Course: BIS 105 Environmental Biology

Unit 5 Learning Module

Future Growth

Future Population Growth: Does Earth Have a Carrying Capacity for Humans?

According to the United Nations Population Fund the world population reached the 7 billion mark on October 31, 2011. The US Census Bureau estimated a slightly later date of March 12, 2012 (visit http://www.census.gov/main/www/popcld.html for a current estimate). Historically, we didn’t hit the one-billion mark until 1804 (having begun 200,000 years earlier), but we needed just 12 years to grow by our last billion. Projections by the United Nations and the U.S. Census Bureau predict that by 2050 Earth will host over 9 billion people.

See http://www.youtube.com/watch?v=4BbkQiQyaYc (7:31) for an animation of world population growth.

Cornucopians welcome such growth, believing more people are better for technology and innovation. The demographic transition model predicts that when all nations are industrialized, the human population will eventually reach a stable level – a carrying capacity of sorts. However, many scientists believe that humans have already overshot the carrying capacity of Earth for our unique levels of resource exploitation and habitat alteration. They and other Neo-Malthusians predict that resource depletion and environmental degradation will eventually lead to famine, epidemics, or war – a Malthusian crisis.

Does Earth have a carrying capacity for humans? Recall that carrying capacity is the maximum population size that a particular environment can support without habitat degradation. Ideally, carrying capacity matches population size to resource availability. Although the human population is clearly continuing to grow, many scientists believe that we over-consume resources and exceed the environment’s capacity to cycle nutrients and process waste. They believe that multiple factors will contribute to a crisis in which disease, starvation, or global conflict will cause a population crash or even extinction.

IPAT Equation

The future well-being of the planet is not just concerned with population size changes. As we saw earlier in the course, ecological footprints are not equal for people in all countries. To better understand of our changing impact on the environment, we need to include factors other than just population size. The IPAT equation arose in the 1970s as discussion regarding the impact of the growing population and consumption would have on the environment. As is the case for any equation, IPAT expresses a balance among interacting factors. It can be stated as

I=P×A×T

where I represents the impacts of a given course of action on the environment, P is the relevant human population for the problem at hand, A is the level of affluence (which affects consumption) per person, and T is technology which represents impact per unit of consumption. Impact per unit of consumption is a general term for how resource intensive the production of affluence is; how much environmental impact is involved in creating, transporting and disposing of the goods, services and amenities used. The equation is not meant to be mathematically rigorous; rather it provides a way of organizing information for a “first-order” analysis.

Suppose we wish to project future needs for maintaining global environmental quality at present day levels for the mid-twenty-first century. For this we need to have some projection of human population (P) and an idea of rates of growth in consumption (A).

The above figure suggests that global population in 2050 will grow from 6.8 billion in 2010 to about 9.2 billion, an increase of 35%. Global GDP (Gross Domestic Product, one measure of consumption) varies from year to year but, using the figure below as a guide, an annual growth rate of about 3.5% seems historically accurate (growth at 3.5%, when compounded for forty years, means that the global economy will be four times as large at mid-century as today).

P 2010 x A 2010 x T 2010 = P 2050 x A 2050 x T 2050
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Thus if we wish to maintain environmental impacts (I) at their current levels
(i.e. I_2050 = I_2010), then

P 2010 × A 2010 × T 2010 = P 2050 × A 2050 × T 2050 P 2010 × A 2010 × T 2010 = P 2050 × A 2050 × T 2050 size 12{P rSub { size 8{"2010"} } times A rSub { size 8{"2010"} } times T rSub { size 8{"2010"} } =P rSub { size 8{"2050"} } times A rSub { size 8{"2050"} } times T rSub { size 8{"2050"} } } {}

or

T 2050 T 2010 = P 2010 P 2050 × A 2010 A 2050 = 1 1 . 35 × 1 4 = 1 5 . 4 T 2050 T 2010 = P 2010 P 2050 × A 2010 A 2050 = 1 1 . 35 × 1 4 = 1 5 . 4 size 12{ { {T rSub { size 8{"2050"} } } over {T rSub { size 8{"2010"} } } } = left [ { {P rSub { size 8{"2010"} } } over {P rSub { size 8{"2050"} } } } right ] times left [ { {A rSub { size 8{"2010"} } } over {A rSub { size 8{"2050"} } } } right ]= left [ { {1} over {1 "." "35"} } right ] times left [ { {1} over {4} } right ]= left [ { {1} over {5 "." 4} } right ]} {}

