1. Wedges Reaffirmed
Robert Socolow
socolow@princeton.edu
Princeton Energy and Climate Scholars
Princeton University
December 1, 2011

2. Motivation for my recent work
We will greatly increase the damage from climate change
if we postpone action for decades.
We might well postpone action as a response to becoming
disheartened.
We could become disheartened as a result of discovering
that we will not achieve the currently discussed, extremely
difficult goal – the only one that is widely espoused.

3. Motivation for my recent work
The extremely difficult goal espoused by many the world’s
diplomats and the environmentalists is “two degrees.” To
achieve “two degrees,” the fossil fuel system must be shut
down by mid-century.
There is no appetite for discussion of any goal that is less
stringent. Yet a consensus could develop—possibly quite
soon—that “two degrees” will not be attained.
It would be desirable to prepare now to discuss some
relatively less difficult goal that nonetheless requires,
starting immediately, major national commitments and
international coordination, and that could be attained.

4. Einstein’s advice
“Make everything as simple as possible, but no simpler.”

5. Historical Emissions
Billions of tons of CO2
60
emitted per year
30 Historical
emissions
6
0
1950 2000 2050 2100

6. The Stabilization Triangle
Billions of tons of CO2
60
emitted per year
Stabilization
Triangle Interim Goal
30 Historical
emissions Flat path
6
0
1950 2000 2050 2100
Today and for the interim goal, global per-capita emissions are ≈ 4 tCO2/yr.

7. Per-capita fossil-fuel CO2 emissions, 2005
World emissions: 27 billion tons CO2
AVERAGE
STABILIZATION
1-
Source: IEA WEO 2007

8. The Stabilization Triangle
Billions of tons of CO2 Easier CO2 target
60
emitted per year ~850 ppm
Stabilization
Triangle Interim Goal
30 Historical
emissions Flat path
2.5oC
6
0
1950 2000 2050 2100

9. Alternative versions of targets
Em: Emission rate at some future time (tCO2/yr)
Conc: Maximum allowed concentration (tCO2) – often ppm.
CumEm: Cumulative emissions (“budget”) for an interval (tCO2)
Temp: Maximum allowed average surface temperature increase
relative to pre-industrial times (oC)
Conc
Em Temp
CumEm

10. Relationships among global targets
Conc
(2) (3)
Em Temp
(1) (4)
CumEm
(1): dCumEm/dt = Em
(2): dConc/dt = λ*Em, λ ≈ 0.5 (“Half Stays In”)
(3): Temp = CS*ln(Conc/Conco)/ln2,
where Conco = pre-industrial concentration ≈ 2200 GtCO2
and CS = climate sensitivity
(central value of CS is 3.0oC; 66% interval: 2.0oC < CS < 4.5oC)
(4): Temp = K*CumEm∞,
where CumEm∞ extends from pre-industrial time to infinity
and, in units of oC/1000GtCO2, the central value of K is 0.48: 90%
interval: 0.27 < K < 0.68. In short, 2000 GtCO2 ≈ 1oC.

11. The 2oC Variant is still tougher
Billions of tons of CO2 Easier CO2 target
60
emitted per year ~850 ppm
Stabilization
Triangle Interim Goal
30 Historical
emissions Flat path
2.5oC
Tougher
6
interim goal 2oC
0
1950 2000 2050 2100

12. “Flat” vs. “down 50%” is about the
developing world’s emissions
X
Up 60% or down 60% Up 140% or up 60%, or down 40%
Analysis of low-carbon industrialization has been far too casual for me
to be comfortable endorsing the lower fifty-year target at this time.
Source of Figure: Socolow and Pacala, “A plan to keep carbon in check,” Scientific American, Sept 2006.

13. The developing world will decide what
kind of planet we live on.
For a while longer, the industrialized
countries will lead.

14. Stabilization Wedges
Billions of tons of CO2
60 16 GtC/y
emitted per year
Eight “wedges”
Interim Goal
30 Historical
emissions Flat path
6
0
1950 2000 2050 2100

15. What is a “Wedge”?
A “wedge” is a strategy to reduce carbon emissions that grows
in 50 years from zero to 4 GtCO2/yr. The strategy has already
been commercialized at scale somewhere.
4 GtCO2/yr
Total = 100 Gigatons CO2
50 years
Cumulatively, a wedge redirects the flow of 100 GtCO2 in its first 50
years. This is six trillion dollars at $60/tCO2.
A “solution” to the CO2 problem should provide at least one wedge.

