ENVS 205- Module 2 Part B

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Carrying Capacity, Limits to Growth Economic Growth and Limits to Growth What does economic growth mean for the environment? Can the economy continue to grow forever on a finite planet? Are there biophysical limits to economic growth? As previously mentioned, economic growth is usually measured in terms of gross domestic product (GDP). A growth in GDP means that more and more resources are being extracted, manufactured, transported to markets to be sold and consumed; and that more and more pollution is being created in every step of this process. Given the current unsustainable ways in which goods are produced, circulated and consumed in the economy, economic growth generally has negative environmental impacts. Similarly, the I=PAT equation also has us consider the potential environmental impacts of a growing population. This raises the question about whether there is a maximum number of people that planet Earth can sustain? Figure 1 shows the global human population between 10,000 BCE until present day. Significant historical events are indicated along the graph. You'll notice that for most of human history, the population of humans was very low. It took all of human history up until around 1800 for the human population to reach 1 billion people, but only 100 additional years to reach two people. Then in the next 100 years, the population rose exponentially by an addition five billion people. Figure 1. Historical human population Apply Your Learning Many environmentalists believe that the world is "overpopulated." Do you think that having as many children as you want is an

individual right and that the Canadian government should not regulate this? Or do you see overpopulation as an issue the government should be helping to address by regulating the number of children each Canadian parent can have; for instance, by instituting a financial penalty for going over the allowable number of children at a value that is geared progressively to one's income level. Carrying Capacity The Earth's limits to economic growth and population growth are studied through the concepts of carrying capacity and planetary boundaries. The concept of carrying capacity was developed by biologists studying population dynamics, and was originally used to describe the number of cattle that could graze on a piece of pasture before degrading it irreparably. The carrying capacity of a given environment refers to the maximum population size that can be sustained indefinitely in that environment. It recognizes that the sustainability of a population size is limited by the availability of habitat, food, water and other requirements provided for by the environment. The maximum population size can only be sustained if it is living off of the flow or yield of a renewable resource rather than the source or stock . The flow refers to the annual growth of a given population (accounting for seasonal and year-over-year variability) that can be harvested or killed without affecting that population's ability to regenerate back to its original population size or source. Example: Sustainable Fishing For example, humans can catch and eat fish from a fishing bank in a sustainable manner by only catching the growth of the fish population each year. If humans kill not only the annual growth of the fish population but also begin to kill the core stock of fish, then each subsequent year the amount of fish available will decline and the fish population could one day collapse.

Figure 2. Stock and Flow Determining Carrying Capacity Definition sinks In the first module we discussed the role oceans play as a carbon sink. Sinks are the part of an ecological (i.e., biogeochemical) cycle that captures and often concentrates a pollutant, nutrient or other element that is flowing through the cycle, and stores it often for an extended period of time. The carrying capacity is determined not only by the amount of resources required to sustain a population indefinitely, but also by the environment's ability to absorb a population's by-products and waste (i.e., pollution) and regenerate itself each year. Ecological processes that absorb pollution are known as pollution sinks . In the first

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module we discussed the role oceans play as a carbon sink. Sinks are the part of an ecological (i.e., biogeochemical) cycle that captures and often concentrates a pollutant, nutrient or other element that is flowing through the cycle, and stores it often for an extended period of time. A given population that is depleting the source of its renewable resources rather than living off of the flow and that is producing more pollution than its habitat can regenerate is said to be living beyond its carrying capacity or living in overshoot . Global overshoot occurs when humanity’s demand on nature exceeds the biosphere’s supply, or regenerative capacity. Such overshoot leads to a depletion of Earth’s life supporting natural capital and a buildup of waste. At the global level, ecological deficit and overshoot are the same, since there is no net-import of resources to the planet. Local overshoot occurs when a local ecosystem is exploited more rapidly than it can renew itself (Global Footprint Network, 2018). As Figure 3 shows, several wide-ranging estimates have been made to calculate the carrying capacity of Earth for humans. Most estimates fall between 8 to 16 billion people (UNEP, 2012).

