Dave Montgomery - Dirt: The Erosion of Civilizations

thank you very much for the invitation to come talk to you today about dirt aka soils and the one question that you might be tempted to ask is why would a geologist presume to write a book about soils another question and I'll try and answer that in a moment but another question might be why would you call it dirt because if you've taken a soil science class you've probably realized that the thing you are never ever ever supposed to call soil is dirt and there and of course lies the answer as to why I would call my book about soils dirt you can take what you will from that but my publisher did express great skepticism that a book called soil would reach a broad audience and why would I want to reach a broad audience with a book about soils well it's in great part and why would a geologist write a book about soil is it's in great part because I've come to view soils as a strategic resource and I don't think that soils are tend to be viewed all that broadly in society as a strategic resource let alone one of the most fundamental and strategic of the resources that we have on this planet we tend to think of oil perhaps even water as a strategic resource but the problem of global soil degradation in my view is one of the most underappreciated environmental crises that we face as a species living on this planet and this talk and indeed this book is an attempt to essentially raise the profile of the issue of soil degradation because it does really matter to the course and fate of human societies and I'm not trying to argue that soil is the ultimate answer to all the problems that have plagued modern or ancient society and because in part there's no real mystery that some of the key controls on the longevity of human societies are things like climate change the Viking colony in Greenland was greatly impacted by the cold snap of the Little Ice Age that greatly curtailed their efforts to colonize that environment natural disasters can greatly impact human societies particularly small human societies like the Bronze Age civilization on the Greek island of Santorini that literally disappeared overnight when their Island home world exploded out from beneath them politics war and social evolution the whole problem of human and II not being able to sort of share toys peacefully with their neighbors every now and again it's obviously one of the things that has greatly shaped the course and fate of human societies and I'm not trying to argue that these three fundamental drivers have not contributed to the longevity of human societies but what I do want to ask is the questions what about soil the because the fundamental condition for sustaining a civilization an agricultural civilization like ours and most prior ones is it is sustaining the soil itself and its fertility and if we look at the you know having written a book with the title like I put on this one kind of telegraphing the answer that I think the way that people have treated soils throughout history has been a component of the element of the longevity of human societies and the common story that I sort of read in that history is the basis for this book and why I would actually try and go through that argument so if you've read environmental histories you've probably run into the argument that soil erosion resulting from deforestation was contributed to the demise of ancient civilizations around the world those societies listed over on the right-hand side of the screens behind me are places where people have made that argument and I cut my geomorphological teeth and actually maybe I should ask how many people here know what a geomorphologist is how could you all do this is easy but for those of you who might not have heard the word before a geomorphologist is the kind of geologist that studies the evolution of topography essentially what shapes the surface features of the earth and I cut my geomorphological teeth down in the Oregon coast range studying problems of erosion what happens essentially when you when you under the guise of timber management to the soil arguments of how fat much erosion increases and I was able to document that the rate of land sliding in the Oregon coast range jumps by at least an order of magnitude following timber harvesting but if you actually look at the pace of soil erosion at the landscape scale the numbers don't add up for deforestation to be the simple cause of the kind of wholesale loss of the soil that has been argued to plague many ancient societies why well because it has a great impact on a small area that can tremendously impact downstream stream channels but it's not spread over the entire landscape I started me to thinking well what if the culprit in ancient societies in terms of the argued effect of soil erosion wasn't simply deforestation but it was the agriculture that followed that the key process in keep and eroding soils in other words might have been the plow and not the axe that's the the process that I wanted to explore in the development of this book to address this question could agricultural soil erosion and degradation limit the lifespan of civilizations this book is essentially an attempt to explore the issues that relate to that as it applies to as many ancient societies as I could synthesize the data for and actually then look at the implications for the next hundred years of our contemporary global society and obviously I think I'm sort of telegraphing the answer again by having written this book and framing the question that way that I think there is a connection there if you'll bear with me for the next 40 minutes or so I'll try and essentially lay out the case starting with a bit of history and then going into sharing a bit of the data from modern studies that try and address the question of whether or not this is a reasonable hypothesis to argue for let's start though with a figure from the from the United Nations that looks at the state of soil degradation today simply to lay the case that soil degradation is a global problem it really is a global strategic problem if you look in terms of the long-term prospects for our species I'm not going to quibble about the definitions of very degraded soil versus degraded soil and I'll be the first to point out that this is painting with a very broad global brush there's areas in terms of in the Amazon that I've been to that are on this map that really don't have degraded soil this is painting with a fairly broad brush it's meant however to essentially illustrate the problem of soil degradation tracks pretty much wherever people are that there's a very strong connection around most parts of the world and that it's a problem of great global concern why well because over the past 40 years or so in essentially over my lifetime soil erosion has caused farmers to abandon something like 430 million hectares of arable land an area equivalent to about one third of all present cropland an area equivalent to the size of about India and China combined when viewed globally and if you look at the problem of feeding the world out 50 years from now we're going to need to essentially increase agricultural production by about at least a third in order to feed the population that we expect to see coming and that's if we maintain productivity about the same rate imagine what the case might the prospects might be for 50 years out if we haven't lost a third of our cropland in the last century at present the estimated rate of world's soil erosion is in excess of new soil production and I'll talk more about that a little later in the talk it's something like 23 billion tons per year or about 0.7 percent loss of the world's soil inventory each year now that's less than one