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 21^st 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
	Consumption		Reserves	Resourcesa	Resources baseb	Additional occurrences
	1860-1998	1998
Oil
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 (Source: 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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