happen when soils are warmed. On the left hand side of the diagram, point to soil warming leading to increased microbial activity and increased respiration.
On the right hand side of the diagram, I point to two other things that can happen. One is the lengthening of the growing season. And the second, and perhaps the most important, is the increasing of the availability of nitrogen. And the reason this happens is that soil organic matter contains both carbon and nitrogen. As the carbon is processed and leaves the system as carbon dioxide, the nitrogen remains behind, is no longer organically bound, and is in either ammonium form or nitrate form, easily taken up by the plants. So you want to keep all of this in mind when you're thinking about what warming of soil is going to mean for net carbon balance in an ecosystem.
Two possibilities, if we have increased microbial respiration as the dominant response, we're going to enhance the fluxes of carbon from the soil to the atmosphere. And on net, if that is the dominant response, the system will lose carbon. If, however, increased nitrogen availability stimulates plant growth and the accumulation of carbon in the growing plants, and if that is the dominant process, we would have net accumulation in the ecosystem. Although we would have some carbon loss from the soils. Is that clear? Does that make sense?
So we set up an experiment at the Harvard Forest to test these simple ideas. This is about 70 miles to the west of here in Petersham Massachusetts. We're working in a mixed deciduous forest. And we are warming the soils with 3 and 1/2 miles of heating cable. The technology is the same technology that they use at Mile High Stadium in Denver to be able to play football during the middle of the winter.
We called them. And they told us about how they did it. And they said, what are you doing? And we tell them what we were doing. And the guy couldn't believe it. He called several people to the phone. And he said, would you repeat that? And so there we are.
But we've been doing this kind of work for a number of years at the Harvard Forest. And the results have been interesting. Initially, we had relatively small plots of 5 by 5 meters. And some of the trees were in, some of the trees were out. And it wasn't very satisfactory. But it was a deal made with the devil, because we couldn't get funding unless we had lots of replication. And there was an agricultural split plot design in somebody's mind that we had to conform to.
But later on, as the first set of results came out, and we published them in 2002 in December in Science, we got additional funding to do a very large plot. So we now have a big 30 by 30 meter plot with lots of trees in it and lots of heating cable. And the bills are becoming astronomical. And we're probably part of the problem, not part of the solution.
This is what we found. This is the set of results that we have after four years of study. And let me tell you, from the original study, we found that there was a period of time, actually, six years, when the soils were basically pumping out carbon at the rate of about almost a metric ton per hectare per year. And then, through time, out to 15 years, that dropped off. And at the end of about 12 years, actually, there was really no difference between the heated and control plots. Well, here we've been running this large experiment for four years. And the results are as follows.
We see substantial loss of carbon from the soils. 90 grams per meter squared, or 900 kilograms per hectare coming out of the soil on net each year in response to warming. This is the delta. However, the trees are also growing faster and accumulating carbon in their wood. And after four years, we've accumulated, on an annual basis, a little more than 50% of the carbon being lost from the soils.
Now, if the pattern that we saw before follows, then eventually, we're going to see that flux of carbon from the soil to the atmosphere winding down to zero. And we think it's because we're exhausting a relatively labile pool of carbon in the soils. And we're going to see this vegetation accumulation of carbon continue.
Because one of the things that we noticed in the earlier experiment is that once you make some nitrogen available to the rapidly cycling portion of the nitrogen cycle in a forest, it stays there for a long time. And each spin of the cycle puts a little in the wood and puts a little in new, recalcitrant organic matter. And the stoichiometry of the system is such that the C to N ratio in the soils, in the upper 30 centimeters or so, is 30 to 1. And the C to N ratio in wood is 300 to 1.
So if you can move one mass unit of nitrogen from the soil to the trees, you get a big carbon benefit. And we calculated that all we had to do is move about 10% of the accelerated nitrogen cycle into the trees each year to account for the carbon uptake. So it's really sort of a marginal benefit that pays big dividends in the long term.