Figure 3. Estimates of Earth's carrying capacity

Pengra, B. (2012, p.3) These estimates are wide-ranging because to some extent the carrying capacity for humans on the planet can be increased through technological innovation and social organization. Humans can both increase and decrease the Earth's capacity for sustaining life in the long term. Humans can increase flows of non-renewable resources through agricultural and silvicultural practices, fish farming and bioengineering. But even these practices and technologies will eventually reach a theoretical biophysical limit in terms of the size of population that they can support. Alternatively, humans can degrade environments so much (e.g., through soil erosion, radiation poisoning, biodiversity loss, climate change, etc.) that the capacity for human life is diminished. As we will see later in the module, some scholars believe that our current world population of 7.6 billion has already overshot Earth's carrying capacity. These studies argue that humans are living beyond our means which is degrading the earth in ways that could limit the size of future populations. Limits to Growth Predicting maximum human populations that Earth can sustain or whether we have already overshot Earth's carry capacity is very difficult if not impossible given the complexity of biogeophysical systems and uncertainties surrounding human social and technological development. Below is an excerpt from a United Nations Environment Program (UNEP, 2012) report that discusses two efforts to model these complex global systems. In the early 1970s a group of computer scientists at the Massachusetts Institute of Technology (MIT) developed just such a model to help use define safe limits to our impact on the Earth system. Jay Wright Forrester was a computer engineer at MIT and the founder of 'System Dynamics,' a modeling approach for studying complex systems. Forrester realized that advances in computers he used for modeling of economic systems might enable modeling of the global economy and the global ecosystem as a single complex system (Bardi, 2011). At the same time, a set of Forrester’s colleagues at MIT, headed by Dennis Meadows, also began working on the same type of global models (Bardi, 2011). The teams worked independently publishing their work in 1971 (Forrester’s 'World Dynamics') and 1972 (Meadows and others’ 'The Limits to Growth').

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Meadows, D., Randers, J., & Meadows, D. (2004) The authors had simulated the relationships of several of the Earth System’s key processes over time, and both teams came to similar conclusions. They found that Earth’s economic system tends to stop growing and collapse from reduced availability of resources, overpopulation, and pollution at some point in the future. Various scenarios of technological innovation, population control, and resource availability could delay the collapse, but only a “carefully chosen set of world policies designed to stop population growth and stabilize material consumption could avoid collapse” (Bardi, 2011). The books were quite successful, particularly Meadows’ book 'The Limits to Growth,' which was written for the layperson and translated into several languages (Bardi, 2011). Many in the sciences responded enthusiastically and many tried to adapt the groundbreaking technical approach to their own fields of study (Bardi, 2011). But in spite of their popularity, criticism came from several directions as well. Many critics saw a political meaning in the works (Schoijet, 1999), many dismissed it as alarmist (Hall & Klitgaard, 2012), but the most enduring push-back came from mainstream economists (Hall & Klitgaard, 2012).

In the past decade, however, many have begun to revisit the Limits to Growth and 'world modeling' of Forester and Meadows (Bardi, 2011; Hall & Klitgaard, 2012; Simmons, 2000; Brown, 2005; Turner, 2008). Several have pointed out that the projections of the Meadows’ World3 model’s 'business as usual' scenario are proving to be remarkably close to reality for the 40 years since they were first published (Bardi, 2011; Simmons, 2000; Turner, 2008). New science, including advances in modeling dynamic systems such as the Earth System, is trying again to see what might lie in the future (Bardi, 2011). (Pengra, B., 2012) Figure 4 is just one of the ten possible future scenarios for society modeled in Limits to Growth . These ten scenarios are not meant to be predictive for specific dates. Rather they depict long-term trends that are best understood relative to the other scenarios. Comparing all ten scenarios can help inform policy-making by identifying the key variables that are undermining sustainability. I am showing you this example so you can understand the types of trends depicted in these models. Figure 4 represents the study's second scenario. It shows a world in which industrial output continues to grow for the short term, peaking sometime in the mid-century. This rise is industrial output is driven by increasing technological efficiencies (not shown on the graph) which lowers the market costs associated with extracting resources and producing industrial output. However, in the medium term, new technological efficiencies becomes increasingly harder to realize, and more expensive. This means that less capital is available for investment in industrial output because it is being increasingly diverted towards exploration and development of increasingly scarce resources. This is shown on the graph by a rapid decline in resources by mid-century, and the eventual decline of industrial output as more and more societal resources are consumed trying to find and develop new resources. A drop in resources coupled with a soaring population causes a rapid drop in food supplies, as shown on the graph ( Figure 4 ). Food production is also hampered by a steep increase in pollution associated with increasing industrial output and growing population. In the second half of the 21st century we see that population levels decline steadily. This increase in death rates is due to increasing food shortages and negative health effects from growing pollution. There is also a corresponding decline in the quality of life which is not depicted.

Figure 4. Scenario 2 from Limits to Growth with high technological efficiency What is your environmental impact? How much of the world's land do you require for all your consumptive needs or desires and to absorb all the waste and pollution you generate? Ecological footprint helps us answer this question. It is defined as: A measure of how much area of biologically productive land and water an individual, population or activity requires to produce all the resources it consumes and to absorb the waste it generates, using prevailing technology and resource management practices. ... the ecological assets that a given population requires to produce the natural resources it consumes (including plant-based food and fiber products, livestock and fish products, timber and other forest products, space for urban infrastructure) and to absorb its waste, especially carbon emissions.