percent a year should we be worried about it well if you think like a geologist something that's even being lost at a half a percent a year you'll essentially run out of it in two centuries now I'm not trying to argue that we're actually going to run out of dirt in the next century or so but I present these data from Pimentel at all essentially to make the point that the pace that we're losing soil globally is not in fact sustainable other things will come into play argue to limit the pace of soil loss and there's a fair amount of variability of what those might be but the key point is is that we'll have to deal with the problem of soil erosion and degradation in the next century and we can either deal with it proactively and as I'll try and argue restore soils globally because it can be done or we'll deal with it indirectly by essentially dealing with the degradation and loss of agricultural productivity and with all the negative consequences that that may entail for society well let's go back to the history I promise to start with there and let's there's been recent archeological studies that have showed that soil erosion played a role in the demise of ancient civilizations and Neolithic Europe classical Greece Rome the southern United States and Central America in all these areas climate changes relations with neighbors all influenced their civilizations as well but the case has been made that soil erosion played a role in their decline and I'm not going to go through all of those civilizations today I try to go through all of them in the book and paint the common elements of the story but I will go through a couple of them but what I want to do first is to invite you to think about soils the way geomorphologist does why well in part because I'm a morphologist so let's give all get on the same page and it's fairly simple to think about soils as a system that are produced from the weathering of rocks rocks break down to create you know two smaller pieces and then the rock forming minerals get transformed into secondary minerals rocks break down by weathering processes get mixed with biological matter both living and dead to form soils and if you're on any kind of a sloping surface you know whether it's a very slight slope or a very steep slope the soil on it is moving down slope at some pace whether from trees falling over and their roots pushing it on down slope or geologists walking along and kicking rocks things tend to go downhill and so if you look at a soil as a system that's produced from the weathering of rocks to create soil and the erosion of the soils on the slopes that eliminates it you can think of it in terms of an analogy to your bank account you have income in which you know you make money you have expenses whereby you spend it and you have hopefully some savings that are essentially your money in the bank that you can draw down in bad times and build up in good times soil is fairly similar you can think of as that kind of a system it's it's produced in the weathering of rocks it's lost through erosion and the soil sitting on a hillside is quite literally nature's capital that's essentially there that can be used to produce plants if you think about it that way think about what happens to your bank account when you spend money faster than you make it eventually you run out of your savings you could having done this several times myself you can burn through your savings and a shockingly short amount of time soil is no different when you view it as this kind of a system other than maybe the timeframe over which it may be lost but people I think don't tend to think about soil as a system that's produced that's lost that's stored that essentially needs to be thought of as a system and soil scientists and geologists think about it that way and if you take a more bit of more of a complicated cartoon diagram view of the world as shown on this slide I want to make sort of to basic points on well three basic points one you can formally model mathematically the production of soil the erosion of soil we could express things in terms of equations I'm not going to do that today I'm going to try and keep it at the conceptual level but there's two big conceptual points I want to make and first is that soils are incredible locally adapted under native vegetation a typical soil thickness will tend to develop that reflects the local climate vegetation topography and geology there's something like 200,000 different discrete identified name types of soils on the planet and I probably have the numbers wrong I'm probably under estimating it but they're very very variable but the thing that they have in common is that essentially over time any net difference between soil production and soil loss will result in a change in soil thickness if soils are eroding faster than they're being reformed then you're essentially running out of them the question is how long by the end of this talk I want to share data with you that essentially tries to use modern data that quantifies an answer to that question and brings it back to bear on the problem of the longevity of civilizations well this idea that soils essentially are a self-regulating system that can form a typical soil thickness that reflects local conditions is not a new one by any stretch of the imagination guy named John Playfair in 1802 in a book that essentially founded the modern discipline of geomorphology if you want to stretch it a little bit wrote that in the permanence of a coat of vegetable mold and that was the Victorian term for soil in the permanence of a coat of vegetable mold on the surface of the earth we have a demonstrative proof of the continual destruction of the rocks and cannot but admire the skill with which the many the powers of the many chemical and mechanical agents employed in this complicated worker so adjusted as to make the supply and the waste of the soil exactly equal to one another now other than pointing out that in the early 19th century you can get away with writing books that had sentences that went on for pages I want to point out the essential wisdom of play first statement he was basically arguing quite explicitly in his analogy that if you went to a hillside and you dug a trench and you measured the thickness of the soil and then you went away for a thousand years and he came back and did it again and then did repeated that for ten thousand years you would find that the hillside would have roughly the same amount of soil on it every time you came back because the rocks were being broken down at the same about the same pace that they were being eroded off a lot of erosion was happening but it was being replaced by soil building processes so the idea that soils are a self dynamic self maintaining system has a couple hundred years worth of scientific pedigree behind it but it's my contention that the invention of the plow fundamentally altered the balance but soil production and soil erosion on dramatically increasing soil erosion on those lands that most societies have used to grow food the arguments not actually limited to the plow but it's a very convenient foil to hold up against the axe the way that I was essentially framing at the start in other words at agricultural soil erosion by leaving by leaving the ground bare and vulnerable to wind and rain for some time of the year the pace of soil erosion can race ahead the pace of the pace of soil production at a pace that can actually result in the loss of the soil over time frames that are relevant to human societies thetan is this a reasonable proposition well think about if you walk around in sort of native vegetation almost anywhere in the world outside of the true outside of the truly arid desert regions of the world