Transcript The Ecological Footprint Model

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 CO2
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)