3. Carbon Dioxide Emissions and Fossil Fuel Resources

• 3.1 Historic
• 3.2 Projected Emissions
• 3.3 Fossil Fuel Reserves and Resources
• 3.4 Oil Reserves
• 3.5 Conclusions

3.1 Historic

The atmospheric load of CO₂ is now over 765 billion tonnes of carbon ( GtC)[13], an increase of around 175 GtC over pre-industrial levels. By 1997 CO₂ concentration was over 360 ppmv, about 30% above the pre-industrial level of 280 ppmv which is believed to have prevailed for the past several thousand years, and is growing at around 1.5 ppmv/yr.

Around half of the approximately 450 GtC of CO₂ emitted over the past two centuries, up until 1995 , remains in the atmosphere.

Coal dominates historic fossil CO₂ emissions, comprising 60% of the estimated 218 GtC of fossil carbon emitted from 1860-1990 (Table 2 and Figure 2). Oil comprises 28% and gas 12% of this volume of carbon. Deforestation is estimated to have contributed a total of around 150 GtC, from pre-industrial times until 1990. Annually industrial CO₂ emissions have been significantly higher than deforestation emissions since the early decades of this century. Cumulative emissions from fossil fuel use exceed those from deforestation now by a significant and growing margin (Figure 3).

Whilst historically coal has dominated emissions from fossil fuel use, from the late 1960's to mid 1980's oil was the dominant global source of CO₂ emissions from fossil fuels. Since the mid 1980s coal and oil combustion have emitted comparable amounts of CO₂ ( see Figure 4). For the decade 1983-1992, oil and coal emitted about the same volume of CO₂ (Table 2) and by the mid 1990s emissions of CO₂ from oil were slightly higher than from coal. Gas contributed around 17% to fossil CO₂ emissions in the 1990's. Table 2 CO₂ Emissions from Fossil Fuels 1860-1992

	Consumption 1860-1990 GtC	%	Consumption 1990	%	Consumption 1983-1992	%
Gas	26	11.9%	1.1	19.3%	9.7	17.3%
Oil	61	28.0%	2.3	40.4%	23.4	41.9%
Coal	131	60.1%	2.3	40.4%	22.9	40.8%
Total	218	100.0%	5.7	100.0%	56.0	100.0%

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Source: IPCC SAR WGII Tables B.3 and B.4 in Sect B.3.3.1 and Gregg Marland, Oak Ridge National Laboratory.

Of the fossil fuels coal is the most carbon intensive[14] with natural gas having the lowest carbon intensity (Table 3). Table 3 Carbon intensity of fossil fuels

Fuel Source	MtC/EJ	Ratio to Natural Gas
Natural Gas	14.4	100%
Crude Oil	19.9	138%
Coal	25.4	177%

The emission factors here are gross emissions only and do not include emissions from production processes[15]. MtC refers to million tonnes of carbon and EJ refers to Exajoules of primary energy, which is 10¹⁸ joules. Total commercial primary energy use globally in 1991 was around 330 EJ.

3.2 Projected Emissions

In 1992 the IPCC generated six scenarios (IS92a-f) of future greenhouse gas and sulphur emissions, in the absence of climate change policies over the period 1990-2100[16]. All of these scenarios show large cumulative CO₂ emissions over this period. Table 4 summarises the assumptions made in these scenarios, as well as their overall cumulative carbon emissions.

The mid-range IPCC scenario (IS92a) projects total emissions of 1,500 GtC over the next century, from 1990 to 2100. The lowest IPCC scenarios would emit around 770-980 GtC of carbon and the highest around 2,190 GtC, with deforestation projected to result in emissions of in the range of 30-95 GtC. Scenario IS92c is the lowest IPCC scenario projecting around 680 GtC of fossil CO₂ emissions, however the population projection for 2100 used in this scenario (and IS92d) is only 6.4 billion. This factor, along with a very low assumed economic growth rate, led the 1994 IPCC WGIII report on emission scenarios to state "users of the IPCC scenarios are cautioned, however, that the lowest (IS92c) has emission levels and some input assumptions that are more characteristic of a policy, rather than a reference scenario."[17] Because of their low population assumptions the two lowest IPCC scenarios are not considered here to be realistic. In the absence of climate policy action, cumulative fossil fuel emissions over the next century are likely to be close to 1,500 GtC.

