The Ecological Footprint Model Is humanity outrunning the ecological capacity of the Earth to sustain human life?

Pop Quiz 2 Solutions  Q: Why did we conclude that high school GPA is a better predictor of college success than SAT?  A: Because regression models that use high school GPA to predict college GPA explain more variance than models that use SAT

Pop Quiz 2 Solutions  Q: Why did investigators look at the unexplained variance for evidence of gender bias?  A: Because their regression models used all the other inputs that might explain salary difference. If there was gender bias, it would show up in the unexplained variance.

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?

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

Modeling goal  A single number to represent the fraction of Earth’s ecological capacity being used  If this number is more than 100%, humans are in trouble and must change our ways  We can track this number to see trends (better or worse) over time.

Candidate: human population size  Ecology: the carrying capacity for a species is the maximum population of that species the environment can sustainably support  Humans are different because their lifestyles can vary (e.g. Americans vs. Europeans vs. Chinese)  A high-consumption individual intuitively uses up more ecological capacity than a low-consumption individual  How to measure total ecological impact?

Estimating total impact  Model needs to “boil down” thousands of items we consume into a single meaningful number  Result is a type of index

IPAT formula by Paul Ehrlich  Impact = Population x Affluence x Technology (I=PAT)  Population x Affluence = Total $ of consumption  Technology factor = how much ecological impact per dollar of consumption  Doubling P, A, or T will double impact

IPAT formula by Paul Ehrlich  Technology factor : smaller is better  Consumption growth affects the environment more than population growth  Cannot calculate actual numbers, so it is only a conceptual model

Ecological Footprint model  Fundamental ecological “currency”: productive land and sea area  Every product measured in usage of four land area types  Total area used is the “Ecological footprint”  Can compare against known total Earth productive area.

Components of a footprint  Energy land (growing plants to soak up CO 2 output from fossil fuel consumption)  Built up land  Farm land  Forest land  Footprint calculations are data-intensive rather than computation-intensive

Footprint Calculation

US Ecological Footprint

Global Ecological Footprint  1961: Total human footprint was 61% of Earth’s productive land area  1998: Total human footprint was 135% of Earth’s productive land area  Total footprint if each person lived US lifestyle = 400% of Earth’s productive capacity

Footprints and ecological Ethics “We part the veil on our killer sun Can’t keep the straight path on this short run The more we take, the less we become.” --Sarah Maclaclan, “World on Fire”

The Ethical questions 1.Is there a finite ecological space that we all must share? 2.If so, are we taking too much of this space away from other humans? 3.Are we taking too much ecological space from other species? Question #1 is factual, #2 and #3 are ethical (but depend on #1)