Working Group III: Mitigation

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3.8.3 Historic Trends and Driving Forces

Table 3.28a categorizes fossil deposits into reserves, resources and additional occurrences for both conventional and unconventional oil and gas deposits. The categories reflect the definitions of reserves and resources given above, with the exception that resources are further disaggregated into resources and occurrences so as to better reflect the speculative nature associated with their technical and economic feasibility (Rogner, 1997, 2000a).

Table 3.28b presents the global fossil resource data of Table 3.28a in terms of their respective carbon content. Since the onset of the industrial revolution, almost 300GtC stored in fossil fuels have been oxidized and released to the atmosphere. The utilization of all proven conventional oil and gas reserves would add another 200GtC, and those of coal more than 1,000 GtC. The fossil fuel resource base represents a carbon volume of some 5,000GtC indicating the potential to add several times the amount already oxidized and released to the atmosphere during the 21st century. To put these carbon volumes into perspective, cumulative carbon emissions associated with the stabilization of carbon dioxide at 450ppm are estimated to be at 670GtC. Figure SPM.2 combines the reserve and resource estimates with cummulative emissions for various reference and stabilization scenarios, taken from other chapters and the IPCC WGI report.

Table 3.28b: Aggregation of fossil energy occurrences, in GtC
1860-1998 1998
   Conventional 97.1 2.7 118 153 271
   Unconventional 5.7 0.2 132 308 440 1,220
Natural gasc
   Conventional 35.9 1.2 82 179 261
   Unconventional 0.5 0.1 123 165 288 245
   Clathrates 11,934
Coal 156.4 2.4 1,094 2,605 3,699 3,122
Total fossil occurrences 295.6 6.5 1,549 3,410 4,959 16,521
- Negligible volumes
a ,b and c see Table 3.28a

Potential coal reserves are large – of that there is little doubt. However, there is an active debate on the ultimate size of recoverable oil reserves. The pessimists see potential reserves as limited, pointing to the lack of major new discoveries for 25 years or so (Laherrere, 1994; Hatfield, 1997; Campbell, 1997; Ivanhoe and Leckie, 1993). They see oil production peaking around 2010. The optimists point to previous pessimistic estimates being wrong. They argue that “there are huge amounts of hydrocarbons in the Earth’s crust” and that “estimates of declining reserves and production are incurably wrong because they treat as a quantity what is really a dynamic process driven by growing knowledge” (Adelman and Lynch, 1997; Rogner, 1998a). They further point to technological developments such as directional drilling and 3D seismic surveys which are allowing more reserves to be discovered and more difficult reserves to be developed (Smith and Robinson, 1997). The optimists see no major supply problem for several more decades beyond 2010.

Estimates of gas reserves have increased in recent years (IGU, 2000; Rogner, 2000a; Gregory and Rogner, 1998) as there is much still to be discovered, often in developing countries that have seen little exploration to date. The problem in the past has been that there needed to be an infrastructure to utilize gas before it could have a market, and without an infrastructure, exploration appeared unattractive. The development of CCGT power stations (discussed below) means that a local market for gas can more readily be found which could encourage wider exploration. In the longer term, it is estimated that very substantial reserves of gas can be extracted from the bottom of deep oceans in the form of methane clathrates, if technology can be developed to extract them economically

With uranium, there has only been very limited exploration in the world to date but once more is required, new exploration is likely to yield substantial additional reserves (Gregory and Rogner, 1998; OECD-NEA and IAEA, 2000) (see Table 3.28a).

The other major supply of energy comes from renewable sources, which meet around 20% of the global energy demand, mainly as traditional biomass and hydropower. Modern systems have the potential to provide energy services in sustainable ways with almost zero GHG emissions (Goldemberg, 2000).

The following sections focus on energy supply and conversion technologies in which there have been developments since the Second Assessment Report and which may be key to achieving substantial reductions in greenhouse gas emissions in the coming decades.

On a global basis, in 1995 coal had the largest share of world electricity production at 38% followed by renewables (principally hydropower) at 20%, nuclear at 17%, gas at 15%, and oil at 10%. On current projections, electricity production is expected to double by 2020 compared to 1995 and energy used for generation to increase by about 80% as shown in Table 3.29 (IEA, 1998b).

  • Coal is projected to retain the largest share with a 90% increase in use from strong growth in countries such as India and China reflecting its importance there, steady growth in the USA but a decline in Western Europe.
  • Gas is projected to grow strongly in many world regions reflecting the increasing availability of the fuel, with an overall increase of 160%.
  • Nuclear power is projected to decline slightly on a global basis after 2010. Capacity additions in developing countries and in economies in transition roughly balance the capacity being withdrawn in OECD countries. Few new power stations will be built in many countries without a change in government policies. IAEA projections for 2020 cover a range from a 10% decline to an optimistic 50% increase in nuclear generating capacity (IAEA, 2000a).
  • Hydropower is projected to grow by 60%, mainly in China and other Asian countries.
  • New renewables have expanded substantially, in absolute terms, throughout the 1990s (wind 21% per year, solar PV more than 30% per year); these are projected to grow by over tenfold by 2020, but they would still supply less than 2% of the market.
Table 3.29: Past and projected global electricity production, fuel input to electricity production and carbon emissions from the electricity generating sector
IEA, 1998b)
Global electricity generation (TWh)
  1971 1995 2000 2010 2020
Oil 1,100 1,315 1,422 1,663 1,941
Natural gas 691 1,932 2,664 5,063 8,243
Coal 2,100 4,949 5,758 7,795 10,296
Nuclear 111 2,332 2,408 2,568 2,317
Hydro 1,209 2,498 2,781 3,445 4,096
Renewables 36 177 215 319 433
Total 5,247 13,203 15,248 20,853 27,326
Fuel input (EJ)
  1971 1995 2000 2010 2020
Oil 11 13 14 15 18
Natural gas 10 24 29 43 62
Coal 26 57 65 85 106
Nuclear 1 25 26 28 25
Hydro 4 9 10 12 15
Renewables 0 1 2 3 5
Total 53 129 146 187 230
CO2 emissions (MtC)
  1971 1995 2000 2010 2020
Oil 224 258 273 307 350
Natural gas 158 362 443 662 946
Coal 668 1,471 1,679 2,185 2,723
Nuclear 0 0 0 0 0
Hydro 0 0 0 0 0
Renewables 0 0 0 0 0
Total 1,050 2,091 2,395 3,155 4,019
Average emissions per kWh
gC/kWh 200 158 157 151 147

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