The full range of the IS92 scenarios shows that cumulative emissions over the next century are likely to add some 4-10 times more fossil carbon to the atmosphere than has been added since the industrial era began. Annual CO₂ emissions in the IS92 scenarios grow considerably over the period to 2100 (see Figure 1), with the exception of the IS92c scenario. In the IS92a case annual emissions are projected to be nearly 3 times 1990 levels in 2100.

One of the features shared by all of the IPCC scenarios is that oil and gas are in limited supply and coal becomes the predominant fossil fuel over the longer term (Table 5). It is assumed that conventional oil and gas resources will be used up over the next century, requiring a shift to a coal intensive energy system. The relationship of the IPCC scenarios to estimates of fossil fuel resources will be examined in the next section. Figure 1 IPCC IS92 fossil fuel CO₂ emission scenarios

Note that the IS92c scenario (the lowest) has both very low population estimates and low economic growth assumptions which mean that it is unlikely to characterise a "no climate policy" scenario. IS92d also has very low population assumptions.

Despite this long term trend towards coal in the IPCC scenarios, estimates of which fuel will dominate emissions over the next few decades vary. In the short to mid-term the International Energy Agency projects that CO₂ emissions from oil will accelerate faster than those from coal combustion to 2010 (Table 6). On the other hand both the IPCC scenarios and the World Energy Council project that, in the absence of policy action, coal use will accelerate faster, particularly in the longer term. In the IPCC business as usual scenario by 2050 coal emits over 60% of CO₂ emissions, with oil having a 20% share (Table 7). Table 4 IPCC 1992 Emissions Scenarios: Assumptions and cumulative carbon emissions[18].

Scenario	Population	Economic Growth	Energy Supplies	Cumulative emissions 1990-2100 GtC
IS92a	World Bank 1991	1990-2025: 2.9%	12,000 EJ conventional oil	1,500
	11.3 billion by 2100	1990-2100: 2.3%	13,000 EJ natural gas
			Solar costs fall to $0.075/kWh
			191 EJ of biofuels available at $70/barrel*
IS92b	as above	as above	as above	1430
IS92c	UN Medium-Low Case	1990-2025: 2.0%	8,000 EJ conventional oil	770
	6.4 billion by 2100	1990-2100: 1.2%	7,300 EJ natural gas
			Nuclear costs decline by 0.4% annually
IS92d	UN Medium-Low Case	1990-2025: 2.7%	Oil and gas same as IS92c	980
	6.4 billion by 2100	1990-2100: 2.0%	Solar costs fall to $0.065/kWh
			272 EJ of biofuels available at $50/barrel
IS92e	World Bank 1991	1990-2025: 3.5%	18,400 EJ conventional oil	2,190
	11.3 billion by 2100	1990-2100: 3.0%	Gas same as IS92a,b
			Phase out nuclear by 2075
IS92f	UN Medium-High Case	1990-2025: 2.9%	Oil and gas same as IS92e	1,830
	17.6 billion by 2100	1990-2100: 2.3%	Solar costs fall to $0.083/kWh
			Nuclear costs increase to $0.09/kWh

This table shows in summary form the assumptions behind the IPCC 1992 (IS92) scenarios. Note that both IS92c and d have very low population estimates for 2100. Some elements of the IS92 scenarios relating to emissions of halocarbons and other greenhouse gases were modified in the IPCC Second Assessment Report, however these changes do not affect the fossil fuel emissions. Table 5 IPCC IS92 Scenarios: Cumulative carbon emissions 1990-2100

Scenario	Coal GtC	Oil GtC	Gas GtC	Total Fossil carbon GtC	Deforestation GtC	Total carbon GtC
IS92a	989	239	187	1,415	85	1,500
IS92b	919	239	187	1,345	85	1,430
IS92c	425	159	105	690	80	770
IS92d	685	159	105	950	30	980
IS92e	1,551	367	187	2,105	85	2,190
IS92f	1,181	367	187	1,735	95	1,830

This table shows the cumulative carbon emissions over the period to 2100 for the six IPCC 1992 scenarios as a total and by source. The carbon emissions from oil and gas have been estimated using the emission factors in Table 3 and coal is a residual of the total for the period. Table 6 International Energy Agency (IEA) Projections of CO₂ emissions by source

