Arquivo de etiquetas: Agricultura

Antropoceno XXV – A Fronteira do Terra e da Água

Land and water use change

In this lecture we’ll go through two of the slow variables constituting critical planetary boundaries that regulate under the hood of the Earth system the big climate system and the large operation of the global hydrological cycle and how biodiversity can operate in our living biosphere, in land and water.


And we’ll start with land. Can you imagine? Over just the last 150 years we have rapidly moved into a situation where we’ve transformed almost 40% of the world’s land area into urban regions and predominantly agriculture.

And this enormous transition is illustrated through this series of maps showing the development over the last decades. Now for land use the absolute critical issue to recognize is that what determines the ability of land areas to regulate fresh water, regulate flows of different nutrients, be habitats for biodiversity, and regulate fresh water flows, is what kind of ecosystems we have.

And what we’re finding is that the number one biome system to regulate the stability of the Earth system is our forest systems. And in the original planetary boundary analysis we used a proxy to define and safeguard the critical forest areas in the world, namely what was the maximum amount of cropland that we could allow ourselves, because cropland is the largest human-caused land use change on Earth.522

And we used it because we have good data on cropland extent and cropland change. Now in the updates that we’re doing we’re focusing much more on what you see on this slide, namely directly analyzing how much of the different critical forest systems do we need to regulate the Holocene stability on planet Earth.

And we’re finding from science that the rainforests in the world, the temperate forests, and the boreal forests are the most critical ones in regulating Earth resilience. Now we are so rapidly changing forest systems in the world.523

One very dramatic example is shown here from Borneo, where almost, or a bit more than fifty percent of rainforests have been cut down so far in order to transform land use to large scale palm oil plantations. And you see in this graph the transition of the growth of palm oil and the reduction in rainforest. And this has dramatic effects for local biodiversity, devastating effect for local indigenous communities, but it also directly affects the entire regulation of the climate system and the regional patterns of rainfall across vast areas. So these are truly regulating functions at the planetary scale. And we only have three remaining rainforest areas: the Indonesian, southeast Asian, the Congo Basin in Africa, and the Amazon rainforest in Latin America.

Now the question one asks is do these shifts associate themselves with tipping points? And evidence suggests that the answer to this question is yes. Very rarely or ever in isolation, but land use change can together with changes in fresh water use trigger large scale abrupt and even irreversible shifts; what we call tipping points.

When you change land use we can have so large [a] shift in fresh water flows that it could actually induce tipping points, meaning for example when we cut down forests, take out fresh water in river basins, that we could have permanent tipping points where large tracts of land get locked into desertified states, as one example.

So there are examples of how we can induce tipping points when pushing land and water systems too far. Now nothing is static, and if you load climate change on top of this we see projections into the future that would put even more strain on particularly fresh water systems.

Here you see a very recent analysis by Jacob Schewea and colleagues at the Potsdam Institute for Climate Impact Research trying to analyze what would happen with fresh water resources in the world at 2 degrees C warming, so a point at which we most likely will be quite soon already within this century.524

Now if you look carefully at this map you’ll see the red areas in the world where the projections show, when we gather all the knowledge that we have today, regions that will lose 25 or more percent of average annual runoff. And losing so large [a] portion of fresh water resources is truly a risk of crossing tipping points for both ecosystems and food supply will be jeopardized.

So these are examples of moving and the risks we would take if several boundaries move out of their safe operating space, in this case climate, land and fresh water.

So if we move into fresh water and the diagnostic of what makes water a planetary boundary it’s in its fundamental diagnostic the role water plays as the bloodstream of the biosphere. Water regulates everything we know in the biosphere, all vegetation growth, all biodiversity depends on fresh water.

Humans depend on fresh water, and this map shows just the degree of water scarcity in the world as projected until 2025, taking into consideration fresh water considerations in ecosystems and human needs.