Nonetheless, if you don't have both carbon and nitrogen in your model, you would never be able to predict this particular behavior of terrestrial ecosystems. The other reason for having both carbon and nitrogen in our model is related to CO2 fertilization. And I'll come back to this. But I want to say that temperate, boreal, and very high latitude ecosystems are basically-- their plant productivity is basically limited by nitrogen. You can put all of the CO2 in the world on those systems and they will be minimally responsive, unless you alleviate the nitrogen limitation.
Warming, in its perverse way, has a chance of alleviating some of that nitrogen limitation. And so you need both carbon and nitrogen. And my last point is that most of the models of the terrestrial biosphere currently being used, for example in IPCC, are carbon only models. This is a problem.
OK, we attempt to validate our modeling activity in a variety of ways. Some of the bars, I have to admit, are very low. But we're continually working at it. And we work on validation across scales in space and time from the eddy flux towers at the Harvard Forest run by Steve Wofsy and Bill Munger, here, to the modeling versions that Ron and his colleagues are doing, and a variety of things in between, including forest inventories. And we've worked with forest inventories in the US and also in the tropics in a very interesting process.
Now, in addition to the modeling activities, I've already shown you one experiment. But we actually attempt to conduct experiments across the globe testing hypotheses that are generated by the model. And I have three examples here. These are done by my colleagues at the Ecosystems Center.
The first one on the top is a manipulation of land use in the Brazilian Amazon. And that's a project of mine, where we've manipulated many tens of hectares looking at different kinds of management practices to evaluate the capacity of these systems to store carbon. This is in the state of Rondonia, the top picture. And the area was originally tropical forest, cleared in the 70s, 80s, and in the early 90s, converted into pasture. The C3 tropical trees were replaced by C4 African grasses that are highly productive in this area and support reasonable stocking levels of cattle.
After a pasture is in place for a decade or so, it begins to become less productive and less capable of supporting the animals. And so one of the things that the farmers are doing is testing different techniques of rejuvenating the productivity of those pastures to make them better suited for grazing cattle. And so they've got all kinds of schemes that involve the planting of rice and cotton, intercrops, different fertilization schemes, and so on. And we're trying to test some of those and look at the consequences for carbon stocks. And having the advantage of stable carbon isotopes being different between the C3 vegetation and the C4 vegetation helps us quite a bit.
That picture there is a picture of the original soil warming project at the Harvard Forest in the early spring. And you can see that we've moved snow melt out about two weeks early in this particular picture. So all of the heated plots are the ones where there is no snow cover. And this study here is in the Alaskan high arctic, north of the Brooks Range, where we're looking at the effects of warming in these greenhouses and the additions of nitrogen on the structure of these ecosystems.
And this is a warm and fertilized system that has a tremendous amount of woody vegetation growth relative to the surrounding area. And this kind of change, which is probably many decades down the road in the real systems in the Arctic could have implications for albedo and climate warming, et cetera. So we try to combine experiments with our modeling, constantly testing the hypotheses that we're generating.
Now this is, again, a cartoon of our model running at half degree by half degree, spatial scale, monthly time scale. And we use a series of-- excuse me.
AUDIENCE: Could you go back to that last picture?
JERRY MELILLO: Sure.
JERRY MELILLO: The experiments are to look at the effects of a variety of agricultural practices on carbon storage in the soils of these systems. And these are common practices that are being put in place. And we're trying to measure the consequences for biogeochemical processes, including carbon storage, trace gas fluxes, leaching of nutrients to the groundwater, and so on.
RON PRINN: Maybe questions should be given at the end?
AUDIENCE: The thing is [INAUDIBLE]. Does [INAUDIBLE] near some of the trees cause the additional melt?
RON PRINN: I think we'll keep the questions for the end.
JERRY MELILLO: Heating cable under the soil. Yeah. OK I guess that's the convention. So I'm going to move ahead. So this is a listing of the model inputs and some of the outputs. The inputs include temperature, precipitation, solar radiation, atmospheric CO2 concentration, land cover and land use, nitrogen deposition, and ozone. And these are dynamic features that change over time. The static features are elevation and soil type. And then the outputs include a whole array of biogeochemical parameters, many of which are relevant to global carbon cycle research.