	IEA 1993 GtC/yr.		IEA 2000 GtC/yr.	%	IEA 2010 GtC/yr.	%
Gas	1.0	16.6%	1.2	17.3%	1.7	18.7%
Oil	2.7	44.0%	3.2	44.3%	3.9	43.3%
Coal	2.4	39.4%	2.7	38.4%	3.4	38.0%
Total	6.2	100.0%	7.1	100.0%	9.0	100.0%

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The IEA projections[19] show an anticipated predominance of oil in the first decade of next century. This is in contrast to the IPCC scenarios which generally show coal being the major source of CO₂ from early in the next century. Table 7 IPCC IS92a Scenario: CO₂ emissions by source

	2010 GtC/yr.	%	2020 GtC/yr.	%	2050 GtC/yr.	%
Gas	1.9	22.9%	2.2	22.7%	2.2	16.7%
Oil	2.8	33.7%	3	30.9%	2.7	20.5%
Coal	3.6	43.4%	4.5	46.4%	8.3	62.9%
Total	8.3	100.0%	9.7	100.0%	13.2	100.0%

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D:\GPI\GHOUSE\POLICY\CO₂POLIC\FOSSIL-1.XLS Figure 2 Carbon Emissions by Source 1765-1990

This figure shows the annual deforestation and fossil carbon emissions estimated from pre-industrial times to the present. Annual fossil fuel emissions significantly exceeded deforestation emissions from the 1920's. Source: CSIRO. Figure 3 Cumulative Carbon Emissions by Source

This figure shows the cumulative contribution to emissions since pre-industrial times. Cumulative fossil fuel emissions overtook deforestation emissions around 1970 although annual fossil fuel emissions exceeded deforestation emissions from 1910 onwards. The fact that cumulative emissions from fossil fuel emissions took so long to exceed deforestation is because of the long period of steady deforestation starting in the 18^th century and extending into the 20^th Figure 4 Fossil Fuel Emissions by Source 1950-1992

This figure shows the relative contribution of the different sources of fossil fuels in the period 1950-1992. Oil became the dominant fossil fuel source of CO₂ from the late 1960's onwards. Coal use however rose steadily across this period and once again rivalled oil in the late 1980's and early 1990's. Source: Gregg Marland, Oak Ridge National Laboratory.

3.3 Fossil Fuel Reserves and Resources

The question that naturally arises, given the large volumes of fossil fuels projected to be burnt over the next century, is whether or not sufficient resources exist in an economically recoverable state. Some have argued that oil and gas are scarce resources and hence their contribution to future climate change is necessarily limited. Before reviewing the estimates for fossil fuel resources it is useful to briefly review some terms:

Fossil fuel reserves are those defined as economically recoverable with known technology and within a price range close to the present or reasonably foreseeable.

Resources are theoretical maximum potentials based on geological information, including reserves defined above.

The economically recoverable reserves are those most likely to be burnt in the short to medium term. Table 8 shows recent IPCC, World Energy Council (WEC), International Institute for Applied Systems Analysis (IIASA) estimates of reserves and resources for the various fossil fuels. The distinction between conventional and unconventional fuels is quite blurred in the literature and here we follow the approach of the IPCC and WEC. Unconventional gas includes coal bed methane, ultradeep gas reserves and gas in aquifers. Gas hydrates, principally as methane clathrates, are vast[20] and are not included in this analysis. Unconventional oil includes oil shales, tar sands and heavy crude oil. Such oils are much more carbon intensive than conventional oils.

The overall estimates of reserves of fossil fuels presented in Table 8 range from 829 GtC to 1,501 GtC. If one compares fossil fuel reserve estimates with the IPCC emissions scenarios to 2100, then only at the upper end are there enough fossil fuels to supply the mid-range (IS92a) scenario. The volume of carbon in the WEC reserve estimates, for example, are only 65% of the cumulative emissions projected from IS92a. However, as will be seen below such a comparison does not take account of ongoing technical advances which continue to "convert" fossil fuel resources to economically recoverable reserves.

Coal predominates in the reserve estimates, totalling 638-1,034 GtC. Conventional oil and gas reserves are much smaller by comparison, but still total 182-205 GtC. Unconventional reserves of oil and gas total a further 133-262 GtC.

