1. CO2 and Energy #2 Jasper Kok Applied Physics Program
Climate science & policy enthusiast
Lecture for AOSS 480, Ricky Rood

2. Outline and review lecture 1
Lecture 1: Current and past energy use
Historic CO2 emissions and energy use
Current sources of energy
Energy use and CO2 emissions of economic sectors
Energy use and CO2 emissions by end use
US energy use by sector
World CO2 emissions by fuel and end use

3. Outline Lecture 2
Lecture 2: Future energy use and climate change mitigation
‘Business as usual’
Do we need to act to prevent ‘dangerous anthropogenic interference’ in the climate system?
‘Wedges’ to mitigate climate change
Energy supply decarbonization ‘tools’
Energy efficiency
Renewable energies
Carbon capture and sequestration
Biofuels
Specific ‘wedges’ of mitigation
Externality: energy and water

4. Key reference
The ‘wedge’ paper: “A plan to keep carbon in check” by Socolow and Pacala, Scientific American, 2006.
This is an influential policy-oriented paper on how to reform energy sector while still achieving economic growth
Accessible through
On local server: Socolow and Pacala: Keeping Carbon in Check (Scientific American, 2006)

5. Future energy policy: What are we trying to achieve?
The 1992 UN Framework Convention on Climate Change was signed by most countries. Stated objective:
“to achieve stabilization of GHG concentrations in the atmosphere at a low enough level to prevent dangerous anthropogenic interference with the climate system”
The green countries have signed UNFCCC!
This should be done in a time frame sufficient:
to allow ecosystems to adapt naturally to climate change
to ensure that food production is not threatened
to enable economic development to proceed in a sustainable manner
Does ‘business as usual’ allow this? If not, then what energy policies should we introduce (as a world community)?

6. Outline Lecture 2
Lecture 2: Future energy use and climate change mitigation
‘Business as usual’
Do we need to act to prevent ‘dangerous anthropogenic interference’ in the climate system?
‘Wedges’ to mitigate climate change
Energy supply decarbonization ‘tools’
Energy efficiency
Renewable energies
Carbon sequestration
Biofuels
Specific ‘wedges’ of mitigation
Externality: energy and water

7. ‘Business as usual’ CO2-trajectory path
IPPC 4AR executive summary; Pacala and Socolow, Science, 2004
‘Business as usual’ has CO2 emissions growing at current rate (1.5%/year)
Likely end-of-century warming: ~2.3 – 3.4 ºC

8. ‘Business as usual’ End-of-century temperature change
“Business as usual” ( ) scenario
Global mean warming 2.8 ºC;
Much of land area warms by ~3.5 ºC
Arctic warms by ~7 ºC

9. Will ‘business as usual’ lead to ‘dangerous’ climate change?
At > 2ºC
Ecosystems become threatened
Food supply jeopardized
Abrupt / irreversible changes (could lead to large-scale economic damage)
Many scientists think should prevent >2ºC warming
 EU policy aimed at < 2ºC warming
So what is a ‘safe’ CO2 trajectory and how do we achieve it?
Likely range of ‘business as usual’ by 2100

10. CO2 stabilization trajectory
Need to stay below ~2 ºC to avoid ‘dangerous’ climate change.
 Stabilize at < 550 ppm. Pre-industrial: 275 ppm, current: 385 ppm.
Need 7 ‘wedges’ of prevented CO2 emissions.
Roberta Hotinski (CMI), Stabilization Wedges: A Concept & Game, 2007

11. Outline Lecture 2 ‘Wedges’ to mitigate climate change
Lecture 2: Future energy use and climate change mitigation
‘Business as usual’
Why we need to act to prevent ‘dangerous anthropogenic interference’ in the climate system
‘Wedges’ to mitigate climate change
Energy supply decarbonization ‘tools’
Energy efficiency
Renewable energies
Carbon sequestration
Biofuels
Specific ‘wedges’ of mitigation
Externality: energy and water