Now, I want to move to some studies that we've been conducting at the regional scale using this modeling approach. We've actually worked in two regions quite intensively. One is China. And the other is the co-terminus US. And our question was, how do the different drivers of carbon storage that I listed earlier operate in those two places?
Now, in order to run the models in each of the places, we have to have background information. And this graphic shows land use change over the 1990s in China based on repeated analyses of Landsat images taken over that time. It's a wall to wall analysis. And it's an incredible data set that Professor Liu, who is at the Chinese Academy of Sciences, and his team produced, with the help of our group in the US.
And there are some transitions shown here that are really quite revealing. Changes of importance for the carbon cycle for example, would be woodland to cropland, grassland to cropland, and the expansion of urban areas. The resolution here is one kilometer on a side degraded to 10 kilometers for security reasons by the Chinese. And I want you to notice the Beihai corridor, the Beijing to Shanghai corridor, that red arc that moves down, the expansion of urban areas. And this is occurring in this ancient landscape at a breakneck pace.
And any of you have been to China recently will agree that building takes place 24 hours a day, every day of the week, 365 days a year. So it's possible to imagine that this is happening. And Landsat doesn't lie, as they say.
A couple of things I'd like you to notice. This business of grassland to cropland. This is one of the biggest changes that is occurring in China these days, where grasslands are being plowed up and turned into croplands in the north of China at quite a rapid rate. And there is also some woodland conversion to cropland, although the Chinese are trying to reforest areas, especially degraded areas that have a high probability of erosion. But this data set is really a treasure. And it will allow us, eventually, to do some very interesting land use analyses in China.
Now here is an application of our model trying to ascribe either carbon sink function or carbon source function relative to the land for the major drivers we talked about earlier, climate, CO2 fertilization, tropospheric ozone, land use change. And they are represented in the different colors. And what we have here is the cumulative effect of the various factors on carbon storage in the ecosystems of China over the 20th century.
And the black line represents the net change relative to 1900. So when the slope is negative, the system is losing, that is all China, is losing carbon from the land. And when it is positive it is gaining carbon. Most of the century in China was basically a carbon loss phenomenon. It's only in the last two decades that the net carbon balance of China is positive.
Several other things to notice, land use change is a major player in the carbon dynamics of this system. CO2 fertilization is a positive force for carbon storage. And tropospheric ozone is playing an increasingly important role in carbon storage in China, reducing plant productivity and reducing the capacity of plants to add carbon to the soils and to themselves, and store it for long periods of time.
Just a couple of things to point out. I wanted to point out the decade of the Great Leap Forward, 1950 to 1959. A lot of deforestation in China to fuel the smelters, the backyard smelters. The biggest net carbon loss year from land to the atmosphere, negative carbon storage on the land. The biggest decade was the 1920s. And on net, over the entire century, according to our model simulations, China lost 4.7 petagrams from the land to the atmosphere.
Same kind of analysis for the US. Again, the same drivers being considered. Again, land use a major player. Nitrogen deposition in the US, a more important phenomenon, than in China, according to our simulations, in terms of promoting carbon storage. And again, tropospheric ozone appearing to become more and more important.
Over the 20th century in the US, we have almost a zero net flux from the land to the atmosphere. Although, over time, there were decades of quite substantial flux. 1920 to 1929, large forestry activities in the west. Agriculture opening up in places and causing tremendous amounts of carbon to be lost from soils as a consequence of plowing, and so on.
The CO2 fertilization question, I want to come back to that. We have tried to use data from places like the Duke Forest, where they're doing these open CO2 fertilization experiments in forest ecosystems. And one of the things that the Duke Forest has shown in their experiments is that there are differences in the ability of CO2 fertilization to stimulate carbon storage in ecosystems depending upon the availability of nitrogen. And they have natural nitrogen availability gradients across this set of circular free air circulation installations. And the clear message that comes from them is that nitrogen availability is critical, back to the point that you want to have a model that deals with both nitrogen and carbon.