Beyond the reserves the total resource base is much higher again, lying in the range 4,166-4,678 GtC. The total oil resource base exceeds 650 GtC and the gas resource is over 500 GtC. Table 8 Fossil Fuels: Economic Reserves and Resource Base

	IPCC 1995 Reserves Identified /Potentials by 2020-2025 GtC	WEC 1993 Conventional reserves GtC	IIASA 1997 Reserves GtC	IPCC 1995 Resource Base Maximum Potentials GtC	WEC 1993 Resource Base Maximum Potentials GtC	IIASA 1997 Resource Base GtC
Gas - conventional	72	69	81	138	133	243
Unconventional gas	103		111	403		260
Oil - conventional	110	114	124	156	167	243
Unconventional oil	130		151	296	497	427
Coal	638	646	1,034	3,173	3,622	3,505
Total	1,053	829	1,501	4,166	4,419	4,678

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This table shows the 1995 IPCC, 1993 World Energy Council[21] (WEC) and 1997 IIASA[22] fossil fuel reserves and resources estimates in GtC. The WEC does not show unconventional gas separately. Reserves are defined as economically recoverable and resources include reserves plus geologically inferred resources.

It is clear from the above estimates that to meet the IPCC scenarios for future oil and gas use, a large amount of the oil and gas currently identified as unconventional, or that is currently defined as not economically recoverable (the difference between the resource base and reserves in Table 8), will need to be `moved' into the resource category.

Oil use in the IPCC emission scenarios spans 159-367 GtC with the mid-range scenario consuming 239 GtC, which is much higher than conventional reserves identified in Table 8, but of the same order as the sum of conventional and unconventional reserves. Recent oil industry estimates span the range of those estimated by the IPCC and WEC (Table 9).

For gas use, the IPCC scenarios span 105-187 GtC. Known conventional reserves are considerably below these volumes. However estimates of natural gas reserves have been increasing in recent years. The International Gas Union has recently estimated that proven reserves stand at 77 GtC[23] with "additional reserves" totalling 136 GtC bringing the total resource to 213 GtC. Additional reserves are defined as being of foreseeable economic interest and include conventional and unconventional gas. The IGU has reported that the increase in reserves is due to technological advances, particularly in exploration in offshore areas, which is changing the economics of gas extraction quite rapidly.

From a policy perspective one of the lessons from the recent expansion of gas reserves is the ongoing role of technological change, even in circumstances where prices have remained relatively low.

3.4 Oil Reserves

The size of oil reserves and their ultimate extent is an area of significant and indeed polarized policy debate. A common perception is that there might not be enough oil to meet growing demand. On the other hand, from an environmental perspective, it is logical to question whether there is too much oil ever to be used.

Of the few certain data in this area it is known that approximately 800 billion barrels (Gb) of oil have been produced to date and that production is currently at around 25 Gb/day. Production has grown at about 1.25%/yr. over the period 1987-1996[24]. Oil reserves, defined as that which has been discovered and remains unused, are estimated, at the end of 1995, to lie between 746 and 1056 Gb[25], with the consensus being around 1,000 Gb. In other words 1,000 Gb of oil, or about 115 GtC of emissions, can be produced at current prices with current technology.

Of the known reserves of oil, Odell estimates that scientific and technological developments may well add a further 400 Gb (46 GtC) to the volume of ultimately recoverable oil in existing reserves. The US Geological Survey estimates that there may be a further 600 Gb (70 GtC) of oil in conventional reserves which remain to discovered. Odell considers this estimate to be conservative. Taken together with the known reserves of 1,000 Gb, these two estimates point to the total unexploited reserve volume being approximately 2,000 Gb, which is equivalent to about 230 GtC[26]. This latter figure is quite close to the resource base estimated by IIASA (Table 8). Table 9 Recent industry estimates of oil reserves[27]

	Oil and Gas Journal: Estimated Proven Reserves at January 96.	World Oil Estimated Proven Reserves at December 95.	Petro Consultants Assessed Reserves, 1995.	US Geological Survey
Regions	GtC	GtC	GtC	GtC
North America	8.9	8.9	7.4	11.9
South America	9.0	9.9	5.9	8.6
Europe	1.9	3.6	3.5	4.3
FSU	6.8	22.1	8.8	14.0
Africa	8.5	9.2	6.1	8.3
Middle East	76.5	68.4	50.9	67.6
Far East	4.9	5.9	4.4	7.2
Australasia	0.2	0.5	0.3	0.5
Total	116.7	128.3	86.5	122.4

Original data are in billions of barrels of oil and have been converted to GtC using the factor of 0.116 GtC/Gb (billion barrels) based on emission factors in Table 3 and the conversion of 5.815 GJ/barrel of crude oil[28]. The emissions factor implied in the IPCC estimates is approximately 10% lower than those used here whereas the IIASA factors are within a few percent of those used in this work.