16. Fill the Stabilization Triangle with Eight Wedges
in six broad categories
Energy Efficiency
Smaller Decarbonized
Families 60 GtCO2/yr Electricity
Stabilization
Methane Triangle Decarbonized
Management Fuels
30 GtCO2/yr
2008 2058
Extra Carbon in Forests, Soils,
Oceans

17. The Virtual Triangle: Large Carbon Savings Are
Already in the Baseline
120 Emissions proportional to
economic growth
90
GtCO2/yr
Virtual
60 Triangle
Historical Stabilization Triangle
30 emissions Flat path
8
0 1957 2007 2057
Models differ widely in their estimates of contributions to the virtual triangle from structural
shifts (toward services), energy efficiency, and carbon-free energy.

18. Legacy: U.S. Power Plants
Source: Benchmarking Air Emissions, April 2006. The report was
co-sponsored by CERES, NRDC and PSEG.

19. U.S. power plant capacity, by vintage
80000 Capacity, total by source
70000
Other
Renewables
60000
Water
50000 Nuclear Issues:
Grandfathering, retirement, relicensing,
megawatt
Gas
40000 Oil retrofit, repowering
Coal
30000
20000
10000
0
1950 1960 1970 1980 1990 2000
year of initial operation
Source: EIA. Joseph.Beamon@eia.doe.gov

20. U.S. CO2 pipeline infrastructure
Denbury proposes to
send Ohio Valley CO2 to
the Gulf states.
Source: "Reducing CO2 Emissions from Coal-Fired Power Plants," John Wheeldon, EPRI, presented at the CCTR Advisory Panel Meeting,
Vincennes University, Vincennes IN, September 10, 2009. Reproduced in Science Applications International Corporation, Indiana and
Coal: Keeping Indiana Energy Cost Competitive, June 2010, Fig. 2-15, submitted to Indiana Center for Coal Technology Research

21. China Appliance Standards
Business as Usual: CO2 emissions from air
conditioners in 2020 are 9x those in 2000.
New Air Conditioner Standard: Down 25% (45
MtCO2/yr) in 2020.
180
160
140
120
100
80
60
40
20
0
2000 2002 2004 2006 2008 2010 2012 2014 2016 2018 2020
50 million new, efficient air conditioners per year in 2020
Analysis of low-carbon industrialization has been far too casual. There’s work to do.

22. The UN’s “low”population projection has almost 10 billion
fewer people in 2100 than its “high” projection.
Billion
people
High:15.8, 2.6 kids/Mom
Medium:10.1, 2.1 kids/Mom
Peak at ≈ Low: 6.2, 1.6 kids/Mom
2050 dPop/dt falls to -0.8%/yr in 2100.
If sustained, 2.8 billion in 2200.
Source: United Nations. http://esa.un.org/unpd/wpp/unpp/panel_population.htm

23. UN Population Projections (2 of 2)
-0.8%/yr in 2100.
If sustained,
2.8 billion in 2200.
Source: United Nations. http://esa.un.org/unpd/wpp/unpp/panel_population.htm

24. We have lost precious time.
Annual Rate of Emissions of CO2 Globally
Year GtC/yr x
2008 8749
2007 8543 x
2006 8350
2005 8086
2004 7782
2003 7397
2002 6981
2001 6916
Source (accessed 10/1/11): http://cdiac.ornl.gov/trends/emis/glo.html.

25. “Wedges reaffirmed,”
a short essay released on Sept 27, 2011
The essay was accompanied by
comments from:
Carter Bales
Ralph Cicerone
Freeman Dyson
Christopher Field
Robert Fri
David Hawkins
Rush Holt
Robert May
Phil Sharp
Nicholas Stern
New trajectory: 550 ppm, 3oC
Released at www.thebulletin.org and www.climatecentral.org.
Comments at www.dotearth.blogs.nytimes.com.

26. What’s in the way of action?
Important factors have been beyond the control of the
environmental community:
•The recent recession
•The political influence of the fossil fuel industries and the
beneficiaries of low-cost power (e.g., the coal-power states)
•Economic development imperatives in countries
undergoing industrialization.
However, advocates for prompt action, of whom I am one, also
bear responsibility for the poor quality of the discussion and the
lack of momentum.

27. Ways to restart the conversation
Advocates for prompt action could and should have
acknowledged that:
•The news is unwelcome
•The science is incomplete
•“Solutions” can bring serious problems of their own.
Might these three domains of political discourse be seedbeds
for the restarting of serious discussion and ensuing action?