Nitrogen, however, is a two edged sword. While it may stimulate carbon storage, it can cascade through ecosystems and cause tremendous problems of eutrophication of water systems, for example, as well as create public health problems. This is a data slide from Chesapeake Bay, midsummer, showing low oxygen conditions in red at the top of the Bay and higher oxygen below. The circles have to do with fish catch.
But the point is that this is a serious problem. The nitrogen loading problem, and this eutrophication is largely the result of nitrogen loading, a serious problem in estuaries all across the world. And so, while nitrogen deposition may enhance plant growth on land, it can create tremendous problems in water systems. And if the nitrogen deposition is excessive on the land, it can cause dieback of vegetation as well.
Now, I want to move to the globe very quickly. I'm well behind here. But I just wanted to say that, as Ron pointed out, we've been working with the MIT Global Change Program for the last decade. And we've tried to work within the framework where possible, deriving climate change scenarios for the future atmospheric chemistry composition, et cetera, generated from a series of economic scenarios deriving from the EPA modeling activity as part of the MIT integrated program.
And I just want to show you the results of one experiment that we did that is a policy related experiment. And basically, we asked the question, how important is it, do we think, to cap ozone at current levels for maintaining or increasing carbon storage on the land? And this is some of the work of Ben Felzer. And just a couple of quick things about this experiment.
The experiment was run for the entire 21st century. The carbon emissions resulted in an end of the century carbon concentration in the atmosphere of about 800 parts per million. And the temperature increase associated with the carbon dioxide increase was estimated to be about 3 degrees C increase. So here is, first of all, down at the bottom, the consequence of having an ozone policy in place. And the idea is that with an ozone policy in place over the century with CO2 temperature and ozone as drivers in this particular case, we held nitrogen and land use constant, we see an increase in carbon storage on the land over the century with an ozone cap of about 180 petagrams. That is about the same amount of carbon stored over the 21st century as was released due to land use activities from the 1700s to the present. So it's a large number and potentially quite significant.
Without the cap, the increase is at least 20% less, at least 20% less. We have a whole bunch of variance as to how we treat agricultural lands and so on. But the point is that if you don't cap ozone pollution, you can diminish, by a significant amount, carbon storage in terrestrial ecosystems according to our simulation.
Now, moving quickly as I think about the 21st century, however, land use has to be the major issue for us. And this is an article that appeared in the New York Times on the 29th of April, the title, Forests in Southeast Asia Fall to Prosperity's Axe. It's a very interesting title. It has to do with large Chinese investment in Borneo to convert tropical rainforests into palm oil plantations. And the palm oil will be used for biodiesel. So they're working on the carbon problem, I guess, and climate change.
The investment is large, $7 billion in 2005. And this and other investments have resulted in clearing of half of the forests in Borneo. This is what the sequence would look like, starting with the large dipterocarp forests of Borneo over to your left, the clearing down at the bottom, and the resulting palm oil forests. You are going to reduce, in a very substantial way, the biomass per hectare on the land that is converted from tropical forests to palm oil plantation. No question about it, these are large losses, will not be replaced. And so when you're doing your long term carbon accounting, we have to think about that.
Brazil, the area of Brazil that I work in, Rondonia Mato Grosso, up in the upper left, an aerial picture of tropical forests in southern Rondonia. The clearing of those forests, and also the clearing of Cerrado here, that is savanna. And the planting, down here, of soybean. Soybean is being used as a food stock. It's being sold abroad, largely to China, by the way. And it is also being used, now, to generate biodiesel for the Brazilian economy. So lots of this kind of activity going on.
Back to Brazil again. And I don't mean to pick on Brazil. In fact, the Brazilians have some of the best records of deforestation that we have for the world. The government is clearly concerned. There are a set of regulations. They're trying to figure out how to move forward in the land use area. And they're very aware of the carbon cycle implications, because I work with a number of the scientists there.
This is a table that lists the deforestation record from the late 70s to 2004. Just look at 2004 for a second. Area cleared, a little over 10,000 square miles, the size of the state of Massachusetts, wall to wall. Total area cleared, about 70% of the state of Texas. If you've ever driven across Texas, it takes a long time. This is a large, large area. And so the prospects for carbon storage on land, if this kind of activity were to continue, is not a pretty picture.
