How Global Change Works

Global Change & World Population Growth

Fig. 1. World Population Trends

Human populations have been rapidly growing in size since the era of cheap energy began with the industrial revolution in the 1800s. The illustration above, courtesy of the United Nations Environmental Program, shows that our species' population is growing at a rate of 1 billion every 12 or 13 years. In October of 2011 we will pass the 7 billion mark. Unless efforts are made to curb this growth, absent some kind of significant global event, we can expect the next billion to come aboard before 2025. This means we a 15% increase in the numbers of people deserving good governance and quality of life alongside their fair share of food, clothing, shelter and related amenities. This in a world of dwindling supplies of cheap energy, available land and renewable natural resources. If there is any good news to be had from the UNEP graphic above it is that the growth rate for industrialized nations seems to be flat, or even slightly declining. This suggests that population growth may level off in nations that can afford to invest in jobs, education and health care. When populations are educated and given opportunities to lead productive lives, when emancipation is realized by all demographic sectors, growth rates can be expected to level off.

Fig. 2. Population trends resulting from over
consumption of available natural resources.

Any population living in a closed environment (such as the earth, our 'container') eventually confronts what environmental resistance factors that constrain continued growth. The limits to growth are achieved when the population achieves the carrying capacity of the environment within which it lives. The population may overshoot the carrying capacity for a brief time, but limitations of available food, water, space or other supporting factors will cause the population to drop, sometimes dramatically (called a 'crash'). Overshoot will result in over consumption of resources leading to degradation of carrying capacity and a more precipitous drop in numbers over time.

Human populations have been able to grow to current levels because they have been supported by cheap energy, a redistribution of natural resources through international trade, and substitutions stemming from increasingly sophisticated technologies. Advances in, for example, mining, manufacturing, agriculture, transportation & distribution, health & environmental care, in concert with the expansion of populations into previously uninhabited areas, have supported continued population growth in every part of the world. But humanity's limits to growth have been under scrutiny for more than 40 years and investigators now conclude that our species has indeed exceeded the carrying capacity of the planet, having been in overshoot for nearly a decade. Global Footprint Network has concluded that:

"Today humanity uses the equivalent of 1.5 planets to provide the resources we use and absorb our waste. This means it now takes the Earth one year and six months to regenerate what we use in a year."

The science describing population growth trends and carrying capacity is well founded. It has been known for decades if not centuries that populations over-consuming (overshooting) available resources will experience a crash. This is true whether you are a wolves hunting moose, or a community of lynx hunting hares.

Fig. 3. Predator-prey relationships between Canadian wolves and moose.

Fig. 4. Predator-prey relationships between Canadian lynx and snowshoe hares.

Based on thirty years worth of assessments of available resources, consumptive demand and human population growth, we can see a very similar pattern confronting our species. Called 'peak everything', this set of trend curves illustrates the dilemma facing humanity when, shortly after the turn of the century, demand for natural resources peaks in relation to resource availability.

Fig. 5. 'Peak Everything' data from
Limits to Growth: The Thirty Year Update,
Meadows et al, 2004.

Examining the environmental effects of population growth in relation to available natural resources, we discover three planet-wide trends that have taken shape since population passed the 5 billion mark in the 1970s. Those trends have to do with:

1. greenhouse gas emissions, global warming (resulting in climate change),
2. over fishing, pollution, interruption of ocean nutrient cycles (resulting in ocean decline), and
3. land use change and appropriation of natural capital exclusively for human use (resulting in species extinction).

Here we will explore these trends, their interconnections and their implications for sustainability and quality of life.


Global Change & Ecosystem Services

Fig. 6. The relationship between ecosystem services and global change drivers.

Ecosystem services are both processes and products of natural systems at work within the planet's biosphere. These services have developed in response to changing environmental conditions influencing the structure and function of ecosystems, including such things the availability of nutrients & water, light & heat, the tilt of the planet’s axis and the length of a day.

Fig. 7. As illustrated by the Millennium Ecosystem Assessment (MEA),
ecosystem services support all aspects of human well being
including, ultimately, individual freedoms.

With these eco-services in place the earth operates like a living factory energized by a massive power plant, our sun, providing light and heat to support factory output. Processes at work within this factory operate like an assembly line producing clean air & water, fertile soil, foodstuffs, fibers and building materials. They operate like regulators to ensure the proper balance of atmospheric gases and climate conditions, to breakdown wastes and recycle nutrients, to mitigate floods and outbreaks of disease. Eco-factory output supports all living things and serves as the basis for all human economic activity. Ecosystem services are the foundation of every aspect of our quality of life.

But the capability of the global eco-factory is being degraded rapidly -- by poor maintenance practices, lack of attention to disappearing parts, and gradual erosion of environmental quality. This means the factory can no longer function at the same level of performance we once enjoyed. The factory's ability to produce consumable goods has declined. Its ability to perform self-regulating tasks has diminished. Climate change, ocean decline and species extinction (Fig. 6), driven by population growth, demand for natural resources and environmental degradation, are creating irreversible changes in the ways the biosphere operates, therefore driving irreversible changes in ecosystem services. Climate change, ocean decline and species extinction are the secondary drivers of global environmental change. Growing human demand for energy and natural resources (Fig. 7), at the current scale and pace, causes domain-scale changes in ecosystem services and is the ultimate cause of rapidly diminishing quality of life.