28. The news is unwelcome.
Never in history has the work of so few led to so much
being asked of so many!
The “few” are today’s climate science researchers.
The “many” are the rest of us.
We are asked to reduce our emissions promptly and
substantially.

29. Greenland: 7 meters.
West Antarctica : 5 meters
1 meter 2 meters
4 meters 8 meters
A falling sea level would also be disruptive!
Source: T. Knutson, Geophysical Fluid Dynamics Laboratory, NOAA. See:
http://www.gfdl.noaa.gov/~tk/climate_dynamics/climate_impact_webpage.html#section4

30. “Shooting the messenger”? No surprise.
The messenger has been shot before.
Galileo argued that the earth wasn’t at the center of the
universe and was excommunicated.
Darwin argued that human beings were part of the animal
kingdom and was cruelly mocked.
The idea that humans can’t change our planet is as out-of-
date and wrong as the earth-centered universe and the
separate creation of Man.
But all three ideas have such appeal that they will fade away
only very slowly.

31. The science is incomplete
1.Neither slow nor rapid arrival of severe
climate change can be ruled out, given our
poor understanding of feedbacks.
2.The probability of very bad outcomes is
poorly known.
3.Breakthroughs are not imminent. We are
not only flying blind, but the fog is not
about to lift.
31

32. Uncertainty across climate models
Projected Percent
Changes in Annual
Runoff, 2041-60 vs.
1901-70
Hatched areas indicate greater confidence due to strong agreement among model
projections. White areas indicate divergence among model projections. A middle-
of-the-road emissions scenario is assumed.
Source: globalchange.gov/usimpacts

33. Uncertain emissions
Thirty year changes for
Massachusetts:
2010-2039:
Done!
2040-2069:
Princeton vs. Washington
2070-2099:
Baltimore vs. Augusta
This graph probably shows how
winters could feel too (to be verified).
Figure from James McCarthy, Harvard NECIA, 2007 (see: www.climatechoices.org/ne/)

34. Which uncertainty is more important?
Source: globalchange.gov/usimpacts
The Committee on America’s Climate Choices
struggled with the relative importance of
uncertain climate science and uncertain Source: NECIA, 2007 (see:
www.climatechoices.org/ne/)
human behavior. Figure from
James McCarthy, Harvard

35. “Solutions” can bring serious
problems of their own.
Every “solution” has a dark side.
Conservation Regimentation
Renewables Competing uses of land
“Clean coal” Mining: worker and land impacts
Nuclear power Nuclear war
Geoengineering Technological hegemony
Risk management: In choosing targets, we must take into account
both the risks of disruption from climate change and the risks of
disruption from mitigation.

36. Iterative risk management
“I will apply, for the benefit of the
sick, all measures that are
required, avoiding those twin traps
of overtreatment and therapeutic
nihilism.”
Hippocrates
* Modern version of the Hippocratic oath, Louis Lasagna, 1964,
http://www.pbs.org/wgbh/nova/doctors/oath_modern.html

37. Iterative risk management: the basis
for a renewed commitment
In another decade we'll know a lot more about the earth, both
because of new climate science and because of what the earth
tells us about itself. Right now: measure, model, and think.
We’ll also know more about the solutions themselves, thanks
to both R&D and field experience. Right now: develop options.
Right now: agree to make decisions iteratively.
Specifically, we can wait at least a decade before deciding whether 1)
flat emissions for 50 years is as heroic an outcome as we can achieve
safely and equitably, or 2) whether we can achieve still more.

38. Grounds for optimism
1. The world today has a terribly inefficient
energy system.
2. Carbon emissions have just begun to be
priced.
3. Most of the 2061 physical plant is not yet
built.
4. Many smart and committed young people
now find energy problems exciting.

39. EXTRA SLIDES

40. Surrogate Goals (1 of 3)
Definition of a surrogate goal
A person who holds Goal A strongly and Goal B weakly, but
believes that achieving Goal B will also achieve Goal A, can
pursue Goal B as a surrogate for Goal A.
Usually, Goal A will be revealed only in special
circumstances. Recognizing that a multiplicity of surrogate
goals is at play has considerable explanatory power.

41. Surrogate Goals (2 of 3)
Surrogate goals and climate change
In the formulation of policy to deal with climate change, the
general objective of slowing the rate of climate change is
often a surrogate for more strongly held goals, such as:
•Augmenting financial transfers to developing countries
•Bringing the fossil fuel era to a close
•Curtailing consumerism and human centeredness
•Promoting self-sufficiency, autonomous communities
•Diminishing the power of technological elites
•Promoting environmental science
•Encouraging entrepreneurship

42. Surrogate Goals (3 of 3)
A problem arises when an action in support of the
surrogate goal negates the person’s more strongly
held goal.
Capturing and storing CO2 prolongs the fossil fuel
era.
Large and distant solar arrays and windfarms do
not promote local self-reliance.