12. What is a ‘wedge’?
A ‘wedge’ is a strategy to reduce carbon emissions that grows from zero to 1 GtC/year in 50 years
The world needs to implement 7 of these wedges to prevent ‘dangerous’ climate change
Examples:
Expand wind energy
Make cars more efficient
Reduce deforestation rates

13. Developing Vs. developed world
Implementation of wedges would lead to large emission reductions in developed world
Developing world would increase emissions, but less than without carbon constraints
Source: Pacala and Socolow, Scientific American, 2006

14. Source Rosina Bierbaum’s 2007 guest lecture

15. How and where to get the wedges
Need 7 wedges for 2xCO2 stabilization
Where and how is most cost-effective to cut CO2?
Tools wedges use:
Improved energy efficiency
Renewable energies (wind, solar)
Carbon capture and sequestration
Biofuels

16. Outline Lecture 2 Energy supply decarbonization tools
Lecture 2: Future energy use and climate change mitigation
‘Business as usual’
Why we need to act to prevent ‘dangerous anthropogenic interference’ in the climate system
‘Wedges’ to mitigate climate change
Energy supply decarbonization tools
Energy efficiency
Renewable energies
Carbon capture and sequestration
Biofuels
Specific ‘wedges’ of mitigation
Externality: energy and water

17. Efficiency Gains The low-hanging fruit! Essentially three kinds:
End-use electricity efficiency (fluorescent bulbs instead of incandescent bulbs)
Energy generation efficiency (coal plant operating at 60 % efficiency instead of current 40 %)
Transportation efficiency (60 mpg instead of 30 mpg)
Efficiency gains are generally cheap mitigation options
But will only get so far before cutting into primary energy used for economic activity

18. Kinds of renewable energy
Hydro-power
Already widely used - not much potential for expansion
Wind
Abundant and competitive
Solar
Photovoltaic (PV)
Concentrating solar

19. Renewable energy: Wind
Wind energy cost in $/kWh
Probably most promising renewable energy source
Supplies ~1 % of world electricity, ~0.3 % in US
Is cost-effective against coal and natural gas
Is undergoing very rapid growth (5-fold increase )
Sources: and “wind energy” lecture by Stephen R. Lawrence, CU

20. Renewable energy: Wind
Advantages:
Wind energy is relatively mature technology and is cost effective
Can be utilized at all scales
Large wind farms
On small agricultural farms
Total theoretical potential of wind energy on land/near shore is 5x current energy consumption
Large potential for expansion
Sources: and “wind energy” lecture by Stephen R. Lawrence, CU

21. Renewable energy: Wind
Disadvantages:
Horizon pollution and NIMBY siting problems
Birds…(though this is often over-stated – about 1-2 birds per turbine per year)
Wind is intermittent! It can therefore not make up a large fraction of base load (unless effective energy storage)
Sources: and “wind energy” lecture by Stephen R. Lawrence, CU;

22. Renewable energy: Solar
Essentially three kinds:
Solar heat
Water is heated directly by sunlight
Used cost-effectively on small scale in houses
Solar photovoltaic (PV)
Uses photo-electric effect (Einstein!) to produce electricity
Supplies ~0.04 % of world energy use
Solar concentrated
Use large mirrors to focus sunlight on steam turbine or very efficient PV panels
More cost-effective than just PV
Source: and
and

23. Renewable energy: Solar
Advantages:
Enormous theoretical potential!
Applicable at various scales (individual houses to solar plants)
Solar heating can be cost effective
Economy of scale and/or breakthroughs might reduce costs of PV and solar concentrated
Disadvantages
PV and solar concentrated are expensive! Currently only cost-effective with government subsidies
Intermittent – can not make up large portion of base load (except with storage capability)
Source: and
and

24. Outline Lecture 2 Carbon capture and sequestration Biofuels
Lecture 2: Future energy use and climate change mitigation
‘Business as usual’
Why we need to act to prevent ‘dangerous anthropogenic interference’ in the climate system
‘Wedges’ to mitigate climate change
Energy supply decarbonization tools
Energy efficiency
Renewable energies
Carbon capture and sequestration
Biofuels
Specific ‘wedges’ of mitigation
Externality: energy and water