So what we’re recognizing increasingly that the global hydrological cycle, which is finite, is fundamentally a prerequisite for the stability of the Earth system: it regulates climate, it regulates biodiversity, and it’s fundamentally important for social and economic development.525

Now what makes water so interesting from a planetary boundary perspective is that it flows yearly in its hydrological cycle, evaporating from land and oceans, creating clouds, falling down as rainfall, infiltrating into the soil into what we call green water, the portion of rainfall that forms soil moisture and then flows back into the atmosphere as evaporation and transpiration, totally constituting vapor flows, and one portion flowing off on land and as groundwater flow, what we call blue water, the liquid water that fills up our lakes, rivers, wetlands, and dams.

Now what we’re learning increasingly is that we have to have sustainable management of landscapes at large scale to safeguard rainfall, what we call precipitation sheds, which is what’s the area that we depend upon as a source of our rainfall?

And this is an illustration not only why water is a planetary boundary, because it’s safeguarding the management of the fresh water cycle, from the local watershed scale to the base of the global scale, regulates the entire flow of fresh water which, again, regulates climate and biomass, but also how intimately coupled fresh water is to land management and deforestation.526

So these are key justifications from science making water and land so important as planetary boundaries. Now the question is how much water do we need to safeguard in order to stay in a Holocene-like state?

In our original analysis we did this from a global perspective, we looked at the global hydrological cycle, we looked at how much water can we take out in the large basins And biomes of the world before we start seeing evidence of tipping points, and calculated a global number of the maximum amount of water that we can consume in our rivers before we end up with a situation where we could see evidence of tipping points. But we did this from a very global analysis, synthesizing literature.527

Now we’re adding a very important piece to the evidence, namely digging ourselves much more down into detail in all the river basins in the world, exploring based on vast amounts of knowledge that is out in the field on how much water do we need to sustain in our rivers to keep ecosystems functioning, what professionals call environmental water flows.

And what you see here in this graph is the latest update of a bottom-up estimate of the global fresh water boundary based on this analysis for every basin in the world, what’s the minimum amount of fresh water we need to sustain in order to keep basins resilient?

And the exciting thing is that we’re now combining these two analyses of a top-down global estimate of the planetary boundary for maximum amount of fresh water use with a bottom-up analysis of how much fresh water must stay in the basins to keep basins, large landscapes operational. And this leads to our estimate of the final planetary boundary.

But before coming to the numbers around where the boundaries land, let me just close with a kind of summary statement with regards to the importance of land and water for the human future on Earth.

We are soon nine billion people on our planet. Everyone with a right to development and the basis for development will be access to food and fresh water. Recent estimates shows [show] that just to feed humanity in a world in 2050 with nine billion people will require potentially an increase of fresh water use from our current 7000 cubic kilometers of fresh water per year, both in irrigation and rain for that culture, to in the order of 9000-10 000 cubic kilometers per year.

This in a planet where already 25% of our large rivers no longer reach the ocean because we’re taking out so much water to produce food. Now the question is can we transition the world on fresh water land within a safe operating space?

And John Foley and colleagues here at the Resilience Centre recently did a very significant synthesis asking this question: can we feed the world within a safe operating space?

And the answer is that yes, in fact we have so many innovations and so much untapped potential to improve the efficiency and productivity of fresh water use that we can in fact attempt to achieve this grand challenge of feeding humanity within a safe operating space. Yes, we are in a very challenging position in terms of sustaining fresh water and land within a safe space. On the other hand we can, within a safe space, also meet demands for a growing population.

In terms of definitions of the boundaries then what we’re done is that the original estimate was to say: what’s the maximum amount of cropland that we can expropriate beyond which we risk tipping risks induced by land use change?

That estimate was set at a maximum cropland extent of 15%, and we have today transformed 12% of the world’s land surface into cropland. It’s 12% for cropland, but it’s forty percent if we include also grazing lands. But we took cropland because that’s a set of data that we have quite a good handle on. In the updates that we’re doing we are, as I mentioned, reversing this to rather say how much forest do we need to maintain in order to sustain Earth resilience? And our estimates show that we need to keep in the order of 75% on average for all the big forest systems, and we are today actually at a situation where we have cut down more Than 25%, we actually only have 62% of forests left on Earth. So we’re already in a danger zone with regard to the planetary boundary on forests.