there's vegetation covering almost everything in grasslands there's very little bare ground the grass is covering it in the forest there's very little bare ground leaving ground bare and vulnerable to wind or rain can literally allow a century's worth of soil erosion to occur in an afternoon and it has in many societies and it still does in our society in many areas let me get to the history I did promise that and I'm going to talk about classical Greece is probably the dominant historical example today and then I revert to talking about the colonial United States in a few minutes but cycles of soil erosion and Fort soil formation in ancient Greece began with the Bronze Age erosion event right after the introduction of plow based agriculture when the plow arrived from the Greek Peninsula from points east the soils on the Greek landscape have been argued to essentially have been started to erode off this is not work that I did tear drain handle and Chris Reynolds did this back in the 1990's when they had the audacity to work with geologists and archeologists actually working together to understand a landscape and sort of pioneering the discipline of geo archeology their contention is that the Greek landscape was open oak woodland right after D glaciation and that you had sort of a 1 to 3 foot thick soil that developed on top of rock on the hillside soils and that farming in the Greek landscape apparently started in the valley bottoms which in many societies that's where it starts why in the valley bottoms well it's flat easily worked land there's not a lot of rocks in the in the eluvian that the rivers deposited there and the water is delivered to you you go up on the hillsides you've got to get the water to the hillsides and you have to deal with the problem fair rocky ground at times but what happened to Greek landscape is that as the population rose farming spread up onto the hillsides and cultivation have essentially reached up onto the hillside environments at that point soil erosion started to race ahead of soil production and over time the soil has stripped off the upper parts of the slopes and deposited down in the valley bottoms leaving behind bare rocky ground and it has been argued I am NOT certain myself what to think of this but it has been argued that the sort of Mediterranean diet of olives and grapes as the key components of it is essentially a response to the extent of bare rocky ground and upper hill slopes because those plants actually like to grow in bare rocky soils but the key point in terms of agriculture is that if you take all your soil and you pile it up in the valley bottoms you've lost the ability to farm much the landscape why well because the ability to farm doesn't depend so much on the amount of soil on the land it depends on the surface area of soil how its distributed you take it and pile it all up in one place you can only work the surface did this matter to Greek society well the figure that I found in vandals and Runnels work that really started me thinking about this problem was this one that's up on the board now I they had the audacity to reconstruct a population density of the southern Argyll at a particular region in southern Greece from about 6000 BC over on the left-hand side to the modern world on the right hand side and you'll notice that there's essentially three cycles population runs up in the Bronze Age crashes in the Dark Age before the Classical Age runs up again in classical Greece and then crashes to a second Dark Age before running up to the modern age and there's two aspects to that curve that I think are worthy of note one is trivial and the other is actually I think really important the trivial one is why does the amplitude go up through each cycle and I think the obvious answer to that is technology people armed with nitrogen based fertilizers and John Deere tractors can grow a lot more food per hectare than people who have digging sticks there's just no doubt that modern technology is more efficient for growing food than Bronze Age technology but what explains the periodicity or at least the apparent periodicity is something with sort of three cycles we were still talking a parent but what about it why is several thousand year run up a crash for another couple thousand years a run up for a thousand years or so and then another crash for a couple thousand years and if this is a pattern that's generalizable what is it you know what does the last you know how do you project this point further off to the right and had and what are the implications for thinking about it globally why this run up crash run up crash could it be that soil erosion and then the timescale it takes to reproduce soils could be essentially setting the long wavelength periodicity of human societies in this region and what would be the implications if that was so for modern society clearly the answer to that in great part depends on data we do not have for classical Greece that would be what is the pace of soil loss what's the pace of soil production how out of balance may they be that's where I'm going to try and turn after we go through a little more history to some modern data because we actually have data in the modern world where we can test that for this moment in time whereas we didn't have geomorphologist running around quantifying things back in the Bronze Age we did though have Plato back on the 3rd 4th century BC Plato noticed the erosion that had happened in the Greek landscape and argued that the erosion of soils off the Greek landscape was limiting the ability of the landscape to support the kinds of large armies that it had in earlier times what was he looking at he was looking at the evidence for the Bronze Age Bronze Age soil erosion event in his own words he wrote that the rich soft soil has all run away leaving the land nothing but skin and bone but in those days the damage had not taken place the hills had high crests the rocky plains of fellows has covered with rich soil and the mountains are covered by thick woods of which there are some traces today now not a lot of my reading of plato is that he was basically taking observations that and integrating them into this statement that could be interpreted as recognizing the Bronze Age soil erosion event he didn't get a lot of support or credence for these ideas and about until the time that vain angles and Runnels were putting together the geo archaeology of southern Greece why well because he these words are taken from one of his dialogues where he discussed the history of Atlantis and it's not sort of recognized as one of the most you know credible of early scientific sources I think though that he actually had some natural history ish insight into the way that the landscape the way that people treated the landscape was a what influenced the way the landscape was actually able to support human societies and in that sense we can consider him sort of the honorary first geomorphologist oh that might be a little controversial among some of my colleagues well let me skip over you know a couple thousand years worth of history and many societies where I will argue to you that the story of the Greek landscape was repeated in different places with different technologies with much the same result but fewer perhaps cycles and let me talk about colonial North America why well there's actually great wealth of historical documentation from colonial North America and a great story in terms of the role of soil erosion on shaping contemporary American society let's start with a letter from from George Washington to Alexander Hamilton in 1796 where he wrote about complaining about the erosive erosive practices that colonial farmers used on their plantations and Washington's