I'm getting near the end now. And I want to talk about three things. In the models that we run, we can simulate with, I think, some degree of confidence a number of things. Maybe the best and the easiest thing to simulate is the consequence of land use change, if you know what it is. But there are complexities and surprises that we want to think about. And I have three quick examples.
Biogeochemical feedbacks, and this is a picture of the pan-arctic. And I just want to point out permafrost thawing. Remember 400 petagrams of carbon sitting in frozen state. If it unfreezes, two potential consequences, either large amounts of CO2 entering the atmosphere or large amounts of methane, or a combination, depending upon soil moisture conditions. Important biogeochemical feedback to keep in mind and to incorporate in forward modeling.
Disturbances, not human driven land use change so much as wildfires in places like the boreal forests. They're a dominant feature of the boreal forests today. But the question is, how will climate change change the rate and the magnitude of the fires in the future. A lot of people who work in the boreal forest are now arguing that there could be a doubling in the rate of fires. And this could be very significant in a negative way for carbon storage on the land.
And finally, threshold responses. And this is a cartoon describing the first, I think, fully coupled model, land-atmosphere-ocean model, from the Hadley Centre that looked at climate change in the future. And one of the things that their model projected was the drying out of areas, especially in the tropics, and ultimately the conversion of the Amazon basin as a consequence of soil water limitations from predominately a forest to predominately a savanna, and the consequent loss of tremendous amounts of carbon stocks. These are the kinds of things, these threshold responses, that are particularly difficult to deal with, but things we have to keep in mind.
OK I want to sum up here very quickly and talk about my look into a very clouded crystal ball. And I see the best case as being what I've put up on the board. I'll catch up with myself in a second here. The best case is a small amount of additional carbon storage in land ecosystems in the 21st century.
Let me break it down to those drivers that I was talking about. I think that the combined effects of climate change and CO2 fertilization will lead to a modest increase in terrestrial carbon stocks of about 200 petagrams on the plus side. That was very close to that 180 petagram number that I talked about. I think the effects of nitrogen fertilization and ozone pollution on terrestrial carbon storage will become progressively less important over the 21st century, especially the first half of the century. And I think by the second half, they will not be issues.
And the reason I think this is that there are a whole series of issues with either ozone pollution or nitrogen pollution that are going to begin to command the attention of local and regional governments for health, for crop yields, and for water quality. And I think they're going to be addressed in time. So I think over the century, they will become less important as drivers. And we might see in our calculation a small net increase in carbon storage as a result of a residual nitrogen benefit.
Land use change, I think, is clearly going to accelerate over the next decades and lead to further reductions in terrestrial carbon stocks. And I think that our challenge is to figure out how to make the use of agricultural lands more efficient. I see more efforts to re-vegetate degraded lands for the purposes of carbon storage, erosion control, and climate modification. But in spite of these worthy efforts, my feeling is that we're still going to lose about 50 to 100 petagrams associated with land use change over the century. The bottom line then is this small increase of carbon storage in terrestrial ecosystems of about 100 petagrams.
This small land sink could either be diminished or increased depending upon what happens with those complexities and thresholds. And I guess one of our great concerns is that one of those will become a dominant feature of the carbon cycle and this 100 petagram sink that we're counting on for retirement is going to disappear.
Now, if our goal is to maintain or enhance our carbon stocks, what should we be doing? I can't give you very good answers. But it seems to me we need to work on changes in the ways we use agricultural land. This seems, to me, critical. We have to use it more intensely, the existing lands more intensely. And we have to somehow figure out how to reduce the biogeochemical communications between the agricultural lands and the surrounding landscape. I think reducing pollution will help enhance carbon storage on land, especially the ozone pollution. And it will certainly have ancillary health and environmental benefits.
And so, in closing, I think that while our knowledge of the global carbon cycle is incomplete, we know that our current approach to managing this cycle is, in the long term, not in the interests of humankind. Finding better ways forward is essential if we want to travel the path to sustainability. Thank you.
