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Global Climate Change
Understanding the MIT study & what
it means for public policy
MIT Study: 1- The Input Data
Emissions, inflow, (billions of tons/year)
7
Anthropogenic CO2 Emissions
6
5
3
4
Emissions
3
2
1
net Removal,
outflow, = 3
0
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
Edward J. Garrity
2000
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MIT Study – 2, Hypothetical Future
Atmospheric CO2 Gradually Rises to 400ppm & Stabilizes
Anthropogenic CO2 Atmospheric level
440
420
400
380
360
CO2
340
320
300
280
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100
Step 3 – Subjects asked to sketch the likely future CO2 emissions given this
scenario above.
Edward J. Garrity
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MIT Study – 3, Example Results
Emissions (inflow), Removal (Outflow)
9
Anthropogenic CO2 Emissions
8
7
6
5
Emissions
4
Net Removal
3
2
1
0
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100
Edward J. Garrity
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Edward J. Garrity
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Why would smart people make this
mistake?
• Cognitive processing
• System 1: Our brains operate automatically,
quickly, little effort, involuntary reaction,
intuitive, infers & invents causes & intentions,
neglects ambiguity & suppresses doubt, is
biased to believe & confirm, frames decisions
narrowly
• System 2: deliberate, effortful, rational
Edward J. Garrity
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System 1 at work
• We tend to use the information that is readily
available (WYSIATI)
• System 1 is designed to jump to conclusions
from little evidence; we construct stories from
the evidence
• IF the story has coherence, then we have
confidence in our opinions
Edward J. Garrity
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MIT Experiment, CO2 levels
• Problem was framed, presented in a simple
manner: Atmospheric concentrations, what
would future emissions look like?
• System 1 at work: Two variables are related,
correlation heuristic
• If atmospheric CO2 levels off, then emissions
must level off to match results
• We easily ignore missing information
Edward J. Garrity
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Mental Model is Missing
• Bathtub analogy for stock & flow dynamics
Emissions,
inflow
Atmospheric
CO2
Edward J. Garrity
removal,
outflow
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Stock & Flow Reasoning
• In order for Atmospheric CO2 levels to level
off (equilibrium), … implies that inflows =
outflows
• In 2000, inflow from human activity is 6 bil.
Tons, but outflow (removal) is 3 bil. tons
• By 2080, inflow (from industrial activity)
would need to be reduced to 3 bil. tons
• Therefore, need to decrease by 50%!
Edward J. Garrity
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Implications
• Public does not understand the problem
• More needs to be done to halt Global Climate
Change than people realize
• Although it is extremely difficult* to get, for
example, a 20% decline in use of fossil fuels, …
simply reducing by 20% means that we are
still losing ground (Earth is heating). We need
to get at least 50% reduction to keep stable
Edward J. Garrity
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