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(Global Footprint Network, 2018a; 2020) As mentioned previously, ecological footprint is a way of quantifying environmental impact within the I=PAT equation. Whereas carrying capacity asks how many people the Earth can sustain indefinitely, ecological footprint tries to quantify human environmental impacts based on past, current or projected levels of consumption and the production of waste. Figure 1. The ecological footprint compares how fast we consume resources and generate waste to how fast nature can absorb our waste and generate new resources Global Footprint Network (n.d.) global hectare (gha) Global hectares are the accounting unit for the Ecological Footprint and biocapacity accounts. These productivity weighted biologically productive hectares allow researchers to

report both the biocapacity of the earth or a region and the demand on biocapacity (i.e., the Ecological Footprint). A global hectare is a biologically productive hectare with world average biological productivity for a given year. Global hectares are needed because different land types have different productivities. A global hectare of, for example, cropland, would occupy a smaller physical area than the much less biologically productive pasture land, as more pasture would be needed to provide the same biocapacity as one hectare of cropland. Because world productivity varies slightly from year to year, the value of a global hectare may change slightly from year to year. (Global Footprint Network, n.d.) Because we consume resources from all over the world, and pollution such as carbon emissions are distributed globally, our ecological footprint is not a measure of the amount of land we would specifically require in, say, the Kitchener-Waterloo region or Canada. People do not simply eat resources or assimilate pollution from their own land. And not all places on Earth have the same biological productivity and regenerative capacity for giving human populations necessary resources or for absorbing human wastes. For example, a semi-arid pasture produces much less food and absorbs much less carbon dioxide pollution than a rainforest. So depending on where you live you would need more or less land if you were only surviving off your local resources. To be able to compare the ecological footprint of people living in different places on Earth, many of whom consume resources from all over the planet, we measure our ecological footprint in something called global hectares (gha). You can think about this as a measurement of "land in general" or land that is productive at the global average. Have humans exceeded Earth's carrying capacity? Ecological footprint and carrying capacity can be brought together in a useful way to evaluate whether humans have already exceeded the Earth's carrying capacity. Figure 2 is by the authors of Limits to Growth . It uses a calculation of humanity's ecological footprint to show that we have already exceeded the Earth's carrying capacity at some point in the late 1970s.

Figure 2. Ecological Footprint vs. Carrying Capacity. Humans may have already exceeded the Earth's carrying capacity according to the authors of Limits to Growth Meadows, D., Randers, J. & Meadows, D. (n.d.) Overshoot can also be understood in terms of what date during the calendar year that humans have overshot the Earth's carrying capacity for that year. In 2018, the " Earth Overshoot Day " was on August 1st. Each year we reach Earth Overshoot Day earlier and earlier in the calendar year, reflecting our increasingly unsustainable use of resource and pollution generation. The Global Footprint Network estimates that we would currently require 1.7 Earths to continue living the way we are (in terms of resource use and absorption of waste).

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Figure 3. Earth Overshoot day is getting earlier and earlier Global Footprint Network (2018) Watch the following video, Ecological footprint: Do we fit on our planet? , on ecological footprint. In this video carrying capacity is referred to as biocapacity. One of the quiz questions will be based on this video. Later on in this section you will be asked to calculate and think about your own ecological footprint. Transcript Ecological Footprint and The "Good Life" Limits to Growth and the concept of overshoot raise the prospect that the high and growing material standing of living currently enjoyed in wealthy countries may in fact be "artificial" or "inflated." To the extent that the current generation has an ecological footprint already beyond the carrying capacity of Earth ( Figure 1 ), the current generation is in fact taking away resources and healthy environmental conditions from future generations. The inflated ecological footprint cannot be sustained and is "robbing" from the future for the material enjoyment of the current populations of wealthy countries. This is an example of an environmental injustice. This environmental injustice is also depicted in Scenario 2 of Limits to Growth by the shape

of the human welfare index (shown in second diagram of Figure 4 ). The human welfare index is used to quantify the average quality of life of humans. It is a similar measure as the Canadian Index of Wellbeing discussed previously or the UN Human Development Index. The Human Welfare Index is a composite of average life expectancy, education levels and income per person. After continuing to rise towards the middle of the 21st century, the human welfare index then falls drastically (due to food shortages and declining resources and industrial output) before levelling off to levels comparable to the last quarter of the 20th century. By the end of the 21st century the human welfare index falls even more due to dwindling resources and industrial output. The current generation (in wealthy countries) would need to lower its ecological footprint so future generations could enjoy a similar material standing of living. This means lowering our resource use, industrial output and pollution levels. But to do this requires that wealthy countries, and wealth people in particular, transform their conception of the "good life" so that it is much less based on consumerism and materialism. Figure 4. Scenario 2 from Limits to Growth. Note the shape of the human welfare index.