RON PRINN: We're open to questions. Yes there.
AUDIENCE: There's a lot of things Carbon going out into the atmosphere. What is the impact of coal-fired power plants? Negligible?
JERRY MELILLO: Well, repeat the question. The influence of coal-fired power plants on the carbon emissions associated with fossil fuels. There are probably experts in the room who can answer this much better than I. I'm sure that it's significant. Is it at least 50% in the US, some energy expert in the?
AUDIENCE: It's about 25% [INAUDIBLE] 3% of the world's population in the United States of America are causing 25%
JERRY MELILLO: No, he was asking about coal-fired power plants in particular.
AUDIENCE: Mostly coal-fired [INAUDIBLE] power plants are covered beneath the power plants. [INAUDIBLE].
JERRY MELILLO: Yeah we were interested, though, in and in a number. Does anyone have one?
AUDIENCE: It's over 50% of electricity. Coal is much more environmentally intensive than natural gas. I don't have a number, but I'm sure it's more than 50% I would guess it might be as high as 65.
Jerry, in your model, what's happening in China. It's a very impressive model. But I'm just puzzled by one term, which I think is missing, the impact of both the primary and secondary [INAUDIBLE] on the photosynthetic flux. There's a number of papers by certain people like [INAUDIBLE] saying that particles suspended in the atmosphere of [INAUDIBLE] plays out on the leaves has a significant impact on the productivity. Is that not in the model yet?
JERRY MELILLO: Not in the model yet. But we've talked with Ron about including this, because I do think you're absolutely right. Incident solar radiation is a driver.
RON PRINN: In the integrated model, we are handling both sulfate and black carbon aerosols, for example. And then that affects the amount of sunlight that gets to the surface. But I don't think we've run enough, in a couple [INAUDIBLE] see what influence that would have on the carbon cycle. We haven't separated that. But it is important, because it decreases the sunlight getting to the surface, which will decrease productivity.
AUDIENCE: Is pH soil [INAUDIBLE] in the model? [INAUDIBLE]
JERRY MELILLO: It is inherently in the model, because the model is specifically parameters for each of the major vegetation types which have soil pH gradients. For example, the temperate and boreal forests tend to have fairly acidic soils in the northern areas, less acidic moving south, so yeah.
JERRY MELILLO: Yeah, well that's one of the negative consequences of nitrogen deposition in the long run. Depending upon how nitrogen leaves that system, if it leaves its nitrate, we have problems.
AUDIENCE: I was very interested in what you had to say about palm oil, because I attended a conference recently which included meeting people, leading analysts of peak oil, leading environmentalists, and leading energy scientists. And a man by the name of Ken [INAUDIBLE] who is known for his analysis of peak oil was talking about his interest in investing in palm oil. And we have very-- and then Lester Brown, who several people know, came over and joined this conversation and gave some alternative perspectives about palm oil.
Could you elaborate a little on the palm oil question. Maybe expand a little bit, if there is more of that you might be able to say about that. You also said something about some of the other changes that we're beginning to see and that people are beginning to promote or consider in terms of crops relating to biofuels, whether it be in the ethanol category or the biodiesel category.
JERRY MELILLO: The central point I was trying to make with the palm oil is that you have, currently, dipterocarp forests that store about 200 metric tons of carbon per hectare in that massive wood. You replace them with palm oil plantations that store maybe a tenth or less of the carbon. So just the very act, having nothing to do with whether it's palm oil or not, the very act of clearing the forests and planting a much smaller stature system has a tremendous impact on the carbon cycle.
Then there are related questions that one would want to think about in planting some of these energy from biomass crops. And that is, what else do they require? Water, nitrogen, et cetera, and the environmental impacts could be quite incredible. I'm talking with a group in Brazil now that the family owns 300,000 contiguous hectares in the Amazon basin. This is a vast land holding. And they want to sell the property. They have five bidders for the property. And the bidders are interested in making a single biomass energy plantation.