25. Carbon Capture and Sequestration (CCS)
Main idea:
Burn fossil fuels for electricity/hydrogen production
Capture CO2
‘Sequester’ it in geological formation, oil/gas field, or ocean floor
This principle is immensely important for future CO2 mitigation!
Fossil fuels are abundant and cheap
Renewable energy generally not mature enough to replace fossil fuels
Coal-fired power plants with CCS could provide low-carbon energy at competitive costs
Currently successfully employed in ‘pilot’ projects
Source: Socolow, 2005, Scientific American;

26. CCS: Carbon Capture
Both conventional and modern types of coal-fired power plants can be adapted for CCS
Conventional coal-fired power plant:
Burn coal in air (much like the old days)
Exhaust gas is ~15 % CO2 (rest is mostly nitrogen and water vapor)
Exhaust gas flows over chemicals that selectively absorb CO2 (‘amines’)
The amines are heated to ~150 ºC to give up the CO2 and produce a (nearly) pure CO2 gas that can be sequestered.
Modern coal-fired power plant:
Coal is burned with pure oxygen in a gasification chamber to produce hydrogen and CO2
The CO2 is filtered out and the hydrogen is burned for electricity

27. CCS: Sequestration
CO2 can be sequestered at ~1 km underground, here pressure is high enough to liquify CO2, which helps prevent it from leaking
Several options for sequestering CO2:
Depleted oil/gas reservoirs (can be even be used to enhance oil/gas recovery – reduces costs)
Deep saline (brine) formations – these are porous media in which CO2 can be stored and dissolve in the salty water
Use for coal-bed methane recovery (one of those ‘unconventional’ fossil fuels)
Ocean floor (very controversial!)

28. CCS: economics
Source: Socolow, 2005, Scientific American
CCS could become cost-effective with future carbon legislation

29. Biofuels Initially hailed as a sustainable substitute for oil
Can help reduce oil imports and improve national security
In US, this is probably main motivation for recent push (“addicted to oil”, Bush’s 2006 State of the Union)
Two main kinds of biofuels:
First generation:
Produced by converting sugar in corn, sugar beets, etc., into ethanol (alcohol)
Second generation:
Produced through “cellulosic conversion” of biomass into sugar, then sugar into ethanol
Climate change impact of different biofuels is very different!
Sources: Scharlemasnn and Laurance, How green are biofuels, Science, 2008; Fargione et al., Land clearing and the biofuel carbon debt, Science, 2008; Searchinger et al., Use of US croplands for biofuels increases GHG…, Science, 2008

30. Biofuels – First Generation
In US, mainly corn-based ethanol
Heavily subsidized by federal government to reduce oil dependence (~$1.90/gallon)
Effect on climate change is negative:
Energy used in production is comparable to energy content
Significant amounts of N2O (a potent GHG) can be produced through fertilizer use
More carbon would be sequestered by letting crop land lie fallow
Raises food prices  Tropical deforestation, which releases more carbon than saved from fuel production over > 30-year period
Sources: Scharlemasnn and Laurance, How green are biofuels, Science, 2008; Fargione et al., Land clearing and the biofuel carbon debt, Science, 2008; Searchinger et al., Use of US croplands for biofuels increases GHG…, Science, 2008
Source: Fargione et al., Science, 2008

31. Biofuels – Second Generation
Produced from plants containing cellulose
Cellulosic conversion to sugar is very difficult and expensive! (cows have 4 stomach compartments for a reason…)
Second generation biofuels are better for climate change:
Similar amount of carbon sequestered as fallow cropland
But, competition with food still leads to tropical deforestation and net release of carbon!
US 1st generation biofuel
US 2nd generation biofuel
Sources: Scharlemasnn and Laurance, How green are biofuels, Science, 2008,