Meadows, D., Randers, J. & Meadows, D. (n.d.) Ecological Footprint Learning Activity 2h. Learning Activity: Ecological Footprint (graded, required) In this section you will calculate your own ecological footprint using the Ecological Footprint Calculator. Details for this activity are available on the Learning Activities page in the Activities and Assignments section. Please complete this activity before continuing with the module content. Ecological Footprint and Social Justice Ecological footprint is an excellent tool for comparing the environmental impacts of different populations, for example, between wealthy countries and low-income developing countries, or between individuals within a country. This is a useful way of quantifying environmental injustices (i.e., the distribution of environmental "goods" and "bads"). There are different positions amongst proponents of environmental justice. One position holds that each person living on Earth should have similar access to the Earth's resources and its regenerative, pollution-absorbing capacity. In this view, environmental justice exists when each person has a similar ecological footprint. To live sustainably within the carrying capacity of the Earth, every person in the world would be entitled to 1.7 global hectares. We are currently quite far from this distribution, as shown in Table 1a and Table 1b . Another position is that low-income (developing) countries actually require greater amounts of resources and should be allowed to pollute more than wealthy countries

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given low-income countries' needs for rapid economic development and inability to afford clean-technologies. In this view, environmental justice exists when low-income countries have relatively greater ecological footprints. Conversely, wealthy countries should have a relatively lower ecological footprint since: they already have their basic needs met; can produce goods and services using advanced clean-technologies; and because they developed economically in ways that historically undermined low-income countries (e.g., through slavery, colonialism, neocolonialism) and the environment (e.g., through deforestation of their own land or by emitting global greenhouse gas emissions since the industrial revolution). Currently, the world is quite far from either vision of environmental justice in terms of ecological footprints. The tables below compare twenty countries with the largest ecological footprint per person and twenty countries with the lowest ecological footprint per person. The ecological footprint per person (or "per capita") is a country's total ecological footprint divided by the country's total population. You can see that Canada at 8.0 gha per capita has the 7th largest ecological footprint (certainly not something to be proud about). I have included the annual income per capita alongside each of these forty countries. This is the average income people in each of these countries earn in one year (usually arrived at by taking the GDP divided by the total population). Thinking about the I=PAT equation, we would expect countries with higher per capita incomes to have a greater per capita ecological footprints relative to countries with lower per capita incomes. And in fact, wealthy countries do tend to have larger ecological footprints. Taken together, the countries with the largest per capita footprints have an average income of $57,280, a median income of $50,600, and besides Mongolia and Aruba, all countries have incomes per capita above $31,000. The countries with the smallest per capita footprints have an average income of $8,610, a median income of $2,200, and all countries have a per capita income below $5,500. Table 1a. Countries with the largest ecological footprint

Table 1b. Countries with the smallest ecological footprint

Complex Systems

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Introduction Sustainability implies maintaining or "sustaining" a system. And yet we know that socio- ecological systems are constantly changing. Sometimes change is a problem—as with climate change, biodiversity loss and deforestation. But we also need rapid and radical socio-ecological transformations if we are to address these types of problems and end global poverty. In this section we examine concepts from ecology and systems theory to help us better understand the processes that regulate (sustain) or change complex socio-ecological systems. Concepts we will cover include: feedback loops; equilibrium; and thresholds (also called limits, boundaries or tipping points). Systems thinking also sheds light on questions about the implications of overshoot: What will eventually happen if humans continue to live in overshoot of the Earth's carrying capacity? Will the population or society completely "collapse" or just decline allowing ecosystems to recover before resurging again (possibly back into overshoot)? Will this recovery be "automatic"? Is some of the ecological degradation irreversible? Are there some limits or thresholds of pollution and ecological degradation that can never be restored or regenerated back to where it was before? Systems thinking helps us identify "vicious cycles" that are driving humanity towards planetary overshoot as well as "virtuous cycles" that can bring us back from overshoot. Feedback Loops The concept of feedback loops if critical for understanding how complex systems function. Negative Feedback Loops Negative feedback loops provide stability (or "balance") to systems; when one part of the system exceeds the normal bounds of the system then negative feedback loops work to reduce the factors driving this change thereby bringing that part back within normal bounds. We see negative feedback loops at work in homeostasis , i.e., the regulation of organisms' internal conditions. For example, if an organism gets too warm then signals are given to the organism's body that allow it to cool down (e.g., by sweating, drinking water, seeking shade, etc.). The regulation of glucose in the blood is another example of a homeostatic equilibrium system. An equilibrium is a state for a system in which opposing forces or influences are balanced. The variable (blood glucose) oscillates around an equilibrium level that does not

change, always being kept within bounds by negative feedback loops (insulin and glucagon secreted by the pancreas). Figure 1. Blood glucose levels are maintained at a constant level in the body by a negative feedback mechanism. When the blood glucose level is too high, the pancreas secretes insulin and when the level is too low, the pancreas then secretes glucagon. The flat line shown represents the homeostatic set point. The sinusoidal line represents the blood glucose level. snegok13/iStock/Getty Images Negative feedback loops were also classically used by ecologists to model predator- prey relationships. As shown in Figure 2 from a classic study, the increase of prey (e.g., rabbits) would eventually be checked by a growth of predators due to an abundance of food. But at a certain point, there would be too many predators for the numbers of prey left and the size of predator populations would decrease. With fewer predators, the prey population would once again be able to rebound and grow and this oscillating cycle would continue. In this case, equilibrium refers to the carrying capacity of the system for lynx and hares.