43. Safe is not fair, and fair is not safe
Define “fairness” as equal access to the
atmosphere for all nations measured by
cumulative per capita emissions over some
time interval.
For a stringent target, fairness in this sense is
not achievable.
Thus, fairness must be redefined: equal
opportunity to develop, while benefiting from
options not available in the past.

44. Beyond per capita
We can’t solve the climate problem
without moving beyond “per capita” –
looking inside countries.
What if “common but differentiated
responsibilities” refers to individuals
instead of nations?
“One-billion high emitters,” PNAS, 2009. Co-authors: Shoibal Chakravarty, Ananth
Chikkatur, Heleen de Coninck, Steve Pacala, Massimo Tavoni.

45. One billion “high-emitters”
USA other OECD China other nonOECD
2003
>10
2030
In
2030, more than
0.00% 20.00% 40.00% 60.00% 80.00% 100.00%
2003 half of these
2-10 “high-emitters”
2030
will live outside
2003 0 0.2 0.4 0.6 0.8 1
the OECD.
<2
2030
0 0.2 0.4 0.6 0.8 1

46. Population distribution across 4 regions
The poor need not be denied fossil fuels
USA other OECD China other nonOECD
2003
>10
2030
0.00% 20.00% 40.00% 60.00% 80.00% 100.00%
2003
A floor at 2 tCO2/yr
2-10
2030
in 2030 and raises
projected 2030
2003 0 0.2 0.4 0.6 0.8 1 global emissions by
only 13%.
<2
2030
The lower half of the
world’s emitters
0 0.2 0.4 0.6 0.8 1
Global distribution of individual emissions. Units: tC02/year

47. NJ CO2 emissions goals
Not included: CO2
emissions from 28%
imported power
Source: A Blueprint for Action:
Policy Options to Reduce New
Jersey’s Contribution to Global
Warming, Environment New Jersey
Research and Policy
Center, September 2006.
Total: 120 MtCO2/yr = 2% of U.S., 0.5% of world
Per capita: (120 MtCO2/yr)/8.7 M people = 13.8 tCO2/yr, 2/3 of U.S., 3x world.

48. Princeton’s CO2 emissions goal
7,100 students
5,400 employees
Per capita emissions:
9 tonsm CO2 per year
Included: On-campus and external energy for cogeneration plant, fuel for vehicle
fleet, but not travel to campus. Note: Princeton expects to add almost 2 million
square feet of building space in the next 10 years.

49. Uncertain future surface temperatures
Box plots of probability distributions elicited from 14 “experts”: global mean surface air temperature
change (ΔT) relative to 2000, for four points shown in the inset.

50. Experts’ median estimates of the transient response of globally averaged temperature change (relative to
2000) for the high (Upper) and low (Lower) forcing trajectories.
Zickfeld K et al. PNAS 2010;107:12451-12456
©2010 by National Academy of Sciences

51. One billion “high-emitters”
USA other OECD China other nonOECD
2003
>10
2030
In
2030, over half of
the “high-
0.00% 20.00% 40.00% 60.00% 80.00% 100.00%
2003
2-10 emitters” will
Units: Estimated
emissions of
2030
live outside the
individuals in
2030, in tons 2003 0 0.2 0.4 0.6 0.8 1 OECD.
CO2/year
<2
2030
0 0.2 0.4 0.6 0.8 1

52. What should we be doing?
Right away:
Phase out the obsolete.
Build well, at all spatial scales.
Via R&D, improve what we can already do.
Move beyond “per capita” to focus on all “high emitters.”
Steadily, for a long time:
Seek new options (but don’t bet the store on finding them).
Encourage transitions that reduced cumulative impact
(including a falling global population).
Build resilience (“adaptation capacity”).

53. Four “study questions”
1. What is a goal? “Targets and timetables” are the currency of
negotiations. A goal can be “aspirational” or can have the force of law.
2. I assume the electorate actually matters, not just interest groups. Have I
been naïve and demonstrated “what the wonk does worst”?
3. How should income inequality be accounted for in international
agreements? Climate change itself menaces the poor, who are least able
to adapt. Climate change mitigation exacerbates poverty if it results in
higher costs for meeting basic needs.
4. How much should one count on breakthroughs? The sufficiency of
current tools vs. putting one’s faith in fundamental breakthroughs.