Unconventional oil includes tar-sands, heavy oils and oil shales and resources and reserves of these are very large compared to conventional supplies. The estimates in Table 8 indicate reserves are of the order of 1,200 Gb (130 GtC) and resources in the range 3,000-4,500 Gb.

On the surface this appears to be a "healthy" supply of oil compared to demand. However neither these numbers, nor the analysis underpinning them, are undisputed. Essentially there are two quite divergent views of the future of oil reserves. These views have quite different policy implications from a conventional oil supply security perspective.

The "oil scarcity" viewpoint is held by oil companies and many petroleum geologists who believe that the volume of oil and the rate at which it can be recovered are inherently and physically limited by the nature of the geological origin of oil. In this view oil is in scarce supply and global production will peak within a few decades and afterwards the world will face a permanent situation of scarce and declining oil availability[29]. Hatfield, for example, argues that the consequence of this situation is that soon this issue may override other environmental concerns:

"Despite the intensive, intergovernmental debates on the environmental effects of energy policies, geological constraints on the amount of inexpensive fluid fuel that can be produced will soon override governments decisions about the future rate of fossil fuel burning" [30]

Contrasted against this point of view is the "economic" view. Dusseault, for example, argues that the idea of oil being limited is "an incorrect and insidious myth" and that technological change and market pressures will bring other resources into the market:

"Limitations on oil use are [therefore] logically related to environmental issues such as global warming and air pollution; resource limits do not for practical purposes exist. Oil shortages are actually short-term shortfalls in cheap conventional crude oil supplies, and have little to do with actual-long term hydrocarbon supplies"[31]

Figure 5 shows that total oil reserves increased over the past twenty five years and are now 70% higher than in 1973. Over this time the reserve size to production ratio has increased from 25 years to nearly 45 years[32]. On the face of it this figure appears to support the "economic" point of view. It shows that the addition to oil reserves over time has outweighed by a wide margin the annual consumption of oil.

However, proponents of the "oil scarcity" view argue that the increasing reserve size shown in Figure 5 is not an accurate picture of the supply balance for oil. Hatfield, argues that much of the increase over the 1973-1995 period results from "political" adjustments in the reserves held by key OPEC countries rather than new discoveries.

In 1988 and 1989 Venezuela, Iran, Iraq, Abu Dhabi and Saudi Arabia revised their oil reserves upward by a total of 277 billion barrels and this accounted for nearly all of the growth in global reserves between 1987 and 1990[33]. Whilst some have suggested that these reserve revisions were essentially political[34] Campbell ( a scarcity advocate) suggests that the main policy point about this revision is that nothing new was discovered - the change were just in reporting[35]. In other words it is argued there have been no new major oil discoveries since the 1960's.

From the "oil scarcity" point of view, growing oil demand essentially means that if there were no new discoveries (and assuming the rate of production could increase until the reserves are depleted) 1,000 Gb of conventional reserves would be used up before 2025 if demand were to grow at 2% per year. Even large additions to this reserve size would delay the extinction of the resource by only a few years. Further, as it is known that the production rate from oil reservoirs peaks and then declines at some point near the mid-point in their production cycle, some geologists consider it unlikely that with the currently estimated reserves (or even large additions) that current or projected production rates could be maintained much beyond 2010-2015.

Viewing the same history, Odell, a proponent of the "economic" view point, argues that the oil industry has in fact demonstrated a "high degree of success ... even through a period of great disturbances in its organisation, structure and commercial fortunes, in maintaining and generally increasing the shelf-stock of reserves at a more than adequate level over a very long period."[36] Whilst a significant portion of the additions to reserves has come from the appreciation of existing reserves there have also been quite significant additions from new discoveries. In relation to the future, Odell argues that there are likely to be large additions to reserves possible through the appreciation of existing reserves and the discovery of new oil reservoirs.[37]

Even if the rate of addition of conventional oil to reserves slows and production begins to decline, from the second "economic" point of view the existence of large volume of unconventional oil, combined with technological change and rising prices, will ensure that these resources will come on stream in large volumes in the future[38].