Figure 2. Predatory-prey relationship of the lynx and hare displaying a negative feedback loop system (linear equilibrium) OpenStax College (2016) Negative feedback loop systems are sometimes known as linear equilibrium systems because the setpoint (or carrying capacity in the case of population dynamics) does not readily change. Positive Feedback Loops In contrast, positive feedback loops drive system changes: as a system changes in one direction, this change itself encourages further change in the same direction. Positive feedback loops are characteristic of exponential growth (e.g., algae blooms in a lake) or decay (e.g., a threatened populations becoming extinct since few species make it harder and harder to find mates). We see positive feedback loops at play with climate change: e.g., the warming climate melts permafrost which, in turn, causes a release of methane that was previously trapped in the permafrost. This released methane then further contributes to the greenhouse effect and further warming which, in turn, leads to more and more release of methane from the permafrost. Viral videos on the internet is another good example of a positive feedback look.

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Vicious & Virtuous Cycles Positive feedback loops that lead to undesirable outcomes are sometimes referred to as vicious cycles. The melting of the polar ice caps and glaciers is one example: as snow melts it exposes darker rocks and soil that then absorbs more heat thereby speeding up further melting. Complexity Labs (2018) provides another example of a vicious cycle: Many South Pacific [island] communities now consume imported packaged and canned foods, disposing of the empty cans and other waste in dumps. Rainwater runoff from the dumps pollutes the lagoons, reducing the quantity of fish and other seafood. With less seafood, people are forced to buy more and more cheap canned food, the pollution becomes worse and the lagoon has fewer fish. This positive feedback loop changes the lagoon ecosystem while also degrading the people’s diet again creating a vicious circle. (Complexity Labs, 2018) In contrast, virtuous cycles are said to occur when a positive feedback loop creates a favourable outcome. Social cooperation can be a virtuous cycle: the more success people have cooperating with one another the more they and others will want to cooperation. Nonequilibrium Ecology Thresholds or Tipping Points In some cases, positive feedback loops can push an equilibrium system to overcome certain thresholds (also known as tipping points) after which the entire system is shifted into another state or equilibrium (e.g., to a lower or higher carrying capacity). This is known as dynamic equilibrium . Figure 3 shows two ways that a system might exceed a threshold and establish a new equilibrium. Equilibrium is represented here as a "basin of attraction" in which the ball likes

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to remain. But in the case on the left hand side, the system moves out of this basin of attraction and over the tipping point due to internal changes within the system itself. Notice that after the shift, the purple ball rests higher than before in a new basin of attraction or equilibrium. In the case on the right hand side, the parameters or landscape of the system changes and pushes the system into a new state. We can see how this type of shift in equilibrium state takes place in the oceans. Researchers with the Oceans Tipping Points (2018b) project have observe that many coral reef ecosystems have already transitioned into an algae-dominated reef ecosystem. The concept of tipping points could help researchers monitor and manage coral reefs: Figure 3. Dynamic equilibrium. Shifts in variables (also called community disturbances) and shifts in parameters ( also called ecosystem drivers or landscape change) may irreversibly push a population over a threshold to a new equilibrium state. Ocean Tipping Points (2018c) Ocean Tipping Points researchers have explored coral reef transitions across the region and are beginning to understand the warning signs for transition from a coral dominated state to an algal dominated state. The findings show that maintaining adequate reef fish biomass could be a key to

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managing for resilient coral reef ecosystems. Ocean Tipping Points (2018d) By monitoring fish density, we can understand the health of the ecosystem and future management scenarios. For example, when the density of fish in a system is similar to the density of fish when no fishing occurs in the system (‘Unfished density’) a healthy coral- dominated reef is more easily maintained. With fishing, a number of metrics including the proportion of fish that feed on invertebrates, the number of fish species, and urchin density, change as fish densities fall below 50-60% of unfished densities. At this point, close monitoring of the system to track potential changes is recommended. When fish densities reach 30% of unfished densities, a suite of changes occur: the ratio of macroalgae to coral increases, the

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proportion of herbivorous fish in the fish community decreases, and coral cover drops markedly. The fact that the reef is in a different state becomes obvious. (Ocean Tipping Points, 2018b) There is a strong idea within many cultures of nature existing in a "balance" or "harmony" if only humans leave it alone—similar to the type of population dynamics modeled in Figure 2 (with the lynx and hare). To be sure, reducing rates of biodiversity loss and deforestation will require less destructive human activities. But ecologists have found dynamic equilibrium systems to be much more common than was once believed. And since humans are inextricably part of nature, the goal should be to decide what types of socio-ecological changes we wish to encourage or bring about and which do we not, rather than how do we re-establish "balance" in nature that never really existed. Complex Systems of Positive and Negative Feedbacks Both positive and negative feedback loops are often in operation in the same system, as discussed here by Complexity Labs (2018): Ecosystems and complex systems, in general, have a tension between forces that resist change, the negative feedback, and forces that promote change, the positive feedback. Negative feedback may dominate at some times and positive feedback may dominate at other times, depending on the situation. As a result, ecosystems may stay more or less the same for long periods, but they can also change very suddenly. This change can be like a rapid switch from one state to another, this flipping is known to be a characteristic of nonlinear systems and complex systems in general. (Complexity Labs, 2018) Example: Forest Succession

