Closing the

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Numerous mitigation measures and policies need to be invoked in the IS92a and SRES scenarios to stabilize CO2 concentration levels. There is no unique solution to closing the gap. In fact, regardless of the reference scenario, it is never the case that a single energy technology closes the gap. In all instances the gap is closed by the deployment of a suite of energy technologies. These technologies include familiar core technologies such as energy efficiency; other energy intensity improvements; production of solar, wind, nuclear, modern commercial biomass, and other renewable energy; and changes in land use practices such as afforestation, other forest management practices, and soil carbon management. Beyond that, technologies that are only minor components in the present

Biopsychosocial Model Anxiety

Year

Figure 4.6. The "gap" for five alternative CO2 concentrations. This panel shows for five alternative CO2 concentrations the range of differences between reference emissions in the six SRES illustrative scenarios and the WRE emissions trajectory associated with stabilization of the concentration of CO2 at the indicated level. This difference between anticipated emissions and emissions along a trajectory that stabilizes CO2 concentrations is referred to as the "gap."

Year

Figure 4.6. The "gap" for five alternative CO2 concentrations. This panel shows for five alternative CO2 concentrations the range of differences between reference emissions in the six SRES illustrative scenarios and the WRE emissions trajectory associated with stabilization of the concentration of CO2 at the indicated level. This difference between anticipated emissions and emissions along a trajectory that stabilizes CO2 concentrations is referred to as the "gap."

global energy system could become major components of the global energy system in the middle and latter half of the 21st century. These technologies could include carbon capture and disposal, hydrogen and advanced transportation systems, and biotechnology.

Many issues remain to be resolved before the technologies assumed to successfully deploy in the reference cases deploy as assumed. The development and deployment of advanced energy technologies raise other research questions.

As discussed elsewhere in this book, carbon capture and disposal could be a major technology in the 21st century. Its deployment would enable the continued employment of abundant fossil-fuel resources to provide energy services. But cost is an important

Table 4.1. The gap for the six SRES illustrative scenarios for atmospheric CO2 concentrations ranging from 450 ppm to 750 ppm (PgC/year)

WRE 350 WRE 450 WRE 550 WRE 650 WRE 750

Scenario 2020 2050 2100 2020 2050 2100 2020 2050 2100 2020 2050 2100 2020 2050 2100

Table 4.1. The gap for the six SRES illustrative scenarios for atmospheric CO2 concentrations ranging from 450 ppm to 750 ppm (PgC/year)

Scenario 2020 2050 2100 2020 2050 2100 2020 2050 2100 2020 2050 2100 2020 2050 2100

A1 AIM

5

15

13

4

10

10

2

6

7

1

4

3

1

3

1

A1G MiniCAM

6

23

28

4

18

25

2

13

21

2

11

18

1

10

16

A1TMESSAGE

3

11

4

1

6

1

NA

NA

NA

NA

NA

NA

NA

NA

NA

A2 ASF

5

16

29

3

12

25

1

7

22

1

5

19

1

4

17

B1 IMAGE

3

10

4

2

5

1

NA

NA

NA

NA

NA

NA

NA

NA

NA

B2 MESSAGE

2

10

13

0

5

10

-2

0

7

-2

-2

3

-2

-3

1

Note: NA indicates not available.

Note: NA indicates not available.

Table 4.2. The gap for the six SRES illustrative scenarios for atmospheric CO2 concentrations ranging from 450 ppm to 750 ppm (EJ/year)

WRE 350 WRE 450 WRE 550 WRE 650 WRE 750

Scenario 2020 2050 2100 2020 2050 2100 2020 2050 2100 2020 2050 2100 2020 2050 2100

Table 4.2. The gap for the six SRES illustrative scenarios for atmospheric CO2 concentrations ranging from 450 ppm to 750 ppm (EJ/year)

Scenario 2020 2050 2100 2020 2050 2100 2020 2050 2100 2020 2050 2100 2020 2050 2100