But importantly we’re actually able today to make the first estimates for how much rainforest we need to keep, and our estimate shows we need to keep 85% of rainforest systems, that we need to keep 50% percent of our temperate forests which play a lesser important role in terms of its total coverage to maintain Earth resilience, and that we need to keep in the order of 85% of our boreal forests to stay within a safe operating space.

And this is a signal or a way of showing that the planetary boundary at the global scale can actually be translated to the operational scale of forest management in large parts of the world. But it does, and I really want to remind ourselves of this, forests do not respect national borders. It shows that it’s a global concern to safeguard the remaining forests on Earth.

Similarly for fresh water we maintain. The original analysis that we need to keep consumptive fresh water at the global scale 4000 cubic kilometers of fresh water per year. That is the boundary that we feel we still have evidence to support. But then we’ve done this bottom-up analysis of the amount of environmental water flow in all the basins in the world, which ends up with an aggregate boundary corresponding to in the order of the same magnitude as our estimates top-down, but it gives us percentages of maximum allowable withdrawable fresh water at each river basin in the world, which ends up in the order of 25 to 50% of fresh water must be kept in the rivers, and that there’s a large variation here is that it depends for each basin on how much fresh water there is, if these are permanent basins, if these are intermediate basins, if these are only infermeral basins, the flux intensity, etc. So there’s a lot of intricacy here but it just shows that we can operationalize this at the level of management.

So overall land and water as fundamental boundaries regulating Earth resilience and our desired Holocene state. They operate at the local level but aggregate into impacts at the global scale, interact very closely with particularly biodiversity and the climate system, and are fundamentally part of the operational management for a sustained prosperous future on planet Earth.

Growth within Planetary Boundaries IV

The Case of Food

You would think, I think intuitively that energy would be the dominant way that humanity is impacting the planet. We’ve just seen how massive energy use translates into rising carbon dioxide and climate change. And energy, of course, is everywhere in our transport systems, our power supplies, our industrial processes, our home use. But it’s quite arguable I would say it is right to say, that the agriculture sector has an even larger impact on the physical planet and the various earth systems than energy. Energy is causing climate change. Agricultural use and agricultural patterns not only have a huge impact on climate but have a huge impact on every aspect of the Earth’s systems and the planetary boundaries.

We’ll see soon that the food production contributes massively to greenhouse gas emissions, therefore to climate change. But we’ll see also that the energy system as we go around the the circle is in a way dwarfed by the food production system in its impacts on each of the other areas of the, the planetary boundaries. The nitrogen and phosphorous cycles, where we get the pollution from the runoff of nitrogen and phosphorus-based fertilizers. The fresh water use, which is about 70% used in the agricultural sector. The change of land use overwhelmingly a reflection of agriculture. The loss of biodiversity  coming from the way that farmlands and  pasture lands and and tree crop plantations absolutely threaten habitats of other species unless uh,agriculture is done in an agro-ecologically friendly manner. Chemical pollution with the heavy application of chemicals such as herbicides and pesticides used in agriculture. There’s a tremendous amount of chemical impact from the farm system. So it is quite arguable that farming dominates the all of the human activities in terms of the anthropogenic effects. Anthropo, human. Genic, caused by. That is the various human-caused impacts on the planet.

Now this is in a way ironic because it takes us right back to the beginning of the modern economic era and to the very beginning of economic studies just like Adam Smith does and just like Adam Smith’s wisdom is still useful today, so too is that of another great thinker Thomas Robert Malthus who wrote famous text in 1798 called Principles of Population. Malthus was afraid. He was also afraid of planetary boundaries, but for a slightly different reason. Malthus said that the human population has a tendency to rise at a geometric rate. And so if left on its own with the basic needs met the human population would continue to expand rapidly. He was right in that when he wrote the Principles of Population in 1798. The total population may have been 800 million, maybe 900 million. Roughly one tenth of the level that it is today. So Malthus was right that human population tends to increase markedly, at a geometric rate he said. Now, he feared that the ability to grow food would only increase at an arithmetic rate. That is adding a certain number of tons of feed grain or food grain per year to the world’s capacity to grow food. And Malthus said, look, any geometric growth will always overtake any arithmetic growth. So the growth of the human population is always going to overtake the ability to grow food, he said. And at some point there will be so many people that hunger will ensue. And when hunger ensues there will be various kinds of devastating feedbacks whether it’s war, whether it’s famine, whether it’s disease or other scourges that will push population back down. But will mean that humanity won’t break free of the physical constraint on the ability to grow food.