The land is divided into two parts. There's a plateau that is almost table land, an escarpment, and then some lowlands near a river. They're going to grow sugarcane in the lowlands, because they can irrigate it. And they're going to turn the entire plateau into soybean plantations for biodiesel. And the analysis is they could produce enough energy to meet, I think that figure was, I may be wrong, 1% of the transportation energy needs of Brazil from this particular plantation.
So I think we're going to see a lot of that kind of activity going on. And it worries me greatly, because I think there may be tremendous false carbon economies operating.
AUDIENCE: There's been considerable optimism about the potential for temperate forests to serve as carbon sinks in the past, but there's been some debate about that recently. Your study would suggest to me that the additional warming that we would see over the next several decades would actually result in net carbon release of the soil. Is that [INAUDIBLE]?
JERRY MELILLO: Well in New England, we have a lot of nitrogen fertilization going on as well. So the balance is, from a drivers perspective, not so clear. We'd have to look at which sites we're talking about. The other thing that we want to remember about New England is a lot of it is still in regrowing forests, having been cut over in the late 19th or early 20th centuries.
In Woods Hole, where I live, if you look at a picture of Woods Hole in about 1905, it is sheep pasture. And now you look at it, and it's entirely tree covered. So this historical land use and the legacy that it has left us for carbon storage is really very important to consider as well. I think, on the whole, the forests of New England are still regrowing from the harvests of the 1920s.
And so I think they're acting as a sink. And the sink could be stimulated a little by carbon dioxide fertilization and by nitrogen fertilization. And the temperature warming could reduce that somewhat, but I don't think significantly.
I think one of the other things to remember about these carbon sinks is they fill up. And eventually, you can't put any more forest biomass in place. Space, light, competition, and so on become limiting. So they're pools for a defined period of time. And then the best you can hope for is maintaining them at the pool size that they have attained at maximum.
AUDIENCE: Did I hear you say that in your model at the end of the century, we're looking at 800 parts per million carbon dioxide in the air?
JERRY MELILLO: That was a model run generated by the MIT Global Change Group. That was, John, correct me, if he's still here-- I don't think he's still here. Chris, you can correct me. Is it almost a business as usual?
AUDIENCE: Yeah, that's a business as usual assumption that we don't do anything about the problem. That's a pretty typical number by the end of the century.
What I was curious about is the relationship of carbon dioxide concentration to the temperature. To me, that's increasing the delta concentration about five-fold over the current concentration compared to the pre-industrial levels. And the temperature, based on the land surface, I think it's less when you consider the oceans as well. On the land surface, we've already got a little 0.8 degrees Celsius warming since pre-industrial times. And it seems that if you increase the CO2 that much, the temperature would increase more than that, especially when we take [INAUDIBLE] work last year that there is a lot of heat stored in the ocean. We [INAUDIBLE] over the coming decades on land.
JERRY MELILLO: Ron, want to handle that question?
RON PRINN: Yeah I think that 800 particle [INAUDIBLE] would be accompanied by three degrees Celsius global warming. And maybe twice that warming with the [INAUDIBLE] warm up more rapidly than [INAUDIBLE].
AUDIENCE: To me, that says a sharp deceleration in the global response to the CO2 carbon concentration.
RON PRINN: I believe that's incorporated in your [INAUDIBLE] is the soil warming. [INAUDIBLE] carbon loss associated. There are no further questions. We have oh, sorry.
AUDIENCE: Can I ask a very trivial question? What is a petagram?
JERRY MELILLO: Oh, sorry. 10 to the 15th grams. I'm sorry I should have mentioned that.
AUDIENCE: I'm an electrical engineer. We Don't deal with petagrams.
JERRY MELILLO: I understand. Sorry about that.
RON PRINN: Do you deal with gigatons? Gigatons.
JERRY MELILLO: Or billion metric tons.
RON PRINN: So thank you sir. Since there are no further questions, we have a very nice on the ninth floor. Very nice reception on the ninth floor, with nice things to eat and drink. Please, come on up. And that will be an opportunity also to talk to Jerry with any special questions you might have.