A1 AIM

270

822

809

180

567

589

92

312

401

71

190

207

61

137

61

A1G MiniCAM

284

1,137

1,335

191

901

1,162

100

665

1,014

78

552

860

68

503

745

A1TMESSAGE

158

626

299

65

360

45

NA

NA

NA

NA

NA

NA

NA

NA

NA

A2 ASF

253

785

1,243

163

557

1,086

74

329

953

53

220

814

42

173

710

B1 IMAGE

166

491

200

79

262

27

NA

NA

NA

NA

NA

NA

NA

NA

NA

B2 MESSAGE

97

534

664

4

278

481

-88

21

325

-110

-101

164

-121

-154

42

Note: NA indicates not available.

Note: NA indicates not available.

question. If the cost issue is successfully addressed, or if the value of carbon is high enough, carbon capture technologies could be deployed at very large scale. Cumulative capture amounting to hundreds of billions of tons of carbon over the course of the 21st century could occur if other technology issues are addressed. Disposal is also a critical question. Many potential reservoir classes exist, including depleted oil and gas wells, deep saline reservoirs, unminable coal seams, basalt formations, and oceans. Monitoring, verification, health, safety, and local environmental issues remain to be resolved before this technology can be deployed at a large scale.

Similarly, hydrogen systems could provide a major contribution to closing the gap. Hydrogen is an energy carrier that has the attractive property of exhausting water vapor when oxidized. It can be used directly in applications ranging from space heating to electric power generation to transport. But hydrogen is not a primary energy form. It is derived either from a hydrocarbon such as a fossil fuel or biomass, or from the splitting of water, H2O, into its constituent parts, hydrogen and oxygen, usually using electricity. The use of hydrocarbons to provide a source of hydrogen raises the question of the disposition of the carbon, and hence may require carbon capture and disposal technology to contribute to closing the gap. Hydrocarbons derived from biomass could contribute to closing the gap by providing hydrocarbon feedstocks for hydrogen production without carbon capture and disposal technology, as the carbon contained in the biomass is obtained from the atmosphere. In combination with carbon capture and disposal, biomass could provide energy with an effectively negative carbon emission. The production of hydrogen using electricity raises both the question of cost and the question of how the electricity was produced.

Once hydrogen is produced, a system must be developed and deployed to cost-effectively utilize the fuel in the provision of energy services while simultaneously providing consumer amenities, and addressing other environment, health, and safety concerns. Fuel cells have attracted considerable attention in that they can convert hydrogen to electricity and heat, while producing only water vapor as exhaust. Fuel cells can be deployed in either stationary or mobile applications. Yet many questions remain to be addressed before either hydrogen systems or fuel cells are widely deployed. Economic issues loom large. The present fossil-fuel—based transportation system with the internal combustion engine has proved a highly cost-effective system for delivering transportation services. Furthermore, even if cost-competitive fuel cells are developed, they could have little or no effect on carbon emissions if they do not employ hydrogen as the fuel.

Both hydrogen and fuel cell technologies will require further research to address economic, technological, environmental, health, safety, and institutional questions.

Biotechnology could similarly play a significant part in closing the gap. Many illustrative scenarios assume that costs and performance will improve to the point where commercial biomass is a major component of the global energy system by the middle of the century. But, as with other technologies that are at an early stage of development, economic, technological, environmental, health, safety, institutional, and ethical ques tions abound. How is crop productivity to be improved? What other implications are implied for land use and land use emissions? Could genetically modified crops be used? How will this approach affect biodiversity?

Other biotechnology options also represent great potential contributions to closing the gap, while raising equally deep questions about technology, environmental impact, health, and safety considerations and ethics. The creation of new life forms to produce hydrogen from hydrocarbons or water, or to capture carbon from the air and store it in soils, for example, has extraordinary ethical implications in addition to technological challenges.

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Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

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