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OpenStax College (2016) As an example of these two counteracting forces we can look at the succession of an ecosystem from grass to shrub community, beginning with an ecosystem in which the ground is covered with grasses. Shrubs may be present, but they are young and scattered. The ecosystem may stay this way for five to ten years, or possibly longer, because shrub seedlings grow very slowly. They grow slowly because grass roots are located in the topsoil, while most of the shrub roots are lower down. Grasses intercept most of the rainwater before it reaches the roots of the shrubs. Because the grasses limit the supply of water to the shrub seedlings, they maintain the integrity of the ecosystem as a grass ecosystem. At this stage, negative feedback is acting to keep the biological community the same. However, after a number of years, some of the trees and shrubs, which have been growing slowly, are finally tall enough to shade the grasses below them. The grasses then have less sunlight for photosynthesis, and their growth is restricted. This results in more water for the shrubs, which grow faster and shade the grasses even more. This process of positive feedback

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allows the shrubs to take over in a relatively short period of time. They now dominate the available sunlight and water, and the grasses decrease dramatically Even though a forest reaches a "climax" state, it could still face a landscape change due to fires, earthquakes, windstorms, etc. This could kill the large trees and give sunlight onto the forest floor to once again encourage the dominance of grasses and shrubs. Example: Canada's Atlantic Cod Fishing Banks An unfortunate example of tipping points is Canada's management of its east coast fishing banks. New efficient fishing vessels and government policies contributed to overfishing to the point that the entire fish population collapsed. Figure 4 shows the amount of Atlantic cod caught by year. During the period between 1850-1950 the amount of fish caught was sustainable; the amount of fish left after the catch always allowed the population to recover its numbers. However, after record high levels of fish caught during the 1960s and 1970s, the fish population began to get smaller in size and number. Instead of greatly restricting the fishing catch to allow these younger fish a chance to grow and re-populate, the government continued to allow fishing levels in the 1980s that existed before the record catches of the 1960-1970s. But this meant that the remaining breeding fish were caught and the population then completely collapsed at the start of the 1990s.

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Figure 4. Amount of Atlantic cod caught between 1950-2000 Millennium Ecosystem Assessment (2005). In 1992, the Canadian government put a moratorium on cod fishing. The hope was that the cod population would rebound in about two years according to simple predator-prey equilibrium models (in this case, humans were the main predator). However, even decades after the moratorium the once mighty cod population had not recovered. Instead, it appears that the cod's population has shifted into a new system state with a much lower population size. Modelling and understanding population dynamics is critical for the sustainable

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management of resources. Dynamic equilibrium means that we cannot assume that a system will self-regulate and regenerate back to its previous carrying capacity if the system is just "left alone." High levels of extraction might push a system to an entirely new carrying capacity or setpoint that could be irreversible. We could also think of a global nuclear war: the nuclear fallout and soil contamination would reduce the quality of life irreversibly for thousands of years. Nonequilibrium Ecology & Sustainability Thinking Using nonequilibrium models to understand socio-ecological systems offers several insights for sustainability thinking: ● Earth's biogeophysical systems do not change in linear, predictable ways . Gradual fluctuations around a given equilibrium state may be punctuated by threshold events and feedback loops that shift the system into a new equilibrium state. These shifts cannot always be "reversible" to a previous state. Precautionary and preventative actions are therefore necessary to avoid desirable system shifts. ● Nonequilibrium ecology challenges the premise of "restoration ecology" since it may not always be possible to recreate ecosystems following a significant disturbance. For example, the government and oil companies have promised to eventually reclaim Alberta's tar sands after they have been mined for bitumen, but this may not be possible (Struzik, 2014). Meanwhile, climate change owing in part due to the combustion of that bitumen may permanently change Alberta's weather and ecosystems (i.e., a new equilibrium state). ● The carrying capacity of a system is subject to change . Humans' alteration of the environment may decrease (or increase) the number of animals and humans that the Earth can sustain or the quality of life that is available to the living population. ● "Leaving nature alone" may not always produce ecosystems that are more biodiverse . There are many examples of where human intervention helped create more biological diverse ecosystems—e.g., by planting trees. Resilience and Planetary Boundaries

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Understanding Planetary Boundaries and Resilience Our understanding of feedback loops, thresholds and system shifts from the previous section can help us understand two important concept within sustainability thinking and practice: planetary boundaries and resilience. Planetary Boundaries Thinking in terms of the planet's carrying capacity helps us appreciate the need to reduce overall levels of resource consumption and pollution generation (i.e., reduce our ecological footprints). The concept of planetary boundaries provides a more refined model than carrying capacity for monitoring overshoot using thresholds or boundaries for nine key socio-ecological processes. Planetary boundaries are quantitative limits "within which humanity can continue to develop and thrive for generations to come. Crossing these boundaries increases the risk of generating large-scale abrupt or irreversible environmental changes" (Stockholm Resilience Centre, 2018).