words he wrote that a few years more of increased sterility will drive the inhabitants of the Atlantic states westward for support whereas if they were taught how to improve the old instead of going in pursuit of new and productive soils they would make these acres which now scarcely yield them anything turn out beneficial to themselves Washington was basically arguing that the future of the United States in the earliest days of the country lay in westward expansion across the Appalachian not because of some kind of manifest destiny to overrun and civilize a continent that argument came a century later it is a bit of social reverse engineering he was making the argument based on the idea the farmers on the eastern seaboard were exhausting the soils fast enough that as an agricultural nation we would have to go to the other side of the mountains to stay in business Washington was a plantation owner he was very concerned with the role of soil erosion on agricultural lands in the in the southern United States what way why was a colonial a Greek ocean so erosive well in part because tobacco and cotton were very erosive crops to grow in the way the colonial Agrico or treated them there's a whole section on the book that goes into the causes for that and how it actually contributed to the run-up to the American Civil War but let me simply tonight today focus on the how much soil erosion happened as a result of colonial agriculture in the southern southeastern United States this map shows you the answer to that it was put together by Stan Trimble a couple decades ago and it shows the extent of historical soil erosion a post colonial soil erosion in the Piedmont region or the upland region ranging from Virginia up there in the upper left-hand corner down to Alabama in the lower right-hand corner so we're not talking about the coastal plain whereas relatively flat and erosion wasn't as big a problem we're not talking about the Appalachian swear they weren't farming it but we're talking about the upland hill country farms throughout the southeast I didn't notice that most of it has lost four to ten inches of soil that gray color across there some of it more than 10 inches of soil is that a big deal or a small deal there's only about a foot of fertile black topsoil across this region to begin with so if over 200 years of colonial agriculture we were able to erode off most of the soil across a fairly broad region of a country that was fundamentally dependent on agriculture for its national economic livelihood think about what the Greeks and Romans could have done to their home lands with a thousand years at it think of what the Easter Islanders could have done it with a thousand years at it think of what the Chinese did endure in Oh at the edge of the Tibetan Plateau it was several thousand year run at it I know is the idea that sustained soil erosion from agricultural activity could lead to wholesale loss of the soil starts to become not such a crazy idea when we can demonstrate that it happened in my own country in historical times well the extensive soil erosion across the southeast did not occur because people are ignorant of soil conservation practices Thomas Jefferson invented new kind of plow to do contour plowing to try and reduce soil erosion washing George Washington experimented with filling in gullies with his plantation garbage to try and essentially slow down the pace of erosion Patrick Henry the famous guy who I think said live free or die or something close to that also said he who fills the most gullies is the biggest patriot or something close to that soil erosion was recognized as a big problem in colonial America why wasn't it solved the kinds of techniques that were brought up in the aftermath of the Dust Bowl in the 1930s when soil erosion became a big high-profile issue to the general public all those techniques is the quote on the lower right shows were known to the colonial farmers at during the time when all that soil was stripped off the southeast this brings up the question of why would an agricultural society engage in widespread practices with known solutions but not adopt them in a way that would undercut the but the essentially what should be perceived as the viability the country in the long run well a sociologist named Anthony Craven I think hit the nail on the head in 1925 when he wrote men made because of ignorance or have it ruin their soils but more often economic or social conditions entirely outside their control leader forced them to a treatment of their lands that can end only in ruin in other words farmers can become trapped in social cultural and economic systems that encourage or require them in order to stay in business as a farmer to essentially treat their land in ways that does not preserve the soil over the long run and in that sense the misalignment of individual incentives and large-scale societal incentives becomes a theme that I think plays through this problem of agricultural soil erosion and degradation and that's actually the hardest problem to solve in but I think Craven had the right idea when he essentially said that if you're if you're responding to very short-term stimuli the need to actually pay off the machinery you have for the farm pay off your Agri the agro chemicals you bought this year pay off the bank to actually pay off the farm you can actually be trapped in the model of maximizing short-term production at the expense of the ability to produce over the long run and therein I think why in a nutshell is one of the fundamental problems that Agriculture's had for a long time in many societies well I can't actually talk about soil erosion in North America without talking about the Dust Bowl so I'll reduce it shamelessly to simply one slide there's this great quote by this first chief of the Soil Conservation Service you Bennett who in 1941 in talking about how it was the array of to establish the Soil Conservation Service in the United States he wrote that I suspect that when people along the seaboard of the eastern United States began to taste fresh soil from the plains two thousand miles away many of them realized for the first time that somewhere something had gone wrong with the land you were not supposed to be eating your bagels on the street of New York City with a light dusting of Nebraska and Kansas soil this is you know when the great clouds of soil made it to the urban population centers on the eastern seaboard the idea that something had gone wrong with American agriculture really started to gain credence in the population centers where policy was decided and the Soil Conservation Service was established in the mid 1930s and I just want to quickly disabuse you of any thoughts that might have actually solved the soil erosion problem in the United States and this is not to denigrate the work of the Soil Conservation Service as I write in that the the preface to my book it's one of the most innovative and I think important governmental institutions ever invented with an incredible mission and they've cut down soil erosion in the United States but probably a factor of two or three but they haven't solved the problem this and and this slide of a winter wheat field in western Washington I'm sorry Eastern Washington the Palouse region of Washington on the dry side of the state shows the problem of why a geomorphologist would look at farming as essentially a long-term problem in the weights conventionally has been practiced with plow based agriculture you'll notice that this is this field doesn't have a lot of vegetative cover it's during the offseason and you'll notice all these little channels that are carved into it those adju morphologist would call those rills which basically means a little