Now Malthus did not anticipate the scientific advances of the Green Revolution, for example. He didn’t anticipate modern seed breeding of course even Mendel who invented the modern science of genetics would come basically about three quarters of a century after Malthus. Malthus also didn’t anticipate the breakthroughs in the science of soil nutrients and the use of chemical fertilizers to replenish soil nutrients and to boost food yields. Nor did he anticipate at least the potential for the human potential to stabilize by means of modern contraception, family planning, and choices that households make. So Malthus, couldn’t see the full dynamic ahead, but he worried that the human population would outstrip the carrying capacity of the planet itself. For a long time, economists and others laughed at Malthus. They said, you’ve got it all wrong. You see modern science allows us to grow enough food for a geometric rise of the population. We know how to add fertilizer, we know how to have high yield seed varieties. But, you know, Malthus’ a pretty clever guy and he had a real insight and we’re not done with his story yet because his warning rings true today.While it is the case that increases of food production technology in agronomy and food processing, storage, transport and the ike has made it possible to feed 7.2 billion people though not all of them by any means fed well or nutritiously. It is also the case that the food production system is so destructive of the environment that Malthus is still there, waving his finger saying not so fast. You haven’t proven that you can grow this amount of food sustainably.

What’s going to happen when the water runs out? What’s going to happen when the nitrogen and phosphorus loadings become so large and so forth. So I would say we’re not at the end of the Malthusian story yet. Sustainable development calls for a renovation, a reform, an upgrading of the technological systems to grow food. It calls for us to eat more wisely as well. Eating the kinds of food products that don’t threaten the natural environment. For example, not eating endangered fish species or endangered species of land mammals. Unfortunately some of which are in huge supply as delicacies, even to the point of illegal hunting and poaching and threatening the very survival of these species. So, changing farm systems and changing human behavior, in terms of our diet and use of agricultural products, is possible. But in order to meet Malthus’s challenge, we still have to prove that it’s possible to grow food in a sustainable manner

For all of the people properly nourished on the planet, and with the food system recognizing and respecting the planetary boundaries. Boy, are we far from this today. Let’s think about some of the ways that the food system is impinging on the planetary boundaries.

First, the food system is an enormous source of greenhouse gases. Of course agriculture uses a lot of energy. For planting, for harvesting, for storing, transforming and transporting food and other agricultural commodities. There’s a lot of energy stored in chemical fertilizers, because to make urea, or other nitrogen based fertilizers, one requires a lot of energy to create the chemical compounds in those fertilizers. But what’s interesting and important for us to note, is that agriculture emits greenhouse gases in other ways as well. Remember, the two other major greenhouse gases, anthropogenically caused, that is, caused by human beings in addition to CO2 are methane and nitrous oxide. Now methane or CH4 is emitted in a variety of ways. It’s emitted by anaerobic processes in flooded or paddy field rice for example. Where the metabolic processes of the bacteria release methane into the atmosphere. It’s also released from the gut of ruminant livestock. When cows chew their cud, and digest their food they are also emitters of methane on, on a large scale. Nitrous oxide is emitted partly through industrial processes and electricity production at coal fired power plants. But it’s also emitted by the chemical decomposition of nitrogen based fertilizers. So fertilizers are a source of nitrous oxide in the air.

But they’re also a source of water pollution in the sea. In both cases, the nitrogen is supplied on the farms, but it’s not taken up by the plants themselves. It either volatilizes into the atmosphere or it runs off into the water and then, on the way through the rivers and ground water to the ocean. So greenhouse gases is one major way that that the agriculture system impinges causing climate change. Land use change and habitat loss is another obvious way. Humans use land primarily, not for our cities, not for our highways, but for our farms and our pasture land and our timber land. And we have already taken hold of so much land, so much photosynthetic potential, to feed us, that we’re depriving other species, not only of their natural habitats, but of the food that they need to stay alive. And that’s why we’re driving numbers of other species down sharply. Agriculture, as I mentioned earlier, is a major source of chemical pollutants often very long lasting and very toxic chemicals that are used as pesticides and as herbicides and as other parts of the food production chain.