This means that just to maintain current environmental quality in the face of growing population and levels of affluence, our technological decoupling will need to reduce impacts by about a factor of five. So, for instance, many recently adopted “climate action plans” for local regions and municipalities, such as the Chicago Climate Action Plan, typically call for a reduction in greenhouse gas emissions (admittedly just one impact measure) of eighty percent by mid-century. The means to achieve such reductions, or even whether or not they are necessary, are matters of intense debate; where one group sees expensive remedies with little demonstrable return, another sees opportunities for investment in new technologies, businesses, and employment sectors, with collateral improvements in global and national well-being.

Human Consumption and the "Rebound" Effect

In 1865 William Jevons (1835-1882), a British economist, wrote a book entitled “The Coal Question,” in which he presented data on the depletion of coal reserves yet, seemingly paradoxically, an increase in the consumption of coal in England throughout most of the 19^th century. He theorized that significant improvements in the efficiency of the steam engine had increased the utility of energy from coal and, in effect, lowered the price of energy, thereby increasing consumption. This is known as the Jevons paradox, the principle that as technological progress increases the efficiency of resource utilization, consumption of that resource will increase. Increased consumption that negates part of the efficiency gains is referred to as “rebound,” while overconsumption is called “backfire.” Such a counter-intuitive theory has not been met with universal acceptance, even among economists (see, for example, “The Efficiency Dilemma”). Many environmentalists, who see improvements in efficiency as a cornerstone of sustainability, openly question the validity of this theory. After all, is it sensible to suggest that we not improve technological efficiency?

Part of the problem in analyzing data pertaining to whether or not such “overconsumption” is happening depends on the specific good or service in question, the degree to which the data truly represent that good or service, and the level of detail that the data measure. The table below summarizes some recent findings from the literature on the comparative efficiency and consumption for several activities over extended periods of observation. Taken collectively these activities capture several basic enabling aspects of modern society: major materials, transportation, energy generation, and food production. In all cases the data show that over the long term, consumption outpaces gains in efficiency by wide margins, (i.e., the ratio of (Consumption / Efficiency) is greater than 1). It should also be noted that in all cases, the increases in consumption are significantly greater than increases in population. The data do not verify Jevons paradox; we would need to know something about the prices of these goods and services over time, and examine the degree to which substitution might have occurred (for instance aluminum for iron, air travel for automobile travel). To see if such large increases in consumption have translated into comparable decreases in environmental quality, or declines in social equity, other information must be examined. Despite this, the information presented does show a series of patterns that broadly reflect human consumption of goods and services that we consider essential for modern living and for which efficiency gains have not kept pace; in a world of finite resources such consumption patterns cannot continue indefinitely.

Historical Efficiency and Consumption Trends in the United States Source: Dahmus and Gutowski, 2011
Activity | Time Period | Avg Annual Efficiency Improvement (%) | Avg Annual Increase in Consumption (%) | Ratio: Consumption/Efficiency
Pig Iron | 1800-1990 | 1.4 | 4.1 | 3.0
Aluminum | 1900-2005 | 1.2 | 9.8 | 7.9
Fertilizer | 1920-2000 | 1.0 | 8.8 | 8.9
Electricity-Coal | 1920-2007 | 1.3 | 5.7 | 4.5
Electricity-Oil | 1920-2007 | 1.5 | 6.2 | 4.2
Electricity-Nat Gas | 1920-2007 | 1.8 | 9.6 | 5.5
Freight Rail Travel | 1960-2006 | 2.0 | 2.5 | 1.2
Air Passenger Travel | 1960-2007 | 1.3 | 6.3 | 4.9
Motor Vehicle Travel | 1940-2006 | 0.3 | 3.8 | 11.0

Our consumption of goods and services creates a viable economy, and also reflects our social needs. For example, most of us consider it a social good that we can travel large distances rather quickly, safely, and more or less whenever we feel the need. Similarly, we realize social value in having aluminum (lightweight, strong, and ductile) available, in spite of its energy costs, because it makes so many conveniences, from air travel to beverage cans, possible. This is at the center of the sustainability paradigm: human behavior is a social and ethical phenomenon, not a technological one. Whether or not we must “overconsume” to realize social benefits is at the core of sustainable solutions to problems.