channel and you could plow right across them to essentially be an inconvenience for the farmer whose field this is but it wouldn't necessarily in any one year be a terribly major inconvenience but they add up over time this slide shows you a fence in the upper left-hand corner and that fence surrounds a water cistern that was put in around a winter wheat wheat field in 1911 also in eastern Washington in the Palouse region that was first broken the sod was first broken in 1911 and between 1911 and 1961 essentially the the ground surface was lowered between that upper orange line and that low orange line creating a cliff around the water cistern much like the kind of things that Plato is looking at in classical Greece around olive trees that the farmers didn't plow over well how big a deal is this you may not be able to see very well on this negative but there's a stadia rod there's a little black bit right above where my finger is there you can probably barely see it shows up a little better than the negative but it's basically a five-foot cliff on five feet of soil eroded between 1911 and 1961 that's a foot a decade that's about an inch a year there's no place on the planet that soils form that fast now is this an extreme example well of course that's why I'm using it but it's an illustrative one if soils can essentially road off agricultural fields at the pace of an inch a year when they're subject to that kind of a repeated real erosion it doesn't take a lot of imagination to think that it could add up to a significant effect over a few centuries but how typical is that I've already admitted that's an extreme example how extreme is it well in researching this book I did something that has become increasingly rare to do I went to the library and and I went there for about three weeks I just copied every paper I could find where there was data on rates of soil erosion both from agricultural systems and long term natural rates of erosion why pull because long term geologic rates of erosion if you think back to that quote from John Playfair are probably about the pace of long-term soil production at least if there's always been soil on a landscape than the rate that the rocks are being eroded is about the rate at which the soil is being produced and I basically collected about 1,400 papers and this graph it's one dimensional graph it shows you the fruit of that data now I wasn't able to put data like this in the book because the book is aimed at a popular audience and I was assured that if I put a whole bunch of XY plots and some probability distribution functions and any calculus into it you know nobody at Barnes & Noble is going to pick the book up and do anything other than go and put it right back down the shelf and the goal is to try and actually reach a broad audience but I also being a scientist I didn't want to a book that made the argument that the pace of agricultural soil erosion could be fast enough to be a societal of concern without actually doing due diligence on collecting the data and determining for myself whether I believe my own argument this is the data that helped push me over the top it there's the y-axis is erosion rate you'll notice it's a logarithmic axis so it goes from the pace over on the left-hand side from a ten thousandth of a millimeter a year over to on the right a hundred millimeters a year decimeter a year you know incredible erosion rates vary greatly over the surface of the planet those places there's four kinds of data that I've shown on this graph three kinds of geological erosion rate data those are the white circle the white data symbols and the black ones are essentially a conventional plow based agriculture let me draw your attention to the white ones first everybody's heard the word kraton before it's it's a flat dead part of a continent it's essentially the American Midwest the heart of Africa the Amazon basin low gradient terrain that's roading really slowly and you'll notice they erode at rates of about a hundredth of a millimeter a year or less in other words fairly slowly if you think about that as the long-term pace of soil production in those landscapes it's also very slow soil mantle terrain that's like the rolling hills of California and Tennessee probably most of northern Europe those areas erode at rates of a millimeter a year or less soil mantle terrain and crayons are the places that we tend to farm you notice that Alpine and glaciated terrain places we don't tend to farm eroded paces greater than about a millimeter a year or so and that's a fairly simplistic reading of that figure but it holds up pretty well notice where conventional plow based agricultural data plots all those black lines all those black data points they at the high end of the soil mantle terrain and in the Alpine and glaciated terrain if you basically this two basic conclusions one can draw from this fairly simple plot first one is the upper one in the bottom that conventional farms are roading like steep Alpine topography we've managed at a global scale to turn places that we grow food that places that are in the cratons in the soil mountain terrain that are not typically in the high alpine terrain we've turned it into places that road like a high Emily um this is actually quite a trick um the second one is that that red line that I've added now is the range of USDA soil loss tolerance values they range from about 0.4 millimeters a year to a millimeter a year and that's what the USDA uses to define sustainable agricultural soil loss from the sustainably sustainable agriculture from a soil loss perspective those rates were established essentially in the 1950s as a result of both economic and scientific criteria we've learned a lot about soil production since then and you'll notice that that red line sits the far right side of the soil mantle terrain and it cratons the places we actually grow food and farm and therefore I'll submit to you that this demonstrates that can that and notice that there's sort of a much of the modern agricultural data lies to the right of those values and that conventional agriculture is unsustainable in soil math landscapes the way that it's defined by the USDA they're acceptable soil toss alarms values are not actually sustainable why because the soils aren't built back as fast as those paces allow them to be lost and that goes back to the bank account analogy okay that was the bad news slide believe it or not this is the good news slide this is the slide that essentially adds a second dimension and it's a probability distribution function this is the one I was assured was a deal-killer for a popular book basically what I've done is I've shown the two kinds of data that I showed in the last slide and I've added three more data sets the ones from before are shown in black so that lower black line over and on the graph is that all the geological erosion rate data or have combined the three different physiographic types into a single curve the way you would read that graph is if you want the median or average value you'd go to the 50th percentile read up go over to the left and that would tell you what the erosion rate for the average was but this shows you all the data the full distribution that upper black line that's the the conventional plow based agriculture data but what are those other three data sets that are shown on there in white symbols the upper one that the circles is soil production data there's an awful lot of data that's been produced on great rates of soil production over the last few decades and I was able to generate enough data to generate a pretty reasonable curve there's the white triangles our date erosion rate data under native vegetation what's the natural rate of erosion in