Technological development, often subsidised by governments, has meant that the cost of extracting oil from unconventional sources such as heavy oil has declined. Dusseault gives the example of heavy oil production in Canada whose cost has more than halved from the late 1980's to 1996. He points out that heavy oil resources are much larger than conventional oil and if only 20% of Canadian heavy oil is economically recoverable this would supply the USA and Canada with oil for the next 100 years or more[39]. Further, he argues, a large increase in the production cost of oil could be sustained without significant increases of the price of fuel on the market in Europe if governments are prepared to shift the tax burden from fuel in the future.

An indication of the relative volume of near term substitutes for conventional oil available from technical developments can be gained from Table 10. This shows that relatively large volumes of alternatives to conventional oil may be available. These come from enhanced and improved recovery from existing fields (i.e. appreciation of existing reserves), natural gas liquids and from heavy oil and shales. Over the time frame of 10-20 years this could add nearly 50% to current reserves.

3.5 Conclusions

It seems clear, not withstanding the arguments of the "oil scarcity" advocates, that technological change and the price mechanism will, as it has in the past, constantly enlarge the boundaries of conventional reserves and further move resources into reserves. A recent IIASA-World Energy Council analysis of available fossil fuel resources has attempted to evaluate an economic supply curve for fossil fuel resources taking into account technological change. Unlike previous analyses the assessment estimated technology productivity gains in fossil fuel exploration and extraction over time based on historical experience in order to generate a quantity cost curve for each major fossil fuel type. The results of this work are shown schematically in Figure 6 and Figure 7. Figure 5 Oil reserves and production 1973-1995[40]

Over the period 1973-1995 the gross additions to oil reserves exceeded production for most years in the period leading to a sizeable net increase in proven reserves over the period. The jump in gross additions in the period 1987-89 reflects revisions to reserve estimates in several major OPEC countries.

Some of the inferences from the curves in Figure 6 include: 300 GtC of carbon is available at under $US 10/boe (barrel of oil equivalent),[41] 600 GtC is available at under $US 20/boe, 900 GtC is available at under $US 30/boe; around 300 GtC of oil and gas is available at around $US15-16/boe and around 400 GtC at or below $US20/boe (in 1990 prices). In other words if productivity gains in the fossil fuel industry proceed at historical rates then the IIASA study finds that "mankind is well positioned to substantially increase climate destabilizing and local air quality emissions" and "this can be done quite cheaply" [42]. As a consequence, one of the key conclusions of the IIASA assessment of world fossil fuel resources is that "environmental considerations may constrain fossil fuel use to below present-day levels long before global resource scarcity becomes the limiting factor"[43].

From a policy perspective the relationship between resources and reserves is quite fluid. The more investment that occurs in exploration and development of resources the more of these will be converted to reserves (i.e. classified as economically recoverable). Investment in further exploration and development of oil, for example, will be conditioned by market expectations of the future demand. If markets expect increasing demand in the future then investment is likely to be made in "expanding" the reserves available. One of the implications of this is that if the volume of reserves already exceeds some ecological limit (as is found in this report) then further investment in resource development is unnecessary and unwise. Ultimately this would impose higher political and economic costs on future generation's attempts to constrain the amount of fossil fuels exploited. Table 10 Potential liquid fuel substitutes for conventional oil

Category	Sub-category	Present reserves		Potential reserves
		Gb	GtC	Gb	GtC
Heavy oil and bitumens		64	7	740	86
Oil shales		160	19	500	58
Non-heavy
	> 200 m water depth	25	3	75	9
	Hostile (polar)	0	-	30	3
	Small and very small (< 10 Mb)	10	1	30	3
	Infill	0	-	50	6
	Sub-total:	35	4	185	21
Enhanced recovery		45	5	60	7
Improved recovery		45	5	60	7
Natural Gas Liquids -	Condensate	65	8	100	12
	By-processing	130	15	200	23
Total		500	58	2000	232

This table of date was provided in discussion notes by R.W. Bentley, University of Reading as a basis for discussion at a workshop in the future of oil[44]. The values in it should be seen as indicative only of the order of magnitude of potential alternatives to conventional oil. Figure 6 IIASA quantity-cost curve for gas, oil and gas resources

These curves are estimated from the curves presented in Rogner (1996) (see footnote 42) and are schematic only. Figure 7 IIASA quantity-cost curve for total fossil fuel resource base

These curves are redrawn from the curves presented in Rogner (1996) (see footnote 42) and are schematic only.

[13] By convention CO₂ is reported here in tonnes of carbon: 3. 7 tonnes of CO₂ contains 1 tonne of carbon. The mass units used here are gigatonnes of carbon ( GtC). A Gigatonne = 10⁹ tonne or 1 billion tonnes.