Fig. 8. Current rates of population growth have created
three domain-scale drivers of global environmental change.

These secondary, domain-scale global change drivers are not new to scientists, policy makers or attentive individuals. For decades they have been the subject of serious, detailed discussions. What is new, however, is the growing realization that these drivers are indeed of planetary scale, and that they are interdependent, self-perpetuating and accelerating.

Figure 8. illustrates how conditions active in one domain influence conditions is the other two domains. Feedback loops strengthen, and the rate of change increases as the effects interact. With respect to climate change the result of these interactions has been styled as 'runaway', meaning "the climate system passes a threshold or tipping point, after which internal positive feedback effects cause the climate to continue changing without further external forcing." Continued release of greenhouse gases serves as an example of positive feedback to the climate system, but to a much larger extent so do the feedback loops from the two other domain-scale drives of species extinction and ocean decline. Understanding these planetary-scale relationships and their consequences has until now (via this model, for example) escaped the attention of the scientific and policy communities.

Figure 9. The Interdependence of Domain Scale Global Change Drivers

As if they didn't already have enough to contend with, this creates an enormous problem for decision makers. It will not be enough for governments and corporations to come to grips with any one of these issues alone. Or to address even two of them at once. All three issues will have to addressed simultaneously, comprehensively. To do anything less means that solutions are inadequate to meet the challenges illustrated here, that deterioration of ecosystem services will continue, and that quality of life will increasingly suffer as a result.

There is an urgent need for effective international action on these issues, and on the overarching trend of growing world population and demand for renewable natural resources.

An Integrated Global Change Model (Part 2)

In Part 1. we saw that human population growth has been exhausting, at an ever-increasing rate, the world's renewable natural capital (biocapacity). We saw how population growth, people's demand for biocapacity, and their consumption of natural resources has affected the quality of our environment at the global scale. The result of this has been the acceleration of planet-wide environmental change. This change, at the scale in which it is occurring, affects the global climate, the world's ocean, and the mix of animal and plant species supporting ecosystem productivity world wide.

In Part 1. we saw that the three domain scale environmental changes going on across the planet are all interrelated and interdependent. Changes occurring in the atmosphere effect the oceans and the land, as well as support systems for animal & plant species. Accelerating climate change thus accelerates ocean decline and species extinction. The same is true for the other domain scale changes in reverse order.

This means that decision makers must take all three global scale trends into account when designing appropriate fixes. It is not good enough to address any single domain scale trend, all three must be addressed we are to rebalance our relationship with the natural world.

Reductions in environmental quality and in the ability of the planet to support human needs, is a result of lost ecosystem services. These services represent both the processes and the products of ecosystem productivity. Any loss of eco-services impacts both quality of life and overall economic productivity.

Fig. 10. Carrying capacity is the maximum ability of a natural system to support (carry) a population.

There is a lot of information in Fig. 10, so let's look at the various parts one at a time.

The left side of the figure should be familiar by now. We have discussed the relationship between population growth and the three large, secondary drivers of global change. We have discussed how these drivers effect ecosystem services. We have emphasized that population growth leads to an over consumption of renewable biocapacity. Over consumption, or overshoot, creates a rebound effect in terms of lost ecosystem productivity as the environment comes to a new equilibrium point around remaining eco-services (Fig. 11).

Fig. 11. Overshoot leads to loss of ecosystem services, hence reduced ability of the environment to support large populations.

The right side of the Fig. 10 presents new information. For the first time we are studying annual, renewable biocapacity. We will talk about what that is and where it comes from. We will talk about some called Net Primary Productivity (NPP). We will distinguish between 'wild' net primary productivity (WNPP) and 'human appropriated' net primary productivity (HANPP). We will see how growing human populations are rapidly converting wild NPP to human-dominated NPP, and how this changes land use patterns around the world such that ecosystem 'richness' (optimum diversity) is compromised, therefore compromising productivity of the ecosystem factory.

Fig. 12. IPAT, the ecological footprint and global biocapacity.

Figure 12. sets the stage for us to discuss the relationship between two groundbreaking concepts of the 20th century, the IPAT formula and the ecological footprint.

IPAT evolved out of a debate that began in the 1970s between proponents of Paul Ehrlich's view (The Population Bomb, 1968) that population growth was the most significant influence in declining environmental quality, and proponents of Barry Commoner's view (The Closing Circle, 1971) that inefficient industrial capacity and the misuse of technology was to blame.

Fig. 13. Two books that changed the world.

The IPAT formula was proposed in an article in Science magazine [Science 171 (1971): 1212-17] written by Ehrlich and fellow Stanford scientist John Holdren. The IPAT formula proposes that human Impacts on the environment result from a combination of the size of human Population, Affluence or the demand on the planet's biocapacity to support human needs, and the embodied energy or resource intensity of Technology. P x A x T = Impact on the environment.

The ecological footprint was developed by Bill Rees and Mathis Wackernagle in 1992 in an effort to standardize the way in which policy makers accounted for human demands on natural capital, or the stock of renewable resources supporting consumption and quality of life. Natural capital is closely aligned with the term biocapacity, but biocapacity includes not only renewable natural productivity, but natural systems that process waste materials too.