landscapes around the world and the little diamonds are erosion rates for conservation agriculture no-till agriculture that doesn't use a plow that instead uses seed drills to plant through the crop stubble from last year or for highly terraced erosion highly terrorist agriculture agricultural techniques that prioritize soil conservation and therein lies the good news because you notice all those white datasets live pretty much on top of the long-term geological erosion rate data set the only one that's a stand out is the conventional agriculture data set in other words the bottom line is not is that the problem is not that we farm the problem is how we form the problem is that the kinds of agricultural methods that could conserve the soil over the long run are called alternative agriculture now there's one other set of data that want to get into before I pursue another side discussion and that is that if you look at global erosion rates over all of geologic time it's another way to slice the puzzle um and Bruce Wilkinson a colleague at the University of Michigan did this back in 2005 when he basically integrated all the sedimentary rocks in the world through different areas of geologic time to figure out how fast the planet has been roading since before the evolution of land plants you know it's the whole game what he basically determined is that over the last half billion years the last five hundred million years the Earth's terrestrial environments have been eroding at a pace that averages about an inch every fourteen hundred years or so and if you look at the sort of average rate of soil production at present according to the USDA it's on the order of about an inch every five hundred years it's not all that different from the compilation that I just presented but if you look at the average rate of soil erosion at present it's about an inch every 60 years integrated over the whole planet in other words the pace of soil erosion has been jacked up by at least an order magnitude by human activity and this is something that you know any way you slice it whether you look at the sort of anecdotal argument from ancient societies you look at the modern global erosion rate data or you look at erosion rates over geologic time the they all point to the same implication that were slowly but surely using up the Earth's supply of fertile soil well what does this mean back to the theme of the longevity of human societies well notice that the average rate of soil loss under conventional agriculture was somewhere north of about a millimeter a year on those compilations that I showed you let's be a little conservative called about a millimeter a year or so and note that the net loss of soil at that pace of about a millimeter a year implies that erosion of a typical 1/2 meter to 1 meter thick a 1 to 3 foot thick section of soil would only take about five hundred two thousand years and that's approximately the lifespan of most major civilizations outside of the major river floodplains that tend to be referred alized from erosion off of upland areas Egypt has been fertilized for scent for millennia with soils eroded off of Ethiopia I need to did fine with that until they built the Aswan Dam and even turned off the supply of the soil recycled from erosion Ethiopia I obviously don't think there's a coincidence between that sort of casual time scale correspondence between the time you would predict using modern quantitative data that would take for a region to essentially burn through its allotment of fertile soil using conventicle techniques that have been conventional for millennia and the approximate lifespan of most major civilizations and again that's with the eyes of a geologist five hundred years to two thousand years that's about a thousand years it's a privilege of being a geologist obviously there's going to be other factors that affect any civilization of society anywhere in the world at any time through history soil is not the only game in town but I will argue that it's sort of a fundamental basis that helps set the long wavelength periodicity of the prosperity and decline of human societies that I think is actually a very good argument and I'm not the first to make that argument by any stretch of the imagination Walter Loudermilk fifty years ago wrote that here in a nutshell so to speak we have the underlying hazard of civilization for by clearing and cultivating sloping lands for most of our lands are more or less sloping we expose soils to accelerated erosion by water by wind and in doing this we enter upon a regime of self-destructive agriculture this problem has been recognized at very high levels in societies in the modern area Franklin Delano Roosevelt wrote in a letter to the governors of the then 48 states that a nation that destroys that soils destroys itself in the aftermath of the Dust Bowl his words I think are as true today as they were then and they will be increasingly true or increasingly important and pertinent over the course of the next century as we either try and wrestle with the problem of global soil degradation or we simply put off dealing with it the question therefore I think of great pertinence becomes is global soil restoration possible also try and address whether it's desirable but obviously I think that it is can we actually reverse the historical pattern of soil degradation around the world it's a question that we need to essentially wrestle with how might we do it well if the problem is agricultural soil erosion then obviously the answer lies in changing our agricultural practices how might we do that a couple quick ideas before I move on to some other implications is to reduce subsidies for conventional erosive practices my government at least is essentially a lot of our agricultural subsidies do not encourage practices that actually sustain the soil over the long run we could increase support for no-till practices on on land where they are suitable not all land is suitable for farming without the plow or through no-till practices but a lot of it is we could promote practices that increase soil organic matter to both sequester carbon by putting carbon back in the ground and to improve soil fertility these are policy level issues but can it be done can we rebuild soil I'm actually convinced we can the person that convinced me that we can and that we can do it very quickly is my wife how did she do that well she actually did it in our yard this this picture up here shows you on the right essentially there's a till soil that good that tan color underneath is the soil that we have in North Seattle where I live when our house was built they scraped their that scraped the full growth forest soil back off to til underneath because that's what you did um and essentially that's the kind of soil that we got like 90 years later it was basically dead lifeless there wasn't a worm on the lot there was very little life in the soil through adding organic matter back to the soil she was able to bring the are back to life quite literally and build several inches of soil in about eight years in other words we can build soils faster than we degraded them and we can build soils far faster than nature can build soils how through the application of organic matter and labour there seemed to be the two key components and guess what we have a surplus of in most cities on organic matter and labour well ancient societies there are also a few examples of societies that built soils I looked really hard to find them in writing my book I was only able to find a couple examples and I'll share a couple of them here fertile carbon rich soils built by anthropogenic activity are probably best known from the amazon basin the so-called Terra Preta soils and also