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Figure 1. The nine planetary boundaries showing four boundaries that we have already exceeded: climate change; change in biosphere integrity; biogeochemical flows; and land-system change Steffen et al. (2015) Full-Size

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The nine planetary boundaries include: 1. *Climate change 2. *Change in biosphere integrity (biodiversity loss and species extinction) 3. Stratospheric ozone depletion 4. Ocean acidification 5. *Biogeochemical flows (phosphorus and nitrogen cycles) 6. *Land-system change (for example deforestation) 7. Freshwater use 8. Atmospheric aerosol loading (microscopic particles in the atmosphere that affect climate and living organisms) 9. Introduction of novel entities (e.g. organic pollutants, radioactive materials, nanomaterials, and micro-plastics) (Stockholm Resilience Centre, c. 2015a). These nine processes and systems "regulate the stability and resilience of the Earth System—the interactions of land, ocean, atmosphere and life that together provide conditions upon which our societies depend" (Stockholm Resilience Centre, 2015b). The four boundaries with asterisks above are those that we have already exceeded: climate change, change in biosphere integrity, biogeochemical flows, and land-system change. Rather than act as hard limits past which society will collapse, planetary boundaries are set at the start of zones of uncertainty (denoted by yellow and orange in Figure 1 ) where there is increasing risk that we have either: 1. crossed a critical continental or global threshold in an Earth system; or 2. exceeded a boundary level that will: "lead to significant interactions with regional and global thresholds and/or may cause a large number of undesired threshold effects at the local to regional scale, which in aggregate add up to a serious global concern for humanity" (Rockström et al., 2009). Table 1 is a table of the nine planetary boundaries showing the specific quantitative measures used to define each boundary. You do not need to memorize this table, but you should examine what indicators are used for measuring each planetary boundary. For example, we see that for climate change, the planetary boundary zone of uncertainty is set at a concentration of 350 carbon dioxide molecules per million of total molecules in the atmosphere (i.e., "350 ppm"). This information is a resource if you wish to understand and read further into the literature on sustainability science Table 1. Table of the nine planetary boundaries showing key variables, thresholds and quantitative boundaries used to calculate risk levels

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Ecological Resilience Sergey Gordienko/iStock/Getty Images Ecological resilience is both a goal for society as well as an analytical concept for understanding adaptation, maintenance and transformation of complex, uncertain, and non-linear socio-ecological systems. Socio-ecological systems are constantly faced with disturbances such as floods, earthquakes, political violence, pandemics, etc. Ecological resilience is defined as "the capacity of a system to absorb disturbance and reorganize while undergoing change so as to still retain essentially the same function, structure, identity, and feedbacks" (Walker et al., 2004, p.1).

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It has three key features: 1. "Persistence (sometimes called buffer capacity): the capacity of a system to maintain structure and function when faced with shocks and change (e.g. for a forest or coastal town to withstand the shock of a hurricane); 2. Adaptability: the capacity of people in a social-ecological system to manage resilience through collective action in order to stay within a desired state during periods of change (e.g. the ability to safeguard current food production systems under climate change); 3. Transformability: the capacity of people in a social-ecological system to learn, innovate and transform in periods of crisis in order to create a new system when ecological, political, social or economic conditions make the existing system untenable (e.g. turning the current financial crisis into an opportunity to transform the global economy and jump start the age of green economics)" (Folke et al., 2009). Simply put, resilience refers to how well a system can "bounce back" or reinvent itself after facing disturbance or a period of prolonged stress. For example, think about how a tropical coastal ecosystem responds to re-establish itself after a hurricane. Resilience is similar and complementary to sustainability in that both concepts emphasize system persistence. But sustainability tends to look much further into the future whereas resilience is often focused on short-term recovery or more immediate time scales (Marchese et al. 2018). A system might be resilience in the short-to-medium term but still not sustainable in the long run. A sustainable system should be resilient, but given the uncertainty of complex socio-ecological systems, even a well-intentioned sustainable system may prove not to be resilient to certain changes. Policy-makers also talk about building "resilient cities" that can meet residents' needs in the face of environmental changes associated with climate change (e.g., more severe heat waves and more intense storm events and associated flooding). Finally, it should be noted that both sustainability and resilience have positive normative connotations (i.e., they are seen as good things). However, some of the most unsustainable and oppressive systems have proven to be remarkably resilient. For example, the coal and oil industries have managed to maintain government support even after backlash following oil spills and widespread protests demanding the government take action to reduce greenhouse gas emissions. Despite clearly being unsustainable, these industries have made their companies and the oil-based economy resilient in the face of climate change and political turmoil. Applying Resilience Thinking Research on resilience has given rise to seven principles for increasing the resilience of