32. Biofuels – do they help or hurt?
In general, biofuels that compete with food will not contribute to mitigating climate change
Direct link between food demand/prices and tropical deforestation
Production of first generation biofuels (directly from food such as corn) is not a solution to climate change and should be avoided!
Production of second generation biofuels (from biomass) is only helpful if it doesn’t compete with food production (so not grown on cropland)
Second generation biofuels from agricultural waste could play important role, but is currently not cost-effective
In light of these recent results (2007/2008), EU is reconsidering past biofuel mandates and subsidies
Sources: Scharlemasnn and Laurance, How green are biofuels, Science, 2008,

33. Outline Lecture 2 Specific ‘wedges’ of mitigation
Lecture 2: Future energy use and climate change mitigation
‘Business as usual’
Why we need to act to prevent ‘dangerous anthropogenic interference’ in the climate system
‘Wedges’ to mitigate climate change
Energy supply decarbonization ‘tools’
Energy efficiency
Renewable energies
Carbon sequestration
Biofuels
Specific ‘wedges’ of mitigation
Externality: energy and water

34. Where can we create ‘wedges’ in the energy system?
Power generation (40 %)
This is the ‘easy’ target because of availability of cost effective low-carbon options (wind, CCS)
Direct fuel use (36 %)
This can be ‘switched’ to low-carbon electricity
Transportation (24 %)
This is the tough nut to crack!
Currently no real feasible low carbon alternatives
Lot of infrastructure in place for fossil fuel-based transportation!
??? ???
Source: Pacala and Socolow, 2004, Science (supplemental material)

35. How to create ‘wedges’: Power Generation
Several options, each one wedge:
Increase efficiency of coal-fired power plants from 40 to 60 % ($)
Replace coal-fired to natural gas-fired power plants ($)
Double nuclear electricity to replace coal-fired power plants ($$)
Use CCS for low-carbon coal-fired power plants ($$)
Expand wind energy 30x to replace coal-fired power plants ($$)
Expand solar energy 700x to replace coal-fired power plants ($$$)

36. How to create ‘wedges’: Direct Fuel Use
Several options, each one wedge:
Improve building insulation ($)
Replace natural gas heat with low-carbon hydrogen from wind/coal with CCS ($$$)
(and general switch to electricity heat instead of fuel heat)

37. How to create ‘wedges’: Transportation
Several options, each one wedge:
Increase car efficiency from 30 to 60 mpg ($)
More compact world with less travel  5,000 instead of 10,000 miles/vehicle ($)
Switch to low-carbon hydrogen ($$$)
Switch to sustainable biofuels  unlike corn ethanol, these must not compete with food production! ($$$)

38. Source Rosina Bierbaum’s 2007 guest lecture

39. Outline Lecture 2 Externality: energy and water
Lecture 2: Future energy use and climate change mitigation
‘Business as usual’
Why we need to act to prevent ‘dangerous anthropogenic interference’ in the climate system
‘Wedges’ to mitigate climate change
Energy supply decarbonization ‘tools’
Energy efficiency
Renewable energies
Carbon sequestration
Biofuels
Specific ‘wedges’ of mitigation
Externality: energy and water

40. Must address climate change without exacerbating freshwater shortage
Both energy and water are critical resources
Many areas already suffer water stress
note Africa, India, China, where greatest population growth is projected to occur
Projected to become worse with increasing population, pollution, and climate change
Dry areas are generally projected to become drier.
Must address energy challenge without exacerbating water scarcity
Sources: 2nd UN World Water Development Report, 2006; UN 2007 world water day brochure; Energy demands on water resources, Report to congress on the interdependency of energy and water, 2006

41. So where is our fresh water used?
You can take many, many, very long showers for a pound of steak…
Greatly expanding biofuels from ethanol to substitute oil would probably be bad idea…
Sources: 2nd UN World Water Development Report, 2006; UN 2007 world water day brochure; Energy demands on water resources, Report to congress on the interdependency of energy and water, 2006

42. Class on Thursday Ben Santer will be lecturing on Thursday
He’s a well-known climate scientist!
Few contemporary scientists get their own Wikipedia page… (