from the reclaim sea beds in Northern Europe the pluggin soils of holland in particular and you'll notice that they sort of deep rich or black organic rich soils in both these cases are anthropogenic people made them and people made them through intensive farming the Dutch for example had a major program and reintroducing organic matter to their fields to convert sea beds into productive farmland the Indians in the Amazon basin built very fertile soils you could argue about whether it was intentional or whether it was accidental because of the way that they used their fire ashes and and their own organic ways to build soils around their villages but the fact remains they did it and so that human societies actually can build fertile soils and improve soils while still using them intensively why would we bother restoring soils well I would argue to to address global challenges key global challenges of the 21st century among those and climate change how to feed a post-oil world public health and city livability and the increasing problem of biodiversity loss and environment degradation restoring life to soils and restoring soils on a global scale could help address all of these issues it's not going to be a silver bullet for any of them it's not the only answer for any of these issues but it could be a common element of a foundation for essentially attacking all of these issues therein I think lies the great attraction of arguing for global soil restoration as a societal imperative at the moment we're essentially at peak oil this graph back from 2004 oil industry data essentially shows if you go to the peak in that graph with the sort of psychedelic hatcher part of it that's where 2010 sits we're basically at peak oil now you know plus or minus a couple years we could quibble about that but the key point is is you look to the right of that graph the supply is going down it's not coming back up what's that going to do to the price anybody who's ever had an economics 101 or has you know watched eBay for ten years knows that the supply and demand thing kind of works at some level and that if we have a major demand for oil as we run our agricultural enterprise globally with as the supply dwindles the cost will rise this has implications for how we're going to go about the problem of feeding a growing population notice where 2010 sits on this graph we still have a ways to go before the projected maximum of human population about mid-century on the challenge of how you would feed a growing population is of course a one that we've been wrestling with for about 50 years now but we've been wrestling with it with essentially a strategy based on intensification of fertilizer use well what's one of the main a key question to ask we be can we maintain this strategy in the long run is oil supplies dwindle and prices for oil and therefore fertilizers rise dramatically later this century um I don't know anybody who's arguing that fertilizers will become cheaper as a result of the price of oil going through the roof this brings up the question then perhaps posed a bit too simplistically but it's it was a great graphic I had to find a question to go with it how will we feed a post oil world without cheap fertilizer intensive agriculture it's what we rely on today to do it at the great part at the expense of native soil fertility the argument I tried to make in an editorial in the journal Nature last year was that perhaps it's time to start thinking about a greener revolution the Green Revolution I'm not here to argue about the green revolution to help fed the world for the last 50 years or so the real question is what do we need for the next 50 years and then for the 500 years after that I am a geologist after all and I'll argue that in many cases organic crop yields from no-till and organic agriculture appear to be able to match those from conventional agriculture and from Green Revolution techniques key element is doing it in fertile healthy life filled soil no matter how one looks at it I'll submit to you restoring native soil fertility will be important for sustaining agriculture in a post oil and therefore a post cheap fertilizer world I don't think we can afford to essentially count on deriving our soil fertility from artificial inputs the price of which we can forecast is going to go through the roof later this century the only weight reason we would do that would be either for one of two reasons we had no other choice or because we owned a company that actually promoted that view fortunately I think we do have a choice and I don't own a company I grow tech business so I can argue whatever the hell I want let's also look at the problem of soil and climate change by the late 20th century about a third of the carbon that had been added to the atmosphere since the Industrial Revolution came from a degraded soil organic matter plowing up the Great Plains plowing up the steppes of Russia added about a third of the carbon that was added to the atmosphere since the Industrial Revolution we don't tend to think about or hear about or talk about the role of soil degradation in feeding the atmospheric co2 problem but the key thing is is that if we took that much carbon out of the soil and shunted it into the atmosphere we can do the reverse we can put at least that much carbon back in the ground and a third is a big number when you're talking about the global carbon problem rattan loud back in 2004 estimated the changes in agricultural practices globally could sequester somewhere from point four to one point two Giga tons of carbon per year in other words enough to offset 5 to 15 percent call it 10 percent of global fossil fuel emissions simply from changing agricultural practices Ron Robinson noted a few years earlier that cultivation and deforestation release on the order of 4 Giga tons of carbon per year on to the atmosphere equivalent to more than half of global fossil fuel emissions the way that we deal with biomass the way that we deal with soil organic carbon could actually be a big component of possible solutions to the global climate change problem and there's this issue of something that's called biochar charcoal that could be put in the soil so the Terra Preta soils in the Amazon for example were built up in terms of their organic content in great part from fireplace ashes that were deposited by by Amazonian natives over the centuries what biochar is essentially charcoal why is it that a possible element in terms of soil carbon sequestration well it doesn't break down very fast charcoal is relatively inert if you look at the global soil carbon budget there's about twice as much carbon in the world soils as there is in the world's atmosphere soils are a huge carbon reservoir and we could actually increase that reservoir the average residence time though for soil organic carbon is less than about two decades in other words it's a big reservoir but it turns over pretty fast well a good strategy for increasing the net sequestration in a big reservoir that turns over fast is to basically put stuff in it that turns over a lot slower charcoal is that kind of a substance it basically breaks down much slower than most soil organic matter and if you take the buck global biomass decay on the order of 60 Giga tons per year and compare that to the total global fossil fuel emissions it's about ten times higher we got about seven Giga tons per year fossil fuel emissions globally biomass 10 times that much biomass breaks down each year and returns that it's carbon to the atmosphere if you could capture just 10% of that global biomass it could offs and turn it into charcoal and turn into biochar and stick it back in the ground it could offset entirely global fossil fuel emissions