1. Mitigating Climate Change
Sources and sinks of atmospheric CO2
Emissions trading
Historical and projected CO2 emissions
Climate wedges
Alternative energy

2. The Global Carbon Cycle
Atmosphere
/yr
About half the CO2 released by humans is absorbed by oceans and land
“Missing” carbon is hard to find among large natural fluxes
~120
~90
~120
~90
8 GtC/yr
Ocean
38,000
Land
Humans
2000

3. Variable Sinks Half the CO2 “goes away!”
Some years almost all the fossil carbon goes into the atmosphere, some years almost none
Interannual variability in sink activity is much greater than in fossil fuel emissions
Sink strength is related to El Niño. Why? How?

4. European Climate Exchange Futures Trading: Permits to Emit CO2
European “cap-and-trade” market set up as described in Kyoto Protocol (
7/18/2008 price €25.76/ton of CO2 emitted 12/ = $149.73/ton of Carbon
Supply and demand!

5. Present Value of Carbon Sinks
Terrestrial and marine exchanges currently remove more than 4 GtC per year from the atmosphere
This free service provided by the planet constitutes an effective 50% emissions reduction, worth about $600 Billion per year at today’s price on the ECX!
Carbon cycle science is currently unable to quantitatively account for
The locations at which these sinks operate
The mechanisms involved
How long the carbon will remain stored
How long the sinks will continue to operate
Whether there is anything we can do to make them work better or for a longer time

6. Where Has All the Carbon Gone?
Into the oceans
Solubility pump (CO2 very soluble in cold water, but rates are limited by slow physical mixing)
Biological pump (slow “rain” of organic debris)
Into the land
CO2 Fertilization (plants eat CO2 … is more better?)
Nutrient fertilization (N-deposition and fertilizers)
Land-use change (forest regrowth, fire suppression, woody encroachment … but what about Wal-Marts?)
Response to changing climate (e.g., Boreal warming)

7. Coupled Carbon-Climate Modeling
“Earth System” Climate Models
Atmospheric GCM
Ocean GCM with biology and chemistry
Land biophysics, biogeochemistry, biogeography
Prescribe fossil fuel emissions, rather than CO2 concentration as usually done
Integrate model from , predicting both CO2 and climate as they evolve
Oceans, plants, and soils exchange CO2 with model atmosphere
Climate affects ocean circulation and terrestrial biology, thus feeds back to carbon cycle

8. Carbon-Climate Futures Friedlingstein et al (2006)
Atmosphere
Land
Ocean
300 ppm!
Coupled simulations of climate and the carbon cycle
Given nearly identical human emissions, different models project dramatically different futures!

9. Emission Scenarios Each “storyline” used to generate
A1: Globalized, with very rapid economic growth, low population growth, rapid introduction of more efficient technologies.
A2: very heterogeneous world, with self-reliance and preservation of local identities. Fertility patterns across regions converge very slowly, resulting in high population growth. Economic development is regionally oriented and per capita economic growth & technology more fragmented, slower than other storylines.
B1: convergent world with the same low population growth as in A1, but with rapid changes in economic structures toward a service and information economy, reductions in material intensity, introduction of clean and resource-efficient technologies. The emphasis is on global solutions to economic, social, and environmental sustainability, including improved equity, without additional climate initiatives.
B2: local solutions to economic, social, and environmental sustainability. Moderate population growth, intermediate levels of economic development, and less rapid and more diverse technological change than in B1 and A1.
Each “storyline” used to generate
10 different scenarios of population, technological & economic development

10. Emission Scenarios vs Reality
Raupach et al PNAS

11. Carbon intensity of the world economy fell steadily for 30 years
Canadell et al. 2007

12. Until 2000!
Canadell et al. 2007

13. Dramatic contrast – history versus future
Developing
India
China
Former Soviet
Other developed
Japan
Europe
USA
CO2 emissions
Cumulative
Raupach et al. PNAS 2007

14. Dramatic contrast – history versus future
Developing
India
China
Former Soviet
Other developed
Japan
Europe
USA
CO2 emissions
Raupach et al. PNAS 2007

15. Dramatic contrast – history versus future
Developing
India
China
Former Soviet
Other developed
Japan
Europe
USA
CO2 emissions
Raupach et al. PNAS 2007

