Ecological Sustainability: what can models tell us? Dan Everett, CS department These notes available in outline form: http://www.cs.uga.edu/~cs1210/Lectures/Sustainability/index.html

What is sustainability? Humans living in a way that does not diminish Earth’s capacity to sustain life Alternatively: living within Earth’s ecological carrying capacity Are we going through a global ecological crisis?

Why use computer models? A valid model matches reality and can be used to accurately predict the future Unfortunately, we do not have a valid model of human interaction with Earth A useful model illustrates key processes that govern the real system

Models, bias, and objectivity To create models, we must make assumptions This introduces the possibility of bias However, invalid models will not validate! (model predictions do not match reality) By rejecting incorrect ideas, we hope to eventually discover objective reality

What models cannot do Inform us about our values Predict results of conscious human decisions

Positive feedback When a system is changed, the system reacts to reinforce the change: Example: I drink alcohol It makes me feel better I drink more

Population with positive feedback When population size increases, there are more new births More births increases population faster Result: exponential growth

Feedback and growth Positive feedback tend to produce exponential curve: Rises with increasing speed Doubles in constant time (Doubling time =70 / percent increase)

Exponential growth & finite limit Is this a valid/useful model of humans on Earth? If so: Where is the limit? What happens when we reach the limit?

Negative feedback When a system is changed, the system reacts to resist the change Example: I drink more alcohol I feel sufficiently inebriated I stop drinking

Adding negative feedback As population approaches the carrying capacity, growth rate decreases Population continues to increase, but more slowly

Results of logistic model Population makes a “soft landing” right on the carrying capacity When population is small, positive feedback rules As population increases, negative feedback takes over -- the system feels its limits.

Negative Feedback With Delay System responds to the limit, but only after a delay. Result: system overshoots and oscillates around the limit.

Overshoot and collapse Previous model assumes carrying capacity is constant What if a severe overshoot degrades the environment? Carrying capacity might be permanently reduced Image:http://www.dieoff.com/page80.htm

Humans are different… Human carrying capacity is hard to define, because… Technological changes affect food production Complex social factors affect population

Eighteenth Century China “Golden Age” of Qing Dynasty Peace and stability “Mandate” for social welfare Regional “ever-normal granaries” “Hydraulic conservancy” for flood control, irrigation, canals

Ecological Cost of Golden Age Prosperity and stability encouraged population growth Marginal lands brought under cultivation Watershed forests cut down… … increasing erosion and sedimentation

Nineteenth Century China Crushing cost of flood control Yellow River changed course (1855) European depredations (Opium wars, etc.) Internal decay and corruption Rebellion and civil war Extremely severe El Ninos 1873—1900 Result: Massive famines

China Today Current population is much larger than Golden Age… …but is current population sustainable? Massive famines in 1960’s unrelated to population size Government is intent on population stabilization

Population stabilization: a sensitive topic Deeply held religious beliefs about procreation, families, and society People resist interference in their family lives Residue of mistrust from colonialism… … which we need to understand better!

A Global Population Consensus 1994 UN Summit on Population and Development: Population stabilization is an important part of sustainable development Not a separate goal, but in context of better health care and development Key to success: empowering women http://www.iisd.ca/cairo.html --Unfortunately, US coverage of the Cairo conference focused entirely on the abortion debate.

Population: accomplishments World population quadrupled in the last century Average life expectancy rose from 46 to 66 years Developed countries’ fertility is 1.5 Developing countries’ fertility dropped from 6.2 to 3.1 Many countries have passed laws increasing status of women Families with fewer children invest more in their care: Children are an investment, not a lottery.”

Projecting population future Population trends are easy to predict if we know fertility and mortality rates Fertility and mortality are very hard to predict!

UN projections: World population may have passed its inflection point in 1970. Herman Kahn called this time The Year Zero Population may increase 50% in 21st century

A critical generation One billion Earthlings are now in their adolescent years The fate of these young people may be critical to our planet’s future

The IPAT formula I = PAT I = environmental Impact P = population size Proposed by Paul Ehrlich I = environmental Impact P = population size A = Affluence T = Technology factor http://www.stanford.edu/group/CCB/Staff/paul.htm

IPAT: a conceptual model Population is not the only factor An American has more environmental impact than a Bangladeshi or Chinese To reduce environmental impact we must control P, A, T or all three Problem with IPAT: no defined measure of total impact I

Ecological Footprint model Definition of total impact: Ecological fooprint is the total land area that would be needed to support a city, country, or other population unit. http://www.ire.ubc.ca/ecoresearch/ecoftpr.html

Calculating National Ecological Footprints Economic categories are evaluated Land is needed to supply food, space for built structures, wood supply, or to absorb carbon emissions Add these amounts up for all economic categories Result is the ecological footprint

Results of Ecological footprint Were everyone on Earth to live as an average North American… It would require three Earths to sustain this lifestyle.

The Nightmare Scenario World3 model created by MIT systems group for the Club of Rome Model updated, 1990 Graphic: www.dieoff.com

Deconstructing World3 World3 is complex: over 100 variables Assumptions are hidden in equations Critique: “Malthus in, Malthus out”

Deconstructing World3

Deconstructing World3

What has happened? Nonrenewable resources begin to run out Capital is diverted to resource extraction Less capital for agriculture Yields fall, leading to famine and death Malthus in, Malthus out!

The Cornucopians Economist Julian Simon bet ecologist Paul Ehrlich that prices of nonrenewable resources would fall Ehrlich lost and had to pay Simon $1000 Cornucopians argue that human ingenuity will surmount all “limits” to growth. http://www.cato.org/pubs/policy_report/cpr-20n2-1.html

Are there limits? Simon declined this bet. Ehrlich and climatologist Steven Schneider offered to bet Simon $1000 on each of 15 ecological indicators getting worse over time. Simon declined this bet. The limits to growth are not industrial resources, but ecological resources The real limit may be the ability of Earth to absorb pollution

Ecological safety factor? Many scientists believe that humans should use at most 50% of Earth’s ecological capacity This gives us a safety margin in case our calculations are off It also leaves some room for other living things to share our planet

The Big Question: How much do humans have to change in order to live within Earth’s carrying capacity?

And the answer is… Ecological overload factor if every Earthling comes up to US lifestyle: 3 Additional population increase from 6 to 9 billion: 1.5 Further improvement needed to leave 50% of Earth alone 2 TOTAL IMPROVEMENT NEEDED: 9

What does this mean? We need at least a 9-fold reduction in the amount of pollution caused by each dollar of economic activity Design school: Factor Ten Another design school: Zero Waste

Is Zero Waste possible? Nature does it! Bill McDonough: divide materials into industrial nutrients and ecological nutrients Recycle industrial nutrients Compost biological nutrients Voila! Future technology!

A Democracy Deficit? Those most vulnerable are far away… And have little power to promote change Needed: effective planetary democracy Struggle over the global trade system – the front line of the battle to save the Earth?

Acknowledgements Material on China from Mike Davis, Late Victorian Holocausts