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ecosystem services within socio-ecological systems (Simonsen, 2014): 1. Principle one: Maintain diversity and redundancy Systems with many different components (e.g species, actors or sources of knowledge) are generally more resilient than systems with few components. Redundancy provides "insurance" within a system by allowing some components to compensate for the loss or failure of others: "don’t put all your eggs in one basket". It has, for example, been shown in Kenya, Tanzania, the Seychelles, Mauritius and Madagascar that coastal fishermen are more likely to leave fishing in response to declining catches if they come from households with more diverse livelihood portfolios. Not only does such livelihood flexibility increase the resilience of individual households, it also reduces the pressure on parts of the system, thereby enhancing resilience. 1. Principle two: Manage connectivity Connectivity can be both a good and a bad thing. The loss of electricity across the eastern USA and Canada in 2003, which affected some 50 million people, is an example of a network where local failures in a highly connected system eventually led to a total, systemic collapse. Perhaps the most positive effect of landscape connectivity is that it can contribute to the maintenance of biodiversity. The Yellowstone-to-Yukon project in North America is an example of conservation planning that reconnects large habitat patches by re-establishing wildlife corridors. Through a variety of collaborative initiatives with diverse stakeholder groups, Y2Y’s primary objective is to connect eight priority areas that function as either core wildlife habitat or key corridors in an area spanning 1.3 million square kilometres. 1. Principle three: Manage slow variables and feedbacks Imagine an ecosystem such as a freshwater lake that provides you with readily accessible drinking water. The quality of this water is linked to slowly changing variables such as the phosphorus concentration in the sediment, which is in turn linked to fertiliser runoff into the lake. The phosphorous content of the sediment can increase over a long time with no impact on lake water quality. However, if a certain threshold is passed, the lake water can rapidly become eutrified, after which it is very costly and difficult to return to a non-eutrophied state. Managing slow variables and feedbacks is often crucial to make sure ecosystems produce essential services. If these systems shift into a different configuration or regime, it can be extremely difficult to reverse.

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Feedbacks are the two-way "connectors" between variables that can either reinforce (positive feedback) or dampen (negative feedback) change. An example of a positive feedback loop can be seen in Hawaii where introduced grasses cause fires, which promote further growth of the grasses and curb the growth of native shrub species. More grass leads to more fire which, in turn, leads to more grass. This becomes a loop and self-reinforcing feedback. An example of a dampening or negative feedback is formal or informal sanctioning or punishment that occurs when someone breaks a rule. 1. Principle four: Foster complex adaptive systems thinking A complex adaptive systems (CAS) approach means accepting that within a social-ecological system, several connections are occurring at the same time on different levels. It also means accepting unpredictability and uncertainty, and acknowledging a multitude of perspectives. Although there is limited evidence that CAS thinking directly enhances the resilience of a system, there are several examples of how it contributes to it. One example is the Kruger National Park in South Africa where management has moved away from strategies to keep ecosystem conditions, such as elephant populations and fire frequencies, at a fixed level and instead allows them to fluctuate between specified boundaries. The use of threshold indicators provides managers with warning signals when a component of the system (e.g., elephant numbers) is approaching a critical point. The overall intention is to reduce human intervention (and investment) and increase the variety of ecosystems and habitat types. 1. Principle five: Encourage learning Because social-ecological systems are always in development there is a constant need to revise existing knowledge and stimulate learning in order to enable adaptation to change. More collaborative processes can also help make values about different ecosystem services more explicit. One excellent example is the Kristiandstad Vattenrike, a wetland area in the southern part of Sweden. In the 1970’s growing developmental pressures led to increasing degradation of what was considered a vast area of water logged swamps with low value. However, thanks to a broad and collaborative process including local inhabitants and politicians, the perception of the wetlands changed and it is now considered to be water rich, and a highly valued area that has become a UNESCO Biosphere Reserve. 1. Principle six: Broaden participation There are a range of advantages to a broad and well-functioning participation. An informed and well-functioning group have the potential to build trust and a

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shared understanding – both fundamental ingredients for collective action. An example is found in Australia where an extensive public participation and consultancy process was initiated to raise awareness about threats to the Great Barrier Reef. Through greater awareness of the threats facing the Great Barrier Reef, the public participation process was able to raise public support for improved conservation plans. 1. Principle seven: Promote polycentric governance Polycentricity, a governance system in which multiple governing bodies interact to make and enforce rules within a specific policy arena or location, is considered to be one of the best ways to achieve collective action in the face of disturbance and change. It represents flexible solutions for self-organisations where more formal procedures seem to fail. But it is also vulnerable to tensions between actors and negative institutional interactions. Involving a wide range of stakeholders means striking a balance between openness and mandates for decision-making. It also means negotiating trade-offs between various users of ecosystem services. These two trade-offs often lead to the third challenge about "scale-shopping" where groups dissatisfied with politics at one scale simply approach a more favourable political venue in which to frame their interests. A key to successful polycentric governance is therefore to keep the network together and maintain a tight structure, which goes beyond information sharing and ad hoc collaboration.

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