[14 ]Carbon intensity refers to the amount of CO₂ emitted per unit of primary energy.

[15] Lazarus, M (1993), Towards a Fossil Free Energy Future: A Technical Analysis for Greenpeace International, Stockholm Environment Institute, Boston Center, Table 4.6, p. 37.

[16] Leggett, J., W.J. Pepper, R.J. Swart (1992) Emission Scenarios for the IPCC: An Update Chapter A3 in Houghton, J.T., B.A. Callander and S.K. Varney (ed.'s), Climate Change 1992: The Supplementary Report to the IPCC Scientific Assessment, Published for the Intergovernmental Panel on Climate Change, Cambridge University Press, 1992.

[17] IPCC 1994 op.cit. p. 258.

[18 ]IPCC SAR WGII Summary for Policymakers, p. 3 in R. T Watson, M. C. Zinyowera, R. H. Moss, D. J. Dokken (ed.'s) (1996), Climate Change 1995 - Impacts, Adaptations and Mitigation of Climate Change: Scientific-Technical Analysis, Contribution of Working Group II to the Second Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press.

[19] IEA (1996), World Energy Outlook 1996, International Energy Agency, Paris

[20] Estimates range up to 18,000 GtC.

[21] World Energy Council (1993), Energy for Tomorrow's World - The realities, the real options and the agenda for achievement, St. Martin's Press/Kogan Page, London.

[22] Rogner, Hans-Holger (1997) Climate Change Assessments: Technology Learning and Fossil Fuels - How Much Carbon Can Be Mobilized?, Paper presented to International Energy Agency Workshop on Climate Change Damages and the Benefits of Mitigation, 26-28 February 1997, International Institute for Applied Systems Analysis (IIASA).

[23] IGU (1997) World Gas Prospects, Strategies and Economics, International Gas Union, 20th World Gas Conference Proceedings, Copenhagen, June 1997. Units originally in Exajoules (EJ) and converted at the rate of 14.4 MtC/EJ.

[24]. Odell, P. (1997) A Guide to Oil Reserves and Resources: Report to Greenpeace, Energy Advice Ltd, 1997, London.

[25] Odell (1997) op.cit. p. 6.

[26] Odell (1997) op.cit. p. 17.

[27] Odell (1997) op.cit. p. 1

[28] Lazarus (1993) op.cit. p.v. A gigajoule (GJ) is 10⁹ joules.

[29] C.J. Campbell (1997), "Better Understanding Urged for Rapidly Depleting Reserves" in Oil &Gas Journal, OGJ Special, 7 April 1997; pp. 51-52,54.

[30 Hatfield, C. B. (1997), "Oil Back on the Global Agenda" in ]Nature, vol. 387, 8 May 1997; pp. 121.

[31] Dusseault, M. B. (1997), "Flawed Reasoning about Oil and Gas" in Nature, vol. 386, 6 March 1997; pp. 12.

[32] Note that the reserve to production ratio (R/P), whilst widely used in the industry is an extremely poor indicator of supply availability, particularly once supply has peaked and is dropping from an oil reservoir. The R/P ratio can be maintained under this circumstance, event though the rate of production is falling. The ratio has the units of years where the reserve size is the total volume in reserves and the production is a rate of volume of oil produced per year.

[33] Hatfield, op.cit.

[34] Hatfield, op.cit.

[35] Campbell, op.cit, p. 54.

[36] Odell (1997) op.cit. p. 10.

[37] Appreciation of existing reserves occurs when enhanced recovery techniques allow greater volumes than originally estimated to be recovered from known fields. Reserves can also appreciate when fields are found to contain more oil than originally estimated.

[38] Odell (1997) op.cit. p. 22 and Dusseault (1997) op.cit. p. 12.

[39] Dusseault (1997) op.cit. p. 12.

[40 ]Odell (1997) op.cit.

[41] A barrel of oil equivalent is defined here as 5.815 GJ (gigajoules).

[42 ]Rogner, Hans-Holger (1996) An Assessment of World Hydrocarbon Resources, IIASA Working Paper WP-96-56, May 1996, p. 39.

[43] Rogner op.cit. p. 38.

[44] Bentley, R.W. (1997) Briefing Notes for Workshop on `The Future of Oil', Black Horse House, The University of Reading. Friday, June 13th 1997.