now this has led to some sort of crazy ideas like cutting down the Amazon rainforest and burning it to make charcoal and then sticking it back in the ground I mean there's no sort of net gain if you've got a standing tree and you turn to charcoal they both sequester carbon but the key point and I'm not arguing that you could actually capture 10% of the global biomass decay because it does actually all serve a lot of ecosystem cert it provides value to ecosystems in terms of that decaying organic matter the point is simply to point out that if we thought differently about the way that we deal with car the carbon cycle there's another way than just reducing atmospheric outputs and visions and I'm not trying to say we shouldn't manage that problem obviously we should but we can start thinking about how to put carbon back in the ground as well we can start thinking about the other end of the carbon cycle storage in the ground not pumping into sir deep earth reservoirs but putting it back into the soil where it could improve soil fertility and do us good on multiple fronts therefore it suggests that it might be time for a new view of the soil this Einstein's famous quote about sort of you know old thinking not solving the same problems is I think very pertinent so let's take a couple minutes to look at how we've looked at soils as a species for the last ten thousand years and then try and close up well initially I think for the bulk of human existence we tended to treat soil as a mystery fertility was to be personified deified and revered we've kind of moved beyond that for many people still in the world today soil is a means to living land is to be worked and the sort of the history of plow based agriculture is captured in those images dating from the earliest image we have of the plow and the upper one where it looks like space aliens behind llamas which actually it started something off of a cylinder seal with rolled clay from ancient Mesopotamia it's from about I think 4000 BC if I'm remembering the dates right so the plow hasn't changed that much through history we just pull it around with bigger machinery and so then in the Renaissance soil started to be seen as a decipherable mystery you know a mystery but one that we could unlock one that we could understand something to be studied and understood and Leonardo's quote about we know more about the movement of the celestial bodies than about the soil underfoot it's probably as true today as it was when he made it we know more about both yes but we still for our fundamental dependence on soil it's amazing how little we understand about it how the world of soil ecology is still being essentially explored and developed then in the 19th century soil was started to be viewed as a chemical reservoir me a medium to be fertilized as needed just as Liebig in developing the idea of fertilizers and the application of fertilizers based on what what element missing from the soil limits the productivity is an idea that I'm not going to quibble with it may a lot of sense but the problem is is that if you base agriculture essentially on the view of soil is simply to be add the right chemicals and you get the right mix in the end I think you basically miss the fundamental more modern realization that it's actually the life in the soil and the organic cycling and ecological activity that is the real root of soil fertility and this this means of viewing for soil fertility is essentially misplaced finally that in the so with the rise of mechanized agriculture soil was increasingly viewed as an industrial commodity to be used and potentially used up think about all the inputs to agricultural the agricultural activity soil dirt it's kind of the cheapest one and if you basically treat it as such one would be it's not the one that you would conserve finally I think that in the last couple decades we started to view soils as an ecosystem to be understood and worked with rather than against on and the whole field of soil ecology is one of the youngest sciences that there is and I've been really amazed in looking at the research for the new book that my wife and I are writing about soil restoration about how much has been learned in the last couple decades and how counter to the conventional practices of Agriculture it would lead us to think so I'll posit that soil ecology is that it's sort of the intellectual foundation for the future of Agriculture so we need how we need to think about soils as ecological systems and one of the biggest challenges I see of this century is to harness the insights of soil ecology to figure out how to feed an increasingly populous world based on ecological processes and nutrient cycling rather than liebig's philosophy of essentially chemical additions um there's a big challenge there's a lot of work to be done in that obviously if geologists aren't going to be with the ones that solve that problem but at least I can help point in that direction as the way that we need to go and why would we do this well I think in part to reform agriculture but also because restoring soils could be the foundation for restoring public health even within cities as of 2009 more than half of humanity lives in cities we're now officially in urban species and restoring urban soils can help improve the quality of the built in and thereby people's health by increasing access to green space and urban nature by increasing opportunities for physical activity and providing access for fresh food and environments where it's actually really difficult to find fresh healthy foods at present the so in summary what I want to argue is essentially that restoring soils creating healthy soils on a global basis is not going to be a silver bullet for all the environmental problems that face us but it could be a secret weapon in the fight against many of them why secret weapon well because we're not treating it at the forefront of policy discussions we're not treating it as essentially something that we should be picked up and used it's kind of the tool laying on the soil restoration is almost the tool laying on the ground that we trip over and don't pick up but it could actually help address the problems of feeding the world the climate change and the the linked problems of the physical mental and social health that we cover under the banner of essentially public health in other words even if the restoring soils is only a 25% solution to all three of these problems the key thing is that one common foundation can help with multiple problems it's it's a good deal since the dawn of history humanity has degraded soils it's literally how we've made our living in society after society and we're still doing it this century but I'll argue that this century as a human population is expected to crest and then either be sustained or drop what will happen next this century we really are at a turning point and I'll present I'll submit to you that in my view the challenge is fairly simple if we're to sustain life at the top which fortunately is us we must reinvest in life at the bottom life in and of the soil itself that's the key to providing the foundation for our own species to eat comfortably into the future and global soil restoration will actually help would help us address other linked environmental problems it's well worth doing but just stop by saying that first and foremost soil restoration means that we can no longer really treat soil like dirt so thank you very much for your attention we'll be glad to entertain questions

Channel: The University of British Columbia

Views: 44,626

Rating: 4.8663883 out of 5

Keywords: soil erosion, organic farming, agriculture

Id: sQACN-XiqHU

Length: 57min 42sec (3462 seconds)

Published: Thu Feb 24 2011