16. Dramatic contrast – history versus future
Least Developed
Developing
India
China
Former Soviet
Other developed
Japan
Europe
USA
CO2 emissions
Raupach et al. PNAS 2007

17. CO2 “Budget” of the Atmosphere
AT606 Fall 2006
4/11/2017
CO2 “Budget” of the Atmosphere 2 = 4
billion tons go out
Ocean
Land Biosphere (net)
Fossil Fuel
Burning + 8
800
billion tons carbon
billion
tons go in
ATMOSPHERE
billion tons added every year
CSU ATS Scott Denning

18. How Far Do We Choose to Go?
AT606 Fall 2006
4/11/2017
How Far Do We Choose to Go?
Billions of tons of carbon
“Doubled” CO2
Today
Pre-Industrial
Glacial
800
1200
600
400
billions of tons carbon
ATMOSPHERE (
ppm )
(570)
(380)
(285)
(190)
Past, Present, and Potential Future
Carbon Levels in the Atmosphere
CSU ATS Scott Denning

19. AT606 Fall 2006
4/11/2017
Historical Emissions
Billions of Tons Carbon Emitted per Year 16
Historical
emissions 8
1950
2000
2050
2100
CSU ATS Scott Denning 19

20. The “Stabilization Triangle” Stabilization Triangle
AT606 Fall 2006
4/11/2017
The “Stabilization Triangle”
Billions of Tons Carbon Emitted per Year 16
Current path = “ramp”
Stabilization Triangle
Interim Goal
Historical
emissions 8
Flat path
1.6
1950
2000
2050
2100
CSU ATS Scott Denning 20

21. Stabilization Triangle
AT606 Fall 2006
4/11/2017
The Stabilization Triangle
Billions of Tons Carbon Emitted per Year
Easier CO2 target 16
Current path = “ramp”
~850 ppm
Stabilization Triangle
Interim Goal
Historical
emissions 8
Flat path
Tougher CO2 target
~500 ppm
1.6
1950
2000
2050
2100
CSU ATS Scott Denning 21

22. “Satbilization Wedges”
AT606 Fall 2006
4/11/2017
“Satbilization Wedges”
Billions of Tons Carbon Emitted per Year 16
Current path = “ramp”
16 GtC/y
Eight “wedges”
Goal: In 50 years, same
global emissions as today
Historical
emissions 8
Flat path
1.6
1950
2000
2050
2100
CSU ATS Scott Denning 22

23. AT606 Fall 2006
4/11/2017
What is a “Wedge”?
A “wedge” is a strategy to reduce carbon emissions that grows in 50 years from zero to 1.0 GtC/yr. The strategy has already been commercialized at scale somewhere.
1 GtC/yr
Total = 25 Gigatons carbon
50 years
Cumulatively, a wedge redirects the flow of 25 GtC in its first 50 years. This is 2.5 trillion dollars at $100/tC.
A “solution” to the CO2 problem should provide at least one wedge.
CSU ATS Scott Denning

24. Fifteen Wedges in 4 Categories
AT606 Fall 2006
4/11/2017
Fifteen Wedges in 4 Categories
Energy Efficiency &
Conservation (4)
16 GtC/y
Fuel Switching
(1)
Renewable Fuels
& Electricity (4)
Stabilization
Stabilization
Triangle
Triangle
CO2 Capture
& Storage (3)
8 GtC/y
Forest and Soil Storage (2)
2007
2057
Nuclear Fission (1)
CSU ATS Scott Denning 24

25. AT606 Fall 2006
4/11/2017
Photos courtesy of Ford Motor Co., DOE, EPA
Efficiency
Produce today’s electric capacity with double today’s efficiency
Double the fuel efficiency of the world’s cars or halve miles traveled
Average coal plant efficiency is 32% today
“E,T, H” = can be applied to electric, transport, or heating sectors, $=rough indication of cost (on a scale of $ to $$$)
There are about 600 million cars today, with 2 billion projected for 2055
Use best efficiency practices in all residential and commercial buildings
E, T, H / $
Replacing all the world’s incandescent bulbs with CFL’s would provide 1/4 of one wedge
Sector s affected:
E = Electricity, T =Transport, H = Heat
Cost based on scale of $ to $$$
CSU ATS Scott Denning