Agriculture has another perverse threat which is called invasive species. Invasive species means that humanity advertently, or inadvertently, but generally unwisely takes a species from one part of the world, puts it into another environment, perhaps where there’s no competition with that species. If it’s an animal, it can run wild. If it’s a plant or a weed, it can take over a a land area, or a lake for example, dominating the local biodiversity. Invasive species means that we are rearranging the biogeography. The places on the planet where various species exist. And we’re putting lots of species at risk by invading ecosystems where they don’t belong, where they are not native. Perhaps where they have no predators, or where they can invade and take over a lot of the resources of that ecosystem.

Nitrogen and phosphorus runoff, I’ve already mentioned. And look at this picture. The shocking picture off the coast of China there is so much fertilizer being used by Chinese farmers because it’s heavily subsidized, and because of bad farm practices that that fertilizer runs off the farms into the rivers and ground water. It accumulates in the estuaries and off the coast, and it creates this kind of algal bloom. And algal bloom means that there’s such a sudden massive loading of nutrients, nitrogen and phosphorus in particular that the algae which either naturally grows in a particular place or has been introduced say by fisheries practices, suddenly has this massive feast of nitrogen and phosphorous. And there’s an explosion of the amount of algae. This algae will die. Then it will be decomposed by bacteria. As those bacteria feast on the algae, the dead algae, they will be respirating, and they’ll be using a lot of the oxygen in the water. They will deplete the oxygen as part of the respiration process and by depleting the oxygen they will create an oxygen depleted zone of coastal waters. That’s called a hypoxic zone, low oxygen hypo oxia. And low oxygen kills the fish, kills the other species. Suddenly you have what ecologists and marine biologists call a dead zone. There are dead zones all over the coastal world now, especially in the estuaries.

Estuaries where the freshwater of rivers meets the saltwater of the oceans are wondrous ecosystems. Our shellfish and many other species are often indigenous to those locations, and they’re being threatened by this nutrient loading. By the utrification and then by the hypoxia that results. Creating dead zones and hypoxic regions in more than 130 estuaries around the world. The food system also gives rise to new pathogens. When we have the industrial breeding of poultry, for example, all crowded together, we have learned that there is recombination of genes of bacteria and viruses. When livestock and poultry out in the open mixed with the wild with the wild species of geese and other species, you get further recombinations. And this has given rise to many  emerging infectious diseases, some of which are very, very  frightening, like SARS. Was and remains very, very frightening. And so we have new and emerging diseases coming from industrial agricultural practices. Of course we have massive overharvesting, overhunting, overgrazing,over abstraction and cutting down logging of trees and forests. Most of the world’s major fisheries have been massively over fished.

In the Northeast of the United States where I live there was a collapse of the cod fisheries because of the massive amount of fish that was being hauled up using modern technologies trawlers and other high tech ways to fish a massive amounts of fish under the ocean.

And of course with all this food production we are using up water supplies through ground water depletion, through the diversion of rivers which no longer make it all the way to the sea. And the growing water crisis is extraordinarily frightening.

We see water scarcity as a major threat to well being, to human health, to economic development in many, many parts of the world adding climate change on one side, overuse of water coming from agriculture it’s quite a dangerous brew. So just as we are going to need to find a new pathway for energy basedon energy efficiency and low carbon energy supplies. We are going to need to find a new farm system, or I should say farm systems. Because there are farm systems distinctive all over the world depending on the local climates, local cultures, local soils, local ecological conditions. But what is nearly common to all of the major regions is that our farm systems are not yet sustainable.

We still have to prove Malthus wrong, we still have to take a tip from Malthus that the challenges of food supply are a major and continuing challenge facing humanity, and a core part of any agenda of achieving sustainable development.