26. AT606 Fall 2006
4/11/2017
Fuel Switching
Substitute 1400 natural gas electric plants for an equal number of coal-fired facilities
“E,H” = can be applied to electric or heating sectors, $=rough indication of cost (on a scale of $ to $$$)
Effort needed for 1 wedge:
Build 1400 GW of capacity powered by natural gas instead of coal (60% of current fossil fuel electric capacity)
Requires an amount of natural gas equal to that used for all purposes today
So a slice is 50 LNG tanker discharges/day by m3/tanker, or
one new “Alaska” 4 Bscfd.
Detailed Description: NATURAL GAS TURBINES ARE BEING DEVELOPED TO PRODUCE ELECTRICITY IN A SIMPLE, LOW COST ENVIRONMENTALLY FRIENDLY WAY. DOE'S NATIONAL ENERGY TECHNOLOGY LABORATORY (NETL) INITIATED THE ADVANCED TURBINE SYSTEMS (ATS) PROGRAM AND HAS PARTNERED WITH INDUSTRY TO PRODUCE A NEW GENERATION OF HIGH EFFICIENCY GAS TURBINES FOR CENTRAL STATION ELECTRICITY PRODUCTION, USING CLEAN BURNING NATURAL GAS.
700 1-GW baseload coal plants (5400 TWh/y) emit 1 GtC/y.
Natural gas: 1 GtC/y = 190 Bscfd
Yr 2000 electricity:
Coal : TWh/y; Natural gas: 2700 TWh/y.
Photo by J.C. Willett (U.S. Geological Survey).
A wedge requires an amount of natural gas equal to that used for all purposes today
E, H / $
CSU ATS Scott Denning

27. Carbon Capture & Storage
AT606 Fall 2006
4/11/2017
Carbon Capture & Storage
Implement CCS at
800 GW coal electric plants or
1600 GW natural gas electric plants or
180 coal synfuels plants or
10 times today’s capacity of hydrogen plants
“E,T, H” = can be applied to electric, transport, or heating sectors, $=rough indication of cost (on a scale of $ to $$$)
Graphic courtesy of Alberta Geological Survey
There are currently three storage projects that each inject 1 million tons of CO2 per year – by 2055 need 3500.
E, T, H / $$
CSU ATS Scott Denning

28. Nuclear Electricity E/ $$
AT606 Fall 2006
4/11/2017
Nuclear Electricity
Triple the world’s nuclear electricity capacity by 2055
“E” = can be applied to electric sector, $$=rough indication of cost (on a scale of $ to $$$)
Plutonium (Pu) production by 2054, if fuel cycles are unchanged: 4000 t Pu (and another 4000 t Pu if current capacity is continued).
Compare with ~ 1000 t Pu in all current spent fuel, ~ 100 t Pu in all U.S. weapons.
5 kg ~ Pu critical mass.
Graphic courtesy of NRC
The rate of installation required for a wedge from electricity is equal to the global rate of nuclear expansion from
E/ $$
CSU ATS Scott Denning

29. Wind Electricity E, T, H / $-$$
AT606 Fall 2006
4/11/2017
Wind Electricity
Install 1 million 2 MW windmills to replace coal-based electricity, OR
Use 2 million windmills to produce hydrogen fuel
“E,T, H” = can be applied to electric, transport, or heating sectors, $-$$=rough indication of cost (on a scale of $ to $$$)
Photo courtesy of DOE
A wedge worth of wind electricity will require increasing current capacity by a factor of 30
E, T, H / $-$$
CSU ATS Scott Denning

30. Photos courtesy of DOE Photovoltaics Program
AT606 Fall 2006
4/11/2017
Solar Electricity
Install 20,000 square kilometers for dedicated use by 2054
“E” = can be applied to electric sector, $$$=rough indication of cost (on a scale of $ to $$$)
Photos courtesy of DOE Photovoltaics Program
A wedge of solar electricity would mean increasing current capacity 700 times
E / $$$
CSU ATS Scott Denning

31. Remember
Half (4 GtC/yr) of the current emissions (8 GtC/yr) remain in the atmosphere and contribute to greenhouse forcing of downward longwave raditaion
Economic growth is on track to at least doubleCO2 emissions to 16 GtC/yr by 2050
Reducing CO2 emissions requires choosing a combination of efficiency, fuel switching, and alternative energy generation (“wedges”)
Each “wedge